Intrusion of fluids into nanogrooves

Abstract

We study the shape of gas-liquid interfaces forming inside rectangular nanogrooves (i.e., slit-pores capped on one end). On account of purely repulsive fluid-substrate interactions the confining walls are dry (i.e., wet by vapor) and a liquid-vapor interface intrudes into the nanogrooves to a distance determined by the pressure (i.e., chemical potential). By means of Monte Carlo simulations in the grand-canonical ensemble (GCEMC) we obtain the density rho(z) along the midline (x = 0) of the nanogroove for various geometries (i.e., depths D and widths L) of the nanogroove. We analyze the density profiles with the aid of an analytic expression which we obtain through a transfer-matrix treatment of a one-dimensional effective interface Hamiltonian. Besides geometrical parameters such as D and L , the resulting analytic expression depends on temperature T , densities of coexisting gas and liquid phases in the bulk rho g,l(x) and the interfacial tension gamma. The latter three quantities are determined in independent molecular dynamics simulations of planar gas-liquid interfaces. Our results indicate that the analytic formula provides an excellent representation of rho(z) as long as L is sufficiently small. At larger L the meniscus of the intruding liquid flattens. Under these conditions the transfer-matrix analysis is no longer adequate and the agreement between GCEMC data and the analytic treatment is less satisfactory.

Geometrical Aspects of Drying in a Capped Capillary: a DFT Study

“…By changing γ continuously from 0 to ∞ Rascon and Parry [1] predicted by the use of an effective interfacial Hamiltonian model that the order of the liquid-vapor phase transition inside a capillary of two parallel walls [2] can be changed from first to second order by capping the capillary with a third wall. The behavior of a fluid in a capped capillary is closely related to wetting or drying phenomena [3] and is one example of the rich adsorption behavior of a fluid on geometrically structured walls [1,[4][5][6][7]. In a recent density functional theory (DFT) study [9] we have confirmed [8] the scenario predicted by Rascon and Parry [1] using a microscopic theory for a square-well fluid confined by three hard walls.…”

The effect of nanometre-scale structure on interfacial energy

“…The range in domain size where one approximation ends and the other begins, or where either cannot be applied is unknown, yet it is accepted that solvents behave in unique ways when confined or in contact with nanoscale boundaries 28,29 The W SL for these films was measured using macroscopic θ CA and AFM techniques.…”

Drying in a capped capillary

“…Interest in the last decade has been further renewed by technological developments which allow one to pattern and sculpt solid surfaces on the nanometre and micrometre scale. Thus as well as considering adsorption at flat substrates and in capillary slits and pores one can consider corrugated surfaces and wedges/grooves of different cross-section [13][14][15][16][17], and also heterogeneous surfaces patterned into domains with different wetting properties. As well as being of huge practical importance this is of fundamental interest to statistical mechanics since different substrate geometry can induce novel types of interfacial phase transition which lie "between" wetting and capillarycondensation.…”