Particle deposit patterns from evaporation of a sessile colloidal droplet

TL;DR

This study models the complex interplay of fluid flow, heat transfer, and particle interactions during droplet evaporation, revealing how these factors influence deposit patterns like coffee rings or uniform films.

Contribution

It introduces a comprehensive numerical model that incorporates fluid dynamics, heat transfer, phase change, and particle-substrate interactions affecting deposit patterns.

Findings

Particle-substrate interactions promote coffee ring formation.

Thermal Marangoni flow can suppress ring patterns.

Deposit pattern depends on internal flow dynamics.

Abstract

The present work investigates numerically the transport of colloidal particles within an evaporating sessile droplet and their deposition on the substrate in unfavourable conditions. The coupled phenomena of fluid flow and heat and mass transfer with phase change are modelled by taking into account for the evaporative cooling effect, the surface tension gradient effect at liquid air interface and the particles-substrate interaction effect due to DLVO attractive forces.The results show that in presence of the particles-substrate interaction, the outward radial internal flow is the main responsible for the coffee ring effect giving rise a ring like pattern with inner traces, while the thermal Marangoni internal flow reduces this effect giving rise a uniform deposit with a dark periphery.