Temperature- and pressure-dependent composition fluctuations in a polybutadiene/polystyrene polymer blend and diblock copolymer

The phase diagram, the Flory-Huggins parameter Gamma and the Ginzburg param eter Gi of a polybutadiene/polystyrene blend and diblock copolymer were det ermined by small-angle neutron scattering in the pressure range of 0.1 and 200MPa. Both systems show qualitatively the same pressure dependence. The e nthalpic and entropic terms of Gamma are larger in blends. In the diblock c opolymer a constant order-disorder temperature was observed which could be explained by a compensation effect between Gamma and Gi.