Dynamics of Entangled Polymers at Interfaces.

The dynamics of polymers at interfaces is a problem with numerous technological applications for adhesion, coating, lubrication, and colloidal suspensions. We study in this work various aspects of dynamics of a linear polymer near an interface using a lattice model. We first consider a reversible adhesion process with grafted chains. The initial relaxation of a grafted chain after reattachment has been found to consist of two distinct steps: The head of the chain first penetrates rapidly into the gel by diffusion of kinks until it reaches a metastable "runner-like" state. Then the point of entry slowly moves to near the graft site to eventually recover the equilibrium "plume-like" state. The slippage problem on a grafted surface is discussed next. The friction coefficient of a polymer melt or a network on a surface grafted with long polymers is predicted to have a very non-linear functional dependence on the pulling speed. We present our numerical results, obtained through novel Monte Carlo methods, which are in a very good agreement with the theory. We finally study the diffusion of a linear polymer near permeable membranes, which is closely related to the membrane filtration techniques. When the membranes are stacked with uniform spacing, the diffusion of a polymer is predicted to show three different behaviors depending on the spacing; reptation, intermediate, and Rouse ones. In the intermediate regime, the diffusion constants become extremely anisotropic reflecting the underlying anisotropy in the arrangement of membranes.