Experimental and Theoretical Study of the Dynamics of Surface Evaporation of Water Droplets on Different Surfaces

In this paper, the dynamics of evaporation of water droplets on surfaces with different contact angle hysteresis is studied experimentally and theoretically. The evaporation of water droplets on surfaces usually occurs in three distinct stages, namely the constant contact area mode, followed by the constant contact angle mode, and the mixed mode in which both contact angle and contact area are decreased. Due to the unknown nature of the time dependency of both the dynamic contact angle and contact radius, solving the governing equations for the evaporation rate of a droplet is complicated. The experimental observations performed in this study for the evaporation of sessile droplets on different solid substrates under various conditions shows that the surfaces with a high contact angle hysteresis remain more in the constant contact area mode. On the other hand, the surfaces with a low contact angle hysteresis remain more in the constant contact angle mode. Based on these observations, it is assumed that the entire process of evaporation on surfaces with high and low contact angle hysteresis occur in a dominated mode. Next, based on this assumption, the governing equation for the droplet evaporation for both surfaces is solved separately using a theoretical model. A good agreement is observed between the results of the theoretical analysis with those of the experiments; this confirms the validity of the proposed theoretical model.