論文 The compression of deformed microgels at an air/water interface Chemical Communications 2023(Oct.) Author:Takahisa Kawamoto; Kohei Yanagi; Yuichiro Nishizawa; Haruka Minato; Daisuke Suzuki Abstract:The compression of microgels at air/water interfaces was investigated using a Langmuir–Blodgett trough with in situ fluorescent microscopy. The relationship between the structure of the microgel arrays and the compression behavior was clarified.
Single microgel degradation governed by heterogeneous nanostructures Soft Matter,19(27):5068-5075 2023(May) Author:Yuichiro Nishizawa; Hiroki Yokoi; Takayuki Uchihashi; Daisuke Suzuki Abstract:The real-time visualization via high-speed atomic force microscopy revealed that single microgel exhibit heterogeneous degradation behavior.
Closed-loop recycling of microparticle-based polymers Green Chemistry 2023(Mar.) Author:Takumi Watanabe; Haruka Minato; Yuma Sasaki; Seina Hiroshige; Hayato Suzuki; Nahomi Matsuki; Koki Sano; Takeshi Wakiya; Yuichiro Nishizawa; Takayuki Uchihashi; Takuma Kureha; Mitsuhiro Shibayama; Toshikazu Takata; Daisuke Suzuki Abstract:We propose a recycling strategy for tough polymers based on microparticles. The "microparticle-based" concept allows materials recycling without loss of their properties (‘closed-loop’ recycling).
Clarification of Surface Deswelling of Thermoresponsive Microgels by Electrophoresis Langmuir,38(51):16084-16093 2022(Dec. 27) Author:Yuichiro Nishizawa; Takumi Inui; Ryuji Namioka; Takayuki Uchihashi; Takumi Watanabe; Daisuke Suzuki
Durable gelfoams stabilized by compressible nanocomposite microgels. Chemical communications (Cambridge, England) 2022(Oct. 19) Author:Yuichiro Nishizawa; Takumi Watanabe; Tetsuya Noguchi; Masaya Takizawa; Chihong Song; Kazuyoshi Murata; Haruka Minato; Daisuke Suzuki Abstract:Although hydrogel microspheres (microgels) are useful as emulsion stabilizers, typical microgels cannot stabilize foams over a prolonged period of time. Here, we found that compressible nanocomposite microgels with solid nanoparticles can overcome undesired desorption of microgels from the air/water interface of bubbles, and form highly durable, microgel-surrounded foams (gelfoams).
Controlling the shell structure of hard core/hydrogel shell microspheres Colloid and Polymer Science,300(4):333-340 2022(Apr.) Author:Yuichiro Nishizawa; Kenshiro Honda; Matthias Karg; Daisuke Suzuki
Adsorption Races of Binary Colloids with Different Softness at the Air/water Interface of Sessile Droplets Advanced Materials Interface,9(28):2200879-2200879 2022 Author:Haruka Minato; Yuma Sasaki; Kenshiro Honda; Takumi Watanabe; Daisuke Suzuki
High-Frequency Swelling/Deswelling Oscillation of Poly(Oligoethylene Glycol) Methacrylate-Based Hydrogel Microspheres with a Tris(2,2′-bipyridyl)ruthenium Catalyst ACS Applied Polymer Materials (selected as supplementary cover),3(7):3298-3306 2021(Jul. 09) Author:Kohei Inui; Ikuma Saito; Ryo Yoshida; Haruka Minato; Daisuke Suzuki
Temperature-dependent Relationship between the Structure and Mechanical Strength of Volatile Organic Compound-free Latex Films Prepared from Poly(butyl acrylate-co-methyl methacrylate) Microspheres Polymer Journal (featured articles -february 2021-),53(2):345-353 2021 Author:Seina Hiroshige; Haruka Minato; Yuichiro Nishizawa; Yuma Sasaki; Takuma Kureha; Mitsuhiro Shibayama; Kazuya Uenishi; Toshikazu Takata; Daisuke Suzuki
Nanostructures, Thermoresponsiveness, and Assembly Mechanism of Hydrogel Microspheres during Aqueous Free-Radical Precipitation Polymerization Langmuir,37(1):151-159 2021 Author:Yuichiro Nishizawa; Haruka Minato; Takumi Inui; Takayuki Uchihashi; Daisuke Suzuki Abstract:Although techniques to produce uniformly sized hydrogel microspheres (microgels) by aqueous free-radical precipitation polymerization are well established, the details of the polymerization process remain mysterious. In the present study, the structural evolution and thermoresponsiveness of the developing microgels during the polymerization were evaluated by temperature-controlled high-speed atomic force microscopy. This analysis clarified that the swelling properties of the precursor microgels formed in the early stages of the polymerization are quite low due to the high incorporation of cross-linkers and that non-thermoresponsive deca-nanosized spherical domains are already present in the precursor microgels. Furthermore, we succeeded in tracking the formation of nuclei and their growth process, which has never been fully understood, in aqueous solution by real-time observations. These findings will help us to design functional microgels with the desired nanostructures via precipitation polymerization.
Nanostructure and thermoresponsiveness of single and packed poly(N-isopropyl methacrylamide)-based microgels observed by temperature-controllable high speed atomic force microscopy.
Two-Step Yielding Behavior of Densely Packed Microgel Mixtures with Chemically Dissimilar Surfaces and Largely Different Sizes Soft Matter,16(31):7400-7413 2020(Jul. 09) Author:Saori Minami; Takumi Watanabe; Yuma Sasaki; Minato Haruka; Atsushi Yamamoto; Daisuke Suzuki; Kenji Urayama Abstract:Steady-state flow and elastic behavior is investigated for the moderately concentrated binary suspensions of soft microgels (pastes) with chemically dissimilar surfaces, and various degrees of size- and stiffness disparities. The pastes of poly(N-isopropyl acrylamide) (N) and poly(N-isopropyl methacrylamide) (NM) microgels with different values of yield strain γc (γNc > γNMc) are employed as the components. For the single microgel pastes (φ ≈ 1 where φ is apparent volume fraction), the values of γc are governed by the chemical species of constituent polymer in microgel surface whereas γc is insensitive to cross-link density and particle size. We demonstrate that the binary N/NM pastes with large size disparity (RN/NM = DN/DNM < 0.26 where D is the microgel diameter) at low φN (φN: weight fraction of small N microgels) exhibit the peculiarities in several rheological aspects, i.e., the two-step yielding in steady-state flow, and their values of γc and equilibrium shear modulus (G0) being equivalent to those of the single large NM microgel paste. These peculiarities are attributed to the characteristic packing resulting from large size disparity in which all or almost of the small N microgels tend to be accommodated in the gap between the large NM microgels even in moderately concentrated state. This characteristic packing substantially masks the contribution of the small N microgels at low φN, explaining the φN-independent G0 and γc as well as the first yielding governed solely by the large NM microgels. The second yielding results from the emerged contribution of the small N microgels expelled out from the gap by the positional rearrangements after the first yielding. The binary homo-N/N pastes with the similarly large size disparity at low φsmall also exhibit the φsmall-independent values of G0, but they show one-step yielding, indicating that the two-step yielding requires not only sufficiently large size disparity but also chemical dissimilarity (different values of γc) between the two components.
Thermoresponsive structural changes of single poly(N-isopropyl acrylamide) hydrogel microspheres under densely packed conditions on a solid substrate Polymer Journal (highlighted article -september 2020-),52:1137-1141 2020(Jun. 02) Author:Haruka Minato; Yuichiro Nishizawa; Takayuki Uchihashi; Daisuke Suzuki
Hydrophobic Monomers Recognize Microenvironments in Hydrogel Microspheres during Free-Radical-Seeded Emulsion Polymerization. Angewandte Chemie International Edition (selected as hot paper and outside front cover),59(23):8849-8853 2020(Jun. 02) Author:Takumi Watanabe; Yuichiro Nishizawa; Haruka Minato; Chihong Song; Kazuyoshi Murata; Daisuke Suzuki Abstract:The three-dimensional structure of nanocomposite microgels was precisely determined by cryo-electron micrography. Several nanocomposite microgels that differ with respect to their nanocomposite structure, which were obtained from seeded emulsion polymerization in the presence of microgels, were used as model nanocomposite materials for cryo-electron micrography. The obtained three-dimensional segmentation images of these nanocomposite microgels provide important insights into the interactions between the hydrophobic monomers and the microgels, that is, hydrophobic styrene monomers recognize molecular-scale differences in polarity within the microgels during the emulsion polymerization. This result led to the formation of unprecedented multi-layered nanocomposite microgels, which promise substantial potential in colloidal applications.
Criteria for colloidal gelation of thermo-sensitive poly(N-isopropylacrylamide) based microgels Journal of Colloid and Interface Science,568:165-175 2020(May 15) Author:Saori Minami; Atsushi Yamamoto; Shun Oura; Takumi Watanabe; Daisuke Suzuki; Kenji Urayama Abstract:Hypothesis: Suspensions of the poly(N-isopropylacrylamide) (PNIPAM) based temperature(T)-sensitive microgels can undergo colloidal gelation forming a three-dimensional sparse network-like structure in the hydrophobic and shrunken state of T > T* (T*: volume transition temperature), despite their considerably low particle volume fractions (<0.2). The effective surface charge density is expected to be a key factor governing the colloidal gelation and gel modulus.Experiments: The combined analysis of the viscoelasticity and electrophoretic mobility (EPM) was performed varying systematically pH and ionic strength (I). The microgels containing the extremely small content of electrolyte (0.1 mol%) with the T* and swelling degree being insensitive to pH and I were employed to facilitate the exclusive analysis of their effects on colloidal gelation.Findings: The results unambiguously reveal (1) that the gelation requires the adequate suppressions of the interparticle charge repulsion, and (2) that a reduction in the interparticle charge repulsion results in an increase in gel modulus by several orders of magnitude. The long-term linear creep behavior show that the colloidal gels are identified as a viscoelastic fluid with a long relaxation time and a high viscosity whereas they behave elastically at relatively short timescale in conventional oscillatory tests. (C) 2020 Elsevier Inc. All rights reserved.
Quantification for the Mixing of Polymers on Microspheres in Water-borne Latex Films Langmuir,36(18):4855-4862 2020(May 12) Author:Takuma Kureha; Seina Hiroshige; Daisuke Suzuki; Jun Sawada; Daisuke Aoki; Toshikazu Takata; Mitsuhiro Shibayama
The Belousov-Zhabotinsky Reaction in Thermoresponsive Core-Shell Hydrogel Microspheres with a Tris(2,2’-bipyridyl) ruthenium Catalyst in the Core The Journal of Physical Chemistry B,124(18):3828-3835 2020(May 07) Author:Kohei Inui; Takumi Watanabe; Haruka Minato; Shusuke Matsui; Keito Ishikawa; Ryo Yoshida; Daisuke Suzuki Abstract:The Belousov-Zhabotinsky (BZ) reaction shows temporal or spatiotemporal structures such as redox oscillation of the catalyst, [ruthenium(II)tris(2,2'-bipyridine)]-[PF6](2) ([Ru(bpy)(3)][PF6](2)). In this study, autonomously oscillating hydrogel microspheres (microgels) were investigated, which show swelling/deswelling oscillation induced by the redox oscillation of the BZ reaction inside the gel. Despite the periodically and autonomously induced oscillation that does not require an external stimulus, it has not been possible to perform any manipulation of the oscillatory behavior over time. The results of the present study show that it is possible to reversibly switch the microgel oscillations from an "on" active state of the BZ reaction to an "off" inactive state by changing the temperature in combination with thermoresponsive microgels. To realize on-demand switching, the construction of double-shell structures is crucial; the thermoresponsive first shell allows the microgels to modulate the diffusion of the substrates or intermediates in the BZ reaction, while the second shell maintains colloidal stability under high temperatures and high ion concentrations. The functionalized double-shell microgels were prepared via multistep seeded precipitation polymerization. The oscillatory switching behavior of the BZ reaction was observed directly and evaluated by ultraviolet-visible (UV-vis) spectroscopy. The central concept of this study, i.e., "on-off switching" can be expected to benefit the development of advanced bioinspired materials.
Protein uptake into individual hydrogel microspheres visualized by high-speed atomic force microscopy. Chemical communications (selected as outside front cover),55(68):10064-10067 2019(Sep. 04) Author:Shusuke Matsui; Kensuke Hosho; Haruka Minato; Takayuki Uchihashi; Daisuke Suzuki Abstract:The moment of protein uptake into hydrogel microspheres (microgels) was directly monitored at the nanoscale by high-speed atomic force microscopy. The dynamic morphological changes in the microgels during protein uptake are largely different depending on the type of protein, and the properties and structure of the microgels, which would affect the colloidal stability of protein-microgel hybrids both in vitro and in vivo.
Non-Thermoresponsive Decanano-sized Domains in Thermoresponsive Hydrogel Microspheres Revealed by Temperature-Controlled High-Speed Atomic Force Microscopy. Angewandte Chemie International Edition (highlighted article for special issue),58(26):8809-8813 2019(Jun. 24) Author:Yuichiro Nishizawa; Shusuke Matsui; Kenji Urayama; Takuma Kureha; Mitsuhiro Shibayama; Takayuki Uchihashi; Daisuke Suzuki Abstract:Despite the tremendous efforts devoted to the structural analysis of hydrogel microspheres (microgels), many details of their structures remain unclear. Reported in this study is that thermoresponsive poly(N-isopropyl acrylamide) (pNIPAm)-based microgels exhibit not only the widely accepted core-shell structures, but also inhomogeneous decanano-sized non-thermoresponsive spherical domains within their dense cores, which was revealed by temperature-controlled high-speed atomic force microscopy (TC-HS-AFM). Based on a series of experiments, it is concluded that the non-thermoresponsive domains are characteristic for pNIPAm microgels synthesized by precipitation polymerization, and plausible structures for microgels prepared by other polymerization techniques are proposed.
Hydrogel Microellipsoids that Form Robust String-Like Assemblies at the Air/Water Interface. Angewandte Chemie International Edition,58(22):7294-7298 2019(May 27) Author:Kenshiro Honda; Yuka Sazuka; Kojiro Iizuka; Shusuke Matsui; Takayuki Uchihashi; Takuma Kureha; Mitsuhiro Shibayama; Takumi Watanabe; Daisuke Suzuki Abstract:Soft colloidal particles such as hydrogel microspheres assemble at air/water or oil/water interfaces, where the soft colloids are highly deformed and their surface polymer chains are highly entangled with each other. Herein, we report the formation of robust one-dimensional, string-like colloidal assemblies through self-organization of hydrogel microspheres with shape anisotropy at the air/water interface of sessile droplets. Shape-anisotropic hydrogel microspheres were synthesized via two-step polymerization, whereby a hydrogel shell was formed onto preformed rigid microellipsoids. The shape anisotropy of the hydrogel microspheres was confirmed by transmission electron microscopy and high-speed atomic force microscopy as well as by light-scattering measurements. The present findings are crucial for the understanding of natural self-organization phenomena, where "softness" influences microscopic assembled structures such as those of Nostoc bacteria.
マイクロ流動場における異種微粒子の分離に対するやわらかさの影響 高分子論文集,76(3):226-233 2019 Author:大浦舜; 渡邊拓巳; 湊遥香; 鈴木大介 Abstract:In order to realize drug delivery systems, deeper understanding of the relationship between the position of colloidal particles, flowing in a microchannel, and particle characteristics, such as size and softness, is crucial. However, the influence of the softness of the particles on the flowing position (or segregation) in colloidal mixtures containing polymeric microspheres is still not clear. In this study, we investigated the particle position of binary mixtures in microchannels, observed by an optical microscope equipped with a high-speed camera, and clarified the effect of microgel softness on the segregation. These findings help designing carrier microspheres, for some applications, including drug delivery systems and as artificial blood cells.
Hydrophobized Nanocomposite Hydrogel Microspheres as Particulate Stabilizers for Water-in-Oil Emulsion Chemical Communications (selected as outside front cover),55(43):5990-5993 2019 Author:Takumi Watanabe; Masaya Takizawa; Hang Jiang; To Ngai; Daisuke Suzuki Abstract:Selected as Outside Front Cover
Concentration Dependence of Dynamics for Microgel Suspension Investigated by Dynamic Light Scattering Soft Matter (selected as outside front cover),15:5390-5399 2019 Author:Takuma Kureha; Haruka Minato; Daisuke Suzuki; Kenji Urayama; Mitsuhiro Shibayama
Effect of Charge Groups Immobilized in Hydrogel Microspheres during the Evaporation of Aqueous Sessile Droplets Langmuir,35:10412-10423 2019 Author:Haruka Minato; Masaya Takizawa; Seina Hiroshige; Daisuke Suzuki
Monitoring Thermoresponsive Morphological Changes in Individual Hydrogel Microspheres. ACS omega,3(9):10836-10842 2018(Sep. 30) Author:Shusuke Matsui; Yuichiro Nishizawa; Takayuki Uchihashi; Daisuke Suzuki Abstract:Real-time morphology/structure changes in individual hydrogel microspheres (microgels) were directly visualized at high spatiotemporal resolution using high-speed atomic force microscopy (HS-AFM) under temperature control ranging from room temperature to ∼40 °C. The recorded HS-AFM movies demonstrate that the size and morphology of thermoresponsive poly(N-isopropyl acrylamide)-based microgels change with increasing temperature at the individual microgel level. Specifically, the height of the microgels gradually decreases and domain structures appeared even below the volume phase transition temperature. Moreover, the domain structure is retained, even after the microgels have fully collapsed. The present study thus demonstrates that temperature-controlled HS-AFM is a useful tool for monitoring stimulus-responsiveness of microgels. In the near future, it should furthermore be possible to extend this temperature-controlled HS-AFM to other stimulus-responsive materials, including autonomously oscillating microgels.
Seeded Emulsion Polymerization of Styrene in the Presence of Water-Swollen Hydrogel Microspheres Langmuir,34(29):8571-8580 2018(Jul.) Author:Takumi Watanabe; Chihong Song; Kazuyoshi Murata; Takuma Kureha; Daisuke Suzuki Abstract:In a previous study, we have ascertained that the charge distribution in hydrogel microspheres (microgels) plays a crucial role in controlling the nanocomposite structure of the polystyrene obtained from the seeded emulsion polymerization (SEP) of styrene in the presence of microgels. However, all these polymerizations were conducted at high temperature, where most of these microgels were dehydrated and deswollen. In the present study, we initially verified that the nanocomposite microgels can be synthesized even when the seed microgels are swollen and hydrated during the SEP of styrene. These highly swollen microgels were used as the nucleation sites for the polystyrene, and subsequently the propagation of the hydrophobic polystyrenes proceeded within water swollen microgels.
High Reusability of Catalytically Active Gold Nanoparticles Immobilized in Core-Shell Hydrogel Microspheres ACS Omega,3(6):6158-6165 2018(Jun. 07) Author:Takuma Kureha; Yasuhisa Nagase; Daisuke Suzuki Abstract:The reusability of hybrid core-shell microgels, whose core surfaces were decorated with gold nanoparticles, was investigated in terms of catalysis activity. Hybrid core-shell microgels composed of a rigid core and water-swollen gel shell endowed the immobilized gold nanoparticles with a high dispersion stability, which resulted in excellent catalytic activity. In contrast to free Au nanoparticles and conventional hybrid microgels, where the Au nanoparticles are randomly distributed over the entire microgel templates, the hydrogel shell part of the hybrid core-shell microgels suppressed the aggregation between the microgels and Au nanoparticles in individual microgels, which improved the reusability for the catalysis reaction. The results of this study should help to develop advanced catalyst systems that require high reusability even when the chemical reactions occur in aqueous solution and external stimuli are applied.
Self-Organization of Soft Hydrogel Microspheres during the Evaporation of Aqueous Droplets Langmuir,34(15):4515-4525 2018(Apr. 17) Author:Masaya Takizawa; Yuka Sazuka; Koji Horigome; Yuki Sakurai; Shusuke Matsui; Haruka Minato; Takuma Kureha; Daisuke Suzuki Abstract:The unique drying behavior of aqueous droplets that contain soft hydrogel microspheres (microgels) upon evaporation was systematically investigated. Compared to the ring-shaped deposits that are obtained from drying solid microsphere dispersions, we have previously reported that uniformly ordered thin films are obtained from drying ∼1.2 μm-sized poly(N-isopropyl acrylamide) microgel dispersions. In the present study, we thoroughly investigated several hitherto unexplored aspects of this self-organization, such as the effect of the size, chemical structure, and "softness" of the microgels (or rigid microspheres). For the macro- and microscopic observation of the drying behavior of various microsphere dispersions, an optical microscope and a digital camera were employed. The results suggested that the convection in the aqueous droplets plays an important role for the transportation of the microgels to the air/water interface, where the softness and surface activity of the microgels strongly affects the adsorption of the microgels. On the basis of these discoveries, a design concept for the rapid formation of uniform thin films of soft microgels was proposed.
Nanocomposite Microgels for the Selective Separation of Halogen Compounds from Aqueous Solution Langmuir (invited article for special issue, selected as outside front cover),34(3):837-846 2018(Jan. 23) Author:Takuma Kureha; Daisuke Suzuki Abstract:Nanocomposite microgels that selectively adsorb and release halogen compounds were developed. These nanocomposite microgels consist of poly(2-methoxyethyl acrylate) (pMEA) and a poly(oligo ethylene glycol methacrylate) hydrogel matrix. Therefore, the methoxy groups of the former are crucial for the halogen bonding, while the presence of the latter adds colloidal stability and allows controlled uptake/release of the halogen compounds. Such nanocomposite microgels may not only be used as dispersed carriers, but also in films and columnar formations. Thus, these unprecedented polymer/polymer nanocomposite microgels resolve a variety of problems associated with, e.g., the removal of halogen compounds from wastewater, or with the delivery of halogen-containing drugs.
Autonomously Oscillating Hydrogel Microspheres with High-Frequency Swelling/deswelling and Dispersing/flocculating Oscillations ACS Biomaterials Science & Engineering (invited article for special issue),5(11):5615-5622 2018 Author:Shusuke Matsui; Kohei Inui; Yuki Kumai; Ryo Yoshida; Daisuke Suzuki Abstract:*Invited article for special issue “ Biomaterials Science & Engineering in Japan ”.
Elastic and Flow Properties of Densely Packed Microgel Mixtures with Size- and Stiffness Disparitiess Macromolecules,51(23):9901-9914 2018 Author:Ayaki Nakaishi; Saori Minami; Shun Oura; Takumi Watanabe; Daisuke Suzuki; Kenji Urayama Abstract:Densely packed soft microgels (pastes) behave as a yield-stress fluid. They act as soft elastic solids with finite equilibrium shear modulus (G(0)) below a critical stress (sigma(c)) whereas they flow like liquids above sigma(c). The effects of size and stiffness heterogeneities in the constituent microgels on the rheological properties of the pastes are revealed using the binary microgel mixtures by an oscillatory rheometer and diffusive wave spectroscopy (DWS). The binary blends with various degrees of size and stiffness disparities are made by mixing the pastes with the same apparent particle-volume fraction (phi(eff)) at various values of relative weight fraction of soft microgels (f(soft)). The G(0)-f(soft) relations for the soft/hard microgel mixtures are significantly influenced by size disparity: The relations for small size disparities well obey the logarithmic mixing rule, while those for large size disparities have a wide f(soft) regime in which G(0) are almost equal to those of the single small-microgel pastes (G(0,small)), regardless of whether the small microgels are soft or hard. The characteristic f(soft) region with G(0) approximate to G(0,small) for the mixtures with large size disparities is attributed to the developed continuous phase of small microgels (overwhelming in number) where the large microgels are discretely dispersed. The steady-state flow behavior of the binary pastes above sigma(c) obey the classical Hershel-Bulkley (H-B) equation. In each binary paste, the characteristic time (tau(caga)) of the fast local dynamics of microgels trapped in the densely packed structures evaluated from DWS is close to the characteristic time (tau(HB)) obtained from the parameters in the H-B equation and G(0). This agreement shows that the dynamics of the positional rearrangement of microgels in the steady-state flow is closely related to the fast local dynamics in the quiescent state of the pastes, independently of the size and stiffness disparities in the constituent microgels.
The deformation of hydrogel microspheres at the air/water interface Chemical Communications,54(8):932-935 2018 Author:Haruka Minato; Masaki Murai; Takumi Watanabe; Shusuke Matsui; Masaya Takizawa; Takuma Kureha; Daisuke Suzuki Abstract:The deformation of soft hydrogel microspheres (microgels) adsorbed at the air/water interface was investigated for the first time using large poly(N-isopropyl acrylamide)-based microgels synthesized by a modified aqueous precipitation polymerization method. The deformation of the micron-sized soft microspheres could be visualized clearly and analyzed quantitatively at the air/water interface.
Viscoelasticity of dense suspensions of thermosensitive microgel mixtures undergoing colloidal gelation Soft Matter,14(9):1596-1607 2018 Author:Saori Minami; Takumi Watanabe; Daisuke Suzuki; Kenji Urayama Abstract:Dense suspensions of temperature (T)-sensitive poly(N-isopropyl acrylamide) (N) and poly(N-isopropyl methacrylamide) (NM) microgel mixtures with different volume transition temperatures (TNc and TNMc, respectively
TNc <
TNMc) exhibit a characteristic T-dependent viscoelasticity due to T-induced changes in the type of interparticle interaction as well as the volume fraction of each gel. In the range of T <
TNc, where the swollen microgels with repulsive interparticle interactions are densely packed, the equilibrium modulus (G) decreases upon heating due entirely to the packing effect, i.e., a reduction in the total volume fraction of the microgels (φ). At T >
TNc where the attractive interparticle interactions between dehydrated and hydrophobic microgels emerge, the suspensions show solid-like elastic properties due to the network-like flocculation of the shrunken microgels (colloidal gelation), even when φ becomes considerably lower than the threshold for randomly close packing. The T-dependence of G shows a minimum at a characteristic temperature (TB
TB >
TNc) due to the competition between the repulsive interparticle interactions from the packing effect and electrostatic force, and the attractive interactions from the hydrophobicity. The TB in N/NM mixture suspensions shifts to a higher value with a decrease in N content in the mixtures (XN), accompanied by a discontinuous-like change at a specific value of XN (XN∗). The TB at every value of XN agrees approximately with the temperature where the total volume fraction of the attractive hydrophobic microgels is 0.3 regardless of microgel type (N or NM). The discontinuous-like variation in TB at XN∗ reflects the change in the network-like flocculation particles, from only attractive N microgels in the high XN regime, to the attractive N and NM microgel mixtures in the moderate XN regime. The requirement of the repulsive electrostatic force with an appropriate strength for the stability of the network-like flocculation is also demonstrated using the PNIPAM-co-fumaric acid (NF) microgel suspensions at various pH.
Decoupled Thermo- and pH-Responsive Hydrogel Microspheres Cross-Linked by Rotaxane Networks Angewandte Chemie International Edition,56(48):15393-15396 2017(Nov.) Author:Takuma Kureha; Daichi Aoki; Seina Hiroshige; Keisuke Iijima; Daisuke Aoki; Toshikazu Takata; Daisuke Suzuki Abstract:Rotaxane cross-linked (RC) microgels that exhibit a decoupled thermo- and pH-responsive volume transition were developed. The pH-induced changes of the aggregation/disaggregation states of cyclodextrin in the RC networks were used to control the swelling capacity of the entire microgels. Different from conventional thermo- and pH-responsive microgels, which are usually obtained from copolymerizations involving charged monomers, the RC microgels respond to temperature as intended, even in the presence of charged functional molecules such as dyes in the microgel dispersion. The results of this study should lead to new applications, including drug delivery systems that require a retention of their smart functions even in environments that may contain foreign ions, for example, in invivo experiments.
Fast Adsorption of Soft Hydrogel Microspheres on Solid Surfaces in Aqueous Solution Angewandte Chemie International Edition,56(40):12146-12149 2017(Sep.) Author:Shusuke Matsui; Takuma Kureha; Seina Hiroshige; Mikihiro Shibata; Takayuki Uchihashi; Daisuke Suzuki Abstract:The real-time adsorption behavior of polymeric colloidal microspheres onto solid surfaces in aqueous solution was visualized for the first time using high-speed atomic force microscopy (HS-AFM) to reveal how the softness of the microspheres affects their dynamic adsorption. Studies that focus on the deformability of microspheres upon dynamic adsorption have not yet been reported, most likely on account of a lack of techniques that appropriately depict the dynamic adsorption and deformation behavior of individual microspheres at the nanoscale in real time. In this study, the deformability of microspheres plays a crucial role on the adsorption kinetics, that is, soft hydrogel microspheres adsorb faster than harder elastomeric or rigid microspheres. These results should provide insight towards development of new colloidal nanomaterials that exhibit effective adsorption on specific sites in aqueous solution.
Water-immiscible bioinert coatings and film formation from aqueous dispersions of poly(2-methoxyethyl acrylate) microspheres Colloids and Surfaces B: Biointerfaces,155:166-172 2017(Jul.) Author:Takuma Kureha; Seina Hiroshige; Shusuke Matsui; Daisuke Suzuki Abstract:Poly(2-methoxyethyl acrylate) (pMEA) microspheres are prepared through facile free-radical polymerization in water without additives and impurities, such as surfactants, other polymers, and organic solvents, which are usually used to synthesize pMEA chains. Clean and pure (non-factionalized and non-cross-linking) pMEA microspheres exhibit plasma protein adsorption resistances on their surface regardless of their charged state. They are characterized in terms of the adsorbed amounts of proteins at pH 7. In addition, these soft and deformable pMEA microspheres are suitable for forming substrates coated with pMEA microspheres and free-standing films by injecting pMEA dispersion and evaporating the aqueous medium through fusion between the pMEA chains at the surface without the precoating agent and cross-linker. These pMEA coatings have been used till now in artificial heart/lung fabrication and metal products manufacturing by casting organic solvents such as 1,4-dioxane, toluene, and methanol and dissolving pMEA chains prepared using conventional solution polymerization. In this study, bioinert coatings and adhesive and transferable films are easily obtained due to the rubber-like properties of the pMEA microspheres and stable in mild and biocompatible conditions even when these impurities are not used completely, allowing us to provide a guideline for potential pMEA bioapplications such as coatings, films, barriers, and implant devices. (C) 2017 Elsevier B.V. All rights reserved.
Formation of Tough Films by Evaporation of Water from Dispersions of Elastomer Microspheres Crosslinked with Rotaxane Supramolecules Chemistry - A European Journal,23(35):8405-8408 2017(Jun.) Author:Seina Hiroshige; Takuma Kureha; Daichi Aoki; Jun Sawada; Daisuke Aoki; Toshikazu Takata; Daisuke Suzuki Abstract:Compared to rigid microspheres that consist, for example, of polystyrene or silica, soft and deformable elastomer microspheres can be used to generate colorless transparent films upon evaporating the solvent from microsphere-containing dispersions. To obtain tough films, a post-polymerization reaction to crosslink the microspheres is usually necessary, which requires extra additives during the drying process. This restriction renders this film-formation technology complex and rather unsuitable for applications in which impurities are undesirable. In the present study, it is demonstrated that tough elastomer microspheres that are crosslinked with rotaxanes can form tough bulk films upon evaporation of water from microsphere dispersions, so that post-polymerization reactions are not required. The results of this study should thus lead to new applications including coatings for biomaterials that need complete removal of all impurities from the materials prior to use.
Controlled Separation and Release of Organoiodine Compounds Using Poly(2-methoxyethyl acrylate)-Analogue Microspheres ACS Omega,2(11):7686-7694 2017 Author:Takuma Kureha; Yuichiro Nishizawa; Daisuke Suzuki Abstract:A selective adsorption/desorption of organoiodine compounds was achieved on poly(2-methoxyethyl acrylate)-analogue microspheres, wherein the side chains in the polymers act as halogen-bonding sites. These results demonstrate that the halogen-bonding sites in the side chains exhibit adequate specific affinity for organoiodine compounds. In addition, the water-swollen pMEA-analogue microspheres (microgels) showed a thermoresponsive swelling/deswelling behavior that permitted a controlled release of the organoiodine compounds upon changing the temperature. Thus, it seems plausible that a variety of problems associated with, e.g., the recovery of rare iodine-containing compounds, such as the marine-derived iodine compounds, the delivery of iodine-containing drugs, or the removal of halogen compounds from wastewater, could be resolved by polymer microspheres that exhibit controlled halogen bonding.
Impact of Spatial Distribution of Charged Groups in Core Poly(N-isopropylacrylamide)-Based Microgels on the Resultant Composite Structures Prepared by Seeded Emulsion Polymerization of Styrene Langmuir,32(48):12760-12773 2016(Dec.) Author:Takumi Watanabe; Chiaki Kobayashi; Chihong Song; Kazuyoshi Murata; Takuma Kureha; Daisuke Suzuki Abstract:A series of raspberry-shaped composite microgels were synthesized by seeded emulsion polymerization of styrene in the presence of hydrogel particles with different distributions of charged groups. Unlike microgels whose charged groups are localized in their center,29 polystyrene nanoparticles were formed inside the core microgels when the microgels whose charged groups were localized on their surface were used as cores for seeded emulsion polymerization. The effects of the surface charge densities of the core microgels and the concentration of styrene monomer during the polymerization on the resultant structures of composite microgels were investigated. The surface structures of obtained composite microgels were mainly evaluated by electron microscopy, and their stimuli responsiveness was evaluated by dynamic light scattering and laser Doppler velocimetry. The internal structures of the composite microgels were visualized from ultrathin cross sections observed by transmission electron microscopy (TEM). Cryo-TEM was used to clarify the microscopic structures of composite microgels when they were in hydrated states. Through a series of characterizations, we summarize the effects of structures of core microgels on the resultant composite structures.
Rheological properties of suspensions of thermo-responsive poly(N-isopropylacrylamide) microgels undergoing volume phase transition Polymer Journal,48(11):1079-1086 2016(Nov.) Author:Saori Minami; Takumi Watanabe; Daisuke Suzuki; Kenji Urayama Abstract:The rheological properties of suspensions of thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) microgels are investigated in the swollen and collapsed states using oscillatory and long-time creep measurements. In the swollen state with repulsive interparticle interaction, the zero shear viscosity and quasi-plateau modulus are solely governed by the effective volume fraction (phi(eff)) and are independent of temperature, particle diameter and particle concentration. The long-time creep tests reveal that in the collapsed state with attractive interparticle interactions, the moderately concentrated suspensions with phi(eff)approximate to 0.5 become viscoelastic liquids with high viscosities of >10(5) Pas and long-terminal relaxation times of >10(3) s due to the formation of a network-like aggregation of particles, whereas the suspensions with the same phi(eff) in the swollen state exhibit a Newtonian flow with low viscosities of less than 10(-1) Pas. The network-like aggregation of particles is so fragile that it can be broken by a very small stress of several Pascals. The modulus and viscosity in the collapsed state depend on both phi(eff) and temperature: the modulus and viscosity increase, as the temperature increases due to an increase in the hydrophobic nature of the PNIPAM chains, which govern the attractive interparticle interaction. The particle aggregations in the collapsed state considerably lower the threshold value of phi(eff) (phi(c)), above which the infinite percolation clusters are formed, as compared with the values of phi(c) in the swollen state and for the random close packing of hard spheres.
Investigation of Changes in the Microscopic Structure of Anionic Poly(N-isopropylacrylamide-co-Acrylic acid) Microgels in the Presence of Cationic Organic Dyes toward Precisely Controlled Uptake/Release of Low-Molecular-Weight Chemical Compound Langmuir,32(18):4575-4585 2016(May) Author:Takuma Kureha; Takahisa Shibamoto; Shusuke Matsui; Takaaki Sato; Daisuke Suzuki Abstract:Changes in a microscopic structure of an anionic poly(N-isopropyjacrylamide-co-acrylic acid) microgel were investigated using small- and wide-angle X-ray scattering (SWAXS): The scattering profiles of the microgels were analyzed in a wide scattering vector (q) range of 0.07 <= q/nm(-1) <= 20. In particular, the microscopic structure of the microgel in the presence of a cationic dye rhodamine 6G (R6G) was Characterized in terms of its correlation length (xi), which represents the length scale of the spatial correlation of the network density fluctuations, and characteristic distance.(d*), which originated from the local packing of isopropyl groups of two neighboring chains. In the presence of. cationic R6G, xi exhibited a divergent-like behavior, which was not seen in:the absence of R6G, and d* Was decreased with decreasing the volume of the microgel upon increasing temperature. At the same time, the amount of R6G adsorbed per unit mass of the microgel increased upon heating. These results suggested that a coil-to-globule transition of the poly(N-isopropylacrylamide) chains in the present anionic microgel occurred because of efficiently screened, thus, short ranged electrostatic repulsion between the charged groups, and hydrophobic interaction between the isopropyl groups in the presence of cationic R6G. The combination of hydrophobic and electrostatic interaction between the cationic dye and the microgel affected the separation and volume transition behavior of the microgel.
Direct visualization of swollen microgels by scanning electron microscopy using ionic liquids Polymer Journal,48(3):273-279 2016(Mar.) Author:Koji Horigome; Takeshi Ueki; Daisuke Suzuki Abstract:We developed a simple and versatile method for the visualization of swollen microgels using standard scanning electron microscopy (SEM) that does not require the conventional sample pretreatment steps of sputtering. Specifically, microgels were swollen using ionic liquids (ILs), which remained nonvolatile even under high vacuum conditions. Two types of widely studied stimuli-responsive microgels and their hybrids with Au nanoparticles were visualized via SEM to demonstrate the versatility of the method. In particular, we observed the dispersion of embedded Au nanoparticles within the microgels because of the swelling caused by the ILs, confirming that the approach is versatile and useful for the evaluation of nanocomposite materials, such as hybrid microgels.
Localization of Polystyrene Particles on the Surface of Poly(N-isopropylacrylamide-co-methacrylic acid) Microgels Prepared by Seeded Emulsion Polymerization of Styrene Langmuir,32(6):1429-1439 2016(Feb.) Author:Chiaki Kobayashi; Takumi Watanabe; Kazuyoshi Murata; Takuma Kureha; Daisuke Suzuki Abstract:Composite microgels with polystyrene nano particles were synthesized by seeded emulsion polymerization of styrene in the presence of pH- and temperature-responsive poly(N-isopropylacrylamide-co-methacrylic acid) microgels as seeds. In particular, the core microgels maintained their swelled state as the pH was increased to 10 during seeded emulsion polymerization conducted at an elevated temperature. Furthermore, we tuned the swelling degree of the core microgels at pH 10 by changing the amount of methacrylic acid incorporated during the synthesis of the core microgels. Unlike deswollen microgels, during the seeded emulsion polymerization, the swollen microgels were covered with a monolayer of non-close-packed polystyrene particles on their surface, as confirmed by electron microscopy. A possible mechanism for the seeded emulsion polymerization of styrene in the presence of swollen microgels under alkaline conditions is proposed.
Thermo-sensitive colloidal crystals composed of monodisperse colloidal silica- and poly(N-isopropyl acrylamide) gel spheres Colloid and Polymer Science,293(10):2763-2769 2015(Oct.) Author:Daisuke Suzuki; Kiyoshi Shibata; Akira Tsuchida; Tsuneo Okubo Abstract:Thermo-sensitive colloidal crystals were prepared simply and conveniently by mixing of colloidal silica spheres with a series of thermo-sensitive gel spheres, poly (N-isopropyl acrylamide) (pNIPAm, 225 similar to 1500 nm in hydrodynamic diameter, 0.5 similar to 5 mol% in degree of cross-linking and at 20 similar to 45 A degrees C) in the deionized aqueous suspension. The thermo-reversible change in the lattice spacing of colloidal crystals of monodispersed silica spheres (CS83, 103 nm in diameter) depends on the size of the admixed pNIPAm. For gel spheres with similar or less than that of the silica spheres, the lattice spacing decreased with rising temperature. On the other hand, the spacing increased with temperature for the mixtures with pNIPAm spheres of larger than the size of the silica spheres. A mechanism, which is able to explain properly the several experiments including the present work, is proposed, i.e., balancing between the weak adsorption and segregation effects of silica with gel spheres.
Small-angle X-ray Scattering Study on Internal Microscopic Structures of Poly(N-isopropylacrylamide-co-tris(2,2′-bipyridyl))ruthenium(II) Complex Microgels Langmuir,31(26):7228-7237 2015(Jul.) Author:Shusuke Matsui; Takuma Kureha; Kosuke Okeyoshi; Ryo Yoshida; Takaaki Sato; Daisuke Suzuki Abstract:Internal microscopic structures of poly(N-isopropylacrylamide-co-tris(2,2'-bipyridyl))ruthenium(II) complex microgels were investigated using small-angle X-ray scattering (SAXS) in the extended q-range of 0.07 <= q/nm(-1) <= 20. The microgels were prepared by aqueous free-radical precipitation polymerization, resulting in formation of monodispersed, submicrometer-sized microgels, which was confirmed by transmission electron microscopy and dynamic light scattering. To reveal the changes in the microscopic structures of the microgels during swelling/deswelling or dispersing/flocculating oscillation, the redox state of Ru(bpy)(3) complexes was fixed in the microgels using Ce(IV) or Ce(III) ions under high ionic strength (1.5 M) during the SAXS Measurements. The scattering intensity of the microgels manifested five different structural features. In particular, the correlation length (xi), which was obtained from the fitting analysis using the Ornstein-Zernike equation, of the microgels both in the reduced and oxidized Ru(bpy)(3) states exhibited divergent-like behavior. In addition, a low-q peak centered at q approximate to 5 nm(-1) did not appear clearly in both the reduced [Ru(bpy)(3)](2+) and oxidized [Ru(bpy)(3)](3+) states, indicating that the formation of a polymer-rich domain was suppressed; thus, Ru(bpy)(3) complexes can be active even though the microgels are deswollen Or flocculated during the oscillation reaction.
Relationship between Temperature-Induced Changes in Internal Microscopic Structures of Poly(N-isopropylacrylamide) Microgels and Organic Dye Uptake Behavior Langmuir,30(29):8717-8725 2014(Jul.) Author:Takuma Kureha; Takaaki Sato; Daisuke Suzuki Abstract:Temperature-induced changes in the internal structures of poly(N-isopropylacrylamide) (pNIPAm) microgels were evaluated by small-angle X-ray scattering (SAXS), and the results were used to explain organic dye uptake by the microgels. The dye uptake experiments were conducted using two organic dyes: cationic rhodamine 6G (R6G) and anionic erythrosine. In the SAXS investigation, the internal structures of the microgels were characterized in terms of the correlation length, xi, and the distance, d*, which originated from the local packing of the isopropyl groups of two neighboring chains. With increasing temperature up to the volume phase transition temperature (VPTT) of the microgels, the correlation length, xi, was increased and the distance, d*, was decreased. At the same time, the amounts of the dyes taken up by the pNIPAm microgels were increased, despite a decrease in the volume of the microgels. The results indicated that the pNIPAm chains were closer to each other due to the hydrophobic association of isopropyl groups, which resulted in the growth of the hydrophobic domains. Thus, the hydrophobic interactions between the dyes and pNIPAm were probably accompanied by the domain formation. With a further increase of temperature above the VPTT, the correlation length, xi, was decreased and then not defined because the Ornstein-Zernike type contribution disappeared, and the distance, d*, was not largely changed. At the same time, the uptake amounts of the dyes per unit volume of the microgels were also not largely changed, which behaved similar to the distance, d*. It was probably due to the fact that the internal structures of the microgels were not largely changed because the isopropyl groups were in contact with each other. The view was supported by the result of the uptake study of the nonthermoresponsive microgels which did not have the hydrophobic isopropyl groups.
Raspberry-Shaped Composite Microgel Synthesis by Seeded Emulsion Polymerization with Hydrogel Particles Langmuir,30(24):7085-7092 2014(Jun.) Author:Daisuke Suzuki; Chiaki Kobayashi Abstract:A series of raspberry-shaped composite microgels were synthesized by the seeded emulsion polymerization of styrene with hydrogel particles. Thermoresponsive microgels of poly(N-isopropylacrylamide) cross-linked with N,N'-methylenebis(acrylamide) acted as cores for the polymerization. During the surfactant-free polymerization, the core microgels shrank at 70 degrees C to provide thermoresponsive composite microgels, and the polystyrene particles attached to core microgels became bigger with increasing styrene concentration. Conversely, composite microgels synthesized with sodium dodecyl sulfate (SDS) ([SDS] > 6.5 mM) did not exhibit thermoresponsive deswelling behavior because polystyrene particles covered the core microgels. In particular, polystyrene particles formed composites on the microgel surface as well as inside the microgels when the SDS concentration exceeded a critical value for core microgel swelling at 70 degrees C. A mechanism is proposed based on these results for the seeded emulsion polymerization of water-immiscible monomers with microgels.
Internal Structures of Thermosensitive Hybrid Microgels Investigated by Means of Small-Angle X-ray Scattering The Journal of Physical Chemistry B,118(8):2194-2204 2014(Feb.) Author:Daisuke Suzuki; Yasuhisa Nagase; Takuma Kureha; Takaaki Sato Abstract:Internal structures of thermosensitive microgels and their hybrid counterparts that contain Au nanoparticles are investigated by means of small-angle X-ray scattering (SAXS). Thermosensitive cationic microgels were synthesized by aqueous free radical precipitation polymerization from N-isopropylacrylamide and 3-(methacrylamino) propyltrimethylammonium chloride used as monomers. Using the microgels as templates, Au nanoparticles were synthesized in situ, using the cationic sites in the microgel to nucleate particle growth. To obtain different types of the hybrid microgels, Au nanoparticles were synthesized in the presence of the microgels by changing the reduction conditions of the precursor ions, such as temperature and species of reducing reagent. The hybrid microgels were characterized mainly by TEM and SAXS. For SAXS investigation, the hybrid microgels were analyzed in the wide q-range of 0.07 nm(-1) < q < 20 nm-1, where q is the magnitude of the scattering vector. A quantitative description of the scattering intensities, 1(q), for the nonhybrid microgels requires a sum of five components having different physical origins. An upturn increase of the forward intensity originates from the interface of microgels, obeying the Porod law, 1(q) alpha q(-4). An additional Guinier term found in q < 0.2 nm(-1) seems to arise from solidlike density fluctuation due to the inhomogeneities of chemical cross-links. The power-law behavior manifested in the low- to intermediate-q range is directly linked with the fractal nature of the swollen (coil) polymer networks and well described by the Ornstein-Zernike equation. Two interference peaks centered at q approximate to 5 nm(-1) and q approximate to 15 nm(-1) are likely to reflect inter- and intrachain correlations of pNIPAm, respectively, which are formally fitted by pseudo-Voigt equations. As for the hybrid microgels, a pronounced new contribution from the Au nanoparticles emerges, which calls for an additional scattering component describing polydisperse spheres having a homogeneous internal electron density distribution. The width of the Gaussian distribution for the radius of the Au nanoparticles evaluated from the SAXS data turns out to be consistent with those obtained with TEM observation.
A simple feature of yielding behavior of highly dense suspensions of soft micro-hydrogel particles Soft Matter,10(47):9486-9495 2014 Author:Kenji Urayama; Taku Saeki; Shen Cong; Shota Uratani; Toshikazu Takigawa; Masaki Murai; Daisuke Suzuki Abstract:The highly dense suspensions of soft micro-hydrogels with a narrow size distribution (typically phi(eff) > 0.9 where feff is the apparent volume fraction of the particle), which form a regular lattice structure, exhibit a simple feature in the yielding behavior: the yield strain gamma(c) [ca. 2.5% and ca. 4.8% for poly(N-isopropylmethacrylamide) (PNIPMA) and poly(N-isopropylacrylamide) (PNIPA) hydrogel particles, respectively] is nearly insensitive to the cross-link concentration (c(x)), particle diameter (D-h), and particle concentration (c) in the limited c range examined here, and gamma(c) is almost constant in a wide range of equilibrium shear moduli over two orders of magnitude. In addition, no appreciable difference in gamma(c) is observed in the dense pastes with crystalline and glassy structures which are formed by mono- and bidisperse microgels, respectively. This is in contrast to a finite difference in gamma(c) for the crystal and glass formed by the hard sphere reported by Koumakis et al. [Soft Matter, 4, 2008 (2008)]. Furthermore, the highly dense suspensions of NIPA core-NIPMA shell microgels are similar in gamma(c) to those of NIPMA microgels. These results indicate that gamma(c) for the highly dense suspensions of soft micro-hydrogels depends primarily on the kind of constituent polymer near the particle surface. The yield strain gamma(c) is expected to be governed by short-range interactions such as adhesion and friction.
Assembly of Oppositely Charged Microgels at the Air/Water Interface The Journal of Physical Chemistry B,117(30):9073-9082 2013(Aug.) Author:Daisuke Suzuki; Koji Horigome Abstract:We present an assembly of cationic and anionic microgels at the air/water interface. Monodispersed, micrometer-sized, and oppositely charged microgels were synthesized by aqueous free-radical precipitation polymerization by using N-isopropylmethacrylamide, comonomers, and cross-linkers. The oppositely charged microgels were prepared by using different types of water-soluble initiators. These microgels were mixed in a solution to assemble them at the air/water interface. In particular, linear and branched chainlike structures of the microgels were spontaneously formed at the air/water interface. Effects of salt concentration, microgel concentration, and number ratio of cationic and anionic microgels on the structures of microgel assembly were investigated by optical microscopy and scanning electron microscopy.
Multilayered Composite Microgels Synthesized by Surfactant-Free Seeded Polymerization Langmuir,29(33):10579-10585 2013(Aug.) Author:Daisuke Suzuki; Tomoyo Yamagata; Masaki Murai Abstract:We report on a simple and rapid method to produce multilayered composite microgels. Thermosensitive microgels were synthesized by aqueous free radical precipitation polymerization using N-isopropylacrylamide (NIPAm) as a monomer. Using the microgels as cores, surfactant-free seeded polymerization of an oil-soluble monomer, glycidyl methacrylate (GMA), was carried out at 70 degrees C, where the microgels were highly deswollen in water. All of the oil-soluble monomers were polymerized, and the resultant polymers were attached on the pre-existing microgel cores, resulting in hard shell formation. It is worth mentioning that secondary particles of oil-soluble monomers have never been formed during the polymerization. The composite microgels were characterized by electron microscopy and dynamic light scattering. In particular, X-ray photoelectron spectroscopy (XPS) measurements revealed that the surface of the composite microgels was composed of a hydrogel layer, although microgel cores were covered by polyGMA shell. The mechanism of the trilayered composite rnicrogel formation will be discussed.
Crystal structure of thermosensitive gel spheres of poly(N-isopropylacrylamide) in the deionized aqueous suspension as studied by the static light-scattering measurements Colloid and Polymer Science,291(3):661-668 2013(Mar.) Author:Tsuneo Okubo; Daisuke Suzuki; Akira Tsuchida Abstract:Static light-scattering measurements of deionized suspensions of the thermosensitive gels of poly(N-isopropylacrylamide) with various degrees of cross-linking and sizes were made at 20 and 40 A degrees C. Sharp scattering peaks are observed in the scattering curve, and they were attributed to the face-centered cubic (fcc) and/or body-centered cubic lattices (bcc) in the distribution of gel spheres. The fcc and bcc crystal structures formed in the stable and unstable conditions, respectively, i.e., the former formed more favorably at high sphere concentrations and/or low temperatures. The closest intersphere distances were much longer than the hydrodynamic diameters of the gel spheres especially at low sphere concentrations. These experimental results emphasize the important role of the extended electrical double layers in the crystallization of gel spheres, though the contribution of the double layers in gel systems is weak compared with that in the typical colloidal spheres.
Drying dissipative structures of thermosensitive gel spheres of poly (N-isopropylacrylamide). Influence of gel size Colloid and Polymer Science,290(18):1901-1911 2012(Dec.) Author:Tsuneo Okubo; Daisuke Suzuki; Akira Tsuchida Abstract:Drying dissipative patterns of de-ionized suspensions (colloidal crystal-state at high concentrations) of the thermosensitive gels of poly (N-isopropylacrylamide) with various sizes (ca. 400-1,500 nm in diameter at 20 A degrees C) were observed at 20 and 45 A degrees C on a cover glass, a watch glass, and a Petri glass dish. The broad rings were observed and their size decreased as gel concentration decreased. Formation of the monodispersed agglomerated particles and their ordered arrays were observed irrespective of gel size. The macroscopic flickering spoke-like patterns were observed for the gel spheres from 70 to 600 nm in diameter at 20 A degrees C, but almost disappeared for extremely large spheres, poly(N-isopropylacrylamide)(1500-5). This work clarified the formation of the drying microscopic structures of (a) ordered rings, (b) flickering ordered spoke lines, (c) net structure, and (d) lattice-like ordered structures of the agglomerated particles. The ordered rings became rather vague as gel size increased. The large net structures formed so often for large gels. Size effect on the lattice patterns was not recognized so clearly. The role of the electrical double layers around the agglomerated particles and the interaction of the particles with the substrate surfaces during dryness are important for the ordering. The microscopic drying patterns of gel spheres were quite different from those of linear type polymers and also from typical colloidal hard spheres, though the macroscopic patterns such as broad ring formation at the edges of the dried film were similar to each other.
Drying Mechanism of Poly(N-isopropylacrylamide) Microgel Dispersions Langmuir,28(36):12962-12970 2012(Sep.) Author:Koji Horigome; Daisuke Suzuki Abstract:The drying mechanism of poly(N-isopropylacrylamide) (pNIPAm) microgel dispersions was investigated. The microgels were synthesized by temperature-programmed aqueous free radical precipitation polymerization using NIPAm, N,N'-methylenebis(acrylamide), and water-soluble initiator. Drying processes of the microgel dispersions were observed with a digital camera and an optical microscope, and the resultant dried structures were observed by scanning electron microscopy. We found that the presence of the microgels changed the behavior of the drying process of water. In particular, the microgels were adsorbed at the air/water interface selectively within a few minutes irrespective of the microgel concentration. The relationship between the drying mechanism and structure of the resultant microgel thin film has been clarified by changing the microgel concentration of the dispersions.
Kinetic studies of colloidal crystallization of thermo-sensitive gel spheres of poly(N-isopropylacrylamide) Colloid and Polymer Science,290(14):1403-1412 2012(Sep.) Author:Tsuneo Okubo; Daisuke Suzuki; Kiyoshi Shibata; Akira Tsuchida Abstract:Crystal growth rate coefficients, k of the colloidal crystallization of thermo-sensitive gel spheres of poly(N-isopropylacrylamide) were measured from the time-resolved reflection spectroscopy mainly by the inverted mixing method in the deionized state. Crystallization of colloidal silica spheres were also measured for comparison. The k values of gel and silica systems increased sharply as the sphere concentration and suspension temperature increased. The k values of gel system were insensitive to the degree of cross-linking in the range from 10 to 2 mol% of cross-linker against amount of the monomer in mole and decreased sharply when the degree of cross-linking decreased further to 0.5 %. The k values increased as gel size increased. The k values of gel systems at 20 A degrees C were small and observed only at the very high sphere concentration in volume fraction, whereas those at 45 A degrees C were high but smaller than those of silica systems. Induction time (t (i)) after which crystallization starts, increased as the degree of cross-linking increased and/or the gel size decreased at any temperatures, when comparison was made at the same gel concentration. The t (i) values at 45 A degrees C were high and decreased sharply with increasing sphere concentration, whereas those at 20 A degrees C were high only at the very high sphere concentrations. Significant difference in the k and t (i) values between the soft gels and hard silica spheres was clarified. These kinetic results support that the electrical double layers play an important role for the gel crystallization in addition to the excluded volume of gel spheres. It is deduced further that the electrical double layers of the gel system form from the vague interfaces (between soft gel and water phases) compared with those of typical colloidal hard sphere system.
Hydrogel Particles as a Particulate Stabilizer for Dispersion Polymerization Langmuir,28(29):10629-10634 2012(Jul.) Author:Daisuke Suzuki; Shohei Yamakawa Abstract:Hydrogel particles composed of poly(N-isopropylacrylamide) were used as a particulate steric stabilizer for the dispersion polymerization of styrene for the first time. The effects of the size and concentration of the hydrogel particles on the resultant polystyrene particles were investigated. As expected, the hydrogel particles indeed play the role of steric stabilizer for dispersion polymerization. Moreover, some of the resultant polystyrene particles were covered with hydrogel particles, which was confirmed by electron microscopy and X-ray photoelectron spectroscopy.
Drying dissipative structures of thermo-sensitive gel spheres of poly(N-isopropylacrylamide). Influence of degree of cross-linking of the gels Colloid and Polymer Science,290(10):867-877 2012(Jul.) Author:Tsuneo Okubo; Daisuke Suzuki; Akira Tsuchida Abstract:Drying dissipative patterns of de-ionized suspensions (colloidal crystal state above the critical concentrations of crystallization) of the thermo-sensitive gels of poly(N-isopropylacrylamide) with degrees of cross-linking of 10% and 2% (pNIPAm(200-10) and pNIPAm(200-2)) were observed at 20 A degrees C and 45 A degrees C on a cover glass, a watch glass, and a Petri glass dish. The broad rings were observed, and their size decreased as micro-gel concentration decreased. Formation of the monodispersed agglomerated particles and their ordered arrays were observed. Microscopic drying structures of (a) flickering ordered spoke-lines, (b) ordered rings, (c) net structure, and (d) lattice-like ordered structures of the agglomerated particles are observed. The net and lattice structures formed more favorably at high degrees of cross-linking, at high concentrations of the gels, and/or high temperatures. By the addition of sodium chloride, very large dendrite-like and net structures of the large agglomerated particles formed at 20 A degrees C and 45 A degrees C, respectively. Importance of the cooperated convectional flow of the agglomerated particles during the drying processes is supported for the ordered array formation. The role of the electrical double layers around the agglomerated particles and the interaction of the particles with the substrate surfaces during dryness are also important for the ordering. The microscopic drying patterns of gel spheres were different from those of linear type polymers and also from typical colloidal spheres, though the macroscopic patterns of gel system such as broad ring formation at the edges of the dried film were similar to other two systems.
Drying dissipative structures of thermo-sensitive gel spheres of poly(N-isopropylacrylamide) with low degree of cross-linking Colloid and Polymer Science,290(5):411-421 2012(Mar.) Author:Tsuneo Okubo; Daisuke Suzuki; Akira Tsuchida Abstract:Drying dissipative patterns of deionized suspensions (colloidal crystal state at high concentrations) of the thermo-sensitive gels of poly(N-isopropylacrylamide) with low degree of cross-linking of 0.5% (318 nm and 116 nm in the hydrodynamic diameter at 25 degrees C and 45 degrees C) were observed at 20 degrees C and 45 degrees C on a cover glass, a watch glass and a Petri glass dish. The broad rings were observed and their size decreased as micro-gel concentration decreased. Formation of the monodispersed agglomerated particles and their ordered arrays were observed. This work clarified the formation of the drying microscopic structures of (a) flickering ordered spoke-lines, (b) ordered rings, (c) net structure, and finally (d) lattice-like ordered structures of the agglomerated particles. The net and lattice structures formed more favorably at higher temperatures and/or higher degree of cross-linking of the gels. Importance of the convectional flow of the agglomerated particles during the drying processes is supported for the ordered array formation. The role of the electrical double layers around the agglomerated particles and the interaction of the particles with the substrate surfaces during dryness are also important for the ordering. The microscopic drying patterns of gel spheres were quite different from those of linear-type polymers and also from typical colloidal spheres, though the macroscopic patterns such as broad ring formation at the edges of the dried film were similar to each other.
Colloidal crystallization of thermo-sensitive gel spheres of poly (N-isopropyl acrylamide). Influence of gel size Colloid and Polymer Science,290(2):107-117 2012(Jan.) Author:Daisuke Suzuki; Tomoyo Yamagata; Koji Horigome; Kiyoshi Shibata; Akira Tsuchida; Tsuneo Okubo Abstract:Influence of the gel size on the morphology, phase diagram, and reflection spectroscopy of the colloidal crystals of thermo-sensitive gel spheres, poly (N-isopropylacrylamide) (pNIPAm), was discussed by adding the data of two gel samples of pNIPAm(400-5) and pNIPAm(600-5) of 412 nm (at 25 degrees C) and 220 nm (at 45 degrees C) and of 517 nm (at 20 degrees C) and 294 nm (at 45 degrees C), respectively. Colloidal single crystals formed, but not so large compared with the giant crystals of small pNIPAm gels reported previously. The suspensions even with ion-exchange resins were turbid and hard to observe the single crystals clearly with the naked eyes as gel size increased. The critical concentration of melting decreased sharply as the suspensions were deionized with coexistence of the mixtures of cation-and anion-exchange resins. The critical concentration increased as the gel size increased and/or dispersion temperature increased. Density of the gel spheres increased as their size increased. These results demonstrated that the colloidal crystallization takes place by the extended electrical double layers formed around the gel spheres in addition of the excluded volume effect of the gels. Contribution of the electrical double layers on the crystallization increased sharply as temperature increased and gel concentration decreased, respectively. The contribution also increased slightly as sphere size increased, when comparison was made at the same gel concentration in wt.%. The present work clarified that the colloidal interfaces, which are inevitable for the formation of the electrical double layers, are formed between the water phase and gel spheres, though the gel spheres contain a lot of water molecules at the inner sphere region.
Effect of Nanointegration on Photoinduced Hydrogen-Generating Nanogel Systems Langmuir,28(2):1539-1544 2012(Jan.) Author:Kosuke Okeyoshi; Daisuke Suzuki; Ryo Yoshida Abstract:The nanointegration mechanism for photoinduced hydrogen nano-generators using nanogels is described. By spatially integrating poly(N-isopropylacrylamide-co-Ru(bpy)(3)) nanogels as a photosensitizer and Pt nanoparticles as a catalyst, a mechanism using electrostatic interactions and the shrinking behavior of the thermosensitive polymer network is revealed. In addition, to evaluate the sensitivity to exterior energy, light, and heat, the integrated nanospace is controlled by using thermosensitive nanogels, which drastically shrink above the volume phase transition temperature. Such nanospatial control of multiple kinds of functional molecules in a photochemical reaction, is important for the realization of artificial photosynthetic systems.
Soft actuators of organized self-oscillating microgels Soft Matter,8(45):11447-11449 2012 Author:Daisuke Suzuki; Takeshi Kobayashi; Ryo Yoshida; Toshihiro Hirai Abstract:Autonomously oscillating soft actuators have been successfully obtained by assembling pre-existing microgel particles. The amplitude of the actuator's oscillation could be controlled by selecting the types of oscillations of constituent microelements, i.e., swelling-deswelling or cooperative dispersing-flocculating motion of the microgels. The new actuators prepared by this fabrication process make the oscillating actuators suitable for practical use in microfluidic devices such as self-beating micropumps.
Colloidal crystallization of thermo-sensitive gel spheres of poly (N-isopropyl acrylamide). Influence of degree of cross-linking of the gels Colloid and Polymer Science,289(17-18):1799-1808 2011(Nov.) Author:Daisuke Suzuki; Koji Horigome; Tomoyo Yamagata; Kiyoshi Shibata; Akira Tsuchida; Tsuneo Okubo Abstract:Morphology, phase diagram, and reflection spectroscopy of the colloidal crystals of thermo-sensitive gel spheres, poly (N-isopropylacrylamide) having degrees of cross-linking 10 and 2 mol.% (pNIPAm(200-10) and pNIPAm(200-2)) were studied. Giant colloidal single crystals formed at very low gel concentrations. Critical concentrations of melting increased as the degree of cross-linking decreased in the range from 10 to 0.5 mol.% and/or suspension temperature increased from 20 to 45 A degrees C. The critical concentration decreased sharply as the suspensions were deionized with coexistence of the mixtures of cation- and anion-exchange resins. Density of a gel sphere (gel concentration in weight percent divided by that in volume percent) increased sharply as the degree of cross-linking and/or temperature increased. These results demonstrated that the colloidal crystallization takes place by the extended electrical double layers formed around the gel spheres in addition of the excluded-volume effect of the gels. Most of the researchers including the authors have believed that the crystallization of the gel spheres takes place by the excluded-volume effect. However, the present work clarified that the colloidal interfaces, which are inevitable for the formation of the electrical double layers, are formed firmly between the water phase and gel spheres, though the gel spheres contain a lot of water molecules in the sphere region.
Binary Mixtures of Cationic and Anionic Microgels Langmuir,27(20):12368-12374 2011(Oct.) Author:Daisuke Suzuki; Koji Horigome Abstract:Colloidal behaviors of binary mixtures composed of cationic and anionic microgels are reported. Both microgels were synthesized by aqueous free radical precipitation polymerization using N-isopropylacrylamide and N,N'-methylenebisacrylamide but using different types of water-soluble initiators and comonomer. Effects of temperature and salt concentration on phase behaviors of binary mixtures of cationic and anionic microgels were investigated as well as single-species microgels by UV-vis spectroscopy. We found that the presence of a small amount of NaCl altered the dispersing behavior of the binary mixtures of cationic and anionic microgels when they were in hydrated and swollen states. In particular, scanning electron microscope observation clarified that the binary mixtures containing a small amount of NaCl were not flocculated, and microgels showed non-dose-packed structures on a planar substrate in the dry state. Furthermore, flocculations formed when both microgels were in the swollen states could be redispersed by adding a small amount of NaCl and gently stirring: These tunable properties have not been observed in mixtures of hard particles, and are due to the coexistence of electrostatic interactions and steric hindrance of highly hydrated soft particles.
Drying dissipative structures of thermo-sensitive gel spheres of poly(N-isopropylacrylamide) Colloid and Polymer Science,289(7):807-816 2011(May) Author:Tsuneo Okubo; Daisuke Suzuki; Tomoyo Yamagata; Akihiro Katsuno; Masashi Mizutani; Hiroshi Kimura; Akira Tsuchida Abstract:Drying dissipative patterns were observed at 25 A degrees C, 33 A degrees C, and 45 A degrees C on a cover glass, a watch glass, and a Petri glass dish during the course of dryness of colloidal crystals of the thermo-sensitive gels of poly(N-isopropylacrylamide) (PNIPA). Two kinds of broad rings, i.e., transparent ring at the outside edge and the ring in the inner area from the edge, were observed. Sizes of the former were the same as those of the initial liquids irrespective of gel concentration, whereas sizes of the latter decreased as gel concentration decreased. These broad rings were composed mainly of the monomeric and the agglomerated gel particles, respectively. Formation of the monodispersed agglomerated particles and their ordered arrays in the inner area of the dried film were observed especially on a Petri glass dish and a watch glass. The important role of the electrical double layers formed around the agglomerated particles is supported for the ordering of the agglomerated particles. The essential differences in the drying patterns between PNIPA gel spheres and the typical colloidal particles did not appear.
Effects of pH and temperature on assembly of multiresponsive Janus microgels Colloid and Polymer Science,289(5-6):729-737 2011(Apr.) Author:Yoshitaka Umeda; Takeshi Kobayashi; Toshihiro Hirai; Daisuke Suzuki Abstract:Multiresponsive behaviors of Janus microgels whose properties of both hemispheres are different are presented. We fabricated the multiresponsive Janus microgels by post-polymerization modification at an oil/water interface. To prevent the microgels from wobbling at the interface during the modification process, oil droplets stabilized by microgels were solidified by cooling. Temperature- and pH-responsive behaviors of Janus microgels were characterized both by dynamic light scattering and by optical microscopy. By changing temperature and pH, behaviors of Janus microgels could be controlled; they dispersed individually or assembled into specific structures. The stimuli-responsive behaviors of Janus microgels may be used as microactuators or candidates in developing more precisely controlled particle clusters.
Colloidal crystallization of thermo-sensitive gel spheres of poly (N-isopropyl acrylamide) Colloid and Polymer Science,289(3):291-299 2011(Feb.) Author:Tsuneo Okubo; Daisuke Suzuki; Tomoyo Yamagata; Akihiro Katsuno; Mikito Sakurai; Hiroshi Kimura; Akira Tsuchida Abstract:Morphology, phase diagram, and reflection spectroscopy of the colloidal crystals of thermo-sensitive gel spheres, poly (N-isopropylacrylamide) (224 nm in the hydrodynamic diameter at 25 A degrees C) were studied. Giant colloidal single crystals formed at very low gel concentrations. Critical concentration of melting of gel spheres (0.8 wt.% without ion-exchange resins) decreased sharply to 0.01 wt.% as the gel suspension was deionized exhaustively with coexistence of the mixtures of cation- and anion-exchange resins and increased substantially as concentration of sodium chloride increased. These studies demonstrated that the colloidal crystallization takes place by the extended electrical double layers formed around the gel spheres in addition of the excluded-volume effect of the gels. Most of the researchers including the authors have believed that the crystallization of the gel spheres takes place by the excluded-volume effect, in other words, by the hard-sphere model, exclusively. However, the present work clarified that the colloidal interfaces, which are inevitable for the formation of the electrical double layers, are formed firmly between the water phase and gel spheres, though the gel spheres contain a lot of water molecules in the inner the sphere region.
Photoinduced Hydrogen‐Generating Nanogel Systems Small,7(3):311-315 2011(Feb.) Author:Kosuke Okeyoshi; Daisuke Suzuki; Akihiro Kishimura; Ryo Yoshida
Self-oscillating core/shell microgels: effect of a crosslinked nanoshell on autonomous oscillation of the core Polymer Journal,42(6):501-508 2010(Jun.) Author:Daisuke Suzuki; Ryo Yoshida Abstract:We reported the effects of crosslinked nanoshells covering self-oscillating microgels on their oscillatory behaviors. We carried out seeded precipitation polymerization of N-substituted acrylamide derivatives using preformed, self-oscillating microgels as cores. The core/shell microgels obtained were characterized by dynamic light scattering. Oscillating behaviors were characterized by changes in optical transmittance. In addition, the characteristics (that is, induction period, oscillating period and waveform) of the oscillation of the core/shell microgels were compared with that of the parent core microgel to clarify the effect of the addition of a nanoshell on the autonomous oscillating behaviors of microgels. Polymer Journal (2010) 42, 501-508; doi:10.1038/pj.2010.28; published online 21 April 2010
Characterization of Autonomously Oscillating Viscosity Induced by Swelling/Deswelling Oscillation of the Microgels The Journal of Physical Chemistry B,114(7):2405-2410 2010(Feb.) Author:Hajime Taniguchi; Daisuke Suzuki; Ryo Yoshida Abstract:We report on autonomously oscillating viscosity in microgel dispersions induced by swelling/deswelling oscillations of the microgels. The microgels are composed of poly(N-isopropylacrylamide) in which ruthenium tris(2,2'-bipyridine), (Ru(bpy)(3)), a catalyst for the Belousov-Zhabotinsky (BZ) reaction, is covalently bonded to the polymer chain. At first, we measured hydrodynamic diameters of the microgels tinder the oxidized and reduced ruthenium states by dynamic light scattering. Then, measurements of viscosity in microgel dispersions under various microgel concentrations, ionic strengths, and temperatures were investigated. Next, the BZ reaction was carried out to measure the autonomously oscillating viscosity in the dispersions. In this study, the effect of the concentration of microgels, the concentration of the substrates for the BZ reaction, and the amount of Ru(bpy)(3) immobilized in microgels were investigated to authenticate how swelling/deswelling oscillations of the microgels were linked to the viscosity oscillations.
Autonomously Oscillating Viscosity in Microgel Dispersions Journal of the American Chemical Society,131(34):12058-+ 2009(Sep.) Author:Daisuke Suzuki; Hajime Taniguchi; Ryo Yoshida Abstract:We present autonomously oscillating viscosity in microgel dispersions. The microgels were obtained by introducing the Ru catalyst for the Belousov-Zhabotinsky (BZ) reaction into a cross-linked copolymer. In this microgel system, the chemical energy of the BZ reaction is converted to rhythmic swelling/deswelling oscillation of the microgels. Moreover, self-flocculating/self-dispersing oscillation of the microgels occurs near its phase transition temperature. Through the use of these two oscillations of the microgels, a new function of colloidal dispersions has been discovered, namely, autonomously oscillating viscosity in a microgel dispersion. The viscosity in the dispersion oscillated autonomously, following the swelling/deswelling and self-flocculation/self-dispersion oscillations of the microgels. As a result, we can control the rhythm and amplitude of the oscillation using these two phenomena of the microgels.
Synthesis and Characterization of Submicron-sized, Self-oscillating Hydrogel Particles Transaction of the Materials Research Society of Japan,34(3):465-467-467 2009 Author:Daisuke Suzuki; Ryo Yoshida Abstract:Different from simple stimuli-sensitive microgels, herein, we report "self-oscillating" microgel. This microgel shows an autonomic and periodical swelling/deswelling oscillation that is synchronized with redox oscillation of the Belousov-Zhabotinsky (BZ) reaction. The cross-linked microgels were synthesized by the copolymerization of N-isopropylacrylamide (NIPAm) with ruthenium tris(2,2′-bipyridine) [Ru(bpy)3] as a catalyst for the BZ reaction by surfactant-free aqueous precipitation polymerization. The self-oscillation of the microgels was detected by changes in optical transmittance. The microgels showed not only the swelling/deswelling oscillation, which is synchronized with the redox oscillation of the Ru(bpy)3 complex immobilized in the microgels, but also flocculating/dispersing oscillation around the phase transition temperature of the microgels, with a remarkable change in optical transmittance.
Effect of initial substrate concentration of the Belousov-Zhabotinsky reaction on self-oscillation for microgel system The Journal of Physical Chemistry B,40(112):12618-12624 2008(Oct.) Author:Daisuke Suzuki; Ryo Yoshida Abstract:Self-oscillation for the microgel particles (similar to 200 nm in diameter) was studied by changing initial substrate concentrations (i.e., malonic acid, sodium bromate, and nitric acid) of the Belousov-Zhabotinsky (BZ) reaction that is used for chemical energy for the self-oscillation. The cross-linked microgels are composed of N-isopropylacrylamide and ruthenium tris(2,2'-bipyridine), Ru(bpy)(3), which is a catalyst for the BZ reaction. Comparing with the homogeneous, stirred solution of the bulk solution for the BZ reaction, swelling/deswelling oscillation of the microgels showed longer induction period, different dependence of initial substrate concentrations on oscillation period, and different oscillation rhythm. The change in oscillation for the microgels can be understood by considering the microgel network effect.
Temporal control of self-oscillation for microgels by cross-linking network structure Macromolecules,41(15):5830-5838 2008(Aug.) Author:Daisuke Suzuki; Ryo Yoshida Abstract:Self-oscillating microgel, which undergoes an autonomic and periodical swelling/deswelling oscillation, has been reported. The cross-linked microgels were synthesized by the copolymerization of N-isopropylacrylamide (NIPAm) with ruthenium tris(2,2'-bipyridine) [Ru(bpy)(3)]as a catalyst for the Belousov-Zhabotinsky (BZ) reaction by surfactant-free aqueous precipitation polymerization. The self-oscillation of the microgels was detected by changes in optical transmittance. The microgels showed not only the swelling/deswelling oscillation, which is synchronized with the redox oscillation of the Ru(bpy)(3) complex immobilized in the microgels, but also flocculating/dispersing oscillation around the phase transition temperature of he microgels, with a remarkable change in optical transmittance. These microgel oscillations were further studied by comparing the optical transmittance changes of the microgels and the redox potential change of Ru(bpy)(3) immobilized in the microgels. In order to analyze the microgel self-oscillation in detail, three characteristics (induction period, oscillation period, and waveform) of the microgel oscillation were compared with those of the bulk solution of the BZ reaction. Because of the effect of Ru(bpy)(3) immobilization in the microgels on the BZ reaction, induction time for the microgels became longer than that for the bulk solution; however, the oscillation periods became shorter. The latter can be well explained by the Field-Koros-Noyes (FKN) mechanism.
Synthesis and Assembly of Well-Structured Hybrid Microgels Transactions of the Materials Research Society of Japan,33(2):365-368 2008 Author:Daisuke Suzuki and Haruma Kawaguchi
Synthesis and application of polymeric microspheres containing inorganic particles Transactions of the Materials Research Society of Japan,33(2):205-208 2008 Author:Haruma Kawaguchi, Daisuke Suzuki, and Daisuke Kaneshima
Self-flocculating/Self-dispersing oscillation of microgels Angewandte Chemie International Edition,47(5):917-920 2008 Author:Daisuke Suzuki; Takamasa Sakai; Ryo Yoshida Abstract:*Highlighted in Nature Mater. Microgels in motion” Nature Mater. 7, p95 (2008)
Janus microgels prepared by surfactant-free pickering emulsion-based modification and their self-assembly Journal of the American Chemical Society,129(26):8088-+ 2007(Jul.) Author:Daisuke Suzuki; Sakiko Tsuji; Haruma Kawaguchi Abstract:We present Janus microgels modified using a Pickering emulsion-based approach and demonstrate their self-assembly. Stimuli-responsive microgels composed of cross-linked poly[N-isopropylacrylamide-co-(acrylic acid)] (pNA) were synthesized by means of aqueous free-radical precipitation polymerization. Using pNA microgels as stabilizers, a Pickering emulsion was formed by simple stirring with pNA dispersion and hexadecane. The amino groups were then introduced by means of a carbodiimide coupling reaction using ethylenediamine and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. These microgels were collected by emulsion collapse. Hemispherical distribution of the amino groups in the modified microgels was confirmed using the Au nanoparticle labeling technique. Interestingly, these microgels were aggregated in string structures at pH 4, whereas they were not at pH 6. Such microgel string structures self-assembled from well-structured microgels by simple stimuli-change have potential use as micro-actuators.
Colloidal crystals of thermosensitive, core/shell hybrid microgels Journal of Physical Chemistry C,111(15):5667-5672 2007(Apr.) Author:Daisuke Suzuki; Jonathan G. McGrath; Haruma Kawaguchi; L. Andrew Lyon Abstract:We present the assembly of colloidal crystals composed of various thermoresponsive core/shell microgels and their hybrid microgel counterparts that contain localized Au nanoparticles. To obtain nanostructured microgels, we conducted a three-stage polymerization. First, core microgels composed of cross-linked poly( N-isopropylacrylamide) (pNIPAm) were synthesized by precipitation polymerization. Using these microgels as cores or "seeds", a copolymer shell of pNIPAm was added to these core particles using a functional comonomer. Finally, a second shell consisting solely of cross-linked pNIPAm was added onto the preformed core/shell microgels by using this seeded polymerization technique. With use of these core/shell/shell microgels as templates, Au nanoparticles were synthesized in situ, using the cationic sites in the inner shell to nucleate particle growth. To control the optical properties of the Au nanoparticles, electroless Au plating was carried out with use of the preformed Au nanoparticles in the microgel as seeds. These hybrid microgels retained their thermoresponsive properties and possessed a high degree of size uniformity as confirmed by dynamic light scattering and were assembled into three-dimensional colloidal crystals by using thermal annealing processes. The resulting colloidal crystals were characterized by optical microscopy and reflectance spectroscopy. This synthetic design for producing distinctive, functional building blocks could be expanded to enable the creation of complex tunable optical materials containing refractive index periodicity on multiple length scales.
Stimuli-sensitive core/shell template particles for immobilizing inorganic nanoparticles in the core Colloid and Polymer Science,284(12):1443-1451 2006(Sep.) Author:Daisuke Suzuki; Haruma Kawaguchi Abstract:We synthesize and characterize stimuli-sensitive core/shell particles with functional group (or material) localized in the core. We previously reported two types of hybrid particles prepared by using the template particles which were synthesized by soap-free emulsion copolymerization with N-isopropylacrylamide and glycidyl methacrylate (GMA) as monomers but by different preparation methods. GMA has advantages in immobilizing materials having several functional groups such as thiol ones. In this study, to obtain the suitable template particles for immobilizing any inorganic nanoparticles in the core, we investigated the effect of feed ratio of the two monomers. Obtained template particles were modified by thiol compounds to introduce ionic groups. They were characterized by dynamic light scattering and scanning electron microscopy. After in situ synthesis of magnetic nanoparticles in the templates, the hybrid particles were characterized directly by transmission electron microscopy. Consequently, we could obtain the hybrid core/shell particles which contained a large amount of magnetic nanoparticles (similar to 33 wt%) in the core.
Hybrid microgels with reversibly changeable multiple brilliant color Langmuir,22(8):3818-3822 2006(Apr.) Author:D Suzuki; H Kawaguchi Abstract:We report reversibly color changeable hybrid microgels that tune multiple brilliant colors due to interparticle interactions of SPR using several structured nanoparticles. The interparticle interactions were brought out using the thermosensitive swelling/deswelling property of microgel. We employ N-isopropylacrylamide (NIPAM) and glycidyl methacrylate (GMA) copolymerized microgels (NG microgels) as templates for in Situ synthesis of Au nanoparticles. The seed Au nanoparticles could be stably grown by Successive reduction of Au and Ag in the microgels. Interestingly, the hybrid microgels were able to exhibit multiple brilliant colors by attaching Au/Ag multiple core/shell bimetallic nanoparticles in the microgels, and the color change reversibility of each hybrid microgel was accomplished by adjusting the nanoparticles' sizes. Obtained microgels shown in this study will find important applications such as in biomedical and electronic devices.
Gold nanoparticle localization at the core surface by using thermosensitive core-shell particles as a template Langmuir,21(25):12016-12024 2005(Dec.) Author:D Suzuki; H Kawaguchi Abstract:We report novel thermosensitive hybrid core-shell particles via in situ gold nanoparticle formation using thermosensitive core-shell particles as a template. This method for the in situ synthesis of gold nanoparticles with microgel interiors offers the advantage of eliminating or significantly reducing particle aggregation. In addition, by using thermosensitive microgel structures in which the shell has thermosensitive and gel properties in water-whereas the core itself is a water-insoluble polymer - we wereable to synthesize the gold nanoparticles only at the surface of the core, which had reactive sites to bind metal ions. After the gold nanoparticles were synthesized, electroless gold plating was carried out to control the thickness of the gold nanoshells. The dispersions of the obtained hybrid particles were characterized by dynamic light scattering and UV-vis absorption spectroscopy, and the dried particles were also observed by electron microscopy. Adaptation of the technique shown here will create a number of applications asoptical, electronic, and biomedical functional materials.
Modification of gold nanoparticle composite nanostructures using thermosensitive core-shell particles as a template Langmuir,21(18):8175-8179 2005(Aug.) Author:D Suzuki; H Kawaguchi Abstract:We report the formation of novel thermosensitive hybrid core-shell particles via in situ synthesis of gold nanoparticles using thermosensitive core-shell particles as a template. The template core-shell particles, with cores composed mainly of poly(glycidyl methacrylate) (GMA) and shells composed mainly of poly(N-isopropylacrylamide) (PNIPAM), were synthesized in aqueous medium, and functional groups such as thiol groups were incorporated into each particle. We found that these particles containing thiol groups were effective for the in situ synthesis of gold nanoparticles in long-term storage. The obtained hybrid particles exhibited a reversible color change from red to purple, which originated from the surface plasmon resonance of gold nanoparticles and which was temperature-dependent in the range of 25-40 degrees C. In addition to their thermosensitive property, the hybrid particles exhibited the unique characteristic of uniform distribution on a solid substrate. The particles obtained by this approach have potential thermosensitive applications such as in sensors and photonic or electronic devices.
Development of anisotropic thermo-sensitive hairy particles using living radical graft polymerization Chemistry Letters,34(2):242-243 2005(Feb.) Author:D Suzuki; S Tsuji; H Kawaguchi Abstract:Temperature-responsive anisotropic particles were developed. Au was sputtered onto one side of the particle and, thermo-sensitive polymer was grafted from the other side. Obtained particles were characterized by dynamic light scattering, electrophoresis, and electron microscopy. These particles showed thermo-sensitive behavior when they dispersed in water. They also showed anisotropic adsorption onto the substrate, and the particles were self-assembled into particle chains.
Soft hydrogel microspheres toward functional autonomous materials Pre-symposium of The 1st International Symposium on Molecular Engine 2020(Jan. 07) Presenter:Daisuke Suzuki
Self-Organization of Functional Hydrogel Microspheres at the Fluid Interface Gel Symposium 2018 2018(Aug. 29) Presenter:Daisuke Suzuki
Functional Hydrogel Microspheres at the Air/Water Interface 255th ACS National Meeting 2018(Mar. 21) Presenter:Daisuke Suzuki; Haruka Minato; Masaya Takizawa; Yuka Sazuka
Self-Organization of Soft Hydrogel Microspheres at the Air/Water Interfaces The 6 th Asian Symposium on Emulsion Polymerization and Functional Polymeric Microspheres 2018(Mar. 09) Presenter:Daisuke Suzuki; Masaya Takizawa; Yuka Sazuka; Haruka Minato
Investigation of Interfacial Behaviors of Hydrogel Microspheres 第27回日本MRS年次大会 2017(Dec. 06) Presenter:鈴木大介
Artificial Polymeric Microhydrogels toward Autonomous Soft Materials The 5th International Symposium on Dynamical Ordering of Biomolecular Systems for Creation of Integrated Functions 2017(Jan. 21) Presenter:Daisuke Suzuki
Composite particle synthesis in the presence of hydrogel particles Pacifichem 2015 2015(Dec. 15) Presenter:Daisuke Suzuki; Chiaki Kobayashi; Takumi Watanabe
Control of Spatio-temporal Structures for Polymeric Hydrogel Microspheres The 5th Asian Symposium on Emulsion Polymerization and Functional Polymeric Microspheres (ASEPFPM) 2015(Oct. 25) Presenter:Daisuke Suzuki
Control of Spatio-Temporal Structures for Polymer Microspheres toward Advanced Soft Materials IMS Asian International Symposium 2015(Jun. 13) Presenter:Daisuke Suzuki
Control of Spatio-Temporal Structures for Polymer Colloids toward Advanced Soft Materials International Association of Colloid and Interface Scientists Conference (IACIS 2012) 2012(May 16) Presenter:Daisuke Suzuki; Takeshi Kobayashi; Ryo Yoshida; Toshihiro Hirai
Smart Hydrogel Particles 6th International Conference on Advanced Fiber/Textile Materials 2011 2011(Dec. 07) Presenter:Daisuke Suzuki
Recent Development in the Visualization of Microgels Chemistry Letters (Selected as inside cover),50:1226-1235 2021 Author:Yuichiro Nishizawa; Kenshiro Honda; Daisuke Suzuki
Assembly of rod-shaped hydrogel microspheres at the air/water interface ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY,258 2019(Aug.) Author:Kenshiro Honda; Yuka Sazuka; Kojiro Iizuka; Shusuke Matsui; Takayuki Uchihashi; Takuma Kureha; Mitsuhiro Shibayama; Takumi Watanabe; Daisuke Suzuki
Nanogels and microgels: From model colloids to applications, recent developments and future trends Langmuir (Selected as outside front cover),35:6231-6255 2019 Author:Matthias Karg; Andrij Pich; Thomas Hellweg; Todd Hoare; L. Andrew Lyon; J.J. Crassous; Daisuke Suzuki; Rustam A. Gumerov; Stefanie Schneider; Igor. I. Potemkin; Walter Richtering Abstract:フロントカバーに選出
Rheology of dense suspensions of temperature-responsive microgel mixtures ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY,255 2018(Mar.) Author:Saori Minami; Takumi Watanabe; Daisuke Suzuki; Kenji Urayama
Polymeric hydrogel microspheres: design, synthesis, characterization, assembly and applications Polymer Journal,49(10):695-702 2017(Oct.) Author:Daisuke Suzuki; Koji Horigome; Takuma Kureha; Shusuke Matsui; Takumi Watanabe Abstract:Hydrogel microspheres (microgels), which consist of crosslinked hydrophilic or amphiphilic polymer chains, are components of stable colloidal dispersions. Their typical size is below similar to 10 mu m, and they exhibit fascinating properties in aqueous solution. Owing to their attractive properties, they have been used for a variety of applications (for example, as templates, sensors, catalysts, and coatings) and have promising prospects for advanced chemical technologies such as drug carriers. In this context, we have been conducting research on microgels, including their synthesis, characterization, assembly, and application. In this focus review, we summarize recent results of microgel research conducted mainly by our group as well as work by our collaborators.
Control of colloidal interactions between microgels with stimulus-responsive properties Journal of Polymer Science Part A: Polymer Chemistry,51(14):3021-3026 2013(Jul.) Author:Yoshitaka Umeda; Daisuke Suzuki Abstract:Microgels can switch their chemical/physical properties with external stimulus, and the colloidal behavior of microgels is strongly affected by interparticle interactions. In this article, we introduce smart microgels, focusing on Janus microgels and oscillating microgels developed by our group. Janus microgels show anisotropic shape and chemical/physical properties, and thus the structures of their flocs are also anisotropic. Oscillating microgels show autonomous swelling/deswelling and dispersing/flocculating oscillations through synchronization with chemical reactions. The interparticle interactions of these microgels are discussed. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3021-3026
Balance Between Polymeric and Colloidal Contribution in the Crystallization of Hydro-Gel Spheres SEN-I GAKKAISHI,68(8):P220-P226 2012(Aug.) Author:Tsuneo Okubo; Daisuke Suzuki
ハイドロゲル微粒子の結晶化に見られる高分子性とコロイド性のバランス SENI GAKKAISHI (繊維と工業),68(8):220-226 2012 Author:大久保恒夫; 鈴木大介
Self-oscillating gel as novel biomimetic materials Journal of Controlled Release,140(3):186-193 2009(Dec.) Author:Ryo Yoshida; Takamasa Sakai; Yusuke Hara; Shingo Maeda; Shuji Hashimoto; Daisuke Suzuki; Yoko Murase Abstract:Stimuli-responsive polymers and their application to biomaterials have been widely studied. On the other hand, as a novel biomimetic polymer, we have been studying the polymer with an autonomous self-oscillating function by utilizing oscillating chemical reactions. So far, we succeeded in developing a novel self-oscillating polymer and gels by utilizing the oscillating reaction, called the Belousov-Zhabotinsky (BZ) reaction, which is recognized as a chemical model for understanding several autonomous phenomena in biological systems. The self-oscillating polymer is composed of poly(N-isopropylacrylamide) (PNIPAAm) network in which the catalyst for the BZ reaction is covalently immobilized. Under the coexistence of the reactants, the polymer undergoes spontaneous cyclic soluble-insoluble changes or swelling-deswelling changes (in the case of gel) without any on-off switching of external stimuli. In this paper, our recent studies on the self-oscillating polymer gels and the design of functional material systems using the polymer are summarized. (C) 2009 Elsevier B.V. All rights reserved
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