Search

The lateral motion of a droplet after its impact on groove-patterned superhydrophobic surfaces is numerically studied in the present work. Different from previous studies, the wettability gradient is not required to produce lateral motions. Instead, a substrate with two halves decorated with same Cassie area fractions but different length ratios is used and four different motions can be observed by varying the impact velocity. The asymmetrical penetration into the grooves of the substrate is found to be the main reason for triggering the different motions. The penetrated liquid could bring upward momentum to lift the droplet from one side of the substrate, or it could block the retracting contact line from one side. As a result, different oblique motion components are generated and added to the vertical rebound motion, finally leading to the different lateral motions. Our simulation findings provide a fresh idea for the control of droplet motion by coating the solid surfaces.

Droplet impact on pillar-arrayed polydimethylsiloxane (PDMS) surfaces with different solid fractions was studied. The lower and upper limits of Weber number, We, for complete rebound of impacting droplets decreased with decreasing solid fractions. Gaps were visible during the spreading and retraction processes of bouncing droplets on the surface with a solid fraction of 0.06 while no gaps were observed during the retraction process when We was greater than its upper limit, indicating that there existed a transition from the Cassie-Baxter wetting state to the Wenzel wetting state. Therefore, a novel model accounting for the penetration of a liquid into the cavities between the pillars was developed to predict the upper limit of the impact velocity of bouncing droplets. At high We, partial rebound was observed for surfaces with solid fractions of 0.50 and 0.20 while a sticky state was observed for the surface with a solid fraction of 0.06. Moreover, surface roughness has a great influence on the contact time of bouncing droplets. Besides, the maximum spreading parameter was found to follow a scaling law of We1/4.

A drop of rain falling on a surface, such as the car’s window or the palm of your hand, tends to spread over the surface and even hang onto it. But there are materials, such as the leaf of the lotus flower, from which a drop of water will roll down to the ground as an almost perfect sphere, while cleaning the material of dust particles and other pollutions. In this article, we will investigate what influences the tendency of different materials to be wetted to different extents, and how can we design and produce such materials in the lab.

We analyse the near-rolling motion of nonwetting droplets down a gently inclined plane. Inspired by the scaling analysis of Mahadevan & Pomeau (Phys. Fluids, vol. 11, 1999, pp. 2449), we focus upon the limit of small Bond numbers, where the drop shape is nearly spherical and the internal flow is approximately a rigid-body rotation except close to the flat spot at the base of the drop. In that region, where the fluid interface appears flat, we obtain an analytical approximation for the flow field. By evaluating the dissipation associated with that flow we obtain a closed-form approximation for the drop speed. This approximation reveals that the missing prefactor in the Mahadevan–Pomeau scaling law is (3π/16)p 3/2 ≈ 0.72 — in good agreement with experiments. An unexpected feature of the flow field is that it happens to satisfy the no-slip and shear-free conditions simultaneously over both the solid flat spot and the mobile fluid interface in its vicinity. Furthermore, we show that close to the near-circular contact line the velocity field lies primarily in the plane locally normal to the contact line; it is analogous there to the local solution in the comparable problem of a two-dimensional rolling drop. This analogy breaks down near the two points where the contact line propagates parallel to itself, the local flow being there genuinely three dimensional. These observations illuminate a unique ‘peeling’ mechanism by which a rolling droplet avoids the familiar non-integrable stress singularity at a moving contact line.

Joint probability methods for characterizing storm surge hazards involve the use of a collection of hydrodynamic storm simulations to fit a response surface function describing the relationship between storm surge and storm parameters. However, in areas with a sufficiently low probability of flooding, few storms in the simulated storm suite may produce surge, resulting in a paucity of information for training the response surface fit. Previous approaches have replaced surge elevations for non-wetting storms with a constant value or truncated them from the response surface fitting procedure altogether. The former induces bias in predicted estimates of surge from wetting storms, and the latter can cause the model to be non-identifiable. This study compares these approaches and improves upon current methodology by introducing the concept of &ldquo, pseudo-surge,&rdquo, with the intent to describe how close a storm comes to producing surge at a given location. Optimal pseudo-surge values are those which produce the greatest improvement to storm surge predictions when they are used to train a response surface. We identify these values for a storm suite used to characterize surge hazard in coastal Louisiana and compare their performance to the two other methods for adjusting training data. Pseudo-surge shows potential for improving hazard characterization, particularly at locations where less than half of training storms produce surge. We also find that the three methods show only small differences in locations where more than half of training storms wet.

The hysteresis in two phase relative permeability occurs when the saturation history of the flow changes from drainage to imbibition or vice versa. The imbibition relative permeability is a strong function of initial non-wetting phase saturation from which the imbibition process starts. Hence, it is very time-consuming to conduct many experiments for measuring all possible imbibition relative permeability (kr) data. An alternative approach is to predict the imbibition relative permeability using the measured Land trapping coefficient and primary drainage relative permeability. Some predictive models, found in the literature, such as that of Land, Carlson and Killough are available in commercial simulators. For prediction of imbibition data, these models require the primary drainage kr data and one set of imbibition kr data to calculate the corrected Land trapping coefficient. However, the imbibition relative permeability is not always available and the inappropriate use of these models can introduce significant errors in the calculations. In this study, the limitations of the available models are discussed and a modified method is suggested, which only requires the primary drainage kr data and the measured Land trapping coefficient. The available models for prediction of imbibition kr data are based on the calculations of trapped non-wetting saturation ( S n w t ). Therefore, in this study, a modified method was introduced which improved the estimations of trapped non-wetting phase saturation. The predicted values of imbibition relative permeability using this improved method were in good agreement with the experimental data. It was shown that this method can be used for both gas and oil as non-wetting phases in a water-wet medium. However, the trapped non-wetting phase is a function of capillary number and the Land trapping coefficient changes as the capillary number changes. Hence, the measured Land trapping coefficient cannot be assumed as constant in cases where severe changes in pressure result in changing interfacial tension (IFT) and fluid viscosity.

This paper presents biological nano-scaffolds (BNS)-assisted formation of non-wetting polymeric surfaces with excellent antibiofouling performance. Particularly, Tobacco mosaic virus (TMV)-templated metallic nanoscaffolds, self-assembled on Au substrates followed by a simple spin-and-dry coating of a fluorinated polymer solution, provide complex micro/nanoscale structured surfaces with non-wetting properties. The BNS-based superhydrophobic surfaces demonstrated significantly enhanced water-repellent properties compared to a planar/non-structured counterpart, 1) showing no sign of solid-liquid attraction (contact angle: ~180o) with DI water, and 2) achieving complete and repeated droplet bouncing without surface pinning events. More significantly, in a static 48-hour biofilm growth experiment, the BNS-based superhydrophobic surfaces resulted in a 6-fold reduction in adherent biofilm compared to their planar counterparts, most likely attributed to the extreme non-adherent property combined with complex surface morphology. Combined results provide a simple and powerful method for achieving the robust non-wetting/anti-biofouling surfaces needed in a broad range of applications.

In the present study, the spontaneous uptake of droplets into non-wetting capillaries was simulated by using many-body dissipative particle dynamics. The simulated results show that the droplets undergo a spontaneous uptake even for a non-wetting capillary. In contrast to the liquid in a reservoir in which the direction of liquid spontaneous movement in the capillary depends on the wettability, the moving direction of droplets in the capillary relies not only on the surface wettability but also the radius of the droplets. We give an explanation from the viewpoint of force balance. Our results demonstrate that capillary force could be used to drive liquid in microfluidics.

In the present work the results of experimental studies of relaxation of non-wetting liquid captured by the system of nanopores of Fluka 100 C8+C1 medium are presented. New data on dependence of filling degree on time in the process of outflow at partial initial filling have been obtained. In all the experiments carried out, fluid outflow was carried out in two stages: in the first stage of fast relaxation the characteristic time of outflow is a few seconds, in the second stage of slow relaxation the characteristic time can reach 104 seconds. It was found that “fast” states exist at any initial filling, and the degree of these states increases both with increasing temperature and with increasing initial filling of nanoporous medium with non-wetting liquid.

In the present paper we present the results of experimental and theoretical studies of intrusion-extrusion and relaxation of non-wetting liquid in three Fluka porous media. New data on hysteresis of intrusion-extrusion and dependence of the degree of filling of a porous body on time in the process of extrusion were obtained experimentally. It has been established that in all the conducted experiments the liquid extrusion took place in two stages: at the first stage of fast relaxation the characteristic time of outflow is several seconds, at the second stage of slow relaxation the characteristic time is several hundred seconds. The experimental data obtained are described in the theoretical model [1]. For the studied porous media, the existence at the initial moment of time of local states with short leakage times (a few seconds or less) and states with large leakage times (hundreds of seconds) was established. Porous bodies in which the coexistence of fast and slow states at the initial moment of time is established are investigated for the first time.

In this work critical constant filling pressure conditions for systems “nanoporous medium - non-wetting liquid” under impact were studied. To determine the conditions influencing on the occurrence of a constant filling pressure, a series of impact experiments have been carried out on four porous media with distilled water as non-wetting liquid. On the basis of the obtained experimental data for the systems under investigation, a method for determining the flow rate of liquid in the pores was developed and its values for the systems under investigation in a given range of impact energies were determined. It is shown that the liquid flow rate in the pores is one of the key parameters determining the presence of a constant critical filling pressure. It was also found that in the investigated energy range the liquid flow rate increases and goes to limit with increasing impact energy.

To understand the thermodynamics, transport and physical phenomena in porous media today, the most effective way is to use various models of porous media and conduct numerical experiments on their basis. It has been shown that such models are an effective tool for research of transport processes from the local scale at the level of individual pores to the level of individual granules. The approach proposed in this paper is based on numerical calculations based on known theoretical approaches. The principal difference from the previously used approaches and novelty lies in the absence of simplifications associated with the narrowing of the distribution of pores in size and the number of nearest neighbors, which allows us to take into account in detail the possible geometric configurations, when the pore of the same radius can be surrounded by a different number of neighboring pores. In addition, the use of numerical modelling allows us to obtain a large number of different parameters, ranging from structural characteristics (the number of nearest neighbors, connectivity, etc.), cluster (percolation thresholds) and ending with volume dependencies on pressure and time and the visualization of filling processes.

It is known that for the most nanoporous medium - non-wetting liquid systems are observed non-outflow phenomenon. It is shown that this phenomenon may depend on many factors, one of which is a waiting time. The observed anomalously slow relaxation (non-wetting liquid outflow) caused by formation of strongly interacting states of liquid clusters in pores. Previously was shown that relaxation of such states can occur due to relaxation of metastable local configurations of filled and empty pores. In the present work the relaxation of non-wetting liquid (water) dispersed in disordered nanoporous medium (hydrophobic silica gel Libersorb 23) for 6 and 9° C is considered. The pore size distribution functions of captured liquid for 9° C are obtained. Some local configurations for 6 and 9° C are analyzed and their lifetimes are defined.

Non wettable surfaces have attracted attention for their promising potential in anti-fouling and self-cleaning applications. However, the complex fabrication and loss of super-hydrophobicity because of poor durability have restricted their commercial applications. To address these issues, a robust super-hydrophobic surface was fabricated through construction of a coral-reef like fibrous structure, followed by adhesive-assisted dip coating. Wrinkled fibrous nano silica (WFNS) was synthesized using the Winsor III system. WFNS having hierarchal surface and enhanced surface area was modified by salinizing agent and by coated on various substrates. This fibrous structure aids to minimize the water/solid interface resulted to achieve the super-hydrophobic surface with a water contact angle of 167°. To impart mechanical and chemical robustness, an adhesive-assisted approach was used. The as-prepared surface maintained a remarkable super-hydrophobicity even after mechanical and chemical stresses. The prepared super-hydrophobic surface illustrated excellent anti-fouling performance against corrosive liquids and an antimycotic property. The combination of liquid repellency and exceptional robustness exhibited indicates the WFNS as a promising candidate for super-hydrophobic and self-cleaning applications.

The paper is a synthesis of essential data regarding the wetting conditions in aluminium – silicon carbide mixtures. Non wetting conditions between the reinforcing element and the matrix turns difficult the incorporation of particles in the aluminium melt. The wettability depends on several elements, like the presence of the oxide layer at the melt surface, temperature, pressure or shape of the complementary material. To improve wetting conditions, several measures are necessary: alloying of the melt with surface active elements, overheating of the melt; coating of the particles with a metallic thin layer. Also, by using existing data reported in the field, some parameters were calculated and interpreted.

We consider the flotation of deformable, non-wetting drops on a liquid interface. We consider the deflection of both the liquid interface and the droplet itself in response to the buoyancy forces, density difference and the various surface tensions within the system. Our results suggest new insight into a range of phenomena in which such drops occur, including Leidenfrost droplets and floating liquid marbles. In particular, we show that the floating state of liquid marbles is very sensitive to the tension of the particle-covered interface and suggest that this sensitivity may make such experiments a useful assay of the properties of these complex interfaces., 21 pages, 9 figures. Minor typos corrected

The procedure to fabricate an industrially-producible, practically-applicable and easily-reconstructible transparent paint coating with luminescence is introduced step- -by-step in this paper. Without chemical modification, an ultrahydrophobic transparent paint coating with luminescence can be readily created using cost-effective commercially available materials. Grinding the ultrahydrophobic transparent paint coating surfaces using appropriate emery papers can generate appropriate surface roughness and thereby endows the coating surfaces with super-non-wettability and self-cleaning property. The applications of the coating to the external walls of buildings can provide the walls with self-cleaning property, decorate the walls and save outdoor illumination power during the night.

In this study, the spreading characteristics of water droplets impacted on a solid spherical target have been investigated experimentally and theoretically. Droplet impact and postimpact feature studies have been conducted on hydrophilic and superhydrophobic spherical surfaces. Effects of the impact Weber number and target-to-drop diameter ratio on the spreading hydrodynamics have been discussed. Postcollision dynamics are explored with side and top views of impaction phenomenon using a high speed imaging technique. The morphological outcome of this impingement process has been quantitatively discussed with three geometric parameters, namely, liquid film thickness at the north-pole of the target surface, spread factor, and the maximum spread angle. Observations revel that spread factor and the maximum spread angle increases with the decrease in the size of the spherical target, whereas opposite of this is true for liquid film thickness at the north-pole of the target surface. Temporal variations of liquid film thickness at the north pole of the target have been plotted and found in agreement with the theoretical predictions made in the earlier studies. Finally, a mathematical model based on the energy balance principle has been proposed to predict the maximum spread angle on spherical targets. The theoretical values are found in good agreement with the experimental results for a wide range of spherical diameters studied. The findings may have implications toward a better understanding of fluid wetting, spraying, and coating behavior of complex shapes and geometries.

A novel strategy for a directed nanoparticle coupling to isolated Stephanopyxis turris valves is presented. After pyrolysis, the valves exhibit incomplete wetting due to their characteristic T-shaped profiles as a prerequisite for a regioselective coupling reaction. A micromanipulation system allows for precise handling and their immobilization onto an adhesive substrate and manipulation into arrays.

In this work, we investigate the impact of co-current to counter-current flow reversals on the migration dynamics of a non-wetting phase plume in a porous medium. The presented results and observations have direct application to CO2 injection into saline aquifers where a less dense CO2-rich plume migrates during and following the injection period. Counter-current gravity segregation experiments were performed in a vertical glass-bead pack with brine and iC8 as analog fluids to mimic the behavior of a CO2/brine system of relevance to CO2 sequestration processes. Four-electrode resistivity measurements were used to monitor the migration of the non-wetting phase (iC8) by relating the resistivity index (RI) to the brine saturation. The observations are compared with numerical calculations to demonstrate that standard co-current relative permeability measurements are inadequate to reproduce the experimental observations. A reduction in the relative permeability of both phases, in particular for the non-wetting phase, is required to improve the agreement between experimental observations and numerical calculations. Numerical calculations based on co-current input data predicts a much faster migration of the non-wetting phase to the top of the column than what is observed in the segregation experiments. Our findings demonstrate that counter-current flow affects the phase's mobilities, because of interfacial coupling, and should therefore be considered in the modeling of injection/storage of CO2 in saline aquifers: simulation of CO2/brine dynamics based on co-current relative permeability measurements is likely to render estimates of migration time/distance in significant error.

Non-wetting surfaces are imperative to the survival of terrestrial and semi-aquatic insects as they afford resistance to wetting by rain and other liquid surfaces that insects may encounter. Thus, there is an evolutionary pay-off for these insects to adopt hydrophobic technologies, especially on contacting surfaces such as legs and wings. The cranefly is a weak flier, with many species typically found in wet/moist environments where they lay eggs. Water droplets placed on this insect's wings will spontaneously roll off the surface. In addition, the insect can stand on water bodies without its legs penetrating the water surface. The legs and wings of this insect possess thousands of tiny hairs with intricate surface topographies comprising a series of ridges running longitudinally along the long axis of the hair fibre. Here we demonstrate that this fine hair structure enhances the ability of the hairs to resist penetration into water bodies.

During the reflood of a Pressurised Water Reactor (PWR) following a loss of coolant accident, precursory cooling prior to the arrival of the rewetting front is of vital importance in limiting the rise in cladding temperature before rewet. This precursory cooling is achieved by a flow of superheated vapour, with entrained saturated drops, which evaporate into the vapour and act as a heat sink. In this paper we investigate a complementary mechanism; the direct cooling of the cladding by the drops themselves. Cladding temperatures are such that wetting by these droplets does not occur. On the contrary, droplets bounce off a vapour cushion formed during the ∼10 ms or so that they are in close proximity to the cladding. Using a combination of previous experimental correlations and recent CFD calculations, we estimate the rate of heat removal from the cladding surface as a result of the droplet impingement. Thus, we estimate the heat removed as a result of one impingement and estimate the total rate of heat removal by estimating the number droplets impinging on the cladding per unit surface area. The heat extracted by those droplets is found to be about 1/10 of the heat extracted by single-phase vapour under typical reflood conditions. Though there significant uncertainties in these estimates, it does seem that direct cooling by droplets, not generally incorporated in analyses of reflood, could actually be making a significant contribution to keeping cladding temperatures down to acceptable levels.

The analysis of redistribution functions of non-wetting liquid (water) dispersed in disordered nanoporous media of Libersorb 23, obtained in work [22]. Local configurations which describe the time relaxation of a non-wetting liquid dispersed in a disordered nanoporous medium are studied. It is shown that various possible local configurations can be used to describe the temporal relaxation of a liquid dispersed in a nanoporous medium. A qualitative picture is presented of the possible mutual arrangement of the pores in the porous medium Libersorb 23. The presented approach allows qualitatively to restore the spatial distribution of pores of a porous medium.

In this paper was studied the non-outflow phenomenon of a non-wetting liquid dispersed in nanoporous medium and the influence of porous medium surface modification and size of porous medium granules. The study of this phenomenon is important for development of mechanical energy dampers and for extraction of medicinal substances under certain conditions devices. The presented results for four commercial hydrophobized porous media Fluka 100 C18 (60756), Fluka 100 C18 (60758), Fluka 100 C8 (60755) and Fluka 100 C8 (60759) with the different thickness of the modifying layer and the size of the granules are show that the less of granules size and more narrow pore size distribution lead to decreasing of non-outflow phenomenon. The study of non-outflow phenomenon of non-wetting liquid from the pores of a nanoporous medium was carried out by time relaxation method and dispersed non-wetting liquid distribution recovery method at different temperatures.

Research into formation of hollow granules from liquid marbles is an emerging field in hydrophobic granulation. A liquid marble is formed by a network of self-assembled hydrophobic powder around a droplet, and this paper investigates the conditions required for forming hollow granules from a liquid marble precursor. Single drops of fluid were produced using a syringe and placed onto loosely packed powder beds of hydrophobic powders. Liquid marbles formed from several powder/liquid combinations were dried at several conditions to investigate the drying conditions required for formation of a stable hollow granule. The formation of stable hollow granules was found to depend on drying temperature and binder concentration. For HPMC and PVP binder, formation of hollow granule is proportional to binder viscosity and for HPC binder, this relationship is constant. Different combinations of powder and binder at both drying temperatures – 60 °C and 100 °C – had mixed success rates in forming hollow granules, but generally the success rate was improved by using higher drying temperatures, smaller particles or higher viscosity binder fluids.

We measure the trapped non-wetting phase saturation as a function of the initial saturation in sand packs. The application of the work is for carbon dioxide (CO2) storage in aquifers where capillary trapping is a rapid and effective mechanism to render injected CO2 immobile. We used analogue fluids at ambient conditions. The trapped saturation initially rises linearly with initial saturation to a value of 0.11 for oil/water systems and 0.14 for gas/water systems. There then follows a region where the residual saturation is constant with further increases in initial saturation.

The film thickness of free-meniscus coating of a polymeric fiber with a non-wetting fluid was investigated. A polypropylene monofilament fiber was coated with various glycerol/water mixtures. With a small capillary number (Ca), a detectable liquid film did not form on the fiber due to the non-wettability of the fiber-liquid system. Above a certain threshold velocity, liquid was forced to wet the fiber by hydrodynamic forces, thus forming a film. However, the film thickness in this region is lower than Landau–Levich–Derjaguin (LLD) theoretical value for the wetting system. At a moderate velocity range, the film thickness increases to a value predicted either by the LLD law or White–Tallmadge (WT) model, depending on the velocity, mimicking that of the wetting system. At a higher Ca, the film thickness increases much more rapidly, deviating from any predictions, due to the inertial effect.

This introductory chapter covers the thermodynamic fundamentals of non-wetting. It starts with a short general description of non-wetting, followed by comments on terminology. It continues, still as a background, with wetting equilibrium in general. Then, the definition and mechanism of non-wetting is discussed. Special emphasis is given to the recent studies of the stability of the thermodynamic states of the system, which, in fact, determines the extent of non-wettability. The non-wetting systems that are discussed include a drop on a solid surface (hydrophobic as well as hygrophobic), and underwater non-wetting.

Liquid marbles are liquid drops made non-wetting by the use of a powder which coats them. Because of the absence of a contact line, quick motions without leakage of small amounts of liquid are allowed, which can be of interest in microfluidic applications. After characterizing the static liquid marble, we focus on its properties and study experimentally the viscous motion of liquid marbles. Then, we describe qualitatively possible ways for putting marbles into motion and quantify the robustness of this object.

The liquid holdup study has been carried out on a two-dimensional cold model under non-wetting condition with lateral gas injection as it is done in the blast furnace. Non-dimensional numbers for both, cold model and blast furnace have been determined. The measurements of static and dynamic liquid holdups were made under different gas and liquid flow rates using two particulate materials of various diameters. Few experiments were performed under dry and wet bed conditions to ascertain the effect of bed history. Holdups results have been compared with the existing correlations available in the open literature. It is found that existing correlations are unable to predict the correct liquid holdup under the blast furnace conditions.