A pendant drop merging with a sessile drop and subsequently forming a single daughter drop, is known to exhibit complex topologies, but their dynamics are yet to be probed for...

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 à $ 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 à < 1) to an asymptotic value of 1/2 in the viscoelastic regime (c=c à > 1Þ. 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.

Our experiments on the rod-climbing effect with an oil-coated rod revealed two key differences in the rod-climbing phenomena compared to a bare rod. First, an enhancement in the magnitude of climbing height for any particular value of the rod rotational speed and second, a decrease in the threshold rod rotational speed required for the appearance of the rod-climbing effect were observed. Observed phenomena are explained by considering the contact line behavior at the rod−fluid interface. Transient evolution of the meniscus at the rod−fluid interface revealed that the three-phase contact line was pinned for a bare rod and depinned for an oil-coated rod. We modeled the subject fluid as a Giesekus fluid to predict the climbing height. The differences in the contact line behavior were incorporated via the contact angle at the rod−fluid interface as a boundary condition. Agreement was found between the observed and predicted climbing height, establishing that contact line behavior may modulate the rod-climbing effect.