Contact Angle of an Evaporating Droplet of Binary Solution on a Super Wetting Surface

TL;DR

This paper investigates the complex time-dependent behavior of the contact angle of an evaporating binary solution droplet on a super wetting surface, extending previous models to explain experimental observations.

Contribution

It extends existing theory for single-component droplets to binary solutions, revealing complex contact angle dynamics and conditions for constant contact angle during evaporation.

Findings

Contact angle can decrease, increase, then decrease again during evaporation.

Under certain conditions, the contact angle remains constant for a period.

The model explains experimental results on binary droplet evaporation.

Abstract

We study the dynamics of contact angle of a droplet of binary solution evaporating on a super wetting surface. Recent experiments show that although equilibrium contact angle of such droplet is zero, the contract angle can show complex time dependence before reaching the equilibrium value. We analyse such phenomena by extending our previous theory for the dynamics of an evaporating single component droplet to double component droplet. We show that the time dependence of the contact angle can be quite complex. Typically, it first decreases slightly, and then increases and finally decreases again. Under certain conditions, we find that the contact angle remains constant over a certain period of time during evaporation. We study how the plateau or peak contact angle depends on the initial composition and the humidity. The theory explains experimental results reported previously.