Thermomechanical properties of confined fluids exposed to a shear strain

The properties of a molecularly thin film of spherically symmetric molecule s confined to a chemically heterogeneous slit-pore were investigated by Mon te Carlo simulations in a grand mixed stress-strain ensemble. The slit-pore comprises two identical plane-parallel solid substrates, each of which con sists of alternating strips of solid of two types: strongly adsorbing (widt h d(s)) and weakly adsorbing. Under favourable thermodynamic conditions the confined film consists of fluid bridges-that is, a high(er)-density fluid over the strongly attractive strip surrounded by a low(er)-density fluid su pported by the (outer) weakly attractive strips. By misaligning the opposit e substrates, bridge phases can be exposed to a shear strain alpha s(x) (0 less than or equal to alpha less than or equal to 1/2, s(x) the side length of the simulation cell) and the associated shear stress T-zx of(fluidic) b ridge phases can be calculated from molecular expressions. The stress curve T-zx(alpha s(x)) is qualitatively similar to the one characteristic of sol idlike films confined between atomically structured substrates in that the initial response to small shear strains is Hookean, and this is followed by an increasingly nonlinear regime up to the yield point where T-zx (alpha s (x)) assumes its maximum. We also investigated the influence of chemical co rrugation c(r) := d(s)/s(x) on T-zx(alpha s(x)). With increasing c(r), yiel d strain and stress increase at first up to a maximum and decline thereafte r. By employing the theory of corresponding states, T-zx (alpha s(x)) is re normalized by yield stress and strain such that the results can be represen ted uniquely by a master curve independent of any system-dependent paramete rs.