On the Dynamics of Densely Grafted Layers. The Effect of Stretched Configurations

The stretched configurations adopted by densely grafted chains, i.e. chains attached to an interface by a head group only, affect their dynamics. The effect on the characteristic time, τ exp , required by a single "degrafted" chain in order to leave the layer under equilibrium conditions is analysed. τ exp is relevant to the understanding of exchange processes in aggregates formed by polymeric surfactants. Because of the chain stretched configuration this motion is reptative in nature. For flat grafted layers τ exp is determined by driven motion. This arises because of the loss of free energy due to the release from confinement associated with the chain expulsion. As a result τ exp of a chain consisting of N monomers scales as N 2 rather than τ exp ∼ N 3 expected for diffusive motion. For extended spherical grafted layers the τ exp associated with the diffusive and the driven motions are comparable and τ exp ∼ N 9/5 for the driven case.