PRESSURE AND TEMPERATURE EFFECTS IN HOMOPOLYMER BLENDS AND DIBLOCK COPOLYMERS

Thermal composition fluctuations in a homogeneous binary polymer blend and in a diblock copolymer were measured by small-angle neutron scatt ering as a function of temperature and pressure. The experimental data were analyzed with theoretical expressions, including the important e ffect of thermal fluctuations. Phase boundaries, the Flory-Huggins int eraction parameter and the Ginzburg number were obtained. The packing of the molecules changes with pressure. Therefore, the degree of therm al fluctuation as a function of packing and temperature was studied. W hile in polymer blends packing leads, in some respects, to a universal behaviour, such behaviour is not found in diblock copolymers. It is s hown that the Ginzburg number decreases with pressure sensitively in b lends, while it is constant in diblock copolymers. The Ginzburg number is an estimation of the transition between the universality classes o f the 'mean-field' approximation and the three-dimensional Ising model . The phase boundaries in blends increase with pressure, while the pha se boundary of the studied block copolymer shows an unusual shape: wit h increasing pressure it first decreases and then increases. Its origi n is an increase of the entropic and of the enthalpic parts, respectiv ely, of the Flory-Huggins interaction parameter.