Mean-field phenomenology of wetting in nanogrooves

Abstract

In this special issue article we bring together our recent research on wetting in confinement, in particular planar walls, wedges, capillary grooves and slit pores, with emphasis on phase transitions and competition between wetting, filling and condensation, and highlight their similarities and disparities. The results presented are obtained with the classical density functional theory (DFT) for fluids, which is a mean-field statistical mechanical framework for including the spatial variations of the fluid density into the thermodynamic equation of state.For wetting in sculpted substrates, we solve numerically the DFT equations to obtain the fluid density profiles, wetting isotherms and phase diagrams. This allows us to contrast the wetting phenomenology of grooves, planar walls, slit and wedge-shaped pores. Of particular interest are the transitions associated with capillary condensation, planar pre-wetting and mean-field wedge pre-filling lines.

General framework for fluctuating dynamic density functional theory

“…This would allow us to evaluate the impact of the coupling between translational and rotational DoF on characteristic quantities, such as the nucleation barrier and rate. But also effects of walls [71,72] and confinement [73,[74][75][76][77], which in general should lead to definite orientation in the first particle layers near a solid substrate which in turn can induce anisotropy of both equilibrium and transport properties. Orientation coupled with layering can also cause formation of new phases in the fluid with the extreme form of the substrate-induced ordering being 'surface freezing', i.e.…”

Surface nanodrops and nanobubbles: a classical density functional theory study

“…We have introduced a low- cutoff parameter in (2.6) to eliminate the non-physical divergence of at fluid–substrate contact. This is a purely mathematical device and does not affect the physics of adsorption as was shown in our earlier work (Yatsyshin & Kalliadasis 2016).…”

Wetting of a plane with a narrow solvophobic stripe

“…where ρ w is the average density of the material (w) and H 0 is a near-wall cut-off, introduced to avoid a non-physical divergence of V 0 (y) at contact with the fluid. The effect of varying the finite H 0 > 0 on planar wetting is investigated in, e.g., Appendix 1 of Reference [44], where it is shown that such low-y cut-off does not qualitatively affect the wetting phenomenology. When a macroscopically deep stripe of material type (s) of width L with the pairwise fluid-substrate potential ϕ LJ σs,εs (r) is inserted into the wall, the total potential of the decorated substrate is modified to…”

“…This allows us to perform a fully consistent mean-field analysis. Further details on the approximations involved in ( 4)-( 7), as well as full details of the numerical scheme, used to minimize the grand free energy functional and trace the full isotherms can be found elsewhere [28,44,48].…”