# Modelling the evaporation of nanoparticle suspensions from heterogeneous surfaces

## TL;DR

This paper introduces a Monte Carlo grid-based model for simulating nanoparticle suspension evaporation on heterogeneous surfaces, accounting for surface roughness and contact-line pinning, with applications to inkjet-printed electrical connections.

## Contribution

The model accurately reproduces dewetting phenomena and relates material interactions to drying behavior, aiding in optimizing surface designs for better electrical connections.

## Key findings

- The model predicts dewetting behavior on heterogeneous surfaces.
- Surface roughness influences contact-line pinning and drying dynamics.
- Positioning hydrophobic regions below metal height reduces dewetting risk.

## Abstract

We present a Monte Carlo (MC) grid-based model for the drying of drops of a nanoparticle suspension upon a heterogeneous surface. The model consists of a generalised lattice-gas in which the interaction parameters in the Hamiltonian can be varied to model different properties of the materials involved. We show how to choose correctly the interactions, to minimise the effects of the underlying grid so that hemispherical droplets form. We also include the effects of surface roughness to examine the effects of contact-line pinning on the dynamics. When there is a `lid' above the system, which prevents evaporation, equilibrium drops form on the surface, which we use to determine the contact angle and how it varies as the parameters of the model are changed. This enables us to relate the interaction parameters to the materials used in applications. The model has also been applied to drying on heterogeneous surfaces, in particular to the case where the suspension is deposited on a surface consisting of a pair of hydrophilic conducting metal surfaces that are either side of a band of hydrophobic insulating polymer. This situation occurs when using inkjet printing to manufacture electrical connections between the metallic parts of the surface. The process is not always without problems, since the liquid can dewet from the hydrophobic part of the surface, breaking the bridge before the drying process is complete. The MC model reproduces the observed dewetting, allowing the parameters to be varied so that the conditions for the best connection can be established. We show that if the hydrophobic portion of the surface is located at a step below the height of the neighbouring metal, the chance of dewetting of the liquid during the drying process is significantly reduced.