Density functional study of condensation in capped capillaries

Abstract

Abstract. We study liquid adsorption in narrow rectangular capped capillaries formed by capping two parallel planar walls (a slit pore) with a third wall orthogonal to the two planar walls. The most important transition in confined fluids is arguably condensation, where the pore becomes filled with the liquid phase which is metastable in the bulk. Depending on the temperature T , the condensation in capped capillaries can be first-order (at T ≤ T cw ) or continuous (at T > T cw ), where T cw is the capillary wetting temperature. At T > T cw , the capping wall can adsorb mesoscopic amounts of metastable under-condensed liquid. The onset of condensation is then manifested by the continuous unbinding of the interface between the liquid adsorbed on the capping wall and the gas filling the rest of the capillary volume. In wide capped capillaries there may be a remnant of wedge filling transition, which is manifested by the adsorption of liquid drops in the corners. Our classical statistical mechanical treatment predicts a possibility of three-phase coexistence between gas, corner drops and liquid slabs adsorbed on the capping wall. In sufficiently wide capillaries we find that thick prewetting films of finite length may be nucleated at the capping wall below the boundary of the prewetting transition. Prewetting then proceeds in a continuous manner manifested by the unbinding interface between the thick and thin films adsorbed on the side walls. Our analysis is based on a detailed numerical investigation of the density functional theory for the fluid equilibria for a number of illustrative case studies.

Nonequilibrium molecular dynamics simulations of nanoconfined fluids at solid-liquid interfaces

“…This is a manifestation of the Kelvin shift of the bulk coexistence curve, which occurs due to the spatial confinement of the fluid, 59 reflecting the higher degree of effective confinement in the hydrophobic case due to the repulsive wall layer. In fact, the underlying physics can give rise to rich phase equilibria and wetting transitions for capillaries, 60 grooves, 61,62 and more general geometries such as steps and wedges. 63 We note that in the more confined case presented in Fig.…”

Classical density functional study of wetting transitions on nanopatterned surfaces

“…With these shortcomings, the model functional (1) - (4) provides a suitable microscopic starting point to study the interplay between unbending and pre-wetting on a striped substrate. Further discussion of the physical approximations underlying (1) -(4) and possible approaches to their numerical solution can be found elsewhere, e.g., in references [26,32,34,38,39].…”

Dynamical density functional theory with hydrodynamic interactions in confined geometries

“…In particular, we use pseudospectral methods to accurately and efficiently solve the equations either on the full infinite plane or on the full half space, with no truncation or periodisation required. These techniques have been shown to be very successful in a range of DFT [71][72][73][74][75][76] and DDFT 24,25,31 simulations.…”