Effect of evaporation on the contact angle of a sessile drop on solid substrates

The effect of evaporation on the contact angle of a sessile drop of water on glass and polycarbonate substrates has been investigated. It has been observed that the contact radius depends on the initial mass of the drop and remains constant throughout the progress of evaporation. The evaporation rates in both systems are proportional to the contact radii of sessile drops. The contact angle, however, decreases as evaporation proceeds. In the case of water-glass system, the contact angle decreases almost linearly with time. On the other hand, in water-polycarbonate system, the contact angle shows a considerable departure from linearity. It has been shown that the non-linear behavior of contact angle becomes more pronounced with increasing initial contact angle. © 2003 VSP BV.