DEWETTING OF THIN POLYMER-FILMS ADSORBED ON SOLID SUBSTRATES - A MONTE-CARLO SIMULATION OF THE EARLY STAGES

Using an off-lattice bead-spring model of flexible polymer chains cont aining N = 32 beads under bad solvent conditions, thin films of polyme r melts are simulated. The films are confined between two parallel pla tes, the upper plate being purely repulsive while the lower plate exer ts a short range attraction on the polymer layer so that a dense thin film is adsorbed on this plate for large enough attraction strength ep silon. Then ''quenching experiments'' are simulated by suddenly reduci ng \epsilon\ at time t = 0 and monitoring the time evolution of the po lymer film. While for large enough final values of \epsilon\ only the density in the film decreases somewhat, but the film stays laterally h omogeneous, for \epsilon\ less than a critical value \epsilon(c)\ it i s found that the film breaks up into droplets. The early stages of the time evolution of this process in the framework of a dynamic Monte Ca rlo simulation are studied both by recording the time dependence of th e adsorbed amount, the average thickness of the layer, the distributio n function of meansquare displacements, and with the help of snapshot pictures of the system configurations. Also equilibrium properties of the films are investigated including both collective properties such a s density profiles and radial distribution functions, and single-chain properties such as parallel and perpendicular parts of meansquare gyr ation radii, in dependence on the adhesive strength \epsilon\ of the s ubstrate. (C) 1997 American Institute of Physics.