Energy-based model for capillary spreading of power-law liquids on a horizontal plane

The capillary controlled spreading of a spherical-cap droplet of power-law fluid is theoretically investigated using a spreading kinetics model based on the classical energy-based approach. The model gives analytical predictions of the dynamic contact angles and spreading radius for shear-thinning, shear-thickening, and Newtonian fluids in complete or partial wetting systems. The model also shows that the non-Newtonian effects in the power-law liquids bring on an explicit effect of droplet volume on the dynamic contact angle. A modified capillary number, Can,V, which includes the volume, liquid properties and spreading speed, is proposed to characterize the spreading process. Experimental results in literature validate the model up to a modified capillary number of 0.1.