Short time spreading dynamics of elastic drops

Abstract

When a liquid drop makes first contact with any surface, unbalanced surface tension force drives the contact line causing spreading. For Newtonian or weakly elastic, non-Newtonian liquids, either liquid inertia or viscosity or a combination of the two resists spreading. In this work, we investigate the role of drop elasticity on the dynamics of spreading. We conduct dynamical experiments with polyacrylamide drops with varying polymer concentrations imparting varying degrees of elasticity. Using high-speed imaging, we focus on the very first moments of spreading with glass substrates. For moderate and high elasticity values, we observe that the early time spreading dynamics obey a viscous-capillary regime exhibited by a power-law evolution of the spreading radius. However, the process transitions to a different regime on a timescale at par with the characteristic viscoelastic relaxation time scale. We interpret this latter regime using a theoretical model invoking the standard linear model of viscoelasticity. For viscoelastic inks with moderate print speeds, the dynamical behavior investigated in this study, can provide valuable insights on how to efficiently control such moving contact lines with non-trivial elasticity.