Drop Impact on a Solid Surface
TL;DR: In this article, the authors focus on recent experimental and theoretical studies, which aim at unraveling the underlying physics, characterized by the delicate interplay of liquid inertia, viscosity, and surface tension, but also the surrounding gas.
Abstract: A drop hitting a solid surface can deposit, bounce, or splash. Splashing arises from the breakup of a fine liquid sheet that is ejected radially along the substrate. Bouncing and deposition depend crucially on the wetting properties of the substrate. In this review, we focus on recent experimental and theoretical studies, which aim at unraveling the underlying physics, characterized by the delicate interplay of not only liquid inertia, viscosity, and surface tension, but also the surrounding gas. The gas cushions the initial contact; it is entrapped in a central microbubble on the substrate; and it promotes the so-called corona splash, by lifting the lamella away from the solid. Particular attention is paid to the influence of surface roughness, natural or engineered to enhance repellency, relevant in many applications.
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TL;DR: In this paper, a comprehensive review of published literatures concerning the fluid mechanics and heat transfer mechanisms of liquid drop impact on a heated wall is provided, divided into four parts, each centered on one of the main heat transfer regimes: film evaporation, nucleate boiling, transition boiling, and film boiling.
357 citations
TL;DR: An overview of plant surface structures and their evolution is presented, which combines surface chemistry and architecture with their functions and refers to possible biomimetic applications and the major challenge for engineers and materials scientists, the durability of the fragile nanocoatings.
Abstract: An overview of plant surface structures and their evolution is presented. It combines surface chemistry and architecture with their functions and refers to possible biomimetic applications. Within some 3.5 billion years biological species evolved highly complex multifunctional surfaces for interacting with their environments: some 10 million living prototypes (i.e., estimated number of existing plants and animals) for engineers. The complexity of the hierarchical structures and their functionality in biological organisms surpasses all abiotic natural surfaces: even superhydrophobicity is restricted in nature to living organisms and was probably a key evolutionary step with the invasion of terrestrial habitats some 350–450 million years ago in plants and insects. Special attention should be paid to the fact that global environmental change implies a dramatic loss of species and with it the biological role models. Plants, the dominating group of organisms on our planet, are sessile organisms with large multifunctional surfaces and thus exhibit particular intriguing features. Superhydrophilicity and superhydrophobicity are focal points in this work. We estimate that superhydrophobic plant leaves (e.g., grasses) comprise in total an area of around 250 million km2, which is about 50% of the total surface of our planet. A survey of structures and functions based on own examinations of almost 20,000 species is provided, for further references we refer to Barthlott et al. (Philos. Trans. R. Soc. A 374: 20160191, 1). A basic difference exists between aquatic non-vascular and land-living vascular plants; the latter exhibit a particular intriguing surface chemistry and architecture. The diversity of features is described in detail according to their hierarchical structural order. The first underlying and essential feature is the polymer cuticle superimposed by epicuticular wax and the curvature of single cells up to complex multicellular structures. A descriptive terminology for this diversity is provided. Simplified, the functions of plant surface characteristics may be grouped into six categories: (1) mechanical properties, (2) influence on reflection and absorption of spectral radiation, (3) reduction of water loss or increase of water uptake, moisture harvesting, (4) adhesion and non-adhesion (lotus effect, insect trapping), (5) drag and turbulence increase, or (6) air retention under water for drag reduction or gas exchange (Salvinia effect). This list is far from complete. A short overview of the history of bionics and the impressive spectrum of existing and anticipated biomimetic applications are provided. The major challenge for engineers and materials scientists, the durability of the fragile nanocoatings, is also discussed.
290 citations
TL;DR: In this paper, a brief review of potential applications of superhydrophobic surfaces is presented, which thoroughly focuses on the most recent advances regarding dynamics and kinematics of drop impinging super-hydrophilic substrates.
248 citations
01 Jan 2009
TL;DR: The results imply that the multiscale surface roughness at nanoscale plays a minor role in the impact events for small The authors less than or approximately equal 120 but an important one for large They greater than or about equal 120.
Abstract: We experimentally investigate drop impact dynamics onto different superhydrophobic surfaces, consisting of regular polymeric micropatterns and rough carbon nanofibers, with similar static contact angles. The main control parameters are the Weber number We and the roughness of the surface. At small We, i.e., small impact velocity, the impact evolutions are similar for both types of substrates, exhibiting Fakir state, complete bouncing, partial rebouncing, trapping of an air bubble, jetting, and sticky vibrating water balls. At large We, splashing impacts emerge forming several satellite droplets, which are more pronounced for the multiscale rough carbon nanofiber jungles. The results imply that the multiscale surface roughness at nanoscale plays a minor role in the impact events for small We less than or approximately equal 120 but an important one for large We greater than or approximately equal 120. Finally, we find the effect of ambient air pressure to be negligible in the explored parameter regime We less than or approximately equal 150.
246 citations
01 Jan 2004
TL;DR: In this paper, the acceleration experienced by a drop during its impact is interpreted as resulting from the effective acceleration experienced during the drop, and a criterion for predicting if the spreading is limited by capillarity, or by viscosity is proposed.
Abstract: are the liquid density and surface tension).This law is also observed to hold on partially wettable surfaces, provided that liquidsof low viscosity (such as water) are used. The law is interpreted as resulting fromthe effective acceleration experienced by the drop during its impact. Viscous dropsare also analysed, allowing us to propose a criterion for predicting if the spreading islimited by capillarity, or by viscosity.
234 citations
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TL;DR: In this article, a review deals with drop impacts on thin liquid layers and dry surfaces, referred to as splashing, and their propagation is discussed in detail, as well as some additional kindred, albeit nonsplashing, phenomena like drop spreading and deposition, receding (recoil), jetting, fingering, and rebound.
Abstract: The review deals with drop impacts on thin liquid layers and dry surfaces. The impacts resulting in crown formation are referred to as splashing. Crowns and their propagation are discussed in detail, as well as some additional kindred, albeit nonsplashing, phenomena like drop spreading and deposition, receding (recoil), jetting, fingering, and rebound. The review begins with an explanation of various practical motivations feeding the interest in the fascinating phenomena of drop impact, and the above-mentioned topics are then considered in their experimental, theoretical, and computational aspects.
2,077 citations
"Drop Impact on a Solid Surface" refers background in this paper
...…• Drop impact 21 With accelerating improvements in both high-speed sensor technology and computational power, we expect the coming decade to provide even more breakthroughs in the study of drop impact, than have already occurred in the last decade since the review of Yarin (2006)....
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...Moreover, we emphasize recent works, i.e. appearing after the earlier Annual Review by Yarin (2006), which dealt with impacts on both solid and liquid surfaces....
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TL;DR: An easily fabricated, transparent, and oil-rebounding superamphiphobic coating is designed, based on low-energy surfaces and roughness on the nano- and micrometer scales.
Abstract: Coating is an essential step in adjusting the surface properties of materials. Superhydrophobic coatings with contact angles greater than 150° and roll-off angles below 10° for water have been developed, based on low-energy surfaces and roughness on the nano- and micrometer scales. However, these surfaces are still wetted by organic liquids such as surfactant-based solutions, alcohols, or alkanes. Coatings that are simultaneously superhydrophobic and superoleophobic are rare. We designed an easily fabricated, transparent, and oil-rebounding superamphiphobic coating. A porous deposit of candle soot was coated with a 25-nanometer-thick silica shell. The black coating became transparent after calcination at 600°C. After silanization, the coating was superamphiphobic and remained so even after its top layer was damaged by sand impingement.
1,710 citations
"Drop Impact on a Solid Surface" refers background in this paper
...One possible explanation is the soot which he used to superhydrophobize his spectacle glass for releasing the drop (soot also works well as an oleophobic coating, see Deng et al. (2012))....
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TL;DR: It is shown that mixing fine droplets of an antisolvent and a solution of an active semiconducting component within a confined area on an amorphous substrate can trigger the controlled formation of exceptionally uniform single-crystal or polycrystalline thin films that grow at the liquid–air interfaces.
Abstract: Printing electronic devices using semiconducting 'ink' is seen as a promising route to cheap, large-area and flexible electronics, but the performance of such devices suffers from the relatively poor crystallinity of the printed material. Hiromi Minemawari and colleagues have developed an inkjet-based printing technique involving controlled mixing on a surface of two solutions — the semiconductor (C8-BTBT) in its solvent and a liquid in which the semiconductor is insoluble. The products of this antisolvent crystallization technique are thin semiconductor films with exceptionally high and uniform crystallinity. The use of single crystals has been fundamental to the development of semiconductor microelectronics and solid-state science1. Whether based on inorganic2,3,4,5 or organic6,7,8 materials, the devices that show the highest performance rely on single-crystal interfaces, with their nearly perfect translational symmetry and exceptionally high chemical purity. Attention has recently been focused on developing simple ways of producing electronic devices by means of printing technologies. ‘Printed electronics’ is being explored for the manufacture of large-area and flexible electronic devices by the patterned application of functional inks containing soluble or dispersed semiconducting materials9,10,11. However, because of the strong self-organizing tendency of the deposited materials12,13, the production of semiconducting thin films of high crystallinity (indispensable for realizing high carrier mobility) may be incompatible with conventional printing processes. Here we develop a method that combines the technique of antisolvent crystallization14 with inkjet printing to produce organic semiconducting thin films of high crystallinity. Specifically, we show that mixing fine droplets of an antisolvent and a solution of an active semiconducting component within a confined area on an amorphous substrate can trigger the controlled formation of exceptionally uniform single-crystal or polycrystalline thin films that grow at the liquid–air interfaces. Using this approach, we have printed single crystals of the organic semiconductor 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) (ref. 15), yielding thin-film transistors with average carrier mobilities as high as 16.4 cm2 V−1 s−1. This printing technique constitutes a major step towards the use of high-performance single-crystal semiconductor devices for large-area and flexible electronics applications.
1,505 citations
"Drop Impact on a Solid Surface" refers background in this paper
...This quantity, pertinent in the absence of splash, has applications in ink-jet printing Minemawari et al. (2011) or forensic science Attinger et al. (2013); Hulse-Smith et al. (2005) although in these cases the crucial quantity is the residual spreading radius, that can differ from the maximum…...
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...The spreading dynamics is an important aspect in many applications, for instance for inkjet printing in microelectronics (Minemawari et al. (2011)) or in forensic science (Attinger et al. (2013); Hulse-Smith et al. (2005); Laan et al. (2014))....
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TL;DR: Four design parameters are proposed that predict the measured contact angles for a liquid droplet on a textured surface, as well as the robustness of the composite interface, based on the properties of the solid surface and the contacting liquid, that allow two different families of re-entrant surfaces to be produced.
Abstract: Superhydrophobic surfaces display water contact angles greater than 150° in conjunction with low contact angle hysteresis. Microscopic pockets of air trapped beneath the water droplets placed on these surfaces lead to a composite solid-liquid-air interface in thermodynamic equilibrium. Previous experimental and theoretical studies suggest that it may not be possible to form similar fully-equilibrated, composite interfaces with drops of liquids, such as alkanes or alcohols, that possess significantly lower surface tension than water (γlv = 72.1 mN/m). In this work we develop surfaces possessing re-entrant texture that can support strongly metastable composite solid-liquid-air interfaces, even with very low surface tension liquids such as pentane (γlv = 15.7 mN/m). Furthermore, we propose four design parameters that predict the measured contact angles for a liquid droplet on a textured surface, as well as the robustness of the composite interface, based on the properties of the solid surface and the contacting liquid. These design parameters allow us to produce two different families of re-entrant surfaces— randomly-deposited electrospun fiber mats and precisely fabricated microhoodoo surfaces—that can each support a robust composite interface with essentially any liquid. These omniphobic surfaces display contact angles greater than 150° and low contact angle hysteresis with both polar and nonpolar liquids possessing a wide range of surface tensions.
1,132 citations
"Drop Impact on a Solid Surface" refers background in this paper
...Recent mushroom-shaped double-reentrant superomniphobic surfaces show bouncing of fully wettable liquids, like hexadecane (Tuteja et al. (2008)) and even perfluorohexane (Liu & Kim (2014))....
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...Recent mushroomshaped double-reentrant superomniphobic surfaces show bouncing of fully wettable liquids, like hexadecane (Tuteja et al. (2008)) and even perfluorohexane (Liu & Kim (2014))....
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TL;DR: The fluid dynamic phenomena of liquid drop impact are described and reviewed in this article, and specific conditions under which the above phenomena did occur in experiments are analyzed and the characteristics of drop impact phenomena are described in detail.
1,081 citations
"Drop Impact on a Solid Surface" refers background in this paper
...This might have formed a coating on the drop, or an oxidized layer may have formed, or simply the flash duration was too long and smeared out the edge-bumps into radial streaks, as was suggested in the celebrated review of Rein (1993)....
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