Studies on pressure induced phase separation and hydrophobic interaction of polymer solutions and gels by neutron scattering and light scattering

Abstract

The phase behavior and microscopic structure of polymer aqueous solutions and hydrogels were investigated by means of small-angle neutron scattering (SANS) and light scattering (LS). Attention was focused on pressure (P) and/or temperature (T) induced phase transitions, such as microphase and macrophase separation transitions. In the case of poly(N-isopropylacrylamide) solutions and gels, coexistence and spinodal curves in the P-T coordinate were found to be convex-upward functions. At the phase boundary, the correlation length of the solution diverged. When charges were introduced to the gels, a scattering maximum originating from charge interactions appeared. This peak disappeared and reappeared by scanning P, showing reentrancy with respect to P. In the case of block copolymer solutions consisting of thermosensitive and hydrophilic block chains, both microphase and macrophase separation transitions were observed depending on T and P. It was found that the phase behavior was classified into several regimes with respect to the strength of hydrophobic solvation. All of these facts indicate that the roles of T and P in the thermodynamics of hydrophobic interaction are quite different.