Outcomes From a Drop Impact on Solid Surfaces

Rioboo, Romain; Tropea, Cameron; Marengo, Marco

doi:10.1615/atomizspr.v11.i2.40

Cited by 564 publications

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“…In particular, we observe four distinct regimes. In agreement with earlier results [4], we observe a thin-sheet splash on very smooth surfaces and a prompt splash on very rough ones. However, at intermediate roughness, we identify two new regimes: at low viscosities both prompt and thin-sheet splashes occur during a single impact, while at high viscosities neither splash is formed.…”

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confidence: 93%

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Creation of Prompt and Thin-Sheet Splashing by Varying Surface Roughness or Increasing Air Pressure

et al. 2012

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A liquid drop impacting a solid surface may splash either by emitting a thin liquid sheet that subsequently breaks apart or by promptly ejecting droplets from the advancing liquid-solid contact line. Using high-speed imaging, we show that surface roughness and air pressure influence both mechanisms. Roughness inhibits thin-sheet formation even though it also increases prompt splashing at the advancing contact line. If the air pressure is lowered, droplet ejection is suppressed not only during thin-sheet formation but for prompt splashing as well.PACS numbers: 47.20.Cq, 47.20.Gv, 47.20.Ma,Will a drop hitting a dry surface splash? Different criteria [1][2][3][4][5] have been proposed to predict when such a drop will splash by comparing the roughness of the solid surface with hydrodynamic length scales, which depend on parameters such as the drop velocity, radius, viscosity and surface tension. Several years ago Xu et al. [6,7] found that these criteria ignore a crucial parameter: the ambient gas pressure, P . When a drop splashes on a smooth surface it spreads smoothly forming a lamella before ejecting a thin sheet that subsequently breaks up into secondary droplets. As P is reduced below a threshold pressure, the drop no longer splashes [6][7][8][9][10]. On the other hand, when splashing occurs on a rough surface, no thin sheet is formed and droplets are ejected directly from the advancing liquid-substrate contact line via a "prompt" splash [1][2][3][4]8].It has been suggested that thin-sheet splashes depend on air pressure while prompt splashes do not and depend only on surface roughness [8]. Here we show that the situation is more complex in that both types of splashing depend, albeit in opposite ways, on surface roughness. In particular, we observe four distinct regimes. In agreement with earlier results [4], we observe a thin-sheet splash on very smooth surfaces and a prompt splash on very rough ones. However, at intermediate roughness, we identify two new regimes: at low viscosities both prompt and thin-sheet splashes occur during a single impact, while at high viscosities neither splash is formed. In addition, as found for thin-sheet splashing [6], we find that a drop deposits smoothly on a rough surface if P is low enough. Clearly, the role of both air pressure and substrate roughness must be considered in all cases.The experiments were conducted with silicone oil (PDMS, Clearco Products) with kinematic viscosity ν ranging from 5 cSt to 14.4 cSt and surface tension σ between 19.7 dyn/cm and 20.8 dyn/cm. The basic results were replicated using water/glycerin mixtures with a similar viscosity range but higher surface tension: σ=67 dyn/cm. Low-viscosity impacts were studied with ethanol. Drops with reproducible diameter D=3.1 mm were produced using a syringe pump (Razel Scientific, Model R99-E) and released in a chamber from a height above a substrate. This height set the impact velocity u 0 which was varied between 2.7 m/s and 4.1 m/s. These parameters determine the Reynolds number Re=Du 0 /ν giving the rati...

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confidence: 93%

“…As P is reduced below a threshold pressure, the drop no longer splashes [6][7][8][9][10]. On the other hand, when splashing occurs on a rough surface, no thin sheet is formed and droplets are ejected directly from the advancing liquid-substrate contact line via a "prompt" splash [1][2][3][4]8].…”

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confidence: 99%

Creation of Prompt and Thin-Sheet Splashing by Varying Surface Roughness or Increasing Air Pressure

et al. 2012

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“…Also the form of the impact crater and the jet formation is qualitatively the same. Considering only the alginate capsule, we showed there is a complex and reproducible behaviour which can be divided in four characteristic stages: (1) deformation, (2) detachment, (3) recovery and (4) decay to sphere, comparable to investigations on an impact on a solid surface described in (Rioboo et al 2001) and (Jung and Hutchings 2012). In the case of alginate capsules in crosslinking solution, air bubble entrapment (as reported by Mehdi-Nejad et al 2003;Mohamed-Kassim and Longmire 2003) occurred very infrequently and was not considered in our examinations since accurate graft position assignments were not possible.…”

Section: Discussionsupporting

confidence: 73%

A new validation method for clinical grade micro-encapsulation: quantitative high speed video analysis of alginate capsule

et al. 2013

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Micro-encapsulation of cells or tissues is a promising treatment for hormone deficiency diseases (diabetes mellitus, hypoparathyroidism etc.). Alginate, a polymer from marine brown algae, is excellent for encapsulation. Its hydrated structure keeps out large antibodies and immune system cells while allowing diffusion of nutrients and therapeutic factors. Alginate droplets, containing cells, are crosslinked to form stable spherical hydrogel capsules. The position of grafts within the capsule, which decisively affects vulnerability to the host's immune response, has previously not been investigated during the process of crosslinking. We describe for the first time quantitative, high speed video analysis of two perpendicular projections of capsule shape and load during crosslinking. This gives characteristic ''deformation plots'' of the capsule and fully resolved ''trajectories plots'' of capsule load movement. We identify four stages of capsule formation, giving insights into physico-chemical processes involved. Further, we show that mechanical stress on the load can be deduced by measurement of the capsule's shape.

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“…A rich body of literature already exists considering perpendicular drop impacts, with a droplet falling from above onto a flat surface [1][2][3][4][5][6][7][8]. These studies have revealed the underlying mechanics and possible outcomes of droplet splashing and are industrially relevant to processes such as spray coating, spray cooling and inkjet printing.…”

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confidence: 99%

Splashing Threshold of Oblique Droplet Impacts on Surfaces of Various Wettability

Aboud

Kietzig

2015

Langmuir

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Oblique drop impacts were performed at high speeds (up to 27 m/s, We>9000) with millimetric water droplets, and a linear model was applied to define the oblique splashing threshold. Six different sample surfaces were tested: two substrate materials of different inherent surface wettability (PTFE and aluminum), each prepared with three different surface finishes (smooth, rough, and textured to support superhydrophobicity). Our choice of surfaces has allowed us to make several novel comparisons. Considering the inherent surface wettability, we discovered that PTFE, as the more hydrophobic surface, exhibits lower splashing thresholds than the hydrophilic surface of aluminum of comparable roughness. Furthermore, comparing oblique impacts on smooth and textured surfaces, we found that asymmetrical spreading and splashing behaviours occurred under a wide range of experimental conditions on our smooth surfaces, however impacts 2 occurring on textured surfaces were much more symmetrical, and one-sided splashing occurred only under very specific conditions. We attribute this difference to the air-trapping nature of textured superhydrophobic surfaces, which lowers the drag between the spreading lamella and the surface. The reduced drag affects oblique drop impacts by diminishing the effect of the tangential component of the impact velocity, causing the impact behaviour to be governed almost exclusively by the normal velocity. Finally, by comparing oblique impacts on superhydrophobic surfaces at different impact angles, we discovered that although the pinning transition between rebounding and partial rebounding is governed primarily by the normal impact velocity, there is also a weak dependence on the tangential velocity. As a result, pinning is inhibited in oblique impacts. This led to the observation of a new behaviour in highly oblique impacts on our superhydrophobic surfaces which we named the stretched rebound, where the droplet is extended into an elongated pancake shape and rebounds while still outstretched, without exhibiting a recession phase.

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Outcomes From a Drop Impact on Solid Surfaces

Cited by 564 publications

References 0 publications

Creation of Prompt and Thin-Sheet Splashing by Varying Surface Roughness or Increasing Air Pressure

Creation of Prompt and Thin-Sheet Splashing by Varying Surface Roughness or Increasing Air Pressure

A new validation method for clinical grade micro-encapsulation: quantitative high speed video analysis of alginate capsule

Splashing Threshold of Oblique Droplet Impacts on Surfaces of Various Wettability

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