How does poly(N-isopropylacrylamide) trigger phase separation in aqueous alcohol?

Abstract

Short chain alcohols, such as methanol and ethanol, are fairly well miscible in water over full mixing ratios. Moreover, when poly(N-isopropylacrylamide) is added in the same mixtures, the solution phase separates at low alcohol concentrations. From the fundamental understanding of phase separation within the mean-field picture, we can expect interaction parameter χ between water and alcohol to be significantly larger than unity. On the contrary, however, χ remains invariant and close to zero over full mixing ratios of aqueous alcohol mixtures. Here, we show how the preferential binding of poly(N-isopropylacrylamide) with alcohols facilitates local phase separation without altering bulk solution χ.