Filling transitions in acute and open wedges

TL;DR

This study uses a microscopic density functional model to analyze how the order of filling transitions in wedges depends on geometry and wall-fluid interactions, revealing that acute wedges can exhibit continuous filling transitions even when wetting is first-order.

Contribution

It demonstrates that the order of filling transitions in wedges depends on opening angle and wall potential, extending previous predictions to more acute geometries.

Findings

Filling transition order depends on wedge angle and wall potential.

Acute wedges can have continuous filling transitions despite first-order wetting.

Transition change occurs via a tricritical point, not a critical-end point.

Abstract

We present numerical studies of first-order and continuous filling transitions, in wedges of arbitrary opening angle $\psi$, 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 $\psi$. 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.