Understanding under-liquid drop spreading using dynamic contact angle modeling

We present numerical modeling and experimental data to investigate droplet spreading dynamics on a substrate submerged in another liquid. Dynamic contact angle equations are formulated and used to simulate the spreading of different oil drops in the presence of water. Drop spreading in the presence of water starts with a viscosity-dominated regime where a scaling law of r similar to t is observed. For low viscosity drops, an intermediate inertial regime with scaling r similar to t(1/2) is observed after the viscous regime. For high viscosity drops, such an intermediate regime diminishes. At later stages near equilibrium, the spreading dynamics follow Tanner's law for all drops.