Thermodynamic parameters of polystyrene solutions in cyclohexane, determined from sedimentation-diffusion equilibria in the ultracentrifuge. dependence on concentration, temperature and molecular weight

Determination of the sedimentation–diffusion equilibrium is one of the methods furnishing data on the thermodynamic parameters of polymer solutions. By means of this procedure measurements can be performed over a considerable range of concentrations. The equilibria in the ultracentrifuge have been determined for five polystyrene samples of narrow distribution covering the molecular weight range 2 × 104 to 2 × 106, at concentrations up to 40 wt‐% and at temperatures of 30, 45 and 65 °C. The results are expressed in the data for the chemical potential of the solvent, the number‐average chemical potential of the polymer and the interaction parameter ξ. The results are compared with those obtained from osmotic pressure, light scattering and critical miscibility measurements. At very low concentrations the molecular weight dependence of the interaction parameter is in agreement with literature values derived from osmotic pressure and light scattering figures. At higher concentrations this molecular‐weight dependence decreases sharply but remains noticeable up to 40% concentration.