How water droplets evaporate on a superhydrophobic substrate

TL;DR

This study investigates water droplet evaporation on superhydrophobic substrates across a wide range of contact angles, confirming a diffusion-driven, quasi-static process with universal behavior for different droplet sizes and initial angles.

Contribution

It extends previous research by analyzing almost the full range of contact angles on superhydrophobic surfaces and validates a universal evaporation model.

Findings

Experimental data agrees with Popov's model.

Evaporation is diffusion-driven and quasi-static.

Universal curves describe droplet evolution.

Abstract

Evaporation of water droplets on a superhydrophobic substrate, on which the contact line is pinned, is investigated. While previous studies mainly focused on droplets with contact angles smaller than 90^\circ, here we analyze almost the full range of possible contact angles (10^\circ -150^\circ). The greater contact angles and pinned contact lines can be achieved by the use of superhydrophobic Carbon Nanofiber substrates. The time-evolutions of the contact angle and the droplet mass are examined. The experimental data is in good quantitative agreement with the model presented by Popov (Physical Review E 71, 2005), demonstrating that the evaporation process is quasi-static, diffusion-driven, and that thermal effects play no role. Furthermore, we show that the experimental data for the evolution of both the contact angle and the droplet mass can be collapsed onto one respective universal curve for all droplet sizes and initial contact angles.