Thermal Switching of Thermoresponsive Polymer Aqueous\nSolutions

Abstract

Thermal switches are of great importance\nto thermal management\nin a wide variety of applications. However, traditional thermal switches\nsuffer from being large and having slow transition rates. To overcome\nthese limitations, we took advantage of abrupt second-order phase\ntransitions in thermoresponsive polymer aqueous solutions to enable\nfast thermal switching. While thermoresponsive polymers have been\nwidely studied for biomedical applications, their thermal switching\ncapability has not been studied. In this work, we used poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) as a model system to demonstrate\nabrupt thermal conductivity changes of thermoresponsive polymer aqueous\nsolutions across their transition temperatures by using a powerful\napproach, the transient thermal grating technique, which has high\nsensitivity. We observed a thermal switching ratio up to 1.15 in dilute\nPNIPAM aqueous solutions (up to 0.025 g/mL) across the transition.\nThis work may provide new opportunities to engineer thermal switches\nusing second-order phase transitions of thermoresponsive polymer aqueous\nsolutions or abrupt higher-order phase transitions in general.