Self-organization of colloidal microspheres upon water evaporating is desirable, because it provides ordered structures on the microscale, which allows controlling the optical, wetting, and mechanical properties. Given such background, our group has been investigating drying mechanism of droplets containing poly(N-isopropyl acrylamide), pNIPAm-based hydrogel microspheres (microgels). The pNIPAm microgels spontaneously adsorbed at the air/water interface of the droplets, provide the thin films of microscopically ordered microgels from simple drying on a solid substrate. Moreover, such assemble structure and adsorption kinetics can be tuned by changing the properties of microgels such as size and softness. Here, we have prepared the rod-shaped microgels and investigated the self-organization of rod-shaped microgels at the air/water interface (Figure a). The real-time assembly of the rod-shaped hydrogel microspheres was directly visualized by optical microscopy. During the water evaporation, the adsorbed rod-shaped microgels were attracted to each other due to capillary interactions, resulting in the formation of chain-like structure (Figure b). Moreover, unlike the case of rod-shaped solid microspheres, the high percentage of side-side structure was maintained during the water evaporation in the case of the rod-shaped microgels due to the interpenetration of the hydrogel layer at the air/water interface (Figure c). Therefore, we believe that both softness and anisotropic shape of colloidal microspheres are crucial factors for design the self-organization of microgels at the air/water interface.

Assembly of rod-shaped hydrogel microspheres at the air/water interface

2019 Fall National Meeting

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