OBSERVATIONS ON CONCENTRATED POLYMER-SOLUTIONS NEAR THE THETA-CONDITION USING SMALL-ANGLE NEUTRON-SCATTERING

Small-angle neutron-scattering measurements are presented here for concentrated solutions of polystyrene-cyclohexane-d at and below the θ temperature, 38 °C. The osmotic modulus, φ(σΊΙ/άφ), evaluated from the intensity, is found to vary faster than if?, where φ = c/p is the polymer volume fraction, c being the concentration and p the density of the pure polymer. The polymer-polymer correlation length, |, however, which in the semidilute region conforms to the simple scaling relation, viz., φ(άΐΙ/δφ) a kT/ξ3, varies only as φ~λ. The observations are consistent with the Muthukumar-Edwards description of solutions, for which at the θ temperature φ(δTΙ/οφ) * yP/(l-<p) + zifß, ζ being a function of the third-order interaction parameter, w. The value ζ = -0.8s ± O.lo deduced from the dependence of scattering intensity upon polymer concentration yields w = 0.03o ± O.Olg. In the single-phase region below 38 °C, the scattering intensity and correlation length both increase, also in agreement with the Muthukumar-Edwards theory. © 1990, American Chemical Society. All rights reserved.