ADSORBED POLYMER-CHAINS UNDER LATERAL EXPANSION AND COMPRESSION - A MOLECULAR-DYNAMICS STUDY

A molecular dynamics simulation of polymeric chains in contact with an attractive surface under good solvent conditions is presented. The ad sorbed chains are in equilibrium with free chains in solution at a ver y low bulk concentration. The response of the layer to a lateral expan sion or compression of the interface area is studied. When the interfa ce is expanded, the total surface excess of the monomers stays relativ ely constant, due to the slow movement of the chains into the layer. U nder compression, expulsion of the chains from the layer into the solu tion is very rapid. The monomer density at the surface and the surface pressure are calculated as a function of the surface area per chain. Both quantities are found to be monotonically decreasing functions of the surface area, for compressed as well as expanded layers.