Scaling law in liquid drop coalescence driven by surface tension

This Letter reports experimental results on the coalescence of two liquid drops driven by surface tension. Using a high speed imaging system, we studied the early-time evolution of the liquid bridge that is formed upon the initial contact of two liquid drops in air. Experimental results confirmed the scaling law that was proposed by Eggers et al. based on a simple and yet elegant physical argument. We found that the liquid bridge radius r_b follows the scaling law r_b^∝t^1/2 in the inertial regime. Further experiments demonstrate that such scaling law is robust when using fluids of different viscosities and surface tensions. The prefactor of the scaling law, r_b/t^1/2, is shown to be ^∝R^1/4, where R is the inverse of the drop curvature at the point of contact. The dimensionless prefactor is measured to be in the range of 1.03-1.29, which is lower than 1.62, a prefactor predicted by the numerical simulation of Duchemin et al. for inviscid drop coalescence.