THE MOLECULAR-DYNAMICS SIMULATION OF BOUNDARY-LAYER LUBRICATION

Molecular dynamics simulations have been performed on bilayers of dioc tadecyldimethylammonium chloride adsorbed between two solid surfaces. The separation of the layers is reduced so that the alkyl chains overl ap to produce a repulsive normal pressure P-zz. The layers are then sh eared at a constant velocity of between 1 ms(-1) and 100 ms(-1) and th e resulting pressure P-xz the boundary and in the direction of the she ar, is calculated. This method provides a measure of the friction coef ficient mu = \P-xz\/P-zz. The friction coefficient has been calculated as a function of the surface density of the amphiphiles, the relative shearing velocity and the applied normal force. This friction coeffic ient decreases with increasing normal force, increases with decreasing amphiphile density, and increases with increasing shearing velocity. Results are given for the translational, orientational and conformatio nal structure of the bilayer under shear.