Critical Opalescence of Polystyrene in Cyclohexane : Range of Molecular Forces and Radius of Gyration

Visible light scattered by binary mixtures of critical concentration of ordinary molecules at small temperature distances above the critical temperature shows an angular dissymmetry which can be related to the range of molecular forces. The theory of critical opalescence is extended to polymer solutions of high molecular weight for which an additional dissymmetry due to the extension of the polymer coil is observed. The range of molecular forces and the radius of gyration at the critical concentration can be determined simultaneously by measurements of the angular dependence of scattered intensity at different temperatures above the critical temperature. Results of experiments on a solution of polystyrene (Mn=2 820 000) in cyclohexane are reported.