Effect of crystal orientation on droplet wetting behavior on single-crystal Al2O3 substrates: An experimental study

The wetting property of liquids on a solid surface is of key relevance to many areas ranging from biological systems to industrial applications. The wetting behavior of water, glycerin, and castor oil (featuring varying viscosities and surface energies) on single-crystal alpha -Al2O3 substrates with various crystal orientations of (0001), (112<overbar></mml:mover>0), (101<mml:mo><overbar></mml:mover>0), and (01<mml:mover accent="true">1<mml:mo><overbar></mml:mover>2) was studied using the improved sessile drop method at room temperature and a closed environment. The effects of substrate crystal orientation on the liquid wetting behavior and its dependence on the liquid type were investigated. The contact angle of all three liquids on the (0001)-orientated substrates was obviously smaller than those of the other substrate orientations. The effects of alpha -Al2O3 substrate crystal orientation on the liquid wetting behavior on the substrates can be attributed to the liquid and substrate surface energies, the liquid viscosity, and the substrate atomic arrangement. The wetting process of water on alpha -Al2O3 could be divided into two stages. The contact angle was basically unchanged in stage I, and evaporation of droplets causes stepwise decreases of the contact angle in stage II. The height and contact angle of glycerin and castor oil on the substrates change very slowly in 1800 s. The findings of this study help provide a better understanding of the wetting behavior of liquids on solids and its mechanism.