Structure of a model lubricant in a mica slit pore

Grand canonical ensemble Monte Carlo computer simulations are used to study a monolayer octamethylcyclotetrasiloxane (OMCTS) film confined between micalike surfaces to better understand the relationship between fluid properties and the atomic structure of the surfaces. OMCTS packs as a well ordered hexagonally close-packed film for all relative alignments of the surfaces. The orientation of the fluid lattice is guided by the mica surfaces. The angle between the symmetry planes of the fluid and the hexagonal oxygen rings on the mica surfaces is approximately 30 degrees. The coupling between OMCTS and the confining mica surfaces is shown to be intermediate in that (1) the film sustains a shear stress and (2) the hexagonal symmetry of the film becomes distorted when the surfaces are out of registry but the film does not melt. Incrementally shifting one of the surfaces laterally leads to periodic distortions in the fluid lattice that are caused by the fluid being stretched to accommodate variations in the pore space potential energy. (C) 2000 American Institute of Physics. [S0021-9606(00)70430-2].