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 Theta point. Deviations from Theta point concentration s caling were observed as the coexistence line was approached. A new sca ling form is suggested which combines the concentration scaling near t he Theta paint with the temperature scaling near a spinodal; it collap ses the experimental data. This approach assumes that the ''bare'' cor relation length xi(0) scales as c(-1). The observed low-angle ''excess scattering'' is best described by the Debye-Bueche random heterogenei ty model, rather than the attractive potential model of Medjahdi and c o-workers. The ''excess scattering'' is virtually independent of tempe rature, suggesting that the inhomogeneities which cause it are not aff ected by the approaching phase transformation.