Dynamics of Drop Coalescence on a Surface: The Role of Initial Conditions and Surface Properties
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 = σ /η, with σ the gas–liquid surface tension and η the viscosity). The dynamics of receding (coalescence) and spreading motion is found to be 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.
Keywordscapillary coalescence contact angle contact line velocity wetting
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- 2.Voué, M., Valignat, M. P., Oshanin, G., Cazabat, A. M., Coninck, J. 1998Langmuir145951Google Scholar
- 4.Ruijter, M. J., De Coninck, J., Oshanin, G. 1999Langmuir152209Google Scholar
- 5.Ruijter, M. J., De Coninck, J., Blake, T. D., Clarke, A., Rainkin, 1997Langmuir137293Google Scholar
- 7.Pomeau, Y. 2000C.R. Acad. Sci., Ser. IIb: Mec., Phys., Chim., Astron.238411Google Scholar
- 9.Zhao, H., Beysens, D. 1995Langmuir11627Google Scholar