Phase transitions and universal dynamics in confined films

We describe molecular dynamics simulations of fluid films confined between two solid walls. The films consist of spherical molecules, or flexible linear chains with up to twenty monomers. When the wall separation is only a few molecular diameters, crystalline or glassy order is induced across the film. The onset of the glassy phase is characterized by rapidly increasing relaxation times. These manifest themselves through changes in the diffusion constant and in the response to shear. The viscosity exhibits the same power-law scaling with shear rate that was observed in recent experiments. Our study suggests that this response is a universal property of lubricants near a glass transition. © 1992 The American Physical Society.