# Probing interface localization-delocalization transitions by colloids

## TL;DR

This paper proposes a method to detect interface localization-delocalization transitions in two-phase fluids using colloids, by observing changes in the force on a colloid, which offers an accessible experimental indicator.

## Contribution

It introduces a novel experimental approach to observe ILDT by measuring colloid forces, bridging theoretical predictions with practical detection methods.

## Key findings

- Force on colloid changes sharply at ILDT
- Proposed detection method is experimentally feasible
- Supports theoretical predictions with simulations

## Abstract

Interface localization-delocalization transitions (ILDT) occur in two-phase fluids confined in a slit with competing preferences of the walls for the two fluid phases. At low temperatures the interface between the two phases is localized at one of the walls. Upon increasing temperature it unbinds. Although intensively studied theoretically and computationally, such transitions have not yet been observed experimentally due to severe challenges in resolving fine details of the fluid structure. Here, using mean field theory and Monte Carlo simulations of the Ising model, we propose to detect these ILDT by using colloids. We show that the finite-size and fluctuation induced force acting on a colloid confined in such a system experiences a vivid change if, upon lowering the temperature, the interface localizes at one of the walls. This change can serve as a more easily accessible experimental indicator of the transition.