Mach–Zehnder interferometry for fluid physics experiments involving contact lines and phase change

Abstract

Mach–Zehnder interferometry is a powerful optical technique for investigating thermo-fluidic phenomena, particularly in experiments involving contact line and phase change measurements. This study presents a comprehensive experimental framework leveraging Mach–Zehnder interferometry to analyze liquid film thickness profiles, vapor concentration fields (vapor clouds), and concentration fields in a Hele-Shaw cell. The technique is applied to sessile droplet profilometry on transparent substrates, revealing wetting dynamics, contact angle evolution, and Marangoni-driven flows and instabilities in spreading and evaporating droplets. Apart from volatile pure droplets, where the thermal Marangoni effect may be essential on account of evaporative cooling, the study also explores the role of solutal Marangoni stresses in hygroscopic binary mixtures. Additionally, vapor interferometry is employed to quantify the concentration field above evaporating droplets and liquid pools, demonstrating the method’s capability for non-invasive measurement of evaporation rates. We also showcase the application of interferometry in ${\mathrm{CO}}_2$ dissolution studies within Hele-Shaw cells. The results highlight the versatility of Mach–Zehnder interferometry in capturing all those complex phenomena, offering valuable insights for the study of evaporation, wetting, and mass transport in confined geometries.