Wetting of prototypical one- and two-dimensional systems: Thermodynamics and density functional theory

Abstract

Consider a two-dimensional capped capillary pore formed by capping two parallel planar walls with a third wall orthogonal to the two planar walls. This system reduces to a slit pore sufficiently far from the capping wall and to a single planar wall when the side walls are far apart. Not surprisingly, wetting of capped capillaries is related to wetting of slit pores and planar walls. For example, the wetting temperature of the capped capillary provides the boundary between first-order and continuous transitions to condensation. We present a numerical investigation of adsorption in capped capillaries of mesoscopic widths based on density functional theory. The fluid-fluid and fluid-substrate interactions are given by the pairwise Lennard-Jones potential. We also perform a parametric study of wetting in capped capillaries by a liquid phase by varying the applied chemical potential, temperature, and pore width. This allows us to construct surface phase diagrams and investigate the complicated interplay of wetting mechanisms specific to each system, in particular, the dependence of capillary wetting temperature on the pore width. C 2015 AIP Publishing LLC. [http://dx

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].…”

“…Note that these pre-wetting lines lay in the gas region of the bulk phase diagram (∆µ < 0), and approach bulk coexistence tangentially at the respective T (i) w , i = w, s. As expected, the deeper well of the fluid-stripe LJ interaction leads to T (s) w < T (w) w , and a more pronounced prewetting line µ (s) pw (T ), which extends deeper into the gas region. Near the respective wetting temperatures T (i) w , the pre-wetting lines are described by their asymptotic behaviour, which follows from analysis of the Clausius-Clapeyron equation [5,34,41]:…”

“…For Cartesian coordinates, with the origin at the center of the stripe, y the distance normal to the wall, and the x-axis aligned with the wall perpendicularly to the stripe, the potential of the stripe V L (x, y) can be obtained from the standard "3-9" potential of a homogeneous LJ wall (L = 0). The latter is given by [34]:…”

“…To this end, we have computed the adsorption Γ 0 , which can be obtained from the density profiles ρ (r) ≡ ρ (y) [32,34]:…”

“…[35,36]). But in the present decade, the explosive growth of available computational power and especially the development of sophisticated numerical methodologies [32][33][34], have provided the necessary tools to perform detailed numerical parametric studies employing classical DFT in problems of wetting. Earlier studies of adsorption mainly focused on planar walls and infinite capillary slits and pores.…”