Language：English   Publishing type：Research paper (scientific journal)  

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).

DOI： 10.1039/d2cc04993g

PubMed

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/admi.202200879

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/admi.202200879

Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsapm.1c00153

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1038/s41428-020-00406-6

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Other Link： https://www.nature.com/articles/s41428-020-00406-6

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1021/acs.langmuir.0c02654

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

<p>Nanostructure and thermoresponsiveness of single and packed poly(<italic>N</italic>-isopropyl methacrylamide)-based microgels observed by temperature-controllable high speed atomic force microscopy.</p>

DOI： 10.1039/d1ra01650d

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Publishing type：Research paper (scientific journal)  

DOI： 10.1039/D1RA02688G

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1038/s41428-020-0372-3

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Other Link： http://www.nature.com/articles/s41428-020-0372-3

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

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.

DOI： 10.1002/anie.202003493

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/ange.202003493

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

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.

DOI： 10.1021/acs.jpcb.0c02238

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry ({RSC})  

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.

DOI： 10.1039/D0SM00366B

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acs.langmuir.9b01933

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry ({RSC})  

DOI： 10.1039/C9CC05116C

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：SOC POLYMER SCIENCE JAPAN  

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.

DOI： 10.1295/koron.2019-0003

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry ({RSC})  

DOI： 10.1039/C9SM01030K

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

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.

DOI： 10.1021/acs.langmuir.8b00230

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© 2018 The Society of Rheology, Japan. Deformation characteristics of micro spherical hydrogels in single state have been examined in recovery processes from elongated states. The micro gel particles with core-shell internal structure and without membrane on its surface were dyed and tested. Deformability of two kinds of the gel particles with different cross-link density in the shell layer were evaluated. The size of these particles with low degree of cross-linking were reduced by the dyeing process. Strain recovery process of the micro gel particles were obtained with a high speed camera and approximated exponential recovery curves in particle height were fitted. Moreover, a characteristic time is defined with the formula. The characteristic times of the micro gel particles with low degree of cross-linking in the shell layer were relatively shorter than those of particles with high degree. It is considered that the structure of the shell layer would be changed by dyeing processes. However, it is revealed that the characteristic time calculated in strain recovery processes are useful to feature the deformability of the micro gels.

DOI： 10.1678/rheology.46.227

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

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.

DOI： 10.1039/c7cc09603h

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