Increased Surface Wettability Research Articles

Surface structures and wettability: Their roles in enhancing nucleate boiling heat transfer of refrigerants

Nucleate boiling is an effective heat transfer mechanism. Previous studies have demonstrated that modifying surface structure or wettability can independently improve nucleate boiling efficiency; however, the combined effects and optimal modification sequence remain underexplored. This research aims to comprehensively analyze the influence of surface structure and wettability on the nucleate boiling heat transfer performance of refrigerants. Different surface structures and wettability were prepared using surface polishing, laser ablation, mechanical cutting, and a combination that involved initially employing laser ablation, followed by the application of chemical etching, and finishing with the treatment using materials possessing low surface energy. The static contact angles on these surfaces were measured via the capillary rise method, followed by pool boiling experiments and bubble behavior visualization. The results show that increasing surface wettability can enhance bubble departure frequency and capillary wicking, thereby improving critical heat flux and heat transfer coefficient. The key to optimizing surface modification to enhance critical heat flux involves constructing alternating high and low nucleation core regions to reduce interactions between bubbles; for enhancing heat transfer coefficient, the key lies in constructing compact nanoscale structures that expand the heat transfer and nucleation area, followed by improving wettability.

Boosting charge transport in the BiVO4 photoanode interface modified with an aluminum hydroxide layer for solar water oxidation

Modifying BiVO4 with Al(OH)3 layers improved its PEC properties due to an increase of surface wettability. The strong interfacial interaction with H2O played a vital role in efficient charge carrier transportation on the BiVO4 interface.

Experimental study on falling film evaporation heat transfer outside a horizontal tube in refrigeration system

Experimental study on falling film evaporation heat transfer outside a horizontal tube in refrigeration system

Ethyl cellulose–graphene oxide composite dense membranes: Kinetic and thermodynamic studies of dye adsorption

Graphene oxide (GO) is extensively used in dye adsorption from wastewater. Polymer–GO composite membranes exhibits improved surface wettability and dye adsorption capacity. In this study, ethyl cellulose (EC)–GO nanocomposite dense membranes (EG membranes) are prepared by the solvent casting method. The morphology and physicochemical properties of the developed nanocomposite membranes are characterized using field emission scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction studies, thermogravimetric analysis, static contact angle measurements, and UV–visible spectroscopy. The derivative thermogravimetry curves indicate the complete degradation of the composites below [Formula: see text]C. The results confirm the homogeneous dispersion of GO in the EC matrix. The addition of GO to the EC matrix leads to a remarkable increase in surface wettability which decreases the contact angle to [Formula: see text] for the membrane with a 0.7% addition of GO. The prepared membranes are used for the separation of methylene blue from water. The adsorption properties of the prepared membranes are found to be varying in accordance with the contact angle values. The equilibrium data fit well for the Langmuir model and the adsorption follows pseudo-second-order kinetics.

Microscopic insight into mechanisms of heat and mass transfer improvement of dropwise condensation on a modified nanopillar surface

In this work, a series of molecular dynamics simulations are carried out to explore the mechanisms of heat and mass transport on textured surfaces during the initiation of condensation. The solid fractions of composite nanopillars on textured surface range from 0.13 to 0.35. The addition of nanopillars with φ=0.35 on bare surface results in a 50 % decrease of the total thermal resistance. Increasing surface wettability brings a higher overlap of phonon vibrational density of states between solid and near-surface atoms, and an order magnitude reduction of interfacial Kapitza resistance can be obtained. Also, enhancing temperature (Thot) gives rise to the formation of droplets that exhibits higher solid-liquid viscous force within multi nanostructure cells. The wetting map with respective to the temperature difference and nanostructure spacing shows that the increases of Thot and spacing l facilitates the formation of Wenzel droplets. For Cassie droplets, the highest condensation rate is found for the case of Thot =130 K and l = 30 Å. While both dense and sparsely arranged nanopillar surfaces have higher Wenzel droplet condensation rates. Compared to the cylindrical structure, the cylinder-hemisphere composite structure shows superior condensation performance after droplet approaches the hemisphere region. In addition, the condensation rate on hybrid wettability surface exhibits a 30 % enhancement than that on uniformly hydrophilic surface.

Biomass derived nitrogen-doped activated carbon and novel biocompatible gel electrolytes for solid-state supercapacitor applications

The development of biocompatible energy storage technologies is crucial for powering implantable devices in the health sector. In the current study, red beetroot (Beta vulgaris L.) is used as a biomass precursor to synthesize microporous nitrogen-doped activated carbon (NACBR). The resulting carbon structure has an improved specific surface area (SSA) of 2200 m2g−1 and a hierarchical sponge-like porosity. In-vitro cytotoxic experiments support the biocompatibility of the as-synthesized carbon. It is known that N-doping increases surface wettability and conductivity, which enhances the electrode material's specific capacitance. According to electrochemical studies, in 1 M Na2SO4 electrolyte, the NACBR electrode has the highest specific capacitance of 492 F g−1 at 1 A g−1 current density. Furthermore, Na2SO4, phosphate-buffered saline (PBS), and simulated bodily fluid (SBF) gel-electrolytes are used to fabricate and test biocompatible solid-state supercapacitor devices. The goal of this research is to construct and test biocompatible supercapacitors that could power implantable devices.

Biological Activity and Thrombogenic Properties of Oxide Nanotubes on the Ti-13Nb-13Zr Biomedical Alloy.

The success of implant treatment is dependent on the osseointegration of the implant. The main goal of this work was to improve the biofunctionality of the Ti-13Nb-13Zr implant alloy by the production of oxide nanotubes (ONTs) layers for better anchoring in the bone and use as an intelligent carrier in drug delivery systems. Anodization of the Ti-13Nb-13Zr alloy was carried out in 0.5% HF, 1 M (NH4)2SO4 + 2% NH4F, and 1 M ethylene glycol + 4 wt.% NH4F electrolytes. Physicochemical characteristics of ONTs were performed by high-resolution electron microscopy (HREM), X-ray photoelectron spectroscopy (XPS), and scanning Kelvin probe (SKP). Water contact angle studies were conducted using the sitting airdrop method. In vitro biological properties and release kinetics of ibuprofen were investigated. The results of TEM and XPS studies confirmed the formation of the single-walled ONTs of three generations on the bi-phase (α + β) Ti-13Nb-13Zr alloy. The ONTs were composed of oxides of the alloying elements. The proposed surface modification method ensured good hemolytic properties, no cytotoxity for L-929 mouse cells, good adhesion, increased surface wettability, and improved athrombogenic properties of the Ti-13Nb-13Zr alloy. Nanotubular surfaces allowed ibuprofen to be released from the polymer matrix according to the Gallagher-Corrigan model.

Pore-scale modeling of gravity-driven superheated vapor flooding process in porous media using the lattice Boltzmann method

In this work, a hybrid method combining interparticle-potential multiphase LBM, finite difference method and characteristic-line wetting scheme, is developed for pore-scale simulation of superheated vapor displacing liquid, driven by gravity, in a porous geometry. The influence of injected vapor superheat, surface wettability and gravity on two-phase displacement and heat transfer processes is investigated. Results show that in thermal displacement, the vapor-liquid interface is unstable and trapped liquid blobs gradually evaporate into vapor. At low vapor superheat degrees, the displacement efficiency, as compared to isothermal displacement, is significantly improved, but it reduces as the vapor superheat degree rises due to the shift of displacement patterns. At all contact angles considered, the displacement always exhibits viscous fingering, although vapor flowpaths become wider with increasing surface wettability. The final vapor saturation is insensitive to surface wettability, but reducing contact angle leads to a less even temperature distribution inside vapor and a decrease in final average vapor temperature. In addition, increasing gravity is found to reduce vapor front temperature, but it almost has no effect on final average vapor temperature because the final average vapor temperature does not only depend on specific interfacial length but also on fingering number and inlet flow rate.

An experimental study on the plate edge effect of frosting characteristics for horizontal flat cold plates with surface wettability considered

Frosting happens frequently in nature and industry and the accumulated frost layer always plays negative effects on a variety of applications. To clarify the frosting characteristics of cold plates with different surface wettability considering the plate edge effect, the frosting experiments of horizontal flat cold plates with hydrophilic, hydrophobic and superhydrophobic surfaces were carried out under forced convection. The results show that, different from the large condensed droplets in the edge-affected regions of the hydrophilic and hydrophobic surfaces, which are small and few on the superhydrophobic surface. The area-average equivalent contact diameter and coverage area ratio of condensed droplets decrease with the increase of surface wettability. The average freezing propagation velocity in the edge-affected region of the superhydrophobic surface is 166.4 × 10−6 m/s, which is 81.8% and 54.5% lower than those on hydrophilic and hydrophobic ones, respectively. And the maximum frost layer growth rate of the superhydrophobic surface is 3.36 × 10−6 m/s, which is 2.78 and 2.30 times the two other ones. The frost layer surface roughness of the superhydrophobic surface is 85.1 × 10−6 m, which is 27.8% and 74.7% higher than those on hydrophilic and hydrophobic ones, respectively. This study can reveal the time–space frosting characteristics in the edge region of horizontal cold plates and provide a reference for anti-frosting in practical applications.

Influence of passive layer fabrication method on physicochemical and antimicrobial properties of the Ta2O5 layer on NiTi alloy

The use of nickel-titanium (NiTi) alloy in implants, despite its good biocompatibility, is not entirely inert to the human body. To reduce nickel ions and improve the hemocompatibility of implants for blood contact, a thin layer of tantalum oxide (Ta2O5) was proposed. Although nitinol self-coats a thin layer of TiO2 titanium dioxide to protect against corrosion, many studies emphasized the need to enhance this protection. Therefore, in the first stage of this study, the alloy surface was prepared by four different methods, producing a passive interlayer. Then a Ta2O5 coating was applied, and the properties with and without the layer were investigated. The resulting coating was applied to the NiTi alloy in the initial state and passivated in water, and perhydrol showed a high adhesion to the substrate. However, the coating deteriorated resistance to pitting corrosion and increased surface wettability. For the initial condition and passivation in perhydrol, the coating affected the reduction of bacterial adhesion to the substrate. Surface preparation directly influenced the optimization of the deposition of this layer on implants in contact with blood. The results suggest that the properties studied were strongly correlated with the type of passive interlayer.

Mesoscale simulation investigation of droplet impacting behaviors on cylindrical surfaces

Understanding and controlling the impacting behaviors of droplets on cylindrical surfaces is a key issue for the design of the process intensification in chemical reaction engineering. In the work, the mesoscale dynamics simulation is performed to systematically investigate the effect of impact conditions on the droplet impacting behaviors. As a result, five impacting modes have been distinguished and the competition mechanisms between the impact parameters are revealed. High impact velocity and low liquid viscosity benefit to the spreading and dispersion of impacting droplets, while the increase of surface wettability can promote and inhibit droplet spreading at low and high velocities, respectively. Besides, the machine-learning models are developed to build the quantitative relation between the impacting behaviors and the impact conditions. The machine-learning models can predict droplets impacting behaviors in experiment and simulation, which is of great importance in relevant chemical engineering applications.

Asymmetric and symmetric spreading for a nanodroplet on an isothermally heated surface in the presence of a parallel electric field

Under parallel electric fields and free evaporation conditions, the statics and dynamics of spreading–evaporating nanodroplets are investigated on an isothermally heated surface via molecular dynamics (MD) simulations. The simulation results show that at the substrate temperature of Ts = 320 K, the static and dynamic contact angles on the left and right edges are initially asymmetric and then symmetric with increasing field strengths of E = 0.00–0.06 V Å−1, resulting in the asymmetric-to-symmetric spreading transition of spreading–evaporating nanodroplets. Under weak evaporation condition, that is, at Ts = 320 K, the asymmetric-to-symmetric spreading transition is triggered by enhancing the intrinsic surface wettability θ0 = 49°–80° at a constant field strength of E = 0.03 V Å−1. However, at the substrate temperature of Ts = 350 K, the symmetric-to-asymmetric spreading transition first appears for the static and dynamic contact angles on the left and right edges, and then the asymmetric-to-symmetric spreading transition appears with increasing field strength. Under strong evaporation condition, that is, at Ts = 350 K, as the field strength is constant at E = 0.03 V Å−1, the asymmetric-to-symmetric spreading transition also appears with increasing surface wettability.

High-frequency supercapacitors with phosphorus-doped Ketjen black

Compact supercapacitors (SCs) have attracted attention for their great potential to replace bulky aluminum electrolytic capacitors (AECs) in alternating current (AC) line filtering applications. Herein, the fabrication of a high-frequency SC is reported using Ketjen black (KB) nanoparticles doped with phosphorus (P) to achieve a high areal capacitance of up to 2.26 mF cm−2 along with a high-rate capability, with a phase angle of –80.2° at 120 Hz. The high performance of the phosphorus-doped KB (designated PKB) SC with a 6 M KOH aqueous electrolyte is associated with its increased surface wettability and additional capacitive sites provided by the P-doping. Density functional theory (DFT) calculations further indicate that the P-doping enhances the interactions between the electrolyte ions and the carbon surface, thus leading to an improved electrochemical performance. These results suggest that the P-doped carbon-based SC could be highly favored in replacing conventional AECs in various high-frequency electronic devices.

Keratin coated titanium as an aid to osseointegration: Physicochemical and mechanical properties

Wool-extracted keratin has been shown to promote bone formation in vivo and may therefore be a potential novel bioactive coating material for osseous implants. This study examined the physicochemical and mechanical properties of keratin-coated titanium, to assess its potential for use in bone-implant applications. Keratin was covalently coupled to silane and glutaraldehyde treated titanium by either (a) molecular grafting or (b), solvent casting. The coated titanium surfaces physicochemical properties including contact angle, roughness, degradation, and swelling characteristics, were subsequently characterized using attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Mechanical properties including the coating adhesion strength and tensile strength were also examined. ATR-FTIR, XPS, XRD, and SEM-EDS all confirmed the presence of keratin on both coated titanium surfaces. SEM imaging showed that solvent casting produced a thick coating which completely covered the titanium surface, while molecular grafting produced a discontinuous thinner coating. The surface roughness increased similarly using either coating methodology while molecular grafting only, increased surface wettability. Both keratin-modified titanium surfaces were stable in solution over 28 days demonstrating suitability for in vivo applications, while the solvent cast titanium also showed good adhesion and tensile bond strength of the coated keratin. These results show a stable keratin coating on the titanium surface was successfully obtained which has both the physiochemical and mechanical properties required for potential dental and or orthopaedic implant applications.

Effect of poly (ethylene glycol) on 3D printed PLA/PEG blend: A study of physical, mechanical characterization and printability assessment

The growing popularity of additive manufacturing in the science, industry is associated with high-quality products for futuristic applications. This study presents an in-depth characterization and analysis of the effect of poly (ethylene glycol) (PEG) having molecular weight 6000 g/mol used with various concentrations (1%,3%,5%) to modify the 3D printed Polylactide (PLA) part. The influence of PEG on the morphology, structure, thermal, wettability and mechanical properties of the 3D-printed PLA/PEG part was investigated. Herein, the mechanical property of injection moulding, 3D printed specimens, and finite element analysis (FEA) simulation results were also compared. The structure and properties of PLA/PEG blends were different from those of virgin PLA. By DSC analysis, it was found that the glass transition temperature (Tg) and cold crystallization temperature decreased in the case of the PLA/PEG blend. From TGA it was observed that PLA/PEG blend was thermally stable. It was shown that with the addition of PEG into PLA the tensile strength and young's modulus decrease, whereas elongation percentage and impact strength increase predominantly. The contact angle results indicate that the addition of PEG lowers the contact angle value of the PLA/PEG blend (from 69.32 ± 1.4° to 45.67 ± 1.2°) and increases surface wettability. With 5% PEG loading, PLA/PEG blend showed optimum structural and mechanical properties together with simple processibility.

Load-bearing capacity of polyamide 6 (PA6) composite to 7075-O aerospace Al-alloy single-lap joints: influence of various laser textured patterns on hot press bonding

In this paper, the effect of the laser-ablated pattern designs on the bonding performance of single-lap dissimilar joints between Polyamide 6 (PA6) composite reinforced with 15% short glass fibers (PA6-15GF) and 7075 aluminium (Al) alloy in O-temper condition, manufactured through hot-pressing technique, is studied by tensile-shear testing. From the optical microscopy (OM) and scanning electron microscopy (SEM) observations, it is found that laser ablation can create a favorable surface morphology for the adhesiveless joints. This is proved by obtaining a significant improvement in the lap-shear strength of the treated samples which can be up to 36%. According to the X-ray photoelectron spectroscopy (XPS) results, the surface chemistry is altered by generating an active oxide layer which is a more suitable condition for the PA6-Al direct bonding. Moreover, achieving favourable surface characteristics is shown by the static contact angle (SCA) findings with the acquired increase in surface wettability after the laser ablation. It is observed that the SCA can be decreased from 83 ± 2 (for as-received Al) by approximately more than 65%. The results gained from the experiments demonstrate that the shape of the laser-induced surface pretreatment markedly affects the strength of metal/composite single-lap joints (SLJs).

Surface Wettability and Coating Performance of Plasma-Treated Wood-Based Composite Panels

The effect of dielectric barrier discharge (DBD) plasma treatment was studied on the surface characteristics and coating performance of transparent epoxy resin on the surface of particleboard (PB) and medium-density fiberboard (MDF). The plasma treatment was performed at three plasma energies (10, 15, and 20 kW) and three distances from the nozzle (10, 20, and 30 mm). Analyzing the samples by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) indicated the changes of their chemical structure by means of the plasma treatment. The contact angle study showed a significant increase in surface wettability after plasma treatment with a pronounced effect observed by treatment parameters. The surface roughness was also significantly increased by the plasma treatment. The strength of the coating adhesion to the surface of the PB and MDF composite panels was also significantly improved by the plasma treatment, while no obvious trend was observed by treatment parameters. The highest adhesion strength of 2.03 MPa and 3.63 MPa were obtained by the PB and MDF samples, respectively, treated at a 10 mm nozzle distance and 15 kW plasma energy. The scratch resistance of the epoxy coatings showed a similar trend as the adhesion strength illustrating an inferior isolated surface of the coating after the plasma treatment.

Molecular investigation on the formation and transition of condensation mode on the surface with nanostructure

To investigate the wetting transition process of vapor condensation on a nanostructured surface, a series of molecular dynamics simulations are performed. With different surface wettability n* and temperature difference, the initiation of condensation and mode transitions are mapped. Compared with smooth surface, the condensation on the nanostructured surface can be initiated at a smaller temperature difference or weaker wettability. When n* < 0.35, the condensate overcomes the viscous force from nanopillars to form Cassie droplets, otherwise, it will immerse into the nanopillars to form Wenzel droplet or liquid film. Cassie droplet is evolved from condensate through spontaneously dewetting transition (SDT). Three modes of SDT are observed and the underlying microscopic mechanisms are discussed. For the mode I of dewetting transition process, it is presented as a single droplet spontaneously overcoming the pinning force of nanostructure to be suspended. For mode II, droplets coalesce inside the nanopillars and gradually dewet over multiple nanopillars, or the adjacent Wenzel droplets contact to form a liquid bridge on the upper of the nanostructures, promoting the SDT. For the mode III, the growing Wenzel droplets coalesce with the suspended Cassie droplets to complete SDT. Meanwhile, the droplet SDT process is accompanied by a decrease in potential energy, which is mainly driven by the surface tension. For a small n* and condensation rates, mode I dominates the droplet dewetting process. With the increase of surface wettability, the proportion of mode I decreases, while the proportion of mode II and mode III increases accordingly.

Bouncing dynamics of nanodroplets impacting superhydrophobic surfaces: The coupling influence of wetting transitions and scale effects

When nanodroplets rebound from nanopillar-arrayed superhydrophobic surfaces, the coupling influence of wetting transitions and scale effects on the bouncing dynamics is for the first time investigated via molecular dynamics (MD) simulations. The simulation results show that two bouncing patterns, the Cassie state bouncing and the Wenzel state bouncing, are always observed on nanopillar-arrayed superhydrophobic surfaces in a wide range of We= 1.5–95 as the coupling influence is changed by various aspect ratios and surface wettability. At same Weber number, the contact time of the Cassie state bouncing is constant, but that of the Wenzel state bouncing being increased with the increased aspect ratio. However, the contact time is always increased with the increased surface wettability regardless of the bouncing pattern. Based on that, scaling laws of contact time are eventually established for these two bouncing patterns, respectively.

Numerical analysis of the effect of ellipsoidal shape on the freezing behavior of impacting water droplets on cold surfaces

A two-dimensional numerical model that investigates the freezing behavior of ellipsoidal impacting water droplets on cold surfaces was established in this paper, focusing on the spreading behavior, impact force evolution and heat transfer behavior of ellipsoidal water droplets. For cold surfaces with a higher temperature, reducing aspect ratio can reduce the contact time of water droplets on the superhydrophobic surface, which is useful for the rebound of impacting water droplets. Increasing aspect ratio can increase the spreading range of water droplets, especially for hydrophilic surfaces. The evolution of impact force of ellipsoidal water droplets on superhydrophobic surfaces exhibits a double-peak feature. With increase of aspect ratio, the first peak of impact force is gradually decreased, while the second peak is gradually increased. The effect of surface wettability on the first peak of impact force is smaller. The feature of the second peak of impact force decreases with increase of surface wettability and finally disappears. Although water droplet with higher aspect ratio has smaller peak of heat transfer rate, the heat transfer between it and cold surface is greater than that with lower aspect ratio. The stronger the surface wettability, the more obvious this phenomenon is. For some applications where the rapid freezing of impacting water droplets is required, increasing aspect ratio of water droplets seems to be a good choice.