Abstract
Abstract
Highlights
A sessile droplet evaporating from a solid substrate is central to a wide variety of processes
We have developed a one-sided model under the lubrication approximation to study the spreading and subsequent evaporation of volatile binary droplets consisting of an ethanol–water type mixtures deposited on a heated substrate
We considered flat droplets, assumed to be very thin such that their radius is much larger than their height
Summary
A sessile droplet evaporating from a solid substrate is central to a wide variety of processes. For ethanol–water droplets, Diddens et al (2017) observed that at long times ethanol had almost entirely evaporated but a strong thermal Marangoni flow was still present – validating the hypothesis of Christy et al (2011) They noted that when the droplet becomes flat, the surface tension gradient leads to shape deformation with a depression in the droplet centre – similar to the observations of Guéna et al (2007). This behaviour is clearly reminiscent of superspreading reported in surfactant-laden flows (Rafaï et al 2002; Karapetsas, Craster & Matar 2011) As it will be shown below, enhanced spreading of binary mixture droplets is due to the presence of strong Marangoni stresses near the contact line, arising due to the preferential evaporation of ethanol in that region. It is shown that the dynamics of the evaporation and droplet shape is dictated by the interplay of thermal and solutal Marangoni stresses and capillary forces
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