Pressure–composition phase diagram of diblock copolymers

Phase diagrams of diblock copolymers as functions of pressure and composition, essential for the molecular design of energy-efficient polymeric materials with pressure processability, are presented. While pressure-dependent modifications of temperature-composition phase diagrams have been investigated in relation to temperature-induced transitions, diagrams explicitly displayed on the pressure-composition plane remain largely underexplored. To establish a fundamental understanding of pressure-induced phase transitions, we construct pressure-composition phase diagrams using compressible random phase approximation theory and self-consistent field theory. The contrast in block compressibility is shown to govern pressure-responsive phase behavior: a large contrast enhances miscibility under pressure, whereas a small contrast reduces it. In highly asymmetric systems with more compressible soft segments, voids preferentially accumulate in soft domains, stabilizing ordered phases and skewing phase boundaries. These results provide a theoretical basis for the rational design of pressure-responsive polymeric systems.