Stratification of drying particle suspensions: Comparison of implicit and explicit solvent simulations

TL;DR

This study compares explicit and implicit solvent molecular dynamics simulations to understand particle stratification during drying, revealing how film thickness and Péclet number influence particle distribution in drying suspensions.

Contribution

It introduces an implicit solvent model that accurately replicates explicit solvent results, enabling simulation of thicker films and analysis of stratification effects.

Findings

Small-on-top stratification occurs in both models.

Stratification degree depends on Péclet number and initial film thickness.

Implicit model allows larger scale simulations of drying films.

Abstract

Large scale molecular dynamics simulations are used to study drying suspensions of a binary mixture of large and small particles in explicit and implicit solvents. The solvent is first modeled explicitly and then mapped to a uniform viscous medium by matching the diffusion coefficients and the pair correlation functions of the particles. `Small-on-top' stratification of the particles, with an enrichment of the smaller ones at the receding liquid-vapor interface during drying, is observed in both models under the same drying conditions. With the implicit solvent model, we are able to model much thicker films and study the effect of the initial film thickness on the final distribution of particles in the dry film. Our results show that the degree of stratification is controlled by the P\'{e}clet number defined using the initial film thickness as the characteristic length scale. When the P\'{e}clet numbers of large and small particles are much larger than 1, the degree of `small-on-top' stratification is first enhanced and then weakens as the P\'{e}clet numbers are increased.