Thermal delay of drop coalescence

Abstract

We present the results of a combined experimental and theoretical study of drop coalescence in the presence of an initial temperature difference 𝛥T[subscript 0] between a drop and a bath of the same liquid. We characterize experimentally the dependence of the residence time before coalescence on 𝛥T[subscript 0] for silicone oils with different viscosities. Delayed coalescence arises above a critical temperature difference 𝛥T[subscript c] that depends on the fluid viscosity: for 𝛥T[subscript 0] > 𝛥T[subscript c], the delay time increases 𝛥T[subscript 0] [superscript 2/3] as 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.