# Kinetic Monte Carlo and hydrodynamic modelling of droplet dynamics on surfaces, including evaporation and condensation

## TL;DR

This paper introduces a combined kinetic Monte Carlo and hydrodynamic model to simulate droplet dynamics on surfaces, capturing evaporation, condensation, and fluid motion at microscopic and macroscopic scales.

## Contribution

It develops a novel lattice-gas model integrating microscopic particle interactions with macroscopic fluid dynamics for droplet behavior on surfaces.

## Key findings

- Droplets can join, spread, and slide under gravity.
- Evaporation and condensation significantly affect droplet dynamics.
- The model links microscopic parameters to macroscopic quantities like contact angle.

## Abstract

We present a lattice-gas (generalised Ising) model for liquid droplets on solid surfaces. The time evolution in the model involves two processes: (i) Single-particle moves which are determined by a kinetic Monte Carlo algorithm. These incorporate into the model particle diffusion over the surface and within the droplets and also evaporation and condensation, i.e. the exchange of particles between droplets and the surrounding vapour. (ii) Larger-scale collective moves, modelling advective hydrodynamic fluid motion, determined by considering the dynamics predicted by a thin-film equation. The model enables us to relate how macroscopic quantities such as the contact angle and the surface tension depend on the microscopic interaction parameters between the particles and with the solid surface. We present results for droplets joining, spreading, sliding under gravity, dewetting, the effects of evaporation, the interplay of diffusive and advective dynamics, and how all this behaviour depends on the temperature and other parameters.