The kinetics of penetration of grafted polymers into a network

We present the results of a neutron reflectometry study of the kinetics of penetration of a grafted polymer layer into a permanently cross-linked, che mically identical network. The polymer used was polystyrene. Initially the grafted chains are completely excluded from the network, and the interface between them is sharp. The segment density profile was measured after a ser ies of annealing times to follow the kinetics of penetration. The range of annealing times was extended over 9 orders of magnitude by using time-tempe rature superposition. We observe a slow approach to equilibrium, in good ag reement with theory, which predicts this to be logarithmic in time. The kin etics of penetration is slower for more densely cross-linked networks and f or greater brush grafting densities. We also note a grafting density depend ence of the equilibrium profile but, somewhat unexpectedly, no dependence o n the density of cross-links.