Impact Dynamics of a Compound Drop on a Plane Solid: Effect of the Core Drop Viscosity

The impact of compound drops consisting of glycerol-water mixture core and Jatropha biodiesel shell on a solid surface is studied. The role of the viscosity of the core liquid on the impact dynamics of the compound drop is examined. The core viscosity is varied by changing the composition of the core drop from 10 G (10% glycerol-water solution) to 90G (90% glycerol-water solution). The impact dynamics of the compound drops is found to depend on the ratio of the viscosities of the core and shell liquids (i.e., μC/μS). For the compound drops having μC/μS<1 (i.e., 10 to 50G), the change in the core viscosity has no significant influence on the maximum spreading factor (βmax). However, as the core viscosity rises from 50 to 90 G, there is a sharp decrease in βmax. This is a direct result of the increase in viscous dissipation (Wvis) during spreading. The viscous forces are very dominant for compound drops with very high core viscosities. Hence, the rise in Wvis is minor with the increase in the core viscosity from 10G to 50G but shows a sharp rise when the core viscosity increases from 50 to 90 G.