Computer simulations of shear and friction between polymer brushes

Surface-polymer interactions are important in many technological applications, such as colloidal stabilization and adherence. During the past few years, considerable progress has been made in understanding these interactions and the forces between polymer-bearing surfaces. Under steady-state shear flow, simulations of end-grafted polymers show that whereas some of the individual polymer chains stretch in the direction of flow, the height of the grafted layer is only weakly dependent on the shear rate. When two surfaces bearing end-grafted chains are brought into contact, the normal force is observed in simulation to increase rapidly whereas the shear force is much smaller leading to a very small effective coefficient of friction. This behavior is in agreement with experiment.