Influence of fluid flows on electric double layers in evaporating colloidal sessile droplets

TL;DR

This paper presents a comprehensive model combining electrostatics, fluid dynamics, and evaporation to simulate charged colloidal particle transport in evaporating droplets, revealing that strong fluid flows can disrupt electric double layers.

Contribution

It introduces a coupled multi-physics model integrating Poisson, Nernst-Planck, Navier-Stokes, and heat equations for the first-principles simulation of colloidal transport in evaporating droplets.

Findings

Electric double layers can be destroyed by strong fluid flows.

The model accurately predicts colloidal particle distribution during evaporation.

Fluid flow significantly influences electrostatic interactions in colloidal droplets.

Abstract

A model is developed for describing the transport of charged colloidal particles in an evaporating sessile droplet on the electrified metal substrate in the presence of a solvent flow. The model takes into account the electric charge of colloidal particles and small ions produced by electrolytic dissociation of the active groups on the colloidal particles and solvent molecules. We employ a system of self-consistent Poisson and Nernst--Planck equations for electric potential and average concentrations of colloidal particles and ions with the appropriate boundary conditions. The fluid dynamics, temperature distribution and evaporation process are described with the Navier--Stokes equations, equations of heat conduction and vapor diffusion in air, respectively. The developed model is used to carry out a first-principles numerical simulation of charged silica colloidal particle transport in an evaporating aqueous droplet. We find that electric double layers can be destroyed by a sufficiently strong fluid flow.