Impact of internal flow and particle-substrate interaction on deposit patterns during evaporation of a colloidal sessile droplet

TL;DR

This numerical study investigates how internal flow dynamics and particle-substrate interactions influence deposit patterns in evaporating colloidal droplets, revealing the dominant role of radial flow and the mitigating effect of Marangoni flow on coffee ring formation.

Contribution

The paper introduces a comprehensive numerical model that incorporates multiple physical effects, providing new insights into deposit pattern formation during droplet evaporation.

Findings

Radial flow dominates deposit pattern formation in the absence of heating.

Marangoni flow reduces the coffee ring effect, leading to more uniform deposits.

Thermal buoyancy has negligible impact without heating.

Abstract

Our numerical study aims to investigate particle deposit patterns from the evaporation of a sessile colloidal droplet. An in house finite volume code is developed to simulate the coupled phenomena of flow and heat and mass transfer with phase change of the evaporating droplet. The numerical model takes into account evaporative cooling effect, surface tension gradient effect at the liquid-air interface, thermal buoyancy effect inside the droplet, thermosolutal buoyancy effect in the surrounding air and electrical double layer and Van der Waals interactions between substrate and colloidal particles. Three models are used in this study: (a) a model that takes into account only the strong evaporation near the pinned contact line (b) a model that takes into account in addition the thermo capillary effect and (c) a comprehensive model that takes into account all effects. The results show that without heating the thermal buoyancy has a negligible effect on the formation of particle deposit. In presence of substrate-particle interactions, dominant radial flow is the main responsible for the coffee ring effect giving a ring-like pattern with inner traces, while the Marangoni flow reduces the coffee ring effect giving a uniform deposit with a dark periphery