RHEOLOGY AND LOCAL-STRUCTURE OF THIN-FILMS CONFINED BETWEEN THERMALLYCORRUGATED WALLS

The rheological behavior of a monolayer film of spherically symmetric molecules confined between two solid surfaces (i.e., walls) is investi gated in isostress-isostrain ensemble Monte Carlo simulations. The wal ls consist of individual atoms interacting with film molecules via the Lennard-Jones potential. By employing the Einstein model, wall atoms are also subject to a harmonic binding potential and may depart from t heir equilibrium lattice sites so that the walls are thermally corruga ted. The film can be exposed to a shear strain by moving the walls rel ative to each other in transverse directions. Molecular expressions fo r the shear stress are derived which differ from the ones previously o btained for thermally decoupled walls (i.e., in which wall atoms are r igidly fixed in their equilibrium lattice positions). Unlike the film' s local structure the shear stress depends sensitively on the degree o f thermal corrugation of the walls. The larger it is the more plastic is the response of the film to an applied shear strain.