Evaporation and Subsequent Adsorption of Alcohol Molecules at Aqueous Droplet Surface Observed by Cavity-Enhanced Raman Spectroscopy.

Mass transfer toward and across liquid surfaces is important for the interpretation of various interfacial phenomena, such as evaporation, adsorption, and mass accommodation, which have been investigated by the use of various methods. These studies, however, have focused on only one of the mass-transfer processes occurring at the surface. We investigate the surface concentration of alcohol molecules at aqueous droplet surfaces on the several-millisecond time scale using cavity-enhanced droplet Raman spectroscopy. A decrease and subsequent increase of the alcohol concentration are observed in a set of measurements, which arise from an evaporation and subsequent adsorption of the alcohol molecules at the surface. This facilitates an understanding of the surface kinetics of molecules at the liquid surfaces.