Small-angle X-ray scattering from semi-dilute solutions of poly(N-isopropylacrylamide) in aqueous acetonitrile solutions

Interaction parameters of poly(N-isopropylacrylamide) in acetonitrile-water mixed solvent were determined by using small-angle X-ray scattering. Small-angle X-ray scattering measurements were carried out in conditions of the semi-dilute poor solvent regime and just below the lower critical solution temperature. From concentration dependence of the correlation length, the binary and ternary cluster integrals were determined. The contribution of the segment-segment interactions to the entropy S_int and the enthalpy H_int has been calculated from the temperature dependence of these cluster integrals. It has been found that both values are positive. On addition of a small amount of acetonitrile into aqueous solution of poly(N-isopropylacrylamide), S_int and H_int increase with increasing acetonitrile content. Upon further addition of acetonitrile, these values decreased.