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The Early and Late-Stage Coalescence of Small Droplets sitting on a Plate
Daniel Beysens (ESPCI)

28 juin 2007

(in collaboration with R.D. Narhe and Y. Pomeau)
We investigate the early stage coalescence of two small sessile drops (diethylene glycol) on silicon wafer. Coalescence is induced either by vapor condensation or syringe deposition. The description of the early stage of the coalescence process of sessile drops implies to describe properly two singularities: one is concerned with the contact point of the merging drops and the other is the solid-liquid-vapor contact line. We find that the bridge evolution between the two coalescing drops can be characterized by only two stages of evolution, an early stage where the capillary number is large and where a dynamic bridge drying is observed with power law evolutions and a late stage where the capillary number is small and the bridge section relax exponentally, with a typical time 10 times larger than for bulk hydrodynamics. In addition to this late stage, a very late stage relaxation – that can be described by a quasi-static approximation – is still present where the composite drop relaxes to a spherical cup with a typical time 6 orders of magnitude larger than what hydrodynamics predict due to high dissipation in the contact line vicinity.

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Daniel Beysens Daniel Beysens (ESPCI)
Physique et Mécanique des Milieux Hétérogènes UMR 7636, Laboratoire Hydrodynamique et Mécanique Physique (HMP) de l’ESPCI