Evaporation of sessile drops on a heated superhydrophobic substrate

TL;DR

This study experimentally examines how water droplets evaporate on a superhydrophobic surface, revealing the vapor shielding effect in two-drop systems and developing models that accurately predict evaporation dynamics across different temperatures.

Contribution

It provides new insights into the vapor shielding effect in paired droplets and introduces comprehensive models that capture evaporation behavior on superhydrophobic substrates at various temperatures.

Findings

Two-drop systems evaporate more slowly due to vapor shielding.

Evaporation modes vary with temperature and configuration.

Models accurately predict evaporation dynamics at different temperatures.

Abstract

We experimentally investigate the evaporation dynamics of sessile water droplets on a micro-nano textured superhydrophobic aluminum substrate at various temperatures using shadowgraphy imaging. By comparing the evaporation behavior of two droplets placed side-by-side with that of an isolated droplet, we find that droplets in the two-drop system evaporate more slowly due to the vapor shielding effect, which increases vapor concentration between the droplets. This leads to asymmetric evaporation and longer lifetimes, particularly at room temperature compared to higher temperatures. At room temperature, the isolated droplet primarily follows a constant contact angle (CCA) mode, with occasional stick-slip events. The two-drop system predominantly exhibits CCA mode for most of its lifetime, with mixed-mode evaporation and some stick-slip behavior. At elevated temperatures, the isolated droplet maintains a nearly constant contact angle for the first half of its lifetime, transitioning to a mixed evaporation mode with occasional stick-slip events. In contrast, the two-drop system follows a mixed evaporation mode throughout, with occasional stick-slip behavior. Furthermore, a comprehensive theoretical model that accounts for diffusion, evaporative cooling, and convection accurately captures the evaporation dynamics of sessile droplets on a superhydrophobic substrate in both isolated and paired configurations at elevated substrate temperatures. In contrast, a diffusion-based model alone adequately describes the evaporation behaviour at room temperature.