Ginzburg number and phase behavior of binary polymers blends in pressure fields

In some polymer blends the temperature and pressure dependence of thermal c omposition fluctuations have been measured with small angle neutron scatter ing. The Ginzburg number Gi, the Flory-Huggins parameter Gamma, and the pha se boundaries were determined for pressure fields up to 150 MPa. In polymer blends the compressibility leads to a strongly increased Gi which could be appreciably larger than in low molecular liquids and which decreases with increasing pressure fields. Usually, the phase boundaries of UCST as well a s of LCST blends shift with pressure to higher temperatures. One blend havi ng PDMS as one component, however, shows an abnormal decrease of the phase boundaries with increasing pressure. The Clausius-Clapeyron equation correc tly predict from the experimentally determined Gamma and Gi the observed pr essure dependence of the phase boundaries.