Spectral methods for the equations of classical density-functional theory: Relaxation dynamics of microscopic films

J. Phys.: Condens. Matter

Parry

Rascón

et al. 2017

Abstract.Even simple fluids on simple substrates can exhibit very rich surface phase behaviour. To illustrate this, we consider fluid adsorption on a planar wall chemically patterned with a deep stripe of a different material. In this system, two phase transitions compete: unbending and pre-wetting. Using microscopic density-functional theory, we show that, for thin stripes, the lines of these two phase transitions may merge, leading to a new two-dimensional-like wetting transition occurring along the walls. The influence of intermolecular forces and interfacial fluctuations on this phase transition and at complete pre-wetting are considered in detail.

Section: Classical Density Functional Theorymentioning

confidence: 99%

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

Section: Wetting Phenomenologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Classical density functional study of wetting transitions on nanopatterned surfaces

J. Phys.: Condens. Matter

Parry

Rascón

et al. 2017

“…The expression above exhibits a non-physical divergence at contact with the fluid. As a result, the fluid density decays super-exponentially at contact with the substrate walls [31]. Capturing this behaviour of the fluid density numerically requires a lot of mesh points near the wall, which unnecessarily increases the computational cost, given that the present study is focused on liquid-gas interfaces.…”

Section: Density Functional and Governing Equationsmentioning

confidence: 99%

“…Here, we perform a parametric study of the DFT model of adsorption for a number of illustrative case studies. Most of the technical complexity of the approach can be encapsulated within our numerical methodologies [31], as they provide the means to obtain the phase portrait of the system in a systematic manner. This allows us to argue in terms of the fluid structure and its phenomenology, and elucidate the connections between wetting of different systems.…”

Section: Introductionmentioning

confidence: 99%

Density functional study of condensation in capped capillaries

J. Phys.: Condens. Matter

Savva

Kalliadasis

2015

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.

Classical Density-Functional Theory Studies of Fluid Adsorption on Nanopatterned Planar Surfaces

Springer Proceedings in Mathematics &Amp; Statistics

Kalliadasis

2018

Self Cite

This contribution is based on our talk at the BIRS Workshop on "Coupled Mathematical Models for Physical and Biological Nanoscale Systems and Their Applications". Our aim here is to summarize and bring together recent advances in wetting of nanostructured surfaces, using classical density-functional theory (DFT). Classical DFT is an ab initio theoretical-computational framework with a firm foundation in statistical physics allowing us to systematically account for the fluid spatial inhomogeneity, as well as for the non-localities of intermolecular fluid-fluid and fluid-substrate interactions. The cornerstone of classical DFT, is to express the grand free energy of the system as a functional of its one-body density, thus generating a hierarchy of N-body correlation functions. Unconstrained minimization of a properly approximated free-energy functional with respect to the one-body density then yields the basic DFT equation. And since most macroscopic quantities of interest can often be cast as averages over a one-body distribution, this equation provides a very useful and accessible computational tool. Indeed, there has been a rapid growth of classical DFT applications across a broad variety of fields, including phase transitions in solutions of macromolecules, interfacial phenomena, and even nucleation. Here we attempt to give a taste of what simple equilibrium DFT models look like, and what they can and cannot capture, as far as wetting on chemically heterogeneous substrates is concerned. We review recent progress in the understanding of planar prewetting and interface unbending on such substrates and compute substrate-fluid interfaces and wetting isotherms.