Light scattering and pseudospinodal curve of the system polystyrene–cyclohexane in the critical region

Abstract

The angular distribution of scattered light intensity from polystyrene (Mw = 1.1×105, Mw/Mn<1.02) in cyclohexane has been measured over a range of temperatures using a specially designed light-scattering photometer and then a ’’pseudospinodal curve’’ Tsp(φ) described by Tc − Tsp(φ) ∝ (φ(1) − φ(2))1/β+, where φ is the volume fraction of polymer on the spinodal curve, has been investigated for various equilibrium states in the critical neighborhood of the temperature–concentration diagram. An empirical equation of the form (Ic,0/T)−1 ∝ (T−Tsp)γ, in which Ic,0 is the extrapolated zero-angle scattering intensity, is used to effect an extrapolation for the determination of Tsp inside the coexistance curve. The temperature dependence of Ic,0 obeys the same relation with γ=1.20–1.24 for several samples. The long-range correlation length ξ obeys a relation ξ∝ (T−Tsp)−ν with ν=0.59∼0.64. As expected on the ground of the homogeneity hypotheses, the value of β+?0.38 found in the present work is essentially the same as the value of the critical exponent β=0.34±0.01 for the coexistence curve near its critical mixing point.