PRESSURE-DEPENDENCE OF THE FLORY-HUGGINS INTERACTION PARAMETER IN POLYMER BLENDS - A SANS STUDY AND A COMPARISON TO THE FLORY-ORWOLL-VRIJ EQUATION OF STATE

The pressure dependence of the Flory-Huggins interaction parameter of two binary polymer blends was investigated by small-angle scattering o f neutrons (SANS). We studied deuteropolystyrene/poly(vinyl methyl eth er) (d-PS/PVME) and deuteropolystyrene/poly(phenylmethylsiloxane) (d-P S/PPMS) exhibiting lower and upper critical solution temperatures, res pectively. It turned out that in the investigated pressure range betwe en 1 and 1200 bar the enthalpic contribution of the Flory-Huggins para meter is practically independent of pressure. On the other hand, the a bsolute value of the entropic contribution, which is related to the fr ee volume of the blend, decreases with pressure. Furthermore, p VT dat a of the d-PS/PPMS blend and of its components were measured. From the fits of these data with the Flory-Orwoll-Vrij (FOV) equation of state , the Flory-Huggins parameter was derived and compared with the SANS d ata. The comparison with the pressure dependence for the entropic cont ribution is unsatisfactory. The enthalpic contribution is almost press ure independent, as observed in the SANS data.