Maximum spreading of a shear-thinning liquid drop impacting on dry solid surfaces

In the present study, the maximum spreading of Newtonian and shear-thinning drops impacting on dry surfaces was investigated experimentally. Water, glycerin drops (Newtonian liquids) and xanthan drops (shear-thinning liquids) were impinged upon the flat surfaces of glass, stainless steel and parafilm-M substrates, which have hydrophilic, moderate and hydrophobic properties, respectively, at the impact velocities ranging from 0.8 to 4.0 m/s. The impact velocity and the liquid viscosity with the shear-thinning characteristic had dominant effects on the maximum spreading; on the other hand, the surface wettability effect turned out to be minor. Several maximum spreading models for a Newtonian liquid were reviewed briefly and compared with the experimental measurements. The Roisman model showed the best agreement to the experimental results for Newtonian drops. A new empirical correlation for the maximum spreading of a shear-thinning drop was proposed by modifying the Scheller and Bousfield model with the concept of the effective shear viscosity, which is correlated with the shear rate varying with the impact velocity. The correlation agreed to within ±5% for 91% of the shear-thinning drop experiments.