A new experimental method to study kinetics of phase separation in high-pressure polymer solutions. Multiple rapid pressure-drop technique — MRPD

Abstract

A new experimental system has been developed to study phase separation in polymer solutions undergoing pressure reductions. The system consists of two high-pressure cells which are coupled through a magnetic recirculation pump and an air-actuated valve, and permits realization of pressure changes at rates from very slow to about 1000 MPa s −1. Changes in the system undergoing the pressure changes are monitored by recording the scattered- and transmitted-light intensities. This paper describes the general aspects of the system and illustrates the time scales of phase separation accompanying different pressure reduction paths for solutions of polystyrene in n-pentane. It is shown that the time scale of phase separation depends on the rate of approach and the depth of penetration into the immiscibility region. Beyond a characteristic penetration depth, time scale for new phase formation appears to be no longer affected, and this condition may provide a physically meaningful indicator for the spinodal condition.