Salt-induced volume phase transition of poly(N-isopropylacrylamide) gel

The phase transition of N-isopropylacrylamide (NIPA) gel was studied in terms of the salt concentration, and was described as a function of the chemical potential difference of water molecules in solution at the transition. The Raman spectra in water and in various aqueous solutions, reveals that the presence of salts tends to disrupt the water molecules in hydrophobic hydration shell around the NIPA gel. The volume phase transitions, due to the different types of perturbations, can be described in terms of the chemical potential and the collective proton motions of water molecules.