Thermoresponsive hydrogels have been investigated and developed mainly for biotechnology and medical applications with using their phase transition temperature near body temperature. Recently, it was applied for various water flow applications such as microfluidic systems, but only the functions based on reversible volume change of swelling and deswelling were utilized as valves, pistons, and actuators. Irreversible water flow systems have never been developed to the best of our knowledge. Herein, using thermoresponsive hydrogel composites, irreversible water flow could be achieved, which could work repeatedly upon temperature cycles. We made a novel water flow system by using composites of thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) hydrogel and polydimethylsiloxane (PDMS), which has unique swelling and deswelling kinetics. The composites were made by directional melt crystallization (DMC) of solvent. DMC is a method for obtaining a porous material having three-dimensionally continuous pores by controlling the crystallization of a solvent in three dimensions. This enables a co-continuous complexation of two different materials. A porous PNIPAm of cylindrical pores was fabricated by DMC, and the subsequent infiltration of PDMS to the pores of PNIPAm resulted in co-continuous composites. The composites can repeats swelling and deswelling in water following the temperature change. When an asymmetric composite was prepared, PNIPAm/PDMS phase at the bottom of the composite has a faster deswelling rate. After water diffused into the PNIPAm/PDMS phase and swelled the entire composite, water droplets can form on the top surfaces of PNIPAm upon temperature rises. No water flow back to the bottom was noticed: The released water cannot backflow through the PNIPAm/PDMS phase, only flow out. This system was proved to be useful water treatment systems such as oil-water separation and anionic dye adsorption, when the configuration of the PNIPAm/PDMS phase was specially designed for each application.

Poly(N-isopropylacrylamide) hydrogel/polydimethylsiloxane composites for novel water flow systems

2019 Fall National Meeting

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