53 research outputs found
Wettability-Engineered Meshes for Gas Microvolume Precision Handling in Liquids
Get PDFThe interaction of rising gas bubbles with submerged air-repelling or air-attracting surfaces is relevant to various technological applications that rely on gas-microvolume handling or removal. This work demonstrates how submerged metal meshes with super air-attracting/repelling properties can be employed to manipulate microvolumes of air, rising buoyantly in the form of bubbles in water. Superaerophobic meshes are observed to selectively allow the passage of air bubbles depending on the mesh pore size, the bubble volume-equivalent diameter, and the bubble impact velocity on the mesh. On the other hand, superaerophilic meshes reduce or amplify the volume captured from a train of incoming bubbles. Finally, a spatial wettability pattern on the mesh is used to control the size of the outgoing bubble, and an empirical relation is formulated to predict the released gas volume. The study demonstrates how porous materials with controlled wettability can be used to precisely modulate and control the outcome of bubble/mesh interactions
Directional Spreading of Viscous Droplets on Wettability-Patterned Diverging Tracks
No full textSpontaneous pumpless transport of liquid droplets on wettability-patterned tracks is important for a number of diverse applications such as rapid transport and mixing of fluid droplets, enhancing dropwise condensation on surfaces, and in the biomedical sector as well. Recent studies point to the fact that, on an open surface, a superhydrophilic diverging track laid on a superhydrophobic background results in pumpless transport of water from the narrow end to the wide end at unprecedented rates. However, the interplay between the driving capillary force and the resisting viscous force, which governs the spreading behavior of liquid droplets on such surfaces, have so for not been characterized. Potential applications for transporting organic liquids and in point-of-care devices hence calls for understanding the spreading behavior of viscous droplets on such surfaces. An effort to do the same has been made in the present work by experimentally observing the spreading of liquid droplets of different viscosities and surface tensions on the aforementioned wettability-patterned diverging or wedge-shaped tracks. An universal relationship of the spreading behavior in terms of two dimensionless variables is obtained. The liquid spreading front was found to follow three distinct temporal scales, transitioning from a Washburn-type spreading to a much faster Laplace-pressure driven spreading, and finally to an extremely slow, density augmented-Tanner-type spreading
Directional Spreading of Viscous Droplets on Wettability-Patterned Diverging Tracks
No full textSpontaneous pumpless transport of liquid droplets on wettability-patterned tracks is important for a number of diverse applications such as rapid transport and mixing of fluid droplets, enhancing dropwise condensation on surfaces, and in the biomedical sector as well. Recent studies point to the fact that, on an open surface, a superhydrophilic diverging track laid on a superhydrophobic background results in pumpless transport of water from the narrow end to the wide end at unprecedented rates. However, the interplay between the driving capillary force and the resisting viscous force, which governs the spreading behavior of liquid droplets on such surfaces, have so for not been characterized. Potential applications for transporting organic liquids and in point-of-care devices hence calls for understanding the spreading behavior of viscous droplets on such surfaces. An effort to do the same has been made in the present work by experimentally observing the spreading of liquid droplets of different viscosities and surface tensions on the aforementioned wettability-patterned diverging or wedge-shaped tracks. An universal relationship of the spreading behavior in terms of two dimensionless variables is obtained. The liquid spreading front was found to follow three distinct temporal scales, transitioning from a Washburn-type spreading to a much faster Laplace-pressure driven spreading, and finally to an extremely slow, density augmented-Tanner-type spreading
Manipulating Liquid Volumes by Wettability-Patterned Substrates
No full textThe interaction of liquids with surfaces (both impervious and porous) is one of the most commonly observed phenomena in our daily life. Several studies exist that highlight both the fundamentals and applications of liquid impingement (both as droplets and high-flow-rate liquid jets) on surfaces. However, existing studies have almost all been in the area of impermeable substrates. The few studies that exist on the interaction of droplets (and not high-flow-rate liquid jets) with porous materials are on substrates of uniform wettability. On the other hand, literature points to the fact that the wettability of the underlying substrate is essential for determining the outcome of liquid impingement. The potential usefulness of wettability-patterned substrates, i.e., surfaces possessing spatially juxtaposed wettable and non-wettable domains, can also be inferred from those studies. From a scientific point of view, the interaction of liquid jets with wettability-patterned surfaces is a more complex problem than that of a single droplet. The complexity is further compounded when the substrate is permeable. The focus of the present dissertation is to study the interaction of high flow rate (~ 1 L/min) liquid jets with wettability-patterned permeable substrates. However, the inherent difficulty of the problem necessitates it to be divided into three modules. The first module is concerned with the interaction of liquid droplets with wettability-patterned permeable substrates, while the second module presents theoretical and experimental results of orthogonal liquid-jet impingement on wettability-patterned impermeable substrates. Finally, the third module demonstrates the applicability of wettability-patterned permeable substrates for manipulation of orthogonally impinging liquid jets
Manipulating Liquid Volumes by Wettability-Patterned Substrates
No full textThe interaction of liquids with surfaces (both impervious and porous) is one of the most commonly observed phenomena in our daily life. Several studies exist that highlight both the fundamentals and applications of liquid impingement (both as droplets and high-flow-rate liquid jets) on surfaces. However, existing studies have almost all been in the area of impermeable substrates. The few studies that exist on the interaction of droplets (and not high-flow-rate liquid jets) with porous materials are on substrates of uniform wettability. On the other hand, literature points to the fact that the wettability of the underlying substrate is essential for determining the outcome of liquid impingement. The potential usefulness of wettability-patterned substrates, i.e., surfaces possessing spatially juxtaposed wettable and non-wettable domains, can also be inferred from those studies. From a scientific point of view, the interaction of liquid jets with wettability-patterned surfaces is a more complex problem than that of a single droplet. The complexity is further compounded when the substrate is permeable. The focus of the present dissertation is to study the interaction of high flow rate (~ 1 L/min) liquid jets with wettability-patterned permeable substrates. However, the inherent difficulty of the problem necessitates it to be divided into three modules. The first module is concerned with the interaction of liquid droplets with wettability-patterned permeable substrates, while the second module presents theoretical and experimental results of orthogonal liquid-jet impingement on wettability-patterned impermeable substrates. Finally, the third module demonstrates the applicability of wettability-patterned permeable substrates for manipulation of orthogonally impinging liquid jets
Taylor-Culick retractions and the influence of the surroundings
Get PDFWhen a freely suspended liquid film ruptures, it retracts spontaneously under
the action of surface tension. If the film is surrounded by air, the retraction
velocity is known to approach the constant Taylor-Culick velocity. However,
when surrounded by an external viscous medium, the dissipation within that
medium dictates the magnitude of the retraction velocity. In the present work,
we study the retraction of a liquid (water) film in a viscous oil ambient
(\emph{two-phase} Taylor-Culick retractions), and that sandwiched between air
and a viscous oil (\emph{three-phase} Taylor-Culick retractions). In the latter
case, the experimentally-measured retraction velocity is observed to have a
weaker dependence on the viscosity of the oil phase as compared to the
configuration where the water film is surrounded completely by oil. Numerical
simulations indicate that this weaker dependence arises from the localization
of viscous dissipation near the three-phase contact line. The speed of
retraction only depends on the viscosity of the surrounding medium and not on
that of the film. From the experiments and the numerical simulations, we reveal
unprecedented regimes for the scaling of the Weber number of the film
(based on its retraction velocity) or the capillary number of the
surroundings vs. the Ohnesorge number of the surroundings in the regime
of large viscosity of the surroundings (), namely and for the two-phase Taylor-Culick
configuration, and and for the
three-phase Taylor-Culick configuration.Comment: For supplementary movies, visit:
https://www.youtube.com/playlist?list=PLf5C5HCrvhLHsSDmgLAql-hcAEZrejs2
Lateral Spreading of Gas Bubbles on Submerged Wettability-Confined Tracks
Get PDFSpreading of liquid droplets on wettability-confined paths has attracted considerable attention in the past decade. On the other hand, the inverse scenario of a gas bubble spreading on a submerged, wettability-confined track has rarely been studied. In the present work, an experimental investigation of the spreading of millimetric gas bubbles on horizontally submerged, textured, wettability-confined tracks is carried out. The width of the track is kept fixed along its entire length, and the spreading behavior of a gas bubble, dispensed at one end of the track, is studied. The effects of varying track width, bubble diameter, and ambient liquid are investigated. Post-contact, the gas bubble spreads along the track at a linear rate with time, while remaining pinned at its back end; the recorded spreading speed is O(0.5 m/s). An inertio-capillary force balance describes the experimentally observed spreading dynamics with excellent agreement
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