arXiv subjects

Andrew O. Parry

Publications and source records attributed to Andrew O. Parry.

21 records · Page 2Linked to original sources

arXiv2015

Filling transitions in acute and open wedges

We present numerical studies of first-order and continuous filling transitions, in wedges of arbitrary opening angle $ψ$, using a microscopic fundamental measure density functional model with short-ranged fluid-fluid forces and long-ranged wall-fluid forces. In this system the wetting transition characteristic of the planar wall-fluid interface is always first-order regardless of the strength of the wall-fluid potential $\varepsilon_w$. In the wedge geometry however the order of the filling transition depends not only on $\varepsilon_w$ but also the opening angle $ψ$. In particular we show that even if the wetting transition is strongly first-order the filling transition is continuous for sufficient acute wedges. We show further that the change in the order of the transition occurs via a tricritical point as opposed to a critical-end point. These results extend previous effective Hamiltonian predictions which were limited only to shallow wedges.

cond-mat.stat-mech↗

arXiv2014

Condensation and evaporation transitions in deep capillary grooves

We study the order of capillary condensation and evaporation transitions of a simple fluid adsorbed in a deep capillary groove using a fundamental measure density functional theory (DFT). The walls of the capillary interact with the fluid particles via long-ranged, dispersion, forces while the fluid-fluid interaction is modelled as a truncated Lennard-Jones-like potential. We find that below the wetting temperature $T_w$ condensation is first-order and evaporation is continuous with the metastability of the condensation being well described by the complementary Kelvin equation. In contrast above $T_w$ both phase transitions are continuous and their critical singularities are determined. In addition we show that for the evaporation transition above $T_w$ there is an elegant mapping, or covariance, with the complete wetting transition occurring at a planar wall. Our numerical DFT studies are complemented by analytical slab model calculations which explain how the asymmetry between condensation and evaporation arises out of the combination of long-ranged forces and substrate geometry.

cond-mat.stat-mech↗

arXiv2013

Critical Point Wedge Filling

We present results of a microscopic density functional theory study of wedge filling transitions, at a right-angle wedge, in the presence of dispersion-like wall-fluid forces. Far from the corner the walls of the wedge show a first-order wetting transition at a temperature $T_w$ which is progressively closer to the bulk critical temperature $T_c$ as the strength of the wall forces is reduced. In addition, the meniscus formed near the corner undergoes a filling transition at a temperature $T_f<T_w$, the value of which is found to be in excellent agreement with macroscopic predictions. We show that the filling transition is {\it first-order} if it occurs far from the critical point but is {\it continuous} if $T_f$ is close to $T_c$ even though the walls still show first-order wetting behaviour. For this continuous transition the distance of the meniscus from the apex grows as $\ell_w\approx (T_f-T)^{-β_w}$ with critical exponent $β_w\approx 0.46 \pm 0.05$ in good agreement with the phenomenological effective Hamiltonian prediction. Our results suggest that critical filling transitions, with accompanying large scale universal interfacial fluctuation effects, are more generic than thought previously, and are experimentally accessible.

cond-mat.stat-mech↗