A NEW EXPERIMENTAL-METHOD TO STUDY KINETICS OF PHASE-SEPARATION IN HIGH-PRESSURE POLYMER-SOLUTIONS - MULTIPLE RAPID PRESSURE-DROP TECHNIQUE- MRPD

A new experimental system has been developed to study phase separation in polymer solutions undergoing pressure reductions. The system consi sts of two high-pressure cells which are coupled through a magnetic re circulation pump and an air-actuated valve, and permits realization of pressure changes at rates from very slow to about 1000 MPa s-1. Chang es in the system undergoing the pressure changes are monitored by reco rding the scattered- and transmitted-light intensities. This paper des cribes the general aspects of the system and illustrates the time scal es 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 dept h of penetration into the immiscibility region. Beyond a characteristi c penetration depth, time scale for new phase formation appears to be no longer affected, and this condition may provide a physically meanin gful indicator for the spinodal condition.