| Summary: | The aim of this study is to investigate the droplet wetting and evaporation on hydrophilic and hydrophobic surfaces. Different concentrations of ethanol-water solutions are investigated on soda glass lime surface and PTFE surface, which represents hydrophilic and hydrophobic surface respectively. A higher concentration of ethanol increases the wettability of a droplet causing the initial contact angle to be smaller as concentration increases. The time taken for a drop to evaporate is much longer on a PTFE surface than a soda lime glass surface. A hydrophilic surface has a strong pinning effect on the contact line of a drop as it evaporates. It undergoes a CCR evaporation mode where the contact radius remains the same while contact angle reduces. This may be due to the surface not being completely smooth as there are defects on the surface. In comparison, a hydrophobic surface has no pinning effect on the contact line. A droplet shrinks as it evaporates while maintaining a more or less constant contact angle. Evaporation with constant contact angle and decreasing contact radius is the CCA mode. As the droplet continues to evaporate, it moves to a mixed mode where both contact radius and contact angle reduces till the drop is fully evaporated. The trend in volume changes, which reflects the rate of evaporation, is similar for both hydrophilic and hydrophobic surface. The different evaporation modes on different surfaces does not affect the rate of evaporation of a droplet.
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