K. Mortensen et al., PHASE-BEHAVIOR OF DIBLOCK COPOLYMERS - PRESSURE AND TEMPERATURE-DEPENDENCE STUDIED BY SMALL-ANGLE NEUTRON-SCATTERING, Macromolecular symposia, 121, 1997, pp. 245-262
The structure factor of a poly(ethylene-propylene)poly(dimethylsiloxan
e) diblock copolymer has been measured by SANS as a function of temper
ature and pressure. In contradiction to the random phase approximation
the conformational compressibility exhibits a pronounced maximum at t
he order-disorder phase transition. The phase boundary shows an unusua
l shape: with increasing pressure it first decreases and then increase
s. Its origin is an increase in, respectively, the entropic and the en
thalpic part of the Flory-Huggins interaction parameter. The Ginzburg
parameter describing the limit of the mean-field approximation is not
influenced by pressure.