Small-angle X-ray scattering studies of semidilute polystyrene-cyclohexane solutions

Small-angle X-ray scattering was used to study semidilute polystyrene-cyclohexane solutions at temperatures from below the coexistence curve to above the Θ point. Deviations from Θ point concentration scaling were observed as the coexistence line was approached. A new scaling form is suggested which combines the concentration scaling near the Θ point with the temperature scaling near a spinodal; it collapses the experimental data. This approach assumes that the “bare” correlation length ge0 scales as c−1. The observed low-angle “excess scattering” is best described by the Debye-Bueche random heterogeneity model, rather than the attractive potential model of Medjahdi and co-workers. The “excess scattering” is virtually independent of temperature, suggesting that the inhomogeneities which cause it are not affected by the approaching phase transformation.