The wetting properties of solid substrates with customary (i.e., macroscopic) random roughness are considered as a function of the microscopic contact angle of the wetting liquid and its partial pressure in the surrounding gas phase. Analytic expressions are derived which allow for any given lateral correlation function and height distribution of the roughness to calculate the wetting phase diagram, the adsorption isotherms, and to locate the percolation transition in the adsorbed liquid film. Most features turn out to depend only on a few key parameters of the roughness, which can be clearly identified. It is shown that a first order transition in the adsorbed film thickness, which we term 'Wenzel prewetting', occurs generically on typical roughness topographies, but is absent on purely Gaussian roughness. It is thereby shown that even subtle deviations from Gaussian roughness characteristics may be essential for correctly predicting even qualitative aspects of wetting.
We analyze theoretically complete wetting of a substrate supporting an array of parallel, vertical plates which can tilt elastically. The adsorbed liquid tilts the plates, inducing clustering, and thus modifies the substrate geometry. In turn, this change in geometry alters the wetting properties of the substrate and, consequently, the adsorption of liquid. This geometry-wetting feedback loop leads to stepped adsorption isotherms with each step corresponding to an abrupt change in the substrate geometry. We discuss how this can be used for constructing substrates with tunable wetting and adsor…
We study the problem of fluid adsorption at a non-planar wall with a view to understanding the influence of surface roughness on the wetting transition. Starting from an appropriate Landau-type free energy functional we develop a linear response theory relating the free energy of the non-planar system to the correlation functions in its planar counterpart. We generalize the well known graphical construction method used to study the planar surface phase diagram and derive analytical expressions for the shift in the phase boundary for first and second-order wetting transitions. Of particular int…
In thermal equilibrium, a colloidal particle between two parallel plates immersed in a fluid which partially wets both the particle and the plates, is attracted by the walls. However, if the particle moves parallel to the plates, a hydrodynamic lift force away from the plates arises in the limit of low Reynolds number. We study theoretically the competition of these two effects and identify the range of velocity in which the velocity may serve as a parameter controlling the adsorption in microflows.
Molecular dynamics simulations are used to study the behavior of closely-fitting spherical and ellipsoidal particles moving through a fluid-filled cylinder at nanometer scales. The particle, the cylinder wall and the fluid solvent are all treated as atomic systems, and special attention is given to the effects of varying the wetting properties of the fluid. Although the modification of the solid-fluid interaction leads to significant changes in the microstructure of the fluid, its transport properties are found to be the same as in bulk. Independently of the shape and relative size of the part…
The excess adsorption $Γ$ in two-dimensional Ising strips $(\infty \times L)$ subject to identical boundary fields, at both one-dimensional surfaces decaying in the orthogonal direction $j$ as $-h_1j^{-p}$, is studied for various values of $p$ and along various thermodynamic paths below the critical point by means of the density-matrix renormalization-group method. The crossover behavior between the complete wetting and critical adsorption regimes, occurring in semi-infinite systems, are strongly influenced by confinement effects. Along isotherms $T=const$ the asymptotic power law dependences …
The results of Monte Carlo simulation of adsorption and wetting behaviour of a highly non-additive symmetric mixture at selective walls is discussed. We have concentrated on the interplay between the surface induced demixing in the adsorbed films and the properties of the bulk mixture, which exhibits a closed immiscibility loop. It has been shown that the wetting behaviour depends on the absolute values of the parameters determining the strengths of interaction between the mixture components and the surface, as well as on their difference. In general, an increase of the difference between the …
Using molecular dynamics simulations, we study the motion of a closely fitting nanometer-size solid sphere in a fluid-filled cylindrical nanochannel at low Reynolds numbers and for a wide range of fluid-solid interactions corresponding to different wetting situations. For fluids that are not completely wetting we observe an interesting and novel adsorption phenomenon, in which the solid sphere, that was initially moving along the center of the tube, meanders across the channel and suddenly adsorbes onto the wall. Thereafter, the adsorbed sphere either {\it sticks} to the wall and remains motio…
We consider fluid wetting on a corrugated substrate using effective interfacial Hamiltonian theory and show that breaking the translational invariance along the wall can induce an 'unbending' phase transition in addition to unbinding. Both first order and second order unbending transitions can occur at and out of coexistence. Results for systems with short-ranged and long-ranged forces establish that the unbending critical point is characterised by hyperuniversal scaling behaviour. We show that, at bulk coexistence, the adsorption at the unbending critical point is a universal multiple of the …
Adsorption of small amphiphilic molecules occurs in various biological and technological processes, sometimes desired, the other times unwanted (e.g., contamination). Surface-active molecules preferentially bind to interfaces and affect their wetting properties. We study the adsorption of short-chained alcohols (simple surfactants) to the water-vapor interface and solid surfaces of various polarities using molecular dynamics simulations. The analysis enables us to establish a theoretical expression for the adsorption coefficient, which exponentially scales with the molecular surface area and t…
Any solid surface is intrinsically rough on the microscopic scale. In this paper, we study the effect of this roughness on the wetting properties of hydrophilic substrates. Macroscopic arguments, such as those leading to the well-known Wenzel's law, predict that surface roughness should \emph{amplify} the wetting properties of such adsorbents. We use a fundamental measure density functional theory (DFT) to demonstrate the opposite effect from roughness for microscopically corrugated surfaces, i.e., wetting is \emph{hindered}. Based on three independent analyses we show that microscopic surface…
We investigate theoretically the possibility of a wetting transition induced by geometric roughness of a solid substrate for the case where the flat substrate does not show a wetting layer. Our approach makes use of a novel closed-form expression which relates the interaction between two sinusoidally modulated interfaces to the interaction between two flat interfaces. Within the harmonic approximation, we find that roughness-induced wetting is indeed possible if the substrate roughness, quantified by the substrate surface area, exceeds a certain threshold. In addition, the molecular interactio…
The wetting properties of solid substrates with macroscopic random roughness are considered as a function of the microscopic contact angle of the wetting liquid and its partial pressure in the surrounding gas phase. It is shown that Wenzel prewetting, which has been recently predicted for a rather wide class of roughness profiles derived from Gaussian random processes by a general distortion procedure, should in fact be ubiquitous and prevail under even much milder conditions. The well-known transition occurring at Wenzel's angle is accompanied by a prewetting transition, at which a jump in th…
Replica and functional renormalization group methods show that, with short range substrate forces or in strong fluctuation regimes, wetting of a self-affine rough wall in 2D turns first-order as soon as the wall roughness exponent exceeds the anisotropy index of bulk interface fluctuations. Different thresholds apply with long range forces in mean field regimes. For bond-disordered bulk, fixed point stability suggests similar results, which ultimately rely on basic properties of quantum bound states with asymptotically power-law repulsive potentials.
Although realizing wetting transitions of droplets spontaneously on solid rough surfaces is quite challenging, it is becoming a key research topic in many practical applications which require highly efficient removal of liquid. We report wetting transitions of condensed droplets occurring spontaneously on pillared surfaces with two-tier roughness owing to excellent superhydrophobicity. The phenomenon results from further decreased Laplace pressure on the top side of the individual droplet when its size becomes comparable to the scale of the micropillars, which leads to a surprising robust spon…
We have carried out extensive equilibrium molecular dynamics (MD) simulations to study the structure and the interfacial properties in the liquid-vapor (LV) phase coexistence of partially miscible binary Lennard-Jones (LJ) mixtures. By analyzing the structural properties as a function of the miscibility parameter, $ α$, we found that at relatively low temperatures the system separates forming a liquid A-liquid B interface in coexistence with the vapor phase. At higher temperatures and, $ 0<α\leq 0.5 $, we found a temperature range, $T^{*}_{w}(α) \leq T^{*} < T^{*}_{cons}(α)$, where the liquid …
We study the interfacial phenomenology of a fluid in contact with a microstructured substrate within the mean-field approximation. The sculpted substrate is a one-dimensional array of infinitely long grooves of sinusoidal section of periodicity length L and amplitude A. The system is modelled using the Landau-Ginzburg functional, with fluid-substrate couplings which correspond to either first-order or critical wetting for a flat substrate. We investigate the effect of the roughness of the substrate in the interfacial phenomenology, paying special attention to filling and wetting phenomena, and…
Understanding the critical condition and mechanism of the droplet wetting transition between Cassie-Baxter state and Wenzel state triggered by an external electric field is of considerable importance because of its numerous applications in industry and engineering. However, such a wetting transition on a patterned surface is still not fully understood, e.g., the effects of electro-wetting number, geometry of the patterned surfaces, and droplet volume on the transition have not been systematically investigated. In this paper, we propose a theoretical model for the Cassie-Baxter- Wenzel wetting …
We discuss how the wettability and roughness of a solid impacts its hydrodynamic properties. We see in particular that hydrophobic slippage can be dramatically affected by the presence of roughness. Owing to the development of refined methods for setting very well-controlled micro- or nanotextures on a solid, these effects are being exploited to induce novel hydrodynamic properties, such as giant interfacial slip, superfluidity, mixing, and low hydrodynamic drag, that could not be achieved without roughness.
Hypothesis: As a fluid approaches three phase coexistence, adsorption may take place by the successive formation of two intervening wetting films. The equilibrium thickness of these wetting layers is the result of a delicate balance of intermolecular forces, as dictated by an underlying interface potential. The van der Waals forces for the two variable adsorption layers may be formulated exactly from Dzyaloshinskii-Lifshitz-Pitaevskii theory, and analytical approximations may be derived that extent well beyond the validity of conventional Hamaker theory. Calculations: We consider the adsorptio…
This paper is an expanded edition of the rapid communication published several years ago by the author (Phys. Rev. B, v76, 041402(R), 2007) on the simulation of wetting transition of water on graphite, aiming to provide more details on the methodology, parameters, and results of the study which might be of interest to certain readers. We calculate adsorption isotherms of water on graphite using grand canonical Monte Carlo simulations combined with multiple histogram reweighting, based on the empirical potentials of SPC/E for water, the 10-4-3 van der Waals model, and a recently developed induc…
In this two-part study we investigate the phase behaviour of a fluid spatially confined in a semi-infinite rectangular pore formed by three orthogonal walls and connected to a reservoir maintaining constant values of pressure and temperature in the fluid. Far from the capping wall this prototypical two-dimensional system reduces to a one-dimensional slit pore. However, the broken translational symmetry leads to a wetting behavior strikingly different from that of a slit pore. Using a realistic model of an atomic fluid with long-ranged Lennard-Jones fluid-fluid and fluid-substrate interactions,…
We study the adsorption of simple fluids at smoothly structured, completely wet, walls and show that a meniscus osculation transition occurs when the Laplace and geometrical radii of curvature of locally parabolic regions coincide. Macroscopically, the osculation transition is of fractional, $7/2$, order and separates regimes in which the adsorption is microscopic, containing only a thin wetting layer, and mesoscopic, in which a meniscus exists. We develop a scaling theory for the rounding of the transition due to thin wetting layers and derive critical exponent relations that determine how th…
Using fundamental-measure density functional theory we investigate entropic wetting in an asymmetric binary mixture of hard spheres with positive non-additivity. We consider a general planar hard wall, where preferential adsorption is induced by a difference in closest approach of the different species and the wall. Close to bulk fluid-fluid coexistence the phase rich in the minority component adsorbs either through a series of first-order layering transitions, where an increasing number of liquid layers adsorbs sequentially, or via a critical wetting transition, where a thick film grows conti…
Liquid wetting of a surface is omnipresent in nature and the advance of micro-fabrication and assembly techniques in recent years offers increasing ability to control this phenomenon. Here, we identify how surface roughness influences the initial dynamic spreading of a partially wetting droplet by studying the spreading on a solid substrate patterned with microstructures just a few micrometers in size. We reveal that the roughness influence can be quantified in terms of a line friction coefficient for the energy dissipation rate at the contact line, and that this can be described in a simple f…
We calculate the ion and composition distributions around colloid particles in an aqueous mixture, accounting for preferential adsorption, electrostatic interaction, selective solvation among ions and polar molecules, and composition-dependent ionization. On the colloid surface, we predict a precipitation transition induced by strong preference of hydrophilic ions to water and a prewetting transition between weak and strong adsorption and ionization. These transition lines extend far from the solvent coexistence curve in the plane of the interaction parameter χ(or the temperature) and the aver…
The disjoining pressure isotherm in foam films is theoretically studied and an important contribution of adsorption is discovered. On the basis of the interfacial thermodynamics an adsorption disjoining pressure component is derived, which is repulsive and exponentially decaying by the film thickness. Expressions for its magnitude and decay length are derived in terms of well-known thermodynamic characteristics such as the partial Gibbs elasticity and adsorption length. Several adsorption isotherms are considered and the corresponding adsorption disjoining pressure components are calculated. A…
We introduce a new numerical technique, namely triangular tessellation, to calculate the free energy associated with the adsorption of a colloidal particle at a flat interface. The theory and numerical scheme presented here are sufficiently general to handle non-convex patchy colloids with arbitrary surface patterns characterized by a wetting angle, e.g., amphiphilicity. We ignore interfacial deformation due to capillary, electrostatic, or gravitational forces, but the method can be extended to take such effects into account. It is verified that the numerical method presented is accurate and s…
Within the Landau-Ginzburg-Wilson approach we derive the effective Hamiltonian governing fluctuations of an interface between two phases, one of them adsorbed on a disclike substrate. For large disc radii and for temperatures close to the wetting temperature of the corresponding planar substrate the expressions for the hight-hight correlation function and the accompanying correlation angle are derived. Their dependence on the disc radius and the reduced temperature is discussed and the relevant scaling regimes are identified.
Adsorption properties of chain fluids are of interest from both fundamental and industrial points of view. Density Functional Theory (DFT) based models are among the most appropriate techniques allowing to describe surface phenomena. At the same time Statistical Associating Fluid Theory (SAFT) successfully describes bulk PVT properties of chain-fluids. In this publication we have developed novel version of SAFT-DFT approach entitled RS-SAFT which is capable to describe adsorption of short hydrocarbons on geometrically rough surface. Major advantage of our theory is application to adsorption on…
The relation between the contact angle of a liquid drop and the morphological parameters of self-affine solid surfaces have been investigated. We show experimentally that the wetting property of a solid surface crucially depends on the surface morphological parameters such as: (1) root mean square (rms) roughness $σ$, (2) in-plane roughness correlation length $ξ$ and (3) roughness exponent $α$ of the self-affine surface. We have shown that the contact angle monotonically decreases with the increase in the rms local surface slope $ρ$ ($\propto σ/ξ^α$) for the cases where the liquid wets the cre…
The dynamics of the triple gas-liquid-solid contact line is analysed for the case where the gas is the saturated vapour corresponding to the liquid, like in the vapour bubble in boiling. It is shown that even small superheating (with respect to the saturation temperature) causes evaporation of the adsorption liquid film and the true triple contact is established. It is shown that the hydrodynamic contact line singularity cannot be relaxed with the Navier slip condition under such circumstances. Augmented with the second derivative slip condition is proposed to be applied. For the partial wetti…
Previous treatments of three-dimensional (3D) short-ranged wetting transitions have missed an entropic or low temperature Casimir contribution to the binding potential describing the interaction between the unbinding interface and wall. This we determine by exactly deriving the interfacial model for 3D wetting from a more microscopic Landau-Ginzburg-Wilson Hamiltonian. The Casimir term changes the interpretation of fluctuation effects occurring at wetting transitions so that, for example, mean-field predictions are no longer obtained when interfacial fluctuations are ignored. While the Casimir…
Contact angle hysteresis and generation of dynamics angle are two fundamental phenomena about the contact angle deviation from the equilibrium state. Roughness on the solid surface, disjoining pressure in the thin film, and liquid-solid adhesion have all been considered as the origins of the phenomena. This work for the first time made a reduction to absurdity by employing absolutely smooth solid surfaces in ultra-large-scale molecular dynamic simulation. The results showed that the equilibrium angles were well established on the absolutely smooth surface just as regular, while the hysteresis …
The hydrodynamic slippage at a solid-liquid interface is currently at the center of our understanding of fluid mechanics. For hundreds of years this science has relied upon no-slip boundary conditions at the solid-liquid interface that has been applied successfully to model many macroscopic experiments, and the state of this interface has played a minor role in determining the flow. However, the problem is not that simple and has been revisited recently. Due to the change in the properties of the interface, such as wettability and roughness, this classical boundary condition could be violated,…
A microscopic density functional theory is used to investigate the adsorption of short chains on attractive solid surfaces. We analyze the structure of the adsorbed fluid and investigate how the wetting transition changes with the change of the chain length and with relative strength of the fluid-solid interaction. End segments adsorb preferentially in the first adsorbed layer whereas the concentration of the middle segments is enhanced in the second layer. We observe that the wetting temperature rescaled by the bulk critical temperature decreases with an increase of the chain length. For long…
When placed on rough hydrophobic surfaces, water droplets of diameter larger than a few millimeters can easily form pearls, as they are in the Cassie-Baxter state with air pockets trapped underneath the droplet. Intriguingly, a natural evaporating process can drive such a Fakir drop into a completely wetting (Wenzel) state. Our microscopic observations with simultaneous side and bottom views of evaporating droplets upon transparent hydrophobic microstructures elucidate the water-filling dynamics and the mechanism of this evaporation-triggered transition. For the present material the wetting tr…
A mean-field theory is presented which describes the basic observations of recent experiments revealing rich wetting behaviour of n-alkane/methanol mixtures at the liquid-vapour interface. The theory, qualitative and in part heuristic, is based on a microscopic lattice-gas model from which a Cahn-Landau approach is distilled. Besides the physics associated with the short-range components of the intermolecular interactions, effects of the long-range tails of the net van der Waals forces between interfaces are also taken into account. Including weak long-range forces which favour wetting in the …
A liquid droplet impacting on a solvophobic surface normally rebounds. The rebound is suppressed by a small amount of dissolved polymer. In this work, using multi-body dissipative particle dynamics simulations, two anti-rebound mechanisms, the slow-retraction and the slow-hopping mechanisms, are identified. Which of them dominates depends on the polymer-surface attraction strength. However, these two mechanisms are not excluding each other but may coexist. During the droplet rebound, the surface-adsorbed polymer acts in two ways: the adsorbed beads mediate solvent-surface interactions, and hig…
Wetting is often perceived as an intrinsic surface property of materials, but determining its evolution is complicated by its complex dependence on roughness across the scales. The Wenzel state, where liquids have intimate contact with the rough substrate, and the Cassie-Baxter state, where liquids sit onto air pockets formed between asperities, are only two states among the plethora of wetting behaviors. Furthermore, transitions from the Cassie-Baxter to the Wenzel state dictate completely different surface performance, such as anti-contamination, anti-icing, drag reduction etc.; however, lit…
Under partial wetting conditions, making a substrate uniformly rougher enhances the wetting characteristics of the corresponding smooth substrate {--} hydrophilic systems become even more hydrophilic and hydrophobic systems even more hydrophobic. Here we show that spatial texturing of the roughness may lead to spontaneous propulsion of droplets. Individual droplets are driven toward regions of maximal roughness for intrinsically hydrophilic systems and toward regions of minimal roughness for intrinsically hydrophobic systems. Spatial texturing can be achieved by wrinkling the substrate with si…
The surface phase behavior of binary mixtures of colloidal hard rods in contact with a solid substrate (hard wall) is studied, with special emphasis on the region of the phase diagram that includes the smectic A phase. The colloidal rods are modelled as hard cylinders of the same diameter and different lengths, in the approximation of perfect alignment. A fundamental--measure density functional is used to obtain equilibrium density profiles and thermodynamic properties such as surface tensions and adsorption coefficients. The bulk phase diagram exhibits nematic-smectic and smectic-smectic demi…
The wetting behaviour of surfaces is important for various applications like super-hydrophobic surfaces, enhanced oil recovery, mining of metal ores and anti-icing surfaces etc. For rough surfaces, which are the rule rather than the exception, designing textured surfaces that have wetting properties tailored to suit these applications generally involves either bio-mimicry or trial and error. Existing wetting theories such as the well-known Wenzel (1936) and Cassie & Baxter (1944) models do not predict wetting regimes and importantly, only give a single equilibrium angle rather than a range of …
In this contribution we study wetting and nucleation of vapor bubbles on nanodecorated surfaces via free energy molecular dynamics simulations. The results shed light on the stability of superhydrophobicity in submerged surfaces with nanoscale corrugations. The re-entrant geometry of the cavities under investigation is capable of sustaining a confined vapor phase within the surface roughness (Cassie state) both for hydrophobic and hydrophilic combinations of liquid and solid. The atomistic system is of nanometric size; on this scale thermally activated events can play an important role ultimat…
The wetting of a charged wedge-like wall by an electrolyte solution is investigated by means of classical density functional theory. As in other studies on wedge wetting, this geometry is considered as the most simple deviation from a planar substrate, and it serves as a first step towards more complex confinements of fluids. By focusing on fluids containing ions and surface charges, features of real systems are covered which are not accessible within the vast majority of previous theoretical studies concentrating on simple fluids in contact with uncharged wedges. In particular, the filling tr…
We analyze the interplay between wetting and anchoring of nematic liquid crystals on disordering, e.g., rough substrates in the framework of the Landau-de Gennes theory, in situations of competing homeotropic and planar easy axes on the substrate and the nematic-isotropic (NI) interface. The phase diagram for azimuthally symmetric substrates is calculated. We identify two regimes - a strongly coupled regime, where the wetting transition coincides with an anchoring transition, and a weakly coupled regime, where the two are separated. The anchoring transition is first order and switches between …
Plants are protected from the elements by a complex hierarchical epicuticular wax layer which has inspired the creation of super-hydrophobic and self-cleaning surfaces. Although many studies have been conducted on different plant wax systems to determine the mechanisms of water repulsion hardly any have studied the recovery of the epicuticular wax layer. In the current study the wetting properties and crystallographic nature of the wax surface of Brassica oleracea var. Italica (broccoli) has been studied, as well as the time-dependent recovery of the surface after mechanical damage. It was fou…
The adsorption of a single ideal polymer chain on energetically heterogeneous and rough surfaces is investigated using a variational procedure introduced by Garel and Orland (Phys. Rev. B 55 (1997), 226). The mean polymer size is calculated perpendicular and parallel to the surface and is compared to the Gaussian conformation and to the results for polymers at flat and energetically homogeneous surfaces. The disorder-induced enhancement of adsorption is confirmed and is shown to be much more significant for a heterogeneous interaction strength than for spatial roughness. This difference also a…
Hypothesis Emerging energy-related technologies deal with multiscale hierarchical structures, intricate surface morphology, non-axisymmetric interfaces, and complex contact lines where wetting is difficult to quantify with classical methods. We hypothesis that a universal description of wetting on multiscale surfaces can be developed by using integral geometry coupled to thermodynamic laws. The proposed approach separates the different hierarchy levels of physical description from the thermodynamic description, allowing for a universal description of wetting on multiscale surfaces. Theory and …
Using grand canonical Monte Carlo simulations, we have explored the phenomenon of capillary condensation (CC) of Ar at the triple temperature inside infinitely long, cylindrical pores. Pores of radius R= 1 nm, 1.7 nm and 2.5 nm have been investigated, using a gas-surface interaction potential parameterized by the well-depth D of the gas on a planar surface made of the same material as that comprising the porous host. For strongly attractive situations, i.e., large D, one or more (depending on R) Ar layers adsorb successively before liquid fills the pore. For very small values of D, in contrast…
Wetting and drying of a rigid substrate by a Lennard-Jones fluid in molecular dynamics simulations is reported. The size of the substrate particles, being smaller than the fluid particles in former simulations, is now taken to be equal to, respectively larger than, that of the fluid particles. Recently, for the latter type of system a first order drying transition has been reported. Like before we find a continuous-like transition for all systems considered. This also holds for substrates with incompletely-filled top layers, the so-called molecularly rough surfaces. All systems studied behave …
The ability to control wettability is important for a wide range of technological applications in which precise microfluidic handling is required. It is known that predesigned roughness at a micro- or nano- scale enhances the wetting properties of solid materials giving rise to super-hydrophobic or super-hydrophilic behavior. In this work, we study the dependence of the apparent wettability of a stripe-patterned solid surface on the stripe geometry, utilizing systems level analysis and mesoscopic Lattice-Boltzmann (LB) simulations. Through the computation of both stable and unstable states we …
We investigate critical wetting transitions for fluids adsorbed in wedge-like geometries where the substrate height varies as a power-law, $z(x,y) \sim |x| ^γ$, in one direction. As $γ$ is increased from 0 to 1, the substrate shape is smoothly changed from a planar-wall to a linear wedge. The continuous wetting and filling transitions pertinent to these limiting geometries are known to have distinct phase boundaries and critical singularities. We predict that the intermediate critical wetting behaviour occurring for $0<γ< 1$ falls into one of {\it{three}} possible regimes depending on the valu…
In this work, we studied the wetting behavior of impinged and stagnant supercooled water nanodroplet at the atomistic scale using molecular dynamics simulations. We show that water droplet represents a retraction behavior from surface groove nanostructure after indicating maximum penetration. There is a threshold for the value of impinging velocity, v*, below which penetration is not observed which depends on size of the surface roughness. This indicates grooves smaller than a certain size can stop water from penetration, considering v~0.5M in practical situations, which is such a useful infor…
