Pressure Dependence of the Order-to-Disorder Transition in Polystyrene/Polyisoprene and Polystyrene/Poly(methylphenylsiloxane) Diblock Copolymers

The pressure dependence of the order-to-disorder transition in a polystyrene/polyisoprene (PS/PI) ( M = 17 000) and a polystyrene/poly(methylphenylsiloxane) (PS/PMPS) ( M = 29 600) diblock copolymer of symmetric composition has been studied using small-angle X-ray scattering. The order−disorder transition is investigated with a temperature resolution of 0.1 K. The transition can be resolved in a two-step process with a roughening of the interface preceding the breakdown of the lamellar order. For both systems a pressure-induced ordering transition is observed at constant temperature. The application of small pressures leads to a decrease of the transition temperature for both systems. High pressure shows the opposite effect. The minimum transition temperature for the PS/PI is located around p = 8 bar.