Vertical drying of a suspension of sticks: Monte Carlo simulation for continuous two-dimensional problem

TL;DR

This study uses kinetic Monte Carlo simulations to analyze the vertical drying process of a two-dimensional colloidal film with sticks, revealing evaporation-driven self-assembly, stratification, and tunable electrical anisotropy.

Contribution

It introduces a continuous 2D model for drying colloidal films with sticks, incorporating both translational and rotational Brownian motions, and explores how evaporation rate and concentration affect film properties.

Findings

Significant vertical stratification of sticks during drying.

Electrical conductivity anisotropy can be controlled by evaporation rate and concentration.

Evaporation enhances self-assembly and stratification of sticks.

Abstract

The vertical drying of a two dimensional colloidal film containing zero-thickness sticks (lines) was studied by means of kinetic Monte Carlo (MC) simulations. The continuous two-dimensional problem for both the positions and orientations was considered. The initial state before drying was produced using a model of random sequential adsorption with isotropic orientations of the sticks. During the evaporation, an upper interface falls with a linear velocity in the vertical direction and the sticks undergo translational and rotational Brownian motions. The MC simulations were run at different initial number concentrations (the numbers of sticks per unit area), $p_i$, and solvent evaporation rates, $u$. For completely dried films, the spatial distributions of the sticks, the order parameters and the electrical conductivities of the films in both the horizontal, $x$, and vertical, $y$, directions were examined. Significant evaporation-driven self-assembly and stratification of the sticks in the vertical direction was observed. The extent of stratification increased with increasing values of $u$. The anisotropy of the electrical conductivity of the film can be finely regulated by changes in the values of $p_i$ and $u$.