Role of Water/Methanol Clustering Dynamics on Thermosensitivity of Poly(N-isopropylacrylamide) from Spectral and Calorimetric Insights

Abstract

The role of water/methanol clustering dynamics on thermosensitivity of poly(N-isopropylacrylamide) (PNIPAM) chains in concentrated solutions (10 wt %) is investigated by turbidity, FT-IR and calorimetric measurements through point-by-point comparison. FT-IR spectral variations show that PNIPAM−methanol interactions are largely weakened and PNIPAM chains are more collapsed in water/methanol mixture (methanol volume fraction xm = 0.17) than in pure water because of the formation of large water/methanol clusters, which, meanwhile, causes the decrease of hydration sites. On the other hand, weak hysteresis and excess recovery phenomena in the phase transition process can also be observed with addition of methanol to PNIPAM aqueous solution due to the existence of water/methanol clustering dynamics. Two-dimensional infrared correlation spectroscopy and calorimetric analysis finally conclude that the role of water/methanol clustering dynamics is mainly embodied in the inhibition of the hydration process of PNIPA...