Monte Carlo Simulation of Evaporation Driven Self-Assembly in Suspension of Colloidal Rods

TL;DR

This study uses kinetic Monte Carlo simulations to analyze how evaporation influences the self-assembly and orientation of rod-like particles in drying colloidal films, revealing controllable anisotropic electrical properties.

Contribution

It introduces a simulation approach combining RSA and kinetic Monte Carlo to explore evaporation-driven self-assembly and anisotropy in colloidal rod films.

Findings

Significant orientation stratification of rods during evaporation.

Anisotropic electrical conductivity can be tuned by initial concentration, rod length, and evaporation rate.

Stratification increases with longer rods.

Abstract

The vertical drying of a colloidal film containing rod-like particles was studied by means of kinetic Monte Carlo (MC) simulation. The problem was approached using a two-dimensional square lattice and the rods were represented as linear $k$-mers (i.e., particles occupying $k$ adjacent sites). The initial state before drying was produced using a model of random sequential adsorption (RSA) with isotropic orientations of the $k$-mers (orientation of the $k$-mers along horizontal $x$ and vertical $y$ directions are equiprobable). In the RSA model, overlapping of the $k$-mers is forbidden. During the evaporation, an upper interface falls with a linear velocity of $u$ in the vertical direction and the $k$-mers undergo translation Brownian motion. The MC simulations were run at different initial concentrations, $p_i$, ($p_i \in [0, p_j]$, where $p_j$ is the jamming concentration), lengths of $k$-mers ($k \in [1, 12]$), and solvent evaporation rates, $u$. For completely dried films, the spatial distributions of $k$-mers and their electrical conductivities in both $x$ and $y$ directions were examined. Significant evaporation-driven self-assembly and orientation stratification of the $k$-mers oriented along the $x$ and $y$ directions were observed. The extent of stratification increased with increasing value of $k$. The anisotropy of the electrical conductivity of the film can be finely regulated by changes in the values of $p_i$, $k$ and $u$.