Diffuse x-ray scattering study of toluene and polybromostyrene PBrS/toluene solutions

We report measurements and calculations of x-ray diffuse scattering from the liquid-vapor interface of toluene and polybromostyrene(PBrS)/toluene solutions for polymer molecular weights 90 K and 1 M at concentrations up to 11.7 volume %, well into the entangled semidilute regime. We have calculated the static structure factor S(k) and equal time height-height correlation function C(R) for surface hydrodynamic modes based on a coupled two-fluid model where the polymer response is taken to be that of a Maxwell viscoelastic material [Harden et al., 3. Chem. Phys. 94, 5208 (1991)]. We obtain the leading correction term to the capillary-wave result for C(R) dependent on the solution shear modulus E₀, as well as an analytic approximation valid for large E ₀, including the case of pure polymer melt.