Combined static and dynamic light scattering study of associating random block copolymers in solution

We combine static and dynamic light scattering techniques to study the structure and dynamics of hydrophobically modified polyacrylamide in aqueous solution. Two different length scales can be distinguished in the solutions. The first one corresponds to the usual structure of an ideal semidilute polymer solution, with a correlation length given by the size of the blobs. On that length scale, fluctuations of concentration relax by a cooperative diffusion mechanism. On a much larger length scale (>2000 Angstrom), there is experimental evidence for a texture. The corresponding relaxation times appear to be related to the macroscopic viscosity of the surrounding polymer solution and might correspond to a viscoelastic relaxation of the texture embedded in this solution. This texture appears to be responsible for the interesting thickening properties of these associating random block copolymers.