Studies of Liquid−Liquid Demixing of Polystyrene Solutions Using Dynamic Light Scattering. Nucleation and Droplet Growth from Dilute Solution

Abstract

Dynamic light scattering (DLS) measurements of liquid−liquid demixing from dilute polystyrene (PS)/cyclohexane and PS/methylcyclohexane solutions are described. Phase transitions were induced by temperature quenches into the metastable region and beyond using concentrations low enough to ensure liquid−liquid demixing by a nucleation growth (NG) mechanism. In a companion paper the NG results are compared with demixing studies at higher concentration, where the mechanism is spinodal decomposition (SD), and with DLS measurements in a good solvent. The present measurements employed polystyrenes of low or medium molecular weight, Mw,1 = 30 000, ρ1 = Mw/Mn = 1.05, Mw,2 = 90 000, ρ2 = 1.04 and Mw,3 = 400 000, ρ3 = 1.05. In the NG region DLS measurements yield well-behaved correlation lengths for quenches well into the metastable region, but that pattern ends in the immediate vicinity of the cloudpoint where it splits to a bimodal distribution. The larger (slow) component is associated with the nucleation and gro...