Reflected Laser Interferometry Reveals Subtleties Of Low Surface Tension Microdroplet Condensation

Abstract

Using dual wavelength reflected laser interferometry, we developed a simple yet accurate protocol to study the dynamic behavior of condensed microdroplets. For low surface tension liquids, sufficiently sharp experimental interferograms are obtained by appropriately controlling the confocal pinhole. An automated numerical framework is developed to dynamically reconstruct the three-dimensional topography of the droplets from the obtained interferograms. We also report a spontaneous motion during condensation where small microdroplets moved to relatively larger droplets in the vicinity. This movement is exclusive to a combination of low surface tension liquids and hydrophilic surfaces. Although we have demonstrated the framework for dropwise condensation, the protocol finds direct applicability in the study of a wide range of fundamental phenomena involving droplet dynamics which includes wetting, spreading, droplet pinning and motion, contact angle hysteresis, droplet coalescence etc., and suitable adaptation of the developed protocol can assist in unveiling previously unknown fundamental physical processes of practical relevance.