Thermal delay of drop coalescence

We present the results of a combined experimental and theoretical study of drop coalescence in the presence of an initial temperature difference 1T0 between a drop and a bath of the same liquid. We characterize experimentally the dependence of the residence time before coalescence on 1T0 for silicone oils with different viscosities. Delayed coalescence arises above a critical temperature difference 1Tc that depends on the fluid viscosity: for 1T0 > 1Tc, the delay time increases as 1T 2/3 0 for all liquids examined. This observed dependence is rationalized theoretically through consideration of the thermocapillary flows generated within the drop, the bath and the intervening air layer.