COMPARATIVE SWELLING OF GELS AND POLYMER BRUSH LAYERS

The swelling of chemically end-grafted polystyrene brushes in a margin al solvent is investigated as a function of molecular weight M(W), gra fting density sigma, and solvent quality tau = (T - theta)/T by specul ar neutron reflection and these swelling results are compared to previ ous measurements on swollen polymer networks. This comparison is motiv ated by the view of a polymer brush as a variety of ''gel'' where the crosslinks (grafting points) are constrained to lie on a surface. In a ccordance with this analogy, the temperature dependence of the brush a nd the network swelling is found to be qualitatively similar and the r elative degree of brush and network swelling is found to diminish with an increase of sigma and the cross-link density nu, respectively. The network swelling data are taken from a previous study by Zrinyi and H orkay [1] who found an apparent universal master curve describing the swelling of uncharged gels with temperature. An attempt to describe th e swelling of polymer brushes having a range of molecular weights by s imilar reduced variables led to a fairly good description of the brush swelling data, but the scaling curves for the gels and the brushes do not exactly coincide.