Dynamics of Drop Coalescence on a Surface: The Role of Initial Conditions and Surface Properties

R Narhe (1, 2) , D Beysens (3, 1) , Vadim Nikolayev (4, 1)

1 SBT - Service des Basses Températures
2 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
3 PMMH - Physique et mécanique des milieux hétérogenes (UMR 7636)
4 SPEC - UMR3680 - Service de physique de l'état condensé

An investigation of the coalescence of two water drops on a surface is presented and compared with drop spreading. The associated capillary numbers are very low (< 10-5). The drops relax exponentially towards equilibrium. The typical relaxation time tc decreases with contact angle. tc is proportional to the drop size R, thus defining a characteristic velocity U* =R/tc. The corresponding U* values are smaller by many orders of magnitude than the bulk hydrodynamic velocity (U = /, with  the gas-liquid surface tension and  the viscosity). The dynamics of receding (coalescence) and spreading motion is found of the same order when coalescence or spreading is induced by a syringe. The dynamics of coalescence induced with the syringe deposition is systematically faster by an order of magnitude than condensation-induced coalescence. This disparity is explained by the coupling of the contact line motion with the oscillation of the drop observed for syringe deposition but absent for condensation-induced coalescence.

Mots clés: capillary; coalescence; contact angle; contact line velocity; wetting

Domaines: Dynamique des Fluides [physics.flu-dyn]; Mécanique des fluides [physics.class-ph]

R Narhe, D Beysens, Vadim Nikolayev. Dynamics of Drop Coalescence on a Surface: The Role of Initial Conditions and Surface Properties. International Journal of Thermophysics, 2005, ⟨10.1007/s10765-005-8593-4⟩. ⟨hal-01261693⟩