High pressure effects under phase separation of aqueous solutions of poly(N-isopropylacryamide): A HS-DSC study

Abstract The phase separation of aqueous solutions of poly(N-isopropylacrylamide) at different pressures (up to 212 MPa) has been first investigated by high-sensitivity differential scanning calorimetry (HS-DSC). The dependences of the transition temperature, enthalpy and width on pressure have been determined. Upon increasing pressure, the transition temperature passes through a maximum, the enthalpy decreases and the thermodynamic width of the transition notably increases. The transition increment of partial volume of the polymer ( Δ t v ) is found to be positive at low pressures and negative at high ones. The positivity of the increment Δ t v points to a significant role of hydrophobic hydration in the transition mechanism. The negativity of Δ t v can be related to domination of the interchain H-bond formation upon the system phase separation. The transition width increase reflects changes in the shape of the system binodal.