A new apparatus for the detection of phase equilibria in polymer solvent systems by light scattering

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Abstract
New equipment designed to measure the effect of pressure and isotopic substitution on liquid/liquid equilibria in polymer/solvent systems is described. The phase separation is detected by monitoring low‐angle forward scattered light, together with simultaneous loss in transmitted light, from an He–Ne laser shining through the sample. Phase transitions can be induced by varying temperature/time and/or pressure/time profiles or by a combination of such changes. The system operates at high precision (±0.001 K, ±0.002 MPa), and over wide temperature and pressure ranges (240≤T/K≤600, 0.01≤P/Mpa≤35). The temperature, pressure, and transmitted and scattered light intensities are digitally recorded, and the rate of change of the temperature and/or pressure used to induce the phase transition is under computer control. The system is being used to study the temperature, pressure,polymer molecular weight, and molecular weight distribution, and H/D dependences of phase equilibria for polystyrene (PS)/(CH3)2CO and PS/(CD3)2CO solutions. Sample results are reported. The pressure and molecular weight dependences of the coexistence curve, and their isotope effects, are large.