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APPL I ED SC I ENCES AND ENG INEER ING

1CAS Key Laboratory of Bio-inspired Materials and Interfacial Science, Technical Insti-tute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China.2Key Laboratory of Colloid and Interface Science, Institute of Chemistry, ChineseAcademy of Sciences, Beijing 100190, China. 3College of Sciences, Henan AgriculturalUniversity, Zhengzhou, Henan 450001, China.*Corresponding author. Email: dongzhichao@iccas.ac.cn (Z.D.); yilinwang@iccas.ac.cn(Y.W.); jianglei@iccas.ac.cn (L.J.)

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Controlling liquid splash on superhydrophobic surfacesby a vesicle surfactantMeirong Song,1,2,3 Jie Ju,1 Siqi Luo,2 Yuchun Han,2 Zhichao Dong,1* Yilin Wang,2* Zhen Gu,1

Lingjuan Zhang,1 Ruiran Hao,1 Lei Jiang1*

Deposition of liquid droplets on solid surfaces is of great importance to many fundamental scientific principles andtechnological applications, such as spraying, coating, and printing. For example, during the process of pesticidespraying, more than 50% of agrochemicals are lost because of the undesired bouncing and splashing behaviorson hydrophobic or superhydrophobic leaves. We show that this kind of splashing on superhydrophobic surfacescan be greatly inhibited by adding a small amount of a vesicular surfactant, Aerosol OT. Rather than reducing splash-ing by increasing the viscosity via polymer additives, the vesicular surfactant confines the motion of liquid with thehelp of wettability transition and thus inhibits the splash. Significantly, the vesicular surfactant exhibits a distin-guished ability to alter the surface wettability during the first inertial spreading stage of ~2 ms because of its denseaggregates at the air/water interface. A comprehensive model proposed by this idea could help in understandingthe complex interfacial interactions at the solid/liquid/air interface.

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INTRODUCTIONPesticide spraying is “hard” agricultural work, where more than 50%of agrochemicals are lost because of undesired bouncing and splashingbehaviors on crop leaves with “waterproof” properties (1–3). Innatural plants, superhydrophobic leaves are ubiquitous, and they usu-ally get their nonwetting properties from the presence of waxy featureson their surface. Particularly because of the combination of extremelylow energized chemical composition and microstructured/nanostructuredsurface morphology, the superhydrophobic surface was demonstratedto facilitate droplets, even those with surfactant additives (4), bouncingand splashing within shortened contact time (5–17). This increases thedifficulty of droplet retention (18), thus threatening ecological securityand human safety: If pesticides cannot be properly deposited on crops,then pests might not be controlled and plant injury might occur (1).Redundant pesticides might contribute to soil, air, or water pollution,and human health might be negatively affected.

Although adding surfactants to the sprayed liquid is considered tobe a simple method to reduce surface tension and to improve dropretention on a smooth hydrophobic surface, surfactant liquids stillslide or bounce off the hydrophobic surface at a tilted angle and re-duce liquid splashing on the superhydrophobic surface (19). In addi-tion, according to the Kelvin-Helmholtz instability, the wave numberkmax equals 2raU

2/3g, where ra is the air density, g is the fluid surfacetension, and U is the relative velocity between gas and liquid. There-fore, reduced surface tension was believed to play a major role in theincreased instability of the spilt droplet (20, 21). Enhancing liquid dep-osition on the superhydrophobic surface is complex and difficult work,where selected surfactants need to diffuse from the bulk to the newlycreated interfaces quickly, because the contact time is typically only sev-eral milliseconds, and need to decrease retraction velocity to reduceinstability due to the reduced surface tension. Several studies havedemonstrated the difficulty of surfactant drop deposition on the super-

hydrophobic surface. On the basis of these results, it would seem thatsurfactant additives should not be responsible for reducing high-speedliquid splashing on the superhydrophobic surface.

However, we found that this kind of “unavoidable” bouncing or splash-ing behavior was greatly inhibited or even completely reduced on thesuperhydrophobic surface at varied angles by adding a small amount ofa double-chain vesicle surfactant. Unlike themicelle surfactant previous-ly discussed, the vesicular surfactants additive demonstrated here wasable to diffuse from the bulk to the newly formed interfaces duringthe deformation process, enter into the microstructured/nanostructuredmorphology, confine the motion of the liquid with the help of the wet-tability transition during the first inertial spreading stage of ~2 ms, de-crease the retraction velocity down to nearly zero, and reduce bouncingand splashing (Fig. 1). For the first time, we have found that the vesiclesurfactant could exhibit a distinguished ability to alter the surface wetta-bility during the impact process. By taking advantage of this wettabilitytransition, not only have liquid splashing and retraction been completelyreduced but the maximum wetting area is also maintained after theimpact process. This behavior is different from that observed in previousresearch, in which a micelle surfactant drop could bounce off the super-hydrophobic surface (18), viscosity induced the splashing reduction (1), asurfactant drop partly reduced the liquid retraction on the hydrophobicsurface (22–24), and nanoparticles or surface charges suppressed dropletrebound on the superhydrophobic surface (19, 25).

RESULTSFigure 1 shows the impacts of droplets of pure water and aqueoussolutions containing the same mass fraction of the micelle surfactantsodium dodecyl sulfate (SDS), trisiloxane molecules (TSs), and the vesiclesurfactant sodium bis(2-ethylhexyl) sulfosuccinate [Aerosol OT (AOT)]on a Brassica oleracea L. leaf (Fig. 1A) at a velocity of 2.53 ± 0.11 m s−1

using high-speed cameras (movie S1). In the experiment, the impact be-havior was defined by measuring more than 30 different positions of thesame sample and surfactant solutions. The B. oleracea L. leaf sur-face characterized by microstructured/nanostructured morphologies(Fig. 1, B and C) shows a water contact angle of 156.2 ± 4.3° (Fig. 1D),ensuring superhydrophobicity. The impacting water droplet, after reach-ing its maximum spreading at ~1.8 ms, breaks up into numerous droplets

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(Fig. 1E). By adding a certain amount of surfactants, the receding splashbe inhibited by varying degrees (movie S1). Figure 1 (F and G) showsthat aqueous droplets containing 1% SDS or 1% TSs partially reducedthe receding splash but left several streams during retraction and fi-nally broke up into several fragments. In contrast, by adding 1%AOT in the aqueous phase, the impacting drop first spread to alarger wetting area within 2 ms. Then, the liquid broke up and thereceding laminar stream was substantially depressed (Fig. 1H) evenafter the maximum spreading stage (movie S1). Finally, a largewetting area was achieved and maintained. Partial and scarce recedingbehavior at low-speed impact was found in the micelle and vesicleregions (fig. S1), respectively. Furthermore, on artificial superhy-drophobic surfaces with varied structures and tilted angles, aqueousdroplets containing 1% AOT would spread properly (movies S2 toS4). Notably, this kind of liquid deposition behavior is in contrast toprevious works, where surfactant drops have been shown to bounceoff the superhydrophobic surface (18), although surfactants can helpthe liquid wet the hydrophobic surface (movie S5) (25). AOT istherefore a unique surfactant that has a more pronounced effectthan the others in controlling liquid deposition and in reducing un-avoidable splash.

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DISCUSSIONCompared with the mechanism of liquid deposition enhancementusing polymer additives (1), surfactant additives cannot alter viscositybut can reduce the liquid’s surface tension. Although surfactants candecrease the surface tension of the liquid, helping it spread on a hy-drophobic surface under a low-speed impact (25), the reduction ofsurface tension also plays a major role in the increased instabilityand the enhanced droplet’s splash (20, 21). According to the Kelvin-Helmholtz instability, kmax = 2raU

2r/3g, the key to reducing in-

stability is via the retraction velocity Ur, and the brevity of impactcontact time should be enough for liquid droplets to wet the super-hydrophobic surface (18). In our experiment, local pinning is observedfor SDS (Fig. 1F) and TSs (Fig. 1G), and the entire pinning is foundfor AOT in the peripheral area of maximum spreading (Fig. 1H),where the retraction velocity Ur slows down to a low value, resultingin a small kmax. For the AOT drop, the motion of spreading is greatlyconfined, leading to extremely low instability and thus retarding thesplash (movie S1).

The exceptional molecular structure of AOT distinguishes it fromthe other two surfactants in reducing splash and in enhancing liquiddeposition. Cryo-TEM (transmission electron microscope) imaging

Fig. 1. The deposition of high-velocity impacting drops on the superhydrophobic leaf surface. (A) Optical image of the B. oleracea L. leaf. (B and C) Environmentalscanning electron microscope (SEM) images of the leaf surface with a microstructured/nanostructured morphology. (D) Water contact angle reveals the superhydrophobicproperty of the leaf surface. (E) Impact process of a water droplet on the superhydrophobic leaf surface. The splashing of water mainly occurs in the receding stage. (F and G)Inhomogeneous receding behavior: SDS (1%) and TS (1%) additives partially inhibit the receding splash. (H) Reduced receding behavior by the AOT surfactant: The recedingsplash was substantially depressed by 1% AOT additive.

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was used to prove our assumption, which was achieved by allowing afree-falling surfactant drop to impact the Cu mesh followed by immer-sion in liquid nitrogen. This mimics the surfactant packing stage duringthe impact process. The significant differences of the surfactant aggre-gates are shown in Fig. 2 (A1 to C1), where the multilamellar vesicleswere closely packed at the air/water interface for the AOT drop with amass fraction of 1%, whereas micelles only randomly and loosely existedfor the other two surfactant solutions at the same mass fractions. Com-pared with the sample molecular structures of SDS, TSs, and the pre-viously mentioned surfactants in reducing the liquid bouncing (18, 25),AOT has two alkyl chains and a relatively small hydrophilic head group.This particular molecular structure of AOT is the main reason for itscompact and directed alignment and leads to the multilamellar vesiclestructure (26). As shown in Fig. 2 (A2 to C2), among the three surfac-tants, the aqueous solution containing 1% AOT exhibits the lowest DSTwithin a surface age of 80 ms. At the beginning of the bubble pressuremeasurement of ~10 ms, its DST could decrease to a low value of ~32mN/m (Fig. 2C2), whereas both 1% SDS and 1% TSs have DSTs thatbegin in a high value of ~43 mN/m (Fig. 2, A2 and B2). Similar to the

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property reflected in the diffusion coefficients achieved through 1Hnuclear magnetic resonance (NMR) spectrometry (fig. S2) and dy-namic contact angles (fig. S3), the DST results indicate that AOThas the fastest diffusion speed to the air/water interface and thushas the strongest ability to reduce the surface tension when thereare newly created surfaces.

Besides reducing splashing on natural superhydrophobic leaves,AOT is the most effective surfactant that inhibits the bouncing andsplashing of the liquid drops on the artificial superhydrophobic sur-face at both low (~1.2 m s−1) and high (~2.5 m s−1) impact speeds.The artificial superhydrophobic surfaces include a microstructured/nanostructured superhydrophobic surface composed of 20-nm hydro-phobic SiO2 nanoparticle composites with a typical size and spacing ofaround 200 nm and a CuO nanosheet structured superhydrophobicsurface with a typical size of about 3 to 6 mm in length and 200 to 600nm in width. The water contact angles of these artificial superhydro-phobic surfaces are 161.3 ± 0.5° and 159.1 ± 1.7°, respectively, whichare much higher than those of the natural B. oleracea L. leaf. Afluorinated glass slide with a water contact angle of 112.8 ± 1.1° is

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Fig. 2. The molecular structure, dynamic surface tension, and impact behavior of SDS, TSs, and AOT. (A1 and B1) Cryo-TEM images of both 1% SDS and 1% TSs showthe micelle aggregates at a mass fraction of 1%. (C1) Cryo-TEM image of 1% AOT shows that multilamellar vesicles have formed, indicating the dense aggregates of AOTmolecules at the air/water interface. (A2) SDS has a long chain, and its dynamic surface tension (DST) slowly falls in the rapid fall region and cannot reach its equilibrium withina surface age of 100 ms. (A3) The droplets containing SDS are easy to rebound on the superhydrophobic surface even for highly concentrated solution. (B2) TSs have longinduction periods in the first tens or hundreds of seconds. (B3) With the increase of the concentration, the induction period is shortened so that the impact behavior turns frombouncing, emission, to no rebound. On the inclined surface, it is still easy to partially rebound. (C2) AOT distinguishes itself from other surfactants in the fastest diffusion speedto form a densely packed molecular layer at the air/water interface. AOT directly approaches low surface tension of around 32 mN/m at the very beginning of the bubblepressure measurement, showing the lowest DST among the three surfactants within a surface age of 80 ms. The DSTs of 1% SDS and 1% TSs begin nearly at the same value of~43 mN/m. TS quickly decreases to a lower value, and SDS slowly decreases to a higher value. (C3) AOT is the most effective surfactant that inhibits bouncing of the liquiddrops on the superhydrophobic surface.

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also used for comparison. As shown in movie S5, although the dro-plets containing SDS can properly deposit on a smooth hydrophobicsurface, it is difficult to reduce the rebound on a superhydrophobicsurface, no matter how low or how high the impact speed is, evenfor highly concentrated solutions. For TSs, with the increase in con-centration, the induction period is shortened so that the low-speedimpact behavior turns to emission from bouncing, whereas it is stilleasy to partially rebound after a high-speed impact. In contrast, forAOT, the liquid droplets can deposit on the hydrophobic surface ata low concentration of 0.1% and at any superhydrophobic surfaceswith a concentration of 0.3% (movie S5).

A diagram is shown in Fig. 3 to explain how the receding splashcan be substantially depressed by AOT. Driven by the inertia, the im-pacting liquid first spreads to a maximum diameter (27). As shown inthe spreading state of the diagram, the liquid droplet experiences alarge surface deformation during the high-speed impact, and thecurved edge of the spreading drop is completely out of equilibriumwhen it reaches its maximum diameter. Then, surface tension actson the liquid to retract the flow above the substrate. For water, the

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drop would break up into multiple droplets during the receding stateand would splash in the final state (Fig. 1E). For the surfactant drops,if the surfactant molecules cannot replenish the newly created air/water interface in time, typically with high DST, then the surface ten-sion of the deformed drop could not be uniform, where nonuniformreceding behavior occurs (Fig. 3B). Examples can be found for theSDS drop (Fig. 1F), the TS drop (Fig. 1G), and the AOT drop in themicelle region (fig. S4). In contrast, if the surfactant with a lowbeginning DST can effectively saturate the newly created surface within~1.8 ms (corresponding to the spreading time) and maintain the homo-geneous low surface tension at the air/liquid/solid interface, then theliquid can uniformly deposit on the superhydrophobic surface (Fig.3C). As shown in Fig. 1H and fig. S4, a gentle and uniform recedingcontact line will be obtained similar to AOT in the vesicle region. Theseresults provide direct evidence for the role of AOT in controlling thereceding splash.

The underlying mechanism for the abovementioned transientknockdown of the receding velocity at the pinning area can be as-cribed to the wettability transition in the spreading phase. At theperipheral area of maximum spreading, the impacting water dropslides over air cushions that are trapped on or beneath the superhy-drophobic surface, and it is difficult for the water to enter the nano-structures (Fig. 3A). The upward increased capillary force induced bythe squeezed air entrapment in the nanostructures easily makes thewater drop take off the surface (28). Similar behavior is observedfor the micelle surfactant drops (Fig. 3B). The final “floating” stateof the micelle surfactant drop, the 0.1% AOT drop, indicates that mi-celle surfactant drops could not properly reverse surface wettability,which can be seen from the cryo-SEM image in fig. S5. In contrast,the reduction of surface tension induced by the vesicle surfactant leadsto the dropdown, reverses the capillary force, and makes an easier anddeeper entry of the impacting drop in the nanostructure (the side viewin spreading state in Fig. 3C). Cryo-SEM was used to prove the reverseof surface wettability during the impact, where the vesicle surfactantdrop (1% AOT drop) is trapped between the gaps of nanoneedles andfully wets the nanostructured superhydrophobic surface (fig. S5). Theoutward hydrophobic tails of the surfactants at the air/liquid interfaceact as bridges to connect the drop and the nanostructure by hydro-phobic force and to change the wettability of the superhydrophobicsurface. Through this process, the surfactant droplets can be pinnedand thus reduce the receding velocity via the wettability transition atthe peripheral area of maximum spreading. As a result, the high-speedimpacting AOT drops can firmly and quickly deposit on the super-hydrophobic surface.

The wettability transition at the central contact point is easier thanat the peripheral area because capillary forces are overcome by inertialeffects (29) at a high Weber number regime (We > 200). Both thewater drop and the surfactant drop tend to become convex in the na-nostructure of the superhydrophobic surface because of the downwardhammer pressure and the dynamic pressure (8). However, the waterrepellency of structure chemistry and the huge upward Laplace pres-sure induced by the squeezed air entrapment in the nanostructure re-bound the water drop, as shown in Fig. 1E.

AOT also manifests itself in inhibiting rebound and splash on tiltedsuperhydrophobic surfaces. Superhydrophobic surfaces with tiltedangles of 30o, 60o, and 75o are used. In the experiment, the SDS showslittle effect on the liquid deposition within the tested concentrationregion (Fig. 2A3), although it is a good choice to inhibit rebound onthe hydrophobic surface, as shown in movie S5 (15, 16, 23). The TS

Fig. 3. Schematic illustration for splash inhibition on the superhydrophobicsurface by surfactant additives. (A) The impacting water drop mainly breaks upin the receding stage after spreading to the maximum lamellar liquid. The upwardincreased capillary force induced by the squeezed air entrapment in the nanostruc-ture easily makes the water drop take off the surface. (B) For the surfactants in themicelle region, the surfactant molecules cannot replenish the newly created air/waterinterface (high DST), and the surface tension of the deformed drop is not uniform,explaining the nonuniform receding behavior. The nonuniform surface tension leadsto partial wettability transition, and several scattered fragments stick on the substrateas SDS, TSs, and AOT in the micelle region. The reduced surface tension makes theentry of the impacting drop in the nanostructure much easier because of the reverseof capillary force. (C) Because of the lowest DST and dense aggregates at the air/water interface, AOT in the vesicle region effectively saturates the newly created sur-face within a short time and maintains a homogeneous low surface tension at theair/liquid/solid interface so that it can change the surface wettability as long as thedrop contacts the surface, thus leading to hardly receding behavior and a largewetting area.

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drop shows the impact behavior from bouncing, emission, to no re-bound as the concentration increases from 0.01 to 1%, but it still re-bounds partially on the oblique superhydrophobic surface (Fig. 2B3).The percentage of liquid that bounces off the surface can be quanti-tatively measured through an analytical microbalance, and the impactprocesses of surfactant drops on the horizontal and tilted superhydro-phobic surfaces are shown in movie S3. Only AOT can suppress therebound of aqueous droplets on both horizontal and oblique surfacesat a low mass fraction of 0.3% at any inclined angles (Fig. 2C3).

Figure S1 depicts the impact behaviors of aqueous dropscontaining the AOT additive in three regions. At concentrations lowerthan the critical micelle concentration, complete bouncing occursalong with complete receding behavior. At the micelle region, partialreceding of the contact line is accompanied with partial splashing, par-tial rebound, and no rebound. Scarce receding of the contact line takes

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place only at the vesicle region, indicating that both the rebound andreceding splashes have been greatly inhibited.

CONCLUSIONIn conclusion, although we have mainly focused on a specific micro-structured/nanostructured superhydrophobic surface with varyingtilted angles to elucidate the role of the vesicle surfactant (AOT) ininhibiting the receding splash, the scarce or gentle receding behaviorcan also be generalized to apply to other artificially fabricated super-hydrophobic surfaces and other single-drop impact and spray pro-cesses at varied impact velocities (Fig. 4 and movies S6 to S9). Inaddition, AOT is shown to be a stable surfactant molecule (fig. S6).This work helps advance our understanding of how to control liquiddeposition on superhydrophobic surfaces. Therefore, this approach

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Fig. 4. The splash inhibition of vesicle AOT generalizes to other superhydrophobic surfaces. (A1 and A2) SEM images of silicon nanowire–arrayed surface from top andside views. (C1 and C2) SEM images of patterned superhydrophobic surfaces with arrayed silicon micropillars and nanowires from top and cross-sectional views. (E and G) SEMimages of the microstructured/nanostructured superhydrophobic SiO2 surface and the superhydrophobic CuO surface with nanoneedles. (B1, D1, F1, and H1) The impactingwater drop makes a big splash on superhydrophobic surfaces. (B2, D2, F2, and H2) The receding splash is greatly inhibited by 1% AOT on these superhydrophobic surfaces. Theimpact velocity of each impacting drop is 2.53 ± 0.11 m s−1.

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can potentially be used to improve the efficiency of pesticide sprayingand to reduce environmental pollution.

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MATERIALS AND METHODSSuperhydrophobic silicon nanowire structuresA silicon wafer was cleaned with acetone, ethanol, and deionized waterbefore it was immersed in 5 weight % hydrofluoric acid solution for1 min to remove the oxidation layer. Then, it was put in a mixed so-lution of 4.8 M hydrofluoric acid and 0.5 mM silver nitrate for 1 minto deposit silver seed on the substrate. It was successively immersed ina solution of 4.8 M hydrofluoric acid and 0.15 M hydrogen peroxidefor 30 min to realize metal-assisted etching of silicon, which resultedin the acquisition of silicon nanowire structures. The typical length ofthe nanowire was ~1.2 mm, and the space between nanowires wasabout 50 nm. The as-prepared silicon plate was O2 plasma–treatedat 150 W for 30 s and then put in a sealed container together witha piece of glass coated with 0.5 ml of (heptadecafluoro-1,1,2,2-tetrade-cyl)trimethoxysilane. The container was evacuated with a vacuumpump. After 3 hours at 80°C, the plate showed surface superhydro-phobicity with a contact angle of 154.5 ± 3.2°.

Microstructured/nanostructured SiO2 surfaceThe commercial glass plates were cleaned with acetone, ethanol, anddeionized water. In accordance with our previous research (30), thepolymer-particle dispensed solution was prepared by adding 1 ml ofCapstone ST-200 (DuPont Co.) solution and 1 g of hydrophobic fumedsilica nanoparticles (average particle size of 14 nm; Evonik Degussa Co.)in 5 ml of acetone and 20 ml of ethanol. The solution was mixed andstirred for 30 min in a closed bottle. Precleaned glass plates were dippedin this solution at a speed of 80 mm s−1 and pulled out from the solu-tion at a speed of 100 mm s−1. Owing to the rapid evaporation of thesolvent, the semitransparent membrane quickly transformed into awhite coating with extremely high water repellency. From an SEM ob-servation, the aggregate of SiO2 nanoparticles had random features oftypical size and spacing of around 200 nm.

Superhydrophobic CuO nanosheetsThe copper plate was first cleaned with acetone, ethanol, and purifiedwater before modification. It was then immersed in a solution of 0.15 Mammonium persulfate and 2.5 M sodium hydroxide for 20 min andsubsequently immersed in a 0.1 M perfluorodecanoic acid solution for1 hour. The prepared CuO nanosheets were about 3 to 6 mm in lengthand 200 to 600 nm in width. After the copper plate was rinsed withdistilled water and dried with N2, it showed a high water repellencywith a contact angle of 159.1 ± 1.7°.

Patterned pillar-structured silicon substrateSilicon wafers (n-type doped with phosphorus, <100>-oriented, 525 mmthick) were patterned using standard photolithography techniques. Athin layer of positive resist was spray-coated onto the silicon wafer at arotational speed of 3000 rpm, which was followed by an ultraviolet(UV) exposure process (Karl Suss MA6). Then, the UV-exposed Siwafer was immersed in the resist developer to remove the unexposedphotoresist. Subsequently, deep reactive ion etching was performed.Micropillar has a diameter of 10 mm, a space of 10 mm, and a heightof 20 mm. After the substrates were resist-stripped (Microposit Re-mover 1165), they were cleaned with ethanol and acetone beforethe chemical modification process was performed. The as-prepared

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silicon plate was O2 plasma–treated and then put in a sealed containertogether with a piece of glass coated with 0.5 ml of (heptadecafluoro-1,1,2,2-tetradecyl)trimethoxysilane for 2 hours at 80°C.

CharacterizationAnalysis of the droplet deposition on the B. oleracea L. leaf surface andsuperhydrophobic substrates was recorded with i-SPEED 3 (Olympus)high-speed cameras from the oblique view and a FASTCAM MiniUX100 (Photron) from the side view, respectively. SEM images wereobtained using a field-emission SEM at 10 kV (Hitachi S-4800). Theimages of cryogenic electron microscopy were carried out using a field-emission SEM (Hitachi S-4300) equipped with extra low–temperatureequipment at 3 kV (cryo-electron microscope, Leica). Cryo-TEMimages were obtained with FEI Tecnai Spirit BioTwin TEMs. Cryo-transfer holders were used to ensure low-temperature transfer and ob-servation of frozen hydrated specimens. Contact angles were measuredusing a contact angle measurement device (OCA 20, DataPhysics), withdroplets of 3 ml to be removed dynamically. Each reported contact anglewas an average of at least five independent measurements. The diffusionrates were determined with a Bruker AVANCE 600 NMR spectrometer.The DSTs were carried out with an automatic maximum bubble pres-sure tensiometer (Krüss BP100), which measures the behavior of a sur-factant over a wide speed range as part of a single, fully automaticmeasuring process and determines surface tension as a function of sur-face age. The measured range in the time window is from 10 ms to 10 s.The capillary diameter is 0.210 mm.

SUPPLEMENTARY MATERIALSSupplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/3/e1602188/DC1fig. S1. Scarce receding of drop-substrate contact line for the AOT drop.fig. S2. Diffusion coefficient (diffusion speed) of SDS, TSs, and AOT.fig. S3. The dynamic spread (wetting) state of contact angle as a function of time.fig. S4. Different liquid impact behaviors in the micelle and vesicle regions.fig. S5. Cryo-SEM of the final wetting state of micelle and vesicle surfactant drops.fig. S6. NMR characterization of the stability of the AOT surfactant over time.movie S1. Surfactant drop impact on the B. oleracea L. leaf.movie S2. Influence from surface morphology and impact speed.movie S3. Surfactant drop impact on microstructured/nanostructured superhydrophobicsurface with different types, with varied concentrations, and at different tilted angles.movie S4. Controlling liquid splash on superhydrophobic surfaces by a vesicle surfactant: Thecomparison of the water drop’s splashing and the 1% AOT drop’s deposition onsuperhydrophobic surfaces with a long recording time.movie S5. Surfactant drops’ impact on hydrophobic surfaces, microstructured/nanostructuredsuperhydrophobic surfaces, and nanostructured superhydrophobic surfaces at low and highspeeds.movie S6. Water spray impact on horizontal superhydrophobic surface.movie S7. Water spray impact on tilted superhydrophobic surface.movie S8. AOT (1%) spray impact on horizontal superhydrophobic surface.movie S9. AOT (1%) spray impact on tilted superhydrophobic surface.

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Acknowledgments: The high-speed imaging, artificial superhydrophobic surface fabrication,and most of the work were performed in the Key Laboratory of Bio-inspired Materials andInterfacial Science, Technical Institute of Physics and Chemistry. The DSTs of surfactant drop,1H NMR, and SEM (cryo-SEM) measurements were acquired in the Key Laboratory ofColloid and Interface Science, Institute of Chemistry. The B. oleracea L. leaf was provided byHenan Agricultural University. Cryo-TEM was performed in Tsinghua University. Funding:This work was financially funded by the National Research Fund for Fundamental Key Projects(grant 2014CB93220), the National Natural Science Foundation of China (NSFC) (grants21121001 and 91127025), and the Key Research Program of the Chinese Academy of Sciences(grant KJZD-EW-M01). This work was also supported by NSFC (grants 51473172, 51473173,51173190, and 21121001) and the “Strategic Priority Research Program” of the ChineseAcademy of Sciences (grant XDA09020000). M.S. was funded by the Fundamental Key Projects,2014CB93220, in 2014. Author contributions: L.J. and Y.W. conceived and designed theexperiments. M.S. and Z.D. performed the experiments. Z.D. fabricated artificialsuperhydrophobic surfaces. M.S., Y.W., and Z.D. analyzed the data. M.S. and Z.D. wrote theoriginal manuscript, and L.J., Z.D., and Y.W. revised it. All authors discussed the resultsand commented on the manuscript. Competing interests: The authors declare that they haveno competing interests. Data and materials availability: All data needed to evaluate theconclusions in the paper are present in the paper and/or the Supplementary Materials.Additional data related to this paper may be requested from the authors.

Submitted 9 September 2016Accepted 15 December 2016Published 1 March 201710.1126/sciadv.1602188

Citation: M. Song, J. Ju, S. Luo, Y. Han, Z. Dong, Y. Wang, Z. Gu, L. Zhang, R. Hao, L. Jiang,Controlling liquid splash on superhydrophobic surfaces by a vesicle surfactant. Sci. Adv. 3,e1602188 (2017).

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Controlling liquid splash on superhydrophobic surfaces by a vesicle surfactantMeirong Song, Jie Ju, Siqi Luo, Yuchun Han, Zhichao Dong, Yilin Wang, Zhen Gu, Lingjuan Zhang, Ruiran Hao and Lei Jiang

DOI: 10.1126/sciadv.1602188 (3), e1602188.3Sci Adv 

ARTICLE TOOLS http://advances.sciencemag.org/content/3/3/e1602188

MATERIALSSUPPLEMENTARY http://advances.sciencemag.org/content/suppl/2017/02/28/3.3.e1602188.DC1

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