Enthalpic and Volumetric Changes at Phase Transitions of Polystyrene-b-poly(alkyl methacrylate) Copolymers and Their Pressure Dependence

The article examines phase behavior of block copolymers (BCP) that are composed of two or more dissimilar polymer chains by a covalent. The negative pressure dependence of the entropically driven LDOT was characterized as the compressible (or baroplastic) behavior due to the enhanced miscibility between the two blocks with increasing pressure. Even though the film thicknesses were set to around 300 nm to avoid the influence of substrate interactions on the transition behavior, the flat films were selectively confirmed by optical microscopy (OM) before measurements. The strong baroplastic character of the closed-loop transitions should be caused by the significant negative volume changes on mixing at both phase transitions, indicating a dominant entropic origin of the closed-loop behavior rather than the enthalpic change. These pressure coefficients retrieved with the enthalpic and volumetric variables, consistent with the reference values, could be good evidence to a perspective of the pressure dependent phase behaviors in the weakly interacting BCP systems.