Reduction Of Surface Energy Research Articles

Discrete element method simulation of binary blend mixing of cohesive particles in a high‐intensity vibration system

AbstractThe effects of processing intensity, time, and particle surface energy on mixing of binary cohesive powder blends in high‐intensity vibration system were investigated via discrete element method simulations. The mixedness was quantified by the coefficient of variation, Cv; lower being better. The mixing rate, which is the speed at which homogeneity was achieved, was inversely proportional to the mixing Bond number, defined as the ratio of particle cohesion to the shear force resulting from the mixing intensity. Results show that both increasing processing intensity and reducing surface energy led to a faster mixing rate. However, the mixedness improved initially as mixing action (the product of mixing rate and mixing time) increased, but later deteriorated upon its further increase. Thus, both mixing rate and mixing intensity need to be tuned for optimum mixing performance depending on the cohesion level of particles; too high or too low mixing action should be avoided.

3D-imprinted superhydrophobic polyvinylidene fluoride membrane contactor incorporated with CaCO3 nanoparticles for carbon capture

Carbon capture using membrane gas absorption was limited by membrane wetting. In this work, superhydrophobic poly(vinylidene fluoride) (PVDF) membrane contactors were developed through 3D-imprinting and nanoparticle incorporation. Membranes were cast on woven support before phase inversion in a water bath to imprint the micro-roughness. The low-cost and biocompatible calcium carbonate (CaCO3) nanoparticles were blended into PVDF dope solution to build the hierarchical structure. The nanoparticles were premodified using stearic acid to reduce surface energy or removed using ethylenediaminetetraacetic acid for achieving nanotemplating. The presence of CaCO3 nanoparticles could be observed using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The membrane hydrophobicity, pore size, and porosity were significantly improved due to the addition of CaCO3 and stearic acid-modified CaCO3 (SA-CaCO3). Removing CaCO3 nanoparticles enlarged the pore size greatly but affected the surface hydrophobicity slightly. The PVDF membrane incorporated with SA-CaCO3 achieved a CO2 permeation flux as high as 1.86 ± 0.05 × 10−2 mol m−2 s−1 and only showed slight changes in surface hydrophobicity after being immersed in amine solution for 50 h.

Impact of land surface processes on the simulation of sea breeze circulation and tritium dispersion over the Kaiga complex terrain region near west coast of India using the Weather Research and Forecasting (WRF) model

Kaiga, located on the west coast of Karnataka, India is a complex terrain region with dense forest cover often influenced by land-sea breeze flows during warm summer season. In this study, dispersion of tritium released from Kaiga Nuclear Power Plant (NPP) under the influence of land-sea breeze circulations is simulated using FLEXPART-WRF models. Sensitivity experiments with Weather Research and Forecasting (WRF) are conducted with two Land Surface Models (LSMs), Noah and Noah-Multi Physics (Noah-MP) to study their impact on the wind flow and meteorological characteristics. Mini Boundary Layer Masts (MBLMs) and Doppler SODAR observations are used for evaluating the model performance. WRF simulations showed large sensitivity of simulated sea breeze characteristics to the model land surface physics. It has been found that the Noah-MP better represented the onset time, inland extent, intensity and duration of the sea breeze circulation over the Kaiga complex terrain region with lesser error statistics compared to Noah. The improvements with Noah-MP over Noah are due to the better representation of vegetation and soil hydrological processes over the dense forest region, realistic simulation of surface energy and momentum fluxes and reduction in the land-sea temperature contrast by including a separate canopy physics. FLEXPART simulation of tritium releases from the Kaiga NPPs using WRF predicted meteorological fields showed large diurnal variability in the dispersion pattern and air concentrations around the Kaiga valley. Tritium plume is transported to the northwest sector during early morning and morning time by the land-breeze and to the east-southeast sector by the sea breeze during daytime. Predicted tritium concentrations are found to be higher during the morning under stable atmospheric conditions and lower during sea breeze hours due to stronger winds and deep mixed layers. FLEXPART predicted tritium activity concentrations at different measurement locations using WRF-Noah-MP meteorological data are in better agreement with measurements with higher correlation coefficient and index of agreement. • Tritium dispersion over a coastal complex terrain site is modeled by using the coupled WRF-FLEXPART model. • Dispersion of tritium released from a Nuclear Power Plant under mesoscale sea breeze and land breeze circulations is presented. • Sensitivity of Land Surface Models, Noah and Noah-MP in WRF on the simulation of sea breeze characteristics and tritium dispersion are assessed. • Explicit treatment of forest canopy in the Noah-MP LSM over a model domain with dense forest improved the model results.

Variations in aluminum particle surface energy and reactivity induced by annealing and quenching

Surface interface properties of fuel particles play an important role in their reactivity. Since diffusion-controlled reactions occur at the interface between a solid fuel and oxidizer, variations in surface energy alter diffusion rates in ways that can be measured macroscopically. In this study, surface energy was purposefully altered by annealing and quenching aluminum (Al) (3–4.5 µm particle diameter) powder. Bulk aluminum exhibits reduced surface energy resulting from annealing and quenching. In the current work, annealing and quenching was extended to powder media to assess the magnitude of reduced surface energy. An inverse gas chromatography (iGC) technique was used to energetically characterize the particle surface for both dispersive and polar properties. Results show up to a 40% decrease in surface energy with annealing and quenching. Both untreated and thermally processed powder were reacted by launching projectiles into a chamber where the ensuing powder explosions were examined. Experiments were performed in ambient air and repeated in argon environments at projectile velocities of 1200 m/s. Overall, higher surface energy resulted in a more pronounced system performance, i.e., in stronger reactions with higher probability of ignition and combustion. A theory explaining the differences in reactivity links surface energy with a mechanism for particle reaction.

An Integrated Study of Water Weakening and Fluid Rock Interaction Processes in Porous Rocks: Linking Mechanical Behavior to Surface Properties

We investigated the impact of water weakening on the mechanical behavior of Obourg Chalk and Ciply Chalk (Mons Basin, Belgium). Different mechanical tests were conducted to estimate the unconfined compressive strength (UCS), tensile strength, Young’s modulus, mechanical strength under triaxial loading, critical pressure, fracture toughness, cohesion, and internal friction coefficient on samples either dry or saturated with water or brine. This extensive dataset allowed us to calculate wet-to-dry ratios (WDR), i.e., the ratio between any property for a dry sample to that for the water-saturated sample. For both chalks, we found that water has a strong weakening effect with WDR ranging from 0.4 to 0.75. Ciply Chalk exhibits more water weakening than Obourg Chalk. The highest water weakening effect was obtained for UCS, critical pressure, and Young’s modulus. Weakening effects are still present in brine-saturated samples but their magnitude depends on the fluid composition. The mechanical data were correlated to variations in surface energy derived from three different methods: fracture mechanics, contact angle goniometry, and atomic force microscopy. Water weakening in the tested chalks can be explained by a clear reduction in surface energy and by the existence of repulsive forces which lower the cohesion.

Exploiting lack of fusion defects for microstructural engineering in additive manufacturing

Rapid cooling rates and stochastic interactions between the heat source and feedstock in additive manufacturing (AM) result in strong anisotropy and process-induced defects deteriorating the tensile ductility and fatigue resistance of printed parts. We show that by deliberately introducing a high density of lack of fusion (LoF) defects, a processing regime that has been avoided so far, followed by hot isostatic pressing (HIP), we can print Ti-6Al-4V with reduced texture and combinations of strength (TS=1.0 ± 3E-2 GPa) and ductility (ε failure =20 ± 1%) surpassing that of wrought, cast, forged, annealed, solution-treated and aged counterparts. Such improvement is achieved through the formation of low aspect ratio α-grains around LoF defects upon healing, surrounded by α-laths. This occurrence is attributed to surface energy reduction and recrystallization events taking place during the healing of LoF defects via HIP post-processing. Our approach to design duplex microstructures is applicable to a wide range of AM processes and alloys, and can be used in the design of damage tolerant microstructures.

Energy capillary number reveals regime transition of imbibition in porous media

Imbibition, the process of a wetting fluid displacing a nonwetting one in porous media, occurs in many natural and industrial processes, such as enhanced oil recovery and geological carbon sequestration. The phenomenon of imbibition shifts from the capillary regime to the capillary–viscous regime as the externally imposed flow rate (viscous force) increases. In the capillary–viscous regime, there also exists a transition from the capillary-dominated regime to viscous-dominated regime, and the identification of this transition is fundamental to the description of forced imbibition. The main purpose of this work is to explore regime transition in imbibition. We first investigate forced imbibition in a heterogeneous porous media over a broad range of wettability conditions and flow rates. An energy capillary number is proposed to identify regime transitions based on the energy balance analysis of imbibition processes, especially the transition from a capillary-dominated regime to viscous-dominated regime. The energy capillary number is defined as the ratio of the reduced surface energy to the external work, measuring the relative total contribution of the capillary force vs the viscous force to the whole imbibition morphologies. We further present a phase diagram, which allows us to determine the imbibition regime directly from capillary numbers and wettability conditions. The energy capillary number and phase diagram are evidenced by a quantitative analysis of invasion morphologies.

Effects of Glycerol-Waste Antifreeze Based Grinding Aids on Cement Grinding Characteristics

Grinding aids to increase grinding efficiency in cement production are materials that can produce large amounts of high-quality cement in a short time by reducing surface energy by preventing particle agglomeration and improving fluidity. In the paper, a grinding aid using glycerol-waste antifreeze(GAP) is prepared and its effect on the grinding properties of clinker is investigated in contrast to that without the grinding aid. The results are as follows: The angle of repose of the cement powder added with GAP decreases as the grinding time increases (decreases by 3.8° when the grinding time is 60 minutes), indicating that it increases the flowability of the powder. On the contrary, the residual amount of 45µm sieve is also significantly reduced (4.6% decrease) and the specific surface area increases (30.5m2/kg), which results in an increase in the grinding efficiency. In the size range of 3 to 32µm, it increases the particle content, makes the particle size distribution uniform, the 7d and 28d activity index of the powder is improved by 5% and 6%, respectively, and increases the compressive strength of the cement. In addition, it is confirmed that the performance of the TEA grinding aid and the grinding aid are similar, and are very effective in terms of economy.

Surface-Stress Induced Embrittlement of Metals.

Environment-assisted fracture phenomena in metals are usually associated with surface energy reduction due to an adsorbed film. Here we demonstrate a unique embrittlement effect in Al that is instead mediated by surface stress, induced by an adsorbed organic monolayer. Atomistic simulations show that the adsorbate carbon-chain length lc controls the surface stress via van der Waals forces, being compressive for lc < 8 and tensile otherwise. For lc > 8, we demonstrate experimentally that the nanoscale film causes a ductile-to-brittle transition on the macroscale. Concomitant with this transition is a nearly 85% reduction in deformation forces. Additional simulations reveal that the microscopic mechanism for the embrittlement is via suppression of dislocation emission at incipient crack-tips. In addition to challenging long-held views on environment-assisted fracture, our findings pertaining to surface-stress induced embrittlement suggest profitable utility in manufacturing processes such as machining and comminution.

One-Step Fabrication of a Functionally Integrated Device Based on Polydimethylsiloxane-Coated SiO2 NPs for Efficient and Continuous Oil Absorption.

The construction of superhydrophobic surfaces necessitates the rational design of topographic surface structure and the reduction of surface energy. To date, the reported strategies are usually complex with multi-steps and costly. Thus, the simultaneous achievement of the two indispensable factors is highly desired, yet rather challenging. Herein, we develop a novel structure engineering strategy of realizing the fabrication of a functionally integrated device (FID) with a superhydrophobic surface via a one-step spraying method. Specifically, silica nanoparticles are used to control the surface roughness of the device, while polydimethylsiloxane is employed as the hydrophobic coating. Benefitting from the adopted superhydrophobicity, the as-fabricated FID exhibits a continuous, excellent oil-water separating performance (e.g., 92.5% separating efficiency) when coupled with a peristaltic pump. Notably, a smart design of incorporating a gas switch is adopted in this device, thereby effectively preventing water from entering the FID, realizing thorough oil collection, and avoiding secondary pollution. This work opens up an avenue for the design and development of the FID, accessible for rapid preparation and large-scale practical application.

Study of corrosion property and mechanical strength of eco-friendly fabricated superhydrophobic concrete

The complex corrosive environment in the ocean and the hydrophilicity of concrete often leads to corrosion of the rebars in concrete. Endowing concrete with superhydrophobicity is an effective measure to prevent the internal rebars from being corroded. Here, an eco-friendly green method was proposed for fabricating superhydrophobic concrete by adding non-toxic lauric acid into concrete to reduce surface energy and covering stainless steel mesh to obtain rough hierarchical structures. The superhydrophobic concrete exhibited WCA of 153° and WSA of less than 10°. The corrosion property of fabricated concrete immersed into simulated seawater for different time was studied. The results show that the superhydrophobic concrete possesses better corrosion resistance to internal rebars than ordinary concrete. The compressive and flexural strengths of samples with different curing ages were studied. This eco-friendly green method for fabricating superhydrophobic concrete with corrosion resistance may have good application prospects in coastal engineering.

Fabrication of super-wetting copper foam based on laser ablation for selective and efficient oil-water separation

Oil pollution has caused damage to the ecological environment and human health, which cannot be ignored in industrial production and marine economic. It is very vital to explore a simpler and easier to manufacture oil-water separation method. In this work, the super-wetting copper foam with superhydrophobicity or superhydrophilicity on was fabricated based on low-cost nanosecond laser ablation combined chemical modification. The surface of copper foam was covered with fluffy microstructures and smaller nanoparticles after laser ablation, which greatly enhances the hydrophobicity, with a maximum contact angle of 156°. The droplet could rebound many times after being compressed in a cake shape on the superhydrophobic surface but spread rapidly on the superhydrophilic surface. Analysis of chemical composition verified the fluorine-containing long-chain greatly reduces surface energy, while the oxygen group of graphene oxide is the opposite. Based on the oil permeability of the superhydrophobic copper foam and the water permeability of the superhydrophilic copper foam, the separation of heavy oil and light oil can be selectively achieved. The separation efficiency of different oil-water mixtures could be higher than 99%, and the recyclability was better after multiple separations. It provides a convenient and selective way for oil-water separation.

Spatially-resolved characterization of oil-in-water emulsion sprays

When an oil-in-water emulsion is utilized for application in a flat-fan spray, micrometer-sized oil droplets are thought to facilitate hole formation on the spray lamella, leading to an earlier breakup of the spray sheet and an increase in resulting droplet sizes. However, prior work has largely focused on changes to the mean or median droplet size, and has not examined the influence of oil-in-water emulsions on the complete droplet size distribution, as well as other droplet properties such as droplet shape and droplet velocity distributions in flat fan sprays. This study concerns the effects of pressure, spatial location, and application of oil emulsions on the resulting droplet size, eccentricity, as well as velocity distributions, all of which are crucial information in determining the dispersion dynamics of the droplets during the spray applications. Experiments were conducted with a TP6515 nozzle, with the abovementioned droplets information measured using digital inline holography (DIH). Results show that the DIH-inferred volumetric droplet size distributions (VDSD) span widely from sub-100 μm to over 2 mm in size. The application of an oil-in-water emulsion results largely in suppression of smaller droplets, while the VDSD is relatively insensitive to increasing the oil volume fraction beyond a critical level. DIH results are consistent with the observation that smaller ligaments are observed only in the breakup regions for the single-phase water sprays, which break up more violently and earlier than larger ligaments. It is these smaller ligaments that are suppressed in the oil-in-water emulsion, which yield sub-millimeter droplets, some with sizes approaching sub-100 μm dimensions, corresponding to driftable sizes in agricultural settings. Interestingly, the application of oil-in-water emulsion generally decreases the eccentricity more significantly at the center than at the edge of the spray fan. We attribute this decrease to the increase in lamella sheet thickness and thus decrease in characteristic shrinkage rates, consistent with observations of high speed shadowgraphs. In all instances, oil-in-water emulsion droplets have higher velocities than equivalent sized water droplets. We attribute this to the earlier action of the spray breakup process in the oil-in-water emulsion, reduced surface energy generation during breakup (larger droplets), and reduced energy dissipation during breakup with oil-in-water emulsions, leading to increased translational energy after the breakup process. Therefore, it appears that oil-in-water emulsion application simultaneously suppresses small droplet formation and increases droplet velocity, and hence spray penetration in agricultural application.

Effect of chromium coating thickness on surface adhesion of polyethylene terephthalate optical film

Surface accuracy and shape accuracy are the two key factors that determine the reflective performance of electroforming replication mold. However, the adhesion between the master mold and the replica mold sometimes causes the deformation, fracture and stretching of the microstructure of the mold surface. The reflective performance of the mold surface is reduced. For this reason, this paper proposed a method for reducing the adhesion force by means of a metal Cr transition layer, which was deposited on polyethylene terephthalate (PET) optical film using direct current (DC) magnetron sputtering. The effect of the Cr coating thickness on adhesion force was investigated. The surface of the film was analyzed by the measurement of contact angle, surface energy, surface chemical composition and micro-morphology. The measurements indicate that the surface energy of the PTE films is reduced after being deposited with a thin Cr coating. The reduced surface energy could be due to the fact PET′s polar functional groups were covered by the Cr coating, which must have lower surface energy than the PTE′s surface. In addition, the reduction of surface roughness also helps to reduce the adhesion of PET film surface. The study showed that Cr coating can effectively reduce the surface adhesion of PET optical mold and improve the surface quality of duplicated mold. The work provides a new method to reduce the surface adhesion of PET optical molds for application in electroforming demoulding technology and interfacial adhesion can be adjusted by the thickness of the Cr coating.

Ultra-hydrophobic aluminum foam development for potential application in continuous water-oil separation processes

Owing to their applicability as a selective barrier, porous materials with modified surfaces have been presented as alternatives for addressing oil spills in water. For this application, surface treatment seeks both maximization of surface area and formation of a low-energy layer. To achieve an effective selective barrier that is useful in the separation of oil-water mixtures, with future application in oil spill cleanup, this work presents aluminum foams treated with sodium hydroxide and immersed in dodecanoic acid to achieve pickling and reduction of surface energy, respectively. Treatment efficiency was evaluated using the Brunauer–Emmett–Teller method and contact angle measurements. Results were consistent with other hydrophobic materials. Pore sizes of 425 µm, 850 µm, and 1200 µm were used to evaluate separation of water and oil mixtures under static and dynamic conditions. Oil recovery efficiencies for all pore sizes were greater than 98%.

Fluorine-free superhydrophobic characterized coatings: A mini review

The scientific fraternity and coating companies have researched and developed coatings with superhydrophobic features for a wide range of applications, varying from automotive, oceanic, pharmaceutical, and thermal and power sectors, over the preceding few years. The self-cleaning features of superhydrophobic surfaces exhibit pronounced dust repelling and lower dust adhesiveness qualities, along with incomparable water repellence for maritime, automotive, and pharmaceutical applications. The advancement of super-hydrophobic surfaces for averting the accrual of impurities on surfaces is an active space of exploration globally. A lesser hysteresis of contact angle leads to drops of water sliding effortlessly on such surfaces. The solid surfaces’ surface energy can be weakened by fixing materials of lesser surface energy on the exterior, which can be performed by the following dual methods; either by fixing materials of reduced surface energy straight onto the exterior of a substrate in the form of a coating of that material, or by fixing materials of less surface energy on the exterior of nano-architectural structures and then dropping the coating of those nanoscale materials on the exterior of the substrate. The generation of nanoscale irregularities on substrates by dropping nanostructure layers on surfaces makes it an attractive option since, usually, nanomaterials have a minimum of one dimension, ranging from 1 - 100 nm. The nanostructures’ sizes unveil exceptional physical and chemical characteristics, principally owing to their greater specific surface area to volume quotient. This review encompasses the non-fluorinated superhydrophobic coatings developed to date.

Development and Characterization of Electrospun Biopapers of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Derived from Cheese Whey with Varying 3-Hydroxyvalerate Contents.

In the present study, three different newly developed copolymers of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with 20, 40, and 60 mol % contents in 3-hydroxyvalerate (3HV) were produced by the biotechnological process of mixed microbial cultures (MMCs) using cheese whey (CW), a by-product from the dairy industry, as feedstock. The CW-derived PHBV copolyesters were first purified and then processed by solution electrospinning, yielding fibers of approximately 2 μm in cross-section in all cases. The resultant electrospun PHBV mats were, thereafter, post-processed by annealing at different temperatures, below their maximum of melting, selected according to their 3HV content in order to obtain continuous films based on coalesced fibers, so-called biopapers. The resultant PHBV films were characterized in terms of their morphology, crystallinity, and mechanical and barrier properties to assess their potential application in food packaging. The CW-derived PHBV biopapers showed high contact transparency but a slightly yellow color. The fibers of the 20 mol % 3HV copolymer were seen to contain mostly poly(3-hydroxybutyrate) (PHB) crystals, the fibers of the 40 mol % 3HV copolymer a mixture of PHB and poly(3-hydroxyvalerate) (PHV) crystals and lowest crystallinity, and the fibers of the 60 mol % 3HV sample were mostly made of PHV crystals. To understand the interfiber coalesce process undergone by the materials during annealing, the crystalline morphology was also assessed by variable-temperature both combined small-angle and wide-angle X-ray scattering synchrotron and Fourier transform infrared experiments. From these experiments and, different from previously reported biopapers with lower 3HV contents, all samples were inferred to have a surface energy reduction mechanism for interfiber coalescence during annealing, which is thought to be activated by a temperature-induced decrease in molecular order. Due to their reduced crystallinity and molecular order, the CW-derived PHBV biopapers, especially the 40 mol % 3HV sample, were found to be more ductile and tougher. In terms of barrier properties, the three copolymers performed similarly to water and limonene, but to oxygen, the 40 mol % sample showed the highest relative permeability. Overall, the materials developed, which are compatible with the Circular Bioeconomy organic recycling strategy, can have an excellent potential as barrier interlayers or coatings of application interest in food packaging.

Anti-corrosion superhydrophobic surfaces of Al alloy based on micro-protrusion array structure fabricated by laser direct writing

Enhanced corrosion resistance of widely used Al alloys is of great significance to improving its application value. The micro-protrusion array structure covered with nanoparticles was fabricated on the surface of 5083 Al alloy by nanosecond laser vertical crossed scanning. Formation mechanism of the micro-nano structure was attributed to the heat accumulation of the laser pulse acting on the surface, including melting, sputtering and re-solidification. After laser treatment and reduction of surface energy, samples with different scanning times were all superhydrophobic. However, the adhesion of the surfaces with scanning times of 10 and 1 was different, which were shown as ‘lotus leaf effect’ and ‘rose petal effect’, respectively. It was found that the sputtering material during laser ablation oxidized most severely, and the ratio of O increased by 23.65%. The long chains of FAS-17 molecules have been attached on the superhydrophobic surface after modification. The polarization tests showed that the superhydrophobic surface can significantly reduce the corrosion current density, and the inhibition efficiency is 95.7%. Impedance tests verified the anti-corrosion ability of the superhydrophobic surface with the largest impedance of 26.01 kΩ cm2. This study provides an effective and simple preparation method for enhancing the corrosion resistance of aluminum alloy.

Improved hydrophilicity and durability of polarized PVDF coatings on anodized titanium surfaces to enhance mineralization ability

Polyvinylidene fluoride (PVDF) coating with piezoelectric properties was prepared on surface of titanium-based materials to improve the bio inertness of the surface. The surface of titanium-based materials with piezoelectric properties similar to human bone promotes the growth of osteoblasts. However, not only new bone growth but also osseointegration are observed in the process of bone repair. The hydrophobicity of PVDF coating is unfavorable for mineralization. In this study, a PVDF coating was prepared on the titanium surface by using titanium dioxide nanotubes as a transition layer, and PVDF was attached to the wall of the titanium dioxide nanotube. The contact angle of the polarized PVDF coating decreases from 108° to 47°, which indicates that it changes from hydrophobic to hydrophilic due to the reduction in surface energy and the effect of negative surface charge. After the coating is left for a period of time, its contact angle only increases by 20° due to the loss of negative surface charge. After a physiological loading is applied to the polarized PVDF coating, the durability of its surface hydrophilicity is maintained. The mineralization ability of the polarized PVDF coating after being immersed in simulated body fluid (SBF) for 1, 7, and 14 days is significantly higher than that of the unpolarized sample. The increase in mineralization ability is mainly due to the hydrophilicity of the surface and the attraction of negative charges to calcium ions. Notably, after the polarized PVDF coating is subjected to physiological load, the mineralization ability is further improved after being immersed in SBF for 14 days, and its surface is covered with a layer of bone-like apatite. The high mineralization ability of the PVDF coating on the titanium surface after polarization can promote osseointegration and therefore shorten the bone repair cycle. Accordingly, this coating has potential application value in the clinical treatment of bone defect repair in middle-aged and elderly people.

New perspectives on structural parameters and hydrophobic model inspired by a superhydrophobic Cu cone-flower coating

Superhydrophobic films have been successfully prepared on various substrates by finely controlling surface micro/nanostructure's roughness and reducing surface energy. However, there is no unified conclusion about the correlation of surface roughness and 3D volume parameters to wettability. Herein, we fabricated a superhydrophobic film composed of hierarchical Cu cone-flowers via facile one-step pulse electrodeposition with a 30% duty cycle for 20 min. Based on this film, the relationship between roughness/volume parameters and hydrophobicity was well studied. The resulting cone-flower film exhibits excellent corrosion resistance and self-cleaning properties due to a high water contact angle (WCA) of ~160° and a low sliding angle (SA) of ~3°. The large roughness skewness (Rsk = 0.7–1.3) and void volume ratio (Vvc/Vmc > 1.5) are shown to be more desirable to achieve superhydrophobic surfaces. Moreover, a new hydrophobic model is proposed to explain the above results, which means that the nanoscale air cushions share most of the gravity of water droplets to help microscale air cushions closer to the Cassie state. Further experiments by adding or destroying the nanostructures to observe the change of hydrophobicity well verified our conjecture.