Coalescence of polymeric sessile drops on a partially wettable substrate

Coalescence of sessile polymeric fluid drops on a partially wettable substrate exhibits a transition from the inertial to viscoelastic regime at concentration ratio c/c* similar to 1. Our findings unveil that the temporal evolution of the growing bridge height follows a power law behavior t(b), such that the coefficient b continuously decreases from 2/3 in the inertial regime (c/c* < 1) to an asymptotic value of 1/2 in the viscoelastic regime (c/c* > 1). To account for fluid elasticity and characteristic timescale in the viscoelastic regime, a modified thin film equation under lubrication approximation has been proposed using the linear Phan-Thien-Tanner constitutive equation. The temporal evolution of the droplet has been evaluated by solving the modified one-dimensional thin film equation using a marching explicit scheme. The initial droplet shapes are obtained by resorting to energy minimization. Good agreement between numerical and experimental results is obtained.