Delayed coalescence of surfactant containing sessile droplets

Abstract

When two sessile drops of the same liquid touch, they merge into one drop, driven by capillarity. However, the coalescence can be delayed, or even completely stalled for a substantial period of time, when the two drops have different surface tensions, despite being perfectly miscible. A temporary state of non-coalescence arises, during which the drops move on their substrate, only connected by a thin neck between them. Existing literature covers pure liquids and mixtures with low surface activities. In this paper, we focus on the case of large surface activities, using aqueous surfactant solutions with varying concentrations. It is shown that the coalescence behavior can be classified into three regimes that occur for different surface tensions and contact angles of the droplets at initial contact. However, not all phenomenology can be predicted from surface tension contrast or contact angles alone, but strongly depends on the surfactant concentrations as well. This reveals that the merging process is not solely governed by hydrodynamics and geometry, but also depends on the molecular physics of surface adsorption.

arXiv comment10 pages, 8 figures

References in corpus (3)

• Symmetric and Asymmetric Coalescence of Drops on a Substrate
• Non-coalescence of sessile drops from different but miscible liquids: Hydrodynamic analysis of the twin drop contour as self stabilizing, traveling wave
• Sharp Transition between Coalescence and Noncoalescence of Sessile Drops

Cited by in corpus (5)

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• The asymmetric coalescence of two droplets with different surface tensions is caused by capillary waves
• Coalescence of sessile aqueous droplets laden with surfactant
• Capillary filling in drop merging: dynamics of the four-phase contact point
• Solutal Marangoni flow as the cause of ring stains from drying salty colloidal drops