Vapor-Mediated versus Substrate-Mediated Interactions between Volatile Droplets

Area of Science:

• Physics
• Fluid Dynamics
• Surface Science

Background:

• Sessile drop behavior is crucial for capillarity and wetting phenomena.
• Previous studies on interacting evaporating drops focused on binary liquids and vapor-mediated forces.

Purpose of the Study:

• To investigate the interaction mechanisms between two evaporating sessile drops of the same pure liquid.
• To identify and quantify substrate-mediated forces influencing droplet communication.

Main Methods:

• Experimental observation of evaporating sessile drops of various perfectly wetting liquids.
• Analysis of substrate-mediated forces including thermal Marangoni effect and evaporation-induced contact angle variations.
• Development of a force balance model incorporating these interactions.

Main Results:

• Identified three substrate-mediated forces: an attractive force, a weaker repelling force, and a 'cold-trap resistance' acting as drag.
• Demonstrated droplet attraction even when drops are made of the same pure liquid.
• Quantified the influence of thermal effects and contact angle changes on droplet interaction.

Conclusions:

• Substrate-mediated thermal effects play a significant role in the self-organization of evaporating sessile drops.
• The findings extend understanding beyond vapor-mediated interactions, opening new research avenues.
• Thermal effects can be harnessed to control the behavior of liquid entities on substrates.