Evaporation of microdroplets of azeotropic liquids

This work reports data showing the evolution of contact angle with time for mixtures of water and 1-propanol at room temperature on poly(methyl methac rylate) (PMMA). The composition range investigated spans the azeotropic com position, thus encompassing systems containing excess water and excess 1-pr opanol. A discontinuity in the contact angle behavior is observed and it is suggested that this enables the identification of the azeotropic compositi on as 0.39 mole fraction of 1-propanol. This suggestion is supported by boi ling point measurements made at around 20 mmHg. The discontinuity is associ ated with the presence of an instability, which causes a distortion around the droplet perimeter, it is suggested that the distortion is caused by com peting effects of local surface tension maxima and minima.