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Abstract:
Quantitative experimental data on the coalescence behavior of sessile droplets with different but completely miscible
liquids are presented. The liquids consist of various aqueous mixtures of different nonvolatile diols and carbon acids
with surface tensions ranging from 33 to 68 mN/m, contact angles between 9° and 20°, and viscosities from 1 to 12 cP.
Two distinctly different coalescence behaviors, a delayed and a fast regime, are found. The transition between the two
behaviors is remarkably sharp. It is found that the coalescence mode depends predominantly on the differences in the
surface tensions of the two droplets. If the surface tension difference exceeds ∼3 mN/m, the coalescence is delayed. If it is
less, droplet fusion occurs fast. Within the investigated parameter space, the transition seems independent from droplet
size, absolute values of the surface tensions, and viscosity. Certain aspects of the experimental findings are explained
with the simple hydrodynamic model presented in a recent publication.
