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Unexpected concentration dependence of the mass accommodation coefficient of water on aqueous triethylene glycol
Michael J Gleichweit1, Mercede Azizbaig Mohajer1, Dominique P Borgeaud Dit Avocat1
1Department of Chemistry and Applied Biosciences, ETH Zurich, CH-8093 Zurich, Switzerland. ruth.signorell@phys.chem.ethz.ch.
Abstract:
The mass accommodation coefficient αM of water on aqueous triethylene glycol droplets was determined for water mole fractions in the range xmol = 0.1-0.93 and temperatures between 21 and 26 °C from modulated Mie scattering measurement on single optically-trapped droplets in combination with a kinetic multilayer model. αM reaches minimum values around 0.005 at a critical water concentration of xmol = 0.38, and increases with decreasing water content to a value of ≈0.1 for almost pure triethylene glycol droplets, essentially independent of the temperature. Above xmol = 0.38, αM first increases with increasing water content and then stabilises at a value of ≈0.1 at the lowest temperatures, while at the highest temperature its value remains around 0.005. We analysed the unexpected concentration and temperature dependence with a previously proposed two-step model for mass accommodation which provides concentration and temperature-dependent activation enthalpies and entropies. We suggest that the unexpected minimum in αM at intermediate water concentrations might arise from a more or less saturated hydrogen-bond network that forms at the droplet surface.
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