PRESSURE PULSED INDUCED CRITICAL SCATTERING - SPINODAL AND BINODAL CURVES FOR THE SYSTEM POLYSTYRENE PLUS METHYLCYLCOHEXANE

An experimental apparatus has been constructed that enables both spino dal and binodal points to be determined in pressure-temperature-compos ition space. Known as the PPICS (Pressure Pulse Induced Critical Scatt ering) unit, it enables the user to monitor the intensities of light s cattered from polymer-solvent systems at temperatures ranging between -20 and 150-degrees-C and pressures up to 1000 bar. The changes in the scattered light levels are recorded as the system approaches the two phase region. After various corrections are made, the theory of Debye- Scholte is used to determine the location of the spinodal surface. Exp erimental results are presented for the system polystyrene (Mw=22,000) /methylcyclohexane at three polymer concentrations. An interesting tre nd in both the binodal and spinodal temperatures with increasing press ure is observed. At pressures less than 400 bar increasing pressure de creases both the spinodal and binodal temperatures, however at pressur es greater than 500 bar the opposite trend is observed.