Evaporation from water-ethylene glycol liquid mixture

Evaporation rates were determined for water-ethylene glycol liquid mixtures with different mole fractions, where the evaporation rate expressed as mg min(-1)/area was used because of the presence of two kinds of molecular species. The rate increased with increasing temperature and decreased with increasing mole fraction of ethylene glycol, almost obeying ideal mixing of the two components, although a small positive deviation was observed over the mole fraction from 0 to 0.5 of ethylene glycol at higher temperatures. The activation energy of evaporation was determined from the temperature dependence of the evaporation rate, where the energy was an apparent one because the composition of evaporated species was not determined. The activation energy increased with decreasing temperature and with increasing mole fraction of ethylene glycol, where the energy obeyed the ideal mixing at lower temperatures while it positively deviated at higher temperatures. The evaporation rates were examined by surface tension of the liquid mixture, but any definite relation between them was not found. Both the evaporation rate and the activation energy were found to be determined mainly by the mole fraction in the surface layer from which the evaporation takes place. Finally, the new concept of surface excess was presented, where the surfactant molecules were concentrated and formed a bimolecular layer at a certain distance beneath the air/solution interface.