Coalescence of oil drops and films on micropillared substrates enabled by enhanced water drainage through pillar gaps

Park, Chan‐Jin; Ha, Jun Seok; Lee, Jae Hong; Kim, Ho Young

doi:10.1039/d1sm00375e

Cited by 2 publications

(1 citation statement)

References 38 publications

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“…In experiments, [62][63][64][65][66][67][68] droplet coalescence has been studied for various conditions (e.g., in the presence of applied electric fields) and geometries (e.g., micro-channels, fibers, etc. ), mainly by means of high-speed imaging and electrical sensing.…”

Section: Introductionmentioning

confidence: 99%

Coalescence of surfactant-laden droplets

et al. 2023

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Droplet coalescence is an important process in nature and various technologies (e.g., inkjet printing). Here, we unveil the surfactant mass transport mechanism and report on several major differences in the coalescence of surfactant-laden droplets as compared to pure water droplets by means of molecular dynamics simulation of a coarse-grained model. Large-scale changes to bridge growth dynamics are identified, such as the lack of multiple thermally excited precursors, attenuated collective excitations after contact, slowing down in the inertial regime due to aggregate-induced rigidity and reduced water flow, and a slowing down in the coalescence rate (deceleration) when surfactant concentration increases, while at the same time, we also confirm the existence of an initial thermal, and a power-law, inertial, regime of the bridge growth dynamics in both the pure and the surfactant-laden droplets. Thus, we unveil the key mechanisms in one of the fundamental topological processes of liquid droplets containing surfactant, which is crucial in relevant technologies.

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Section: Introductionmentioning

confidence: 99%

Coalescence of surfactant-laden droplets

et al. 2023

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Coalescence of sessile aqueous droplets laden with surfactant

Arbabi,

Deuar,

Bennacer

et al. 2024

Physics of Fluids

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With most of the focus to date having been on the coalescence of freely suspended droplets, much less is known about the coalescence of sessile droplets, especially in the case of droplets laden with surfactant. Here, we employ large-scale molecular dynamics simulations to investigate this phenomenon on substrates with different wettability. In particular, we unravel the mass transport mechanism of surfactant during coalescence, thus explaining the key mechanisms present in the process. Close similarities are found between the coalescence of sessile droplets with equilibrium contact angles above 90° and that of freely suspended droplets, being practically the same when the contact angle of the sessile droplets is above 140°. Here, the initial contact point is an area that creates an initial contact film of surfactant that proceeds to break into engulfed aggregates. A major change in the physics appears below the 90° contact angle, when the initial contact point becomes small and line-like, strongly affecting many aspects of the process and allowing water to take part in the coalescence from the beginning. We find growth exponents consistent with a 2/3 power law on strongly wettable substrates but no evidence of linear growth. Overall bridge growth speed increases with wettability for all surfactant concentrations, but the speeding up effect becomes weaker as surfactant concentration grows, along with a general slowdown of the coalescence compared to pure water. Concurrently, the duration of the initial thermally limited regime increases strongly by almost an order of magnitude for strongly wettable substrates.

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Coalescence of oil drops and films on micropillared substrates enabled by enhanced water drainage through pillar gaps

Abstract: We find that an oil drop colliding with a micropillar array wetted by an oil film immediately coalesces with the film instead of bouncing off, owing to enhanced water drainage through the pillar gaps.

Cited by 2 publications

References 38 publications

Coalescence of surfactant-laden droplets

Coalescence of surfactant-laden droplets

Coalescence of sessile aqueous droplets laden with surfactant

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