Abstract
Abstract An experimental apparatus has been constructed that enables both spinodal and binodal points to be determined in pressure-temperature-composition space. Known as the PPICS (Pressure Pulse Induced Critical Scattering) unit, it enables the user to monitor the intensities of light scattered from polymer-solvent systems at temperatures ranging between 20 and 150°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. Experimental results are presented for the system polystyrene (Mw=22,000)/methylcyclohexane at three polymer concentrations. An interesting trend in both the binodal and spinodal temperatures with increasing pressure is observed. At pressures less than 400 bar increasing pressure decreases both the spinodal and binodal temperatures, however at pressures greater than 500 bar the opposite trend is observed.
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