ADSORPTION-DESORPTION KINETICS IN NANOSCOPICALLY CONFINED OLIGOMER FILMS UNDER SHEAR

The method of molecular dynamics computer simulations is employed to s tudy oligomer melts confined in ultra-thin films and subjected to shea r. The focus is on the self-diffusion of oligomers near attractive sur faces and on their desorption, together with the effects of increasing energy of adsorption and shear. It is found that the mobility of the oligomers near an attractive surface is strongly decreased. Moreover, although shearing the system forces the chains to stretch parallel to the surfaces and thus increase the energy of adsorption per chain, flo w also promotes desorption. The study of chain desorption kinetics rev eals the molecular processes responsible for the enhancement of desorp tion under shear. They involve sequences of conformations starting wit h a desorbed tail and proceeding in a very fast, correlated, segment-b y-segment manner to the desorption of the oligomers from the surfaces.