Roughness and undulations of the free surfaces of ultrathin liquid films of perfluoropolyethers on solid surfaces-effect of polar interaction

Abstract

A rouse-like algorithm applied to a simplified bead spring off-lattice polymer model on NVT Monte Carlo (MC) simulation for perfluoropolyether Z and Zdol (qualitative) has been performed. The surface roughness with no evaporation and undulations of the free surfaces during evaporation of the ultrathin film polymers has been presented. A bead-bead Lennard-Jones (LJ) potential is used in the bulk, and a substrate-bead LJ potential is added in the ultrathin film condition. In addition, a dipole-dipole polar interaction potential is adopted at the two chain ends of Zdol. Simulation is performed with approximately 4000 g/mol molecular weight under the assumption of room temperature and pressure condition. It is observed that the calculated average radius of gyration is almost equal to the experimental value both for the bulk situation. Surface roughness of ultrathin liquid films of 2-nm film thickness has been calculated for Z and Zdol. A top solid surface has been activated over the ultrathin film on the bottom surface and the film has been allowed to evaporate toward the top surface. Undulations of the free surfaces have been observed along with the desorption of the films with increasing MC cycle and compared between Z and Zdol.