Liquid-liquid phase separation in sessile drops induced by evaporation.

The interplay between two phase change mechanisms of evaporation and liquid-liquid phase separation (demixing) in binary sessile drops of partially miscible liquids is investigated. To determine the onset of the demixing phenomenon, a simple model is developed, which predicts a considerable temperature reduction in the mixture due to evaporative cooling. Temperature reduction alongside with the change of composition lead to demixing in the mixtures. Five stages of the process are identified and explained. For the cases studied here, once the demixing begins through nucleation, a growing fingering pattern is formed at the contact line. The length of the fingers is a function of the initial concentration of the low volatile component. Moreover, the final area of deposition increases with the initial concentration. Experimental tests were performed using a double telecentric setup.