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Abstract

Several phosphonium ionic liquid monomers have been shown to possess a lower critical solution temperature [1][2]. This property was kept when the monomers were used to synthesize both linear and crosslinked polymers, thus making them suitable materials for the synthesis of stimuli-responsive hydrogels [2]. Herein, we present the synthesis of a thermo-responsive tributylhexyl phosphonium 3-sulfopropyl acrylate (PSPA) crosslinked PIL, followed by its inclusion in a microfluidic device to be used as a temperature controlled valve. The hydrated hydrogels had their temperature-induced shrinking measured with a digital microscope from 20 °C to 70 °C, in 10 °C intervals. Measurements indicate a relative surface contraction of the hydrogels, in deionized water, of 34.04% ± 4.62% (n = 3) at 50 °C, and 53.37% ± 12.55% (n = 3) at 70 °C. Following this, hydrogels were polymerized in a microfluidic chip and had their flow characteristics analysed. When placed on a heating element and connected to a syringe pump and a flow microsensor, the hydrogels allowed deionized water to flow through the microfluidic chip at a rate of 140 nL·min-1 at 50 °C and ~ 15 nL·min-1 at 25 °C. The required time for the PILc valve to open was ~6s, while the time required for it to close was ~8s. In conclusion, the results confirm the applicability of PSPA hydrogels as thermally controlled valves in microfluidic devices. Furthermore, the study will continue by focusing on the optimization of the valve geometry to ensure higher flowrates, while also increasing the lifetime of the valve.

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• Thermo-responsive poly(ionic liquid) hydrogel microfluidic valves. (deposited 11 May 2016 09:41) [Currently Displayed]