Effect of added organic solvent on interaction parameters of poly(N-isopropylacrylamide) in aqueous solution

Semi-dilute solutions of poly(N-isopropylacrylamide) in aqueous solution of tetrahydrofuran and n-butyl alcohol were measured by small-angle X-ray scattering method just below the lower critical solution temperature. From anglular dependence of the scattered intensity we determined the correlation length. The binary and ternary interaction parameters were evaluated from concentration dependence of the correlation length. The contribution of the segment-segment interactions to the entropy and the enthalpy were calculated from the temperature dependence of the cluster integrals. It has been found that both values are positive and the enthalpy increases with increasing amount of added organic solvent and reaches a maximum for each system. After the maximum those values decrease with increasing amount of added solvent e.g. in the case of 1-propanol-water mixed solvent system.