Reflected Laser Interferometry: A Versatile Tool to Probe Condensation of Low-Surface-Tension Droplets.

Abstract

Experimental investigation of dropwise condensation of low-surface-tension liquids remains prone to error owing to the imaging difficulties caused by the typically low droplet height. Using reflection interference contrast microscopy in confocal mode, we demonstrate a noninvasive framework to accurately capture this condensation dynamics of volatile liquids with low surface tension. The capability of the developed framework is demonstrated in studying the condensation dynamics of acetone, where it accurately describes the growth mechanism of condensed microdroplets with excellent spatiotemporal resolution even for submicron-range drop height and a three-phase contact angle of <5°. From experimentally obtained interferograms, the framework can reconstruct three-dimensional topography of the microdroplets even when the contact line of the droplet is distorted due to strong local pinning. The obtained results exhibit excellent quantitative agreement with several theoretically predicted trends. The proposed protocol overcomes the limitation of conventional techniques (e.g., optical imaging/environmental scanning electron microscopy) and provides an efficient alternative for studying the condensation of low-surface-tension liquids under atmospheric conditions.