Theory of surface deformations of polymer brushes in solution

The excess free energy of small-amplitude deformations of a wet "parabolic" brush consisting of polymer chains attached to a solid plane by one end is calculated. The brush is swollen by a good (marginal) solvent. A generic d eformation involving both compression normal to the grafting surface and la teral shear is considered. It is shown that the free energy attains a minim um as a function of the wave vector of the deformation, q. A shallow maximu m of the scattering function S(q) is thus predicted. The theoretical scatte ring functions calculated for an arbitrary orientation of the scattering ve ctor are compared with evanescent-wave light scattering data.