Optical spectroscopy used to investigate water evaporation rate from aqueous solutions

Evaporation of water is a fundamental process in many technologies for film fabrication from liquid phase and, in the last decade, in nanoscience by the evaporation induced self assembly phenomena. Although the water evaporation seems to be among the very basic physical phenomena, there is a lack of experimental data that could enrich our understanding of this process.Aqueous solutions of glycols and some amphiphilic molecules are valuable for a basic study of the water molecules transport across the air/solution interface. In this study, using UV–VIS reflectometry and Attenuated Total Reflection (ATR) in infrared region, the water evaporation from layers of such aqueous solutions has been investigated. Physical processes as water evaporation and diffusion of water molecules between the glycols' molecules have been revealed. The UV–VIS reflectometry method investigated the evolution in time of the layer thickness due to evaporation, while the ATR-IR method monitored the compositional changes, too. A comparative study of the results obtained via these two measurement methods is made.

► Optical spectroscopy is used to study water evaporation from mixtures with glycols.
► Two evaporation regimes: constant evaporation rate and process limited by diffusion.
► A threshold value for the water concentration delimits the two evaporation regimes.
► The diffusion relaxation-time depends on the water–glycol hydrogen bonds.