Nanoscopic liquid bridges exposed to a torsional strain

In this paper we investigate the response to a torsional strain of a molecularly thin film of spherically symmetric molecules confined to a chemically heterogeneous slit pore by means of Monte Carlo simulations in the grand canonical ensemble. The slit pore comprises two identical plane-parallel solid substrates, the fluid-substrate interaction is purely repulsive except for elliptic regions attracting fluid molecules. Under favorable thermodynamic conditions the confined film consists of fluid bridges where the molecules are preferentially adsorbed by the attractive elliptic regions, and span the gap between the opposite substrate surfaces. By rotating the upper substrate while holding the lower one in position, bridge phases can be exposed to a torsional strain 0< or =theta< or =pi/2 and the associated torsional stress T(theta) of the (fluidic) bridge phases can be calculated from molecular expressions. The obtained stress curve T(theta)(theta) is qualitatively similar to the one characteristic of sheared confined films: as the torsion strain increases, T(theta) rises to a maximum (yield point) and then decays monotonically to zero. By changing the ellipses' aspect ratio while keeping their area constant, we also investigate the influence of the attractive elliptic patterns' shape on T(theta)(theta).