Experimental uptake study of ethanol by water droplets and its theoretical modeling of cluster formation at the interface

Uptake measurements of ethanol were performed to provide experimental values for a theoretical approach of its incorporation into a water droplet. The uptake coefficients of ethanol on pure water were therefore measured as a function of temperature, using the droplet train technique coupled to a mass spectrometric detection. They were found to be independent of the aqueous phase composition and of the gas-liquid contact times. Their values show a negative temperature dependence, varying from 3.8 x 10(-2) to 2.1 x 10(-2) in the temperature range 266-280 K. From these kinetic data, the mass accommodation coefficient alpha was derived and was found to vary from 4.6 x 10(-2) to 2.4 x 10(-2) for the same temperature range. The results are used to discuss the uptake process involved in the incorporation of ethanol into an aqueous phase, using nucleation theory and quantum mechanical calculations. The small value of the experimental N* motivated calculations on very small clusters of the type ethanol-(H2O)(n=1,3). This theoretical work shows the specific role of a cluster containing the ethanol molecule and only one water molecule. It could be a step toward either the growing of the cluster or its uptake by the surface of the drop let. Both the experimental and the theoretical works show that ethanol and methanol behave similarly.