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Abstract
Variation of density in the ultrathin liquid perfluoropolyether films on solid surfaces has been studied by Monte Carlo simulations of Lennard-Jones systems. The liquid film is 8.75 nm thin film consisting of polymer molecules assuming the structure of perfluoropolyether Z having molecular weights of 3840, 2500 and 1700 g/mol and interacting among themselves by Lennard-Jones potential. The substrate is assumed to be continuous without atomic structure and exerting Lennard-Jones potential on liquid molecules in the ultrathin film. The system temperature is considered to be 25 °C and the liquid molecules also have the gravitational potential. It is found that the bead density decreases towards the surface in a thinner sublayer in the ultrathin liquid film above the surface and the thickness of this sublayer just above the surface may increase with the increase of molecular weight of the of polymers in the film. Repulsive potential of the surface further decreases the bead density near the surface. The results are compared with the experimental results of the pefluoropolyether lurbricants by X-ray reflectivity (Shouji, et al., 1998).
