Contact Angle Of Water Droplet Research Articles

ZnO nanostructure fabricated by electrochemical deposition

Electrochemical deposition method was employed to fabricate ZnO nanorods on zinc foil substrate in this paper. The structural observations of ZnO nanorods with different aspect ratios were carried out by field- emission scanning electron microscopy. The microstructures of ZnO nanorods were also characterized by X-ray diffraction and the changes in surface hydroxyls with electrochemical deposition time were analyzed by X-ray photoelectron spectroscopy. The study results show the aspect ratios of ZnO nanorods and the density of their surface hydroxyls are responsible for their superhydrophobicity. The fluorinated polymer coated ZnO nanorods showed an excellent superhydrophobic behavior with 167◦ contact angle of water droplet, which is larger than that of fluorinated polymer flat surface. The more the surface hydroxyls are, the more hydrophilic the surfaces are. Meanwhile, the larger the aspect ratio of ZnO nanorod arrays is, the larger its drophobicity is. The results of this study might have a simple and feasibility pathway to the fabrication of superhydrophobic cleaning materials used in engineering fields.

Mouthpart adaptations of antlion larvae facilitate prey handling and fluid feeding in sandy habitats.

Antlion larvae are fluid-feeding ambush predators that feed on arthropods trapped in their funnel-shaped pits built in sandy habitats; however, details are lacking about their feeding mechanism. Here, we tested the hypothesis that the antlion, Myrmeleon crudelis, has adaptations that facilitate fluid feeding in sandy habitats. We measured contact angles of water droplets and used the capillary-rise technique to assess mouthpart wettability. A structural organization was discovered that provides a hydrophobic-hydrophilic wetting dichotomy that simultaneously supports self-cleaning and fluid uptake and is enabled by antiparallel movements of the maxillae. The mouthparts also are augmented by their mechanical properties, including maxillae and mandible tips that might be heavily sclerotized, as determined by confocal microscopy, which likely facilitates piercing prey. Our findings provide insight into how antlion larvae have overcome the challenges of fluid feeding in sandy habitats, which probably contributed to their success and widespread distribution.

A stearic acid/polypyrrole-based superhydrophobic coating on squeeze-cast Mg-Sr-Y-Ca-Zn alloys for improved salt-water corrosion

A polypyrrole (PPy) and stearic acid (SA)-based superhydrophobic coating was developed to improve the corrosion behavior of squeeze cast Mg-1.0 wt% Sr-1.0 wt% Y-0.6 wt% Ca-0.5 wt% Zn alloy in NaCl solution. The structure and morphology of the coating were analyzed using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), three-dimensional optical surface profilometer, glancing angle X-ray diffraction (GIXRD), and X-ray photoelectron spectroscopy (XPS) reveals variable coating thickness ranging from ~25–120 μm (depending on Mg alloy pretreatment with/without NaOH prior to coating) comprised of primarily Mg, C, O, Cl, and Zr species ascribed to a mixed composition of PPy, Mg(OH)2, and low amount of ZrO2 with mud-crack features and petal-like clusters. Although SA/PPy-based superhydrophobic coating (contact angle of static water droplets ~1640) can improve the corrosion resistance of bare Mg alloy drastically owing to the presence of thin air cushion between NaCl solution and Mg alloy surface preventing saltwater infiltration and advancement of Cl−-ions towards reactive Mg surface, however, the surface pretreatment in NaOH salt bath before superhydrophobic surface treatment has a profound effect on the interphase, bonding, and stability of the coating with Mg and associated corrosion phenomena. The Mg alloy without NaOH pretreatment (NPT) demonstrated excellent instantaneous corrosion resistance in 0.1 M NaCl confirmed by potentiodynamic polarization, polarization resistance (RP), and coating resistance (Rcoat) measured by electrochemical impedance spectroscopy (EIS). On the contrary, NaOH pretreated Mg alloys (1MPT, 5MPT) exhibited excellent corrosion protection ability (up to ~4-5 h) during long-term EIS study owing to the presence of Mg(OH)2 thick film deposited during pretreatment acting as a protective barrier preventing PPy degradation and Mg2+-ion diffusion to the outward surface. Overall, SA/PPy-based superhydrophobic coating juxtaposed with/or without surface pretreatment can shed new insight into the corrosion phenomena of squeeze cast Mg alloy in NaCl solution.

Surface wettability analysis and preparation of hydrophobic microcylindrical arrays by μ-SLA 3D printing

Hydrophobic surface preparation is always complicated because of the different microstructures requirements with specific functions. This paper describes a Stereo Lithography Appearance (SLA) 3D printing method for creating hydrophobic surfaces. In this work, four different shapes of microstructures were prepared to observe the molding effect of the SLA process for the determination of the best printing structures. The contact angles of water droplet on the microarray surface were also measured through a contact angle meter with high-definition camera. The results show that the contact angles of different microarray surfaces were much better than the flat surfaces with chemical coating. Moreover, the cylindrical array shows the most stable hydrophobic effect with a maximum contact angle of 143.6°. The theoretical design and construction of surface wetting microstructures were also explored by calculating the minimum percentage of solid based on the Cassie-Baxter's wetting model. It is believed that the micro-cylindrical array could be adopted to promote the hydrophobic properties of material surfaces, which also indicates that the μ-SLA method could provide a new idea for the preparation of wettability surfaces.

Hydrophobicity/Oleophilicity of Autoclaved Aerated Concrete (AAC) Grains Coated with Oleic and Stearic Acids for Application as Oil/Water Separating Filtration and Adsorbent Materials in Vietnam

Separation of oil and water is an effective technique to treat oily wastewater. For examining the applicability of porous grains coated with hydrophobic agents (HA) as low-cost and easily available filtration and adsorbent materials in the separation of oil and water, this study assessed the hydrophobicity/oleophilicity of porous grains made from autoclaved aerated concrete scrap coated with low-cost and harmless hydrophobic agents such as oleic and stearic acids. Tests using a sessile droplet method showed unique relationships between the contact angles (CA) of water droplets in air (CAwa), oil droplets in water (CAow) and coated HA concentrations. The CAwa increased linearly with increasing HA concentration and then became almost constant and/or gently increased after a specific point, indicating that a minimum coating amount gives the maximum hydrophobicity to HA-coated porous grains exists. The CAow gradually decreased exponentially with increasing HA concentration. In particular, the CAow of porous grains coated with stearic acid decreased with increasing of HA concentration in a two-step process. Furthermore, analyses of the Pearson correlation showed that both CAwa and CAow correlated well with the specific surface area (SSA), implying that the SSA is a good indicator as a quick assessment of hydrophobicity/oleophilicity of HA-coated porous grains.

Facile preparation and properties of superhydrophobic nanocellulose membrane

Superhydrophobic nanocellulose membrane was prepared by synergistically modifying biodegradable nanocellulose with low-carbon perfluoroorganosiloxane and ethyl orthosilicate. The effects of four kinds of low-carbon perfluoroorganosiloxanes with different structures and their ratio to ethyl orthosilicate on the hydrophobic properties of nanocellulose membrane were investigated, and then FT-IR, XPS, XRD, SEM, TEM, AFM, TG and contact angle goniometer were used to characterize the structure and hydrophobic properties of nanocellulose membrane before and after modification. It is found that when the molar ratio of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane (PFOTMS) to ethyl orthosilicate (TEOS) is 1, the modified nanocellulose membrane PFOTMS-TEOS-CNF is loaded with silica nanoparticles both inside and on its surface, and a micro-nano hierarchical rough morphology with low surface energy is constructed. At this point, the root-mean-square roughness (Rq) of nanocellulose membrane is 112 nm, and the static contact angle of water droplet is 153.5°, successfully realizing superhydrophobicity. In addition, compared to unmodified nanocellulose membrane, PFOTMS-TEOS-CNF with better thermal stability includes an additional maximum weight loss rate temperature (491.2 °C). The above advantages markedly improve the shortcomings of pristine nanocellulose, such as superhydrophilicity and insufficient thermal stability, and also broadens its high-value application in many fields.

Green and sustainable chitosan–gum Arabic nanocomposites as efficient anticorrosive coatings for mild steel in saline media

The application of green and sustainable anticorrosive coatings is becoming of upsurge interest for the protection of metallic materials in aggressive environments. Herein, a stable crystalline chitosan/gum Arabic composite (CGAC) nanopowder was successfully synthesized and characterized by various methods. The CGAC nanopowder with different doses (25, 50, 100, and 200 ppm) was used to coat mild steel samples and examined its anticorrosion ability in 3.5 wt.% NaCl solution using gravimetric, electrochemical measurements, and surface characterization techniques. All methods yielded consistent results revealing that nanocomposite coatings can impart good anticorrosive properties to the steel substrate. The obtained protection efficiency was enhanced with increasing CGAC dose in the applied surface layer achieving 96.6% for the 200 ppm-coating. SEM and AFM surface morphologies of uncoated and coated samples after the inundation in the saline solution showed that CGAC coating can block the active corrosive sites on the steel surface, and prevent the aggressive Cl- ions from attacking the metallic substrate. The water droplet contact angle gave further support as it increased from 50.7° for the pristine uncoated surface to 101.2° for the coated one. The current research demonstrates a promising natural and reliable nanocomposite coating for protecting mild steel structures in the marine environment.

Facile fabrication of durable and flexible superhydrophobic surface with polydimethylsiloxane and silica nanoparticle coating on a polyethylene terephthalate film by hot-roll lamination

Practical applications of superhydrophobic surfaces have been limited by several disadvantages such as complex fabrication processes, high modification cost, and low mechanical durability. In this study, we present a facile and low-cost fabrication method to make flexible superhydrophobic films by a hot-roll lamination process. The film consists of a hydrophobic polydimethylsiloxane (PDMS) and hydrophobic silica nanoparticle (SNP) composite coating layer on a polyethylene terephthalate (PET) film. The coated film displayed excellent superhydrophobic properties with an apparent water droplet contact angle of 176.3° and a sliding angle of 2.4°. The surface morphology, roughness, and cross-section chemical composition of the coated films were investigated by field emission scanning electron microscopy and confocal laser scanning microscopy. The mechanical durability of the coated films was evaluated using several tests such as scratching with sandpaper, repeated bending deformation, and adhesion tape tests. The fabricated superhydrophobic films still showed superhydrophobic behavior after 20 tape tests. In addition, the fabricated superhydrophobic films exhibited strong mechanical durability, which preserved their very high contact angle >160° and very small sliding angle <10° after a 350 cm abrasion test with 240 grit sandpaper and a pressure of 1.2 kPa. Also, the coated sample exhibited very stable superhydrophobicity after 100 bending cycles due to the elasticity of PDMS. The chemical stability of flexible PDMS/SNP coated PET films was also investigated in acidic, neutral, and alkaline solutions and showed excellent chemical stability in acidic and neutral media in contrast to the alkaline medium. The obtained results demonstrated the outstanding robustness of the fabricated flexible superhydrophobic films that are promising for self-cleaning and water droplet bouncing performance. • Superhydrophobic surfaces were fabricated by a facile method without toxic chemicals. • The durability of the superhydrophobic films was demonstrated by abrasion and tape tests. • The fabricated films exhibited good flexibility in bending tests. • The self-cleaning property of the fabricated coated surfaces was also observed.

Improved performance of PCBM/MAPbI3 heterojunction photovoltaic cells with the treatment of a saturated BCP/IPA solution

The interfacial contact quality between the hydrophilic MAPbI 3 and hydrophobic PCBM thin films are improved by using the treatment of a saturated bathocuproine/isopropanol (BCP/IPA) solution, which largely increases the power conversion efficiency (PCE) from 12.96% to 18.67%. The atomic force microscopic images, water-droplet contact angle images, viscosity measurement results and near-infrared transmittance spectra show that the increased open-circuit voltage (V OC ) is related to the formation of a denser PCBM thin film and the better contact quality of the PCBM/MAPbI 3 heterojunction. Besides, the power-dependent current density-voltage (J-V) curves show that the lower defect density in the solar cells results in the higher V OC . In other words, the treatment of a saturated BCP/IPA solution can decrease the defect density of the PCBM/MAPbI 3 heterojunction and thereby boosting the photovoltaic performance and extending the device lifespan. • The saturated BCP/IPA solution treatment increases the density of the PCBM thin film. • The saturated BCP/IPA solution treatment strengthens the contact quality at PCBM/MAPbI 3 interface. • The saturated BCP/IPA solution treatment increases the hydrophobicity of PCBM/MAPbI 3 heterojunction. • The saturated BCP/IPA solution treatment improves the PCE of photovoltaic cells from 12.69% to 18.67%.

Plasma nano-patterning for altering hydrophobicity of copper substrate for moist air condensation

Fabrication of durable hydrophobic metallic substrate is an emerging area of research for the condensation process in many industrial devices because its implementation enhances the efficacy of the devices. In this work, effective and durable hydrophobic copper (Cu) substrates were fabricated by plasma nano-pattering. Various discharge voltages were used to create various types of nano-patterns textured on copper substrates. For 30 min of irradiation of Argon gas plasma at various discharge voltages of 500, 650 and 750 V, morphologies of substrates were altered such that micro-litre water droplet has contact angle of 105 ± 3o, 97 ± 5o, and 95 ± 5o, respectively. However, pristine polished Cu substrate has water droplet contact angle of 56±5o. The micro-graph of scanning electron microscope (SEM) showed micro-order to nano-order roughness on etched substrates and the structure of nano-patterns was different for different discharge voltages for given period of argon ions irradiation. The etched copper substrate at 500 V was deployed as a condensing surface for moist air condensation of temperature 28 °C, relative humidity 70% and degree of sub-cooling 10°C. These results showed that the water condensation rate of plasma etching hydrophobic Cu substrate was 438 ml/m2-h, compared to 188 ml/m2-h for pristine Cu substrate.

Laser-Induced Fast Assembly of Wettability-Finely-Tunable Superhydrophobic Surfaces for Lossless Droplet Transfer.

Rose-petal-like superhydrophobic surfaces with strong water adhesion are promising for microdroplet manipulation and lossless droplet transfer. Assembly of self-grown micropillars on shape-memory polymer sheets with their surface adhesion finely tunable was enabled using a picosecond laser microprocessing system in a simple, fast, and large-scale manner. The processing speed of the wettability-finely-tunable superhydrophobic surfaces is up to 0.5 cm2/min, around 50-100 times faster than the conventional lithography methods. By adjusting the micropillar height, diameter, and bending angle, as well as superhydrophobic chemical treatment, the contact angle and adhesive force of water droplets on the micropillar-textured surfaces can be tuned from 117.1° up to 165° and 15.4 up to 200.6 μN, respectively. Theoretical analysis suggests a well-defined wetting-state transition with respect to the micropillar size and provides a clear guideline for microstructure design for achieving a stabilized superhydrophobic region. Droplet handling devices, including liquid handling tweezers and gloves, were fabricated from the micropillar-textured surfaces, and lossless liquid transfer of various liquids among various surfaces was demonstrated using these devices. The superhydrophobic surfaces serve as a microreactor platform to perform and reveal the chemical reaction process under a space-constrained condition. The superhydrophobic surfaces with self-assembled micropillars promise great potential in the fields of lossless droplet transfer, biomedical detection, chemical engineering, and microfluidics.

Conformal Loading Effects of P3CT-Na Polymers on the Performance of Inverted Perovskite Solar Cells

The conformal loading effects of P3CT-Na polymers on ITO/glass samples were investigated using different concentrations of P3TC-Na/water solution, which significantly influenced the device efficiency of the resultant inverted perovskite solar cells. The obtained water-droplet contact angle images, surface morphological images, photoluminescence spectra and X-ray diffraction patterns show that the hydrophilic moiety of the P3CT-Na polymers plays an important role in the conformal loading effects, thereby resulting in a smoother perovskite crystalline film due to the formation of merged grains. It is noted that the average power conversion efficiency increases from 14.83% to 17.27% with a decrease in the concentration of the P3CT-Na/water solution from 60 wt% to 48 wt%.

Visible-light-driven photocatalytic PVDF-TiO2/CNT/BiVO4 hybrid nanocomposite ultrafiltration membrane for dairy wastewater treatment

Enhancing the performance of polymeric membranes by nanomaterials has become of great interest in the field of membrane technology. The present work aimed to fabricate polyvinylidene fluoride (PVDF)–hybrid nanocomposite membranes and modify them with TiO2 and/or BiVO4 nanoparticles and/or carbon nanotubes (CNTs) in various ratios. Their photocatalytic performance under visible light was also investigated. All modified PVDF membranes exhibited higher hydrophilicity (lower contact angle of water droplets) than that of the neat membrane used as a reference. The membranes were characterized by using bovine serum albumin (BSA) as model dairy wastewater. The hybrid membranes had better antifouling properties as they had lower irreversible filtration resistance than that of the neat membrane. Hybrid PVDF membranes containing TiO2/CNT/BiVO4 showed the highest flux and lowest irreversible resistance during the filtration of the BSA solution. PVDF-TiO2/BiVO4 had the highest flux recovery ratio under visible light (70% for the PVDF mixed with 0.5% TiO2 and 0.5% BiVO4). The hydrophilicity of membrane surfaces increased with the incorporation of nanoparticles, preventing BSA to bind to the surface. This resulted in a slight decrease in BSA and chemical oxygen demand rejections, which were still above 97% in all cases.

Synthesis methods of NiOx nanoparticles and its effect on hole conductivity and stability of n-i-p perovskite solar cells

Herein, nickel oxide nanoparticles (NPs) with different routes were synthesized and used as HTLs for MAPbI3-based PSCs. UV-Vis absorption spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), steady-state photoluminescence (PL) spectra, space-charge limited current (SCLC) model, water droplet contact angle and current voltage (I-V) measurements were used to investigate the characteristics of synthesized NiOx, photovoltaic parameters and stability of constructed n-i-p perovskite solar cells. It was found that employing nickel chloride hexahydrate (NiCl2·6H2O) (labeled as NiCl2) as Ni reagent in the synthesis process could be obtained more desirable NiOx NPs for the HTL role in PSC devices. Results showed NiCl2-based NiOx HTL facilitates hole extraction to a gold electrode and suppresses electron-hole recombination rate in PSCs. NiCl2-based NiOx HTL brings a champion power conversion efficiency (PCE) of 12.57% for PSCs, higher than HTL-free PSCs with a champion PCE of 6.78%. In addition, the stability of NiOx-containing PSCs was considerably higher than that of a device without NiOx HTL. NiCl2-based PSC maintained 86% of its initial PCE after keeping in ambient air (25–40% RH) for 45 days, outperforming the control device that only retained ∼ 48% of its initial PCE after 25 days of the stability test. This work provides a deep understanding for efficiency and stability of the NiOx based perovskite solar cells and an approach to improve the using of low-cost HTLs.

Modeling of two-scale array microstructure and prediction of apparent contact angle based on WEDM

The core issue in the theoretical design of superhydrophobic surfaces is to elucidate the relationship between surface microstructure and wettability. In this paper, four two-scale array microstructure models with different shapes are proposed to predict the apparent contact angles (CAs) of EN-GJL-250 (Grey Cast Iron) surface under different wire-cut electrical discharge machining (WEDM) discharge parameters. The primary microstructure is the artificially designed semicircle, rectangular, sawtooth and square column array microstructure, and the secondary microstructure is the micro-nanostructure of the surface machined by WEDM. Firstly, the mechanical analysis of water droplets placed on the primary array microstructure is carried out by the force balance method. According to Newton’s third law, equations containing CA parameters are listed. Secondly, the finite element method (FEM) was used to analogue simulation the distribution of material surface temperature and flow field in the WEDM single-pulse discharge machining process. The surface equivalent geometric model of WEDM was established by a uniform arrangement of single pulse pits obtained by simulation, the surface roughness coefficients under different discharge parameters were calculated, and the influence of the surface roughness coefficients on the surface wettability was studied. The numerical results show that the CA is jointly determined by the surface roughness coefficient under different discharge parameters, and the shape and size parameters of the microstructure. Finally, semicircle, rectangular, sawtooth and square column array microstructures were fabricated on EN-GJL-250 surface by high-speed WEDM. Experimental results show: The CA of water droplets on the square column array microstructure is the largest, the predicted values of the CA were in good agreement with the experimental values, and the average relative error was 7.83%.

Synthesis of a Superhydrophobic Fluorinated Nano-Emulsion and Its Modification on the Wettability of Tight Sandstone.

The water-blocking effect is a serious problem when developing tight sandstone gas reservoirs, which can cause a sharp reduction in gas production. Wettability alteration of near-wellbore sand rock surface from superhydrophilicity to superhydrophobicity is an effective method to decrease capillary pressure. In this study, a superhydrophobic fluorinated nano-emulsion was synthesized via a soap-free emulsion polymerization process using methacryloxyethyl trimethyl ammonium chloride, trifluoctyl methacrylate, and styrene as monomers. The effect of the fluorinated monomer concentration on wettability alteration was evaluated by measuring the contact angle of the formation water droplet on the modified glass slides using nano-emulsions with different fluorinated monomer concentrations. The results showed that the nano-emulsion had a good dispersibility and homogeneous particle size of around 90 nm, and with the increase in fluorinated monomer concentration, the contact angle increased. The contact angle was the largest when the fluorinated monomer mass rate concentration reached 50%. The adsorption of nanoparticles could alter the rock wettability from a super hydrophilic state (θ = 7°) to a superhydrophobic state (θ = 150°). The spontaneous imbibition experiments showed that the formation water adsorption quality of the core decreased by 49.7% after being modified by the nano-emulsion. The nano-emulsion showed a good superhydrophobicity and had the potential to be used to reduce the water-blocking damage in the tight gas reservoirs.

Silanizing nano SiO2 and its application in recycled nitrile rubber to prepare super oil resistant/superhydrophobic/superoleophilic oil/water separator

Polymer wastes and oil slicks are environmental threats in the present century. Accordingly, the reuse of polymer wastes to absorb oil slicks could be an interesting topic. In this research, devulcanized nitrile rubber (DNBR) as oil resistant/recycled material were used to prepare an environmental friendly superhydrophobic/superoleophilic oil sorbent. For this purpose, silica nanoparticles were silanized using vinyltriethoxysilane. HR-TEM, FTIR and XPS analysis were performed to characterize the surface morphology and chemical composition of the pure and silanized nanoparticles. The grafted nano silica illustrated superhydrophobic behavior due to water droplet contact angle which was 156 compared to 53° for pure nano silica. XPS analysis showed that the content of Si, O and C elements on the surface of modified nano silica increased by 18%, 8% and 25%, respectively, compared to pure nano silica. The chemo-thermo-mechanical properties of the DNBR nanocomposites contained 6 phr of pure and silanized nanoparticles were evaluated. Results confirmed improvement in the curing and mechanical performances of the rubbery nanocomposite due to silane grafting. The modified nanocomposite had the highest oil absorption capacity over 2.4 g.g− 1 (i.e. for dense sheet). It efficiently separated about 91% of Persian Gulf oil/water mixtures with remarkable reusability of about 700 cycles.

Seasonal variations in the amount of black carbon particles deposited on the leaf surfaces of nine Japanese urban greening tree species and their related factors

As black carbon (BC) particles can be deposited on the leaf surfaces, urban greening is considered to be effective in purifying urban air. However, little information on the seasonal variations in the amount of BC particles deposited on the leaf surfaces (BC amount on the leaves) is available in Japanese urban greening tree species. Therefore, we investigated seasonal variations in the BC amount on the leaves of evergreen (Quercus glauca, Quercus myrsinaefolia, Osmanthus fragrans and Ilex rotunda) and deciduous (Zelkova serrata, Styrax japonica, Magnolia kobus, Cornus kousa and Cornus florida) broad-leaved tree species. The BC amount on the leaves tended to increase from April for different periods, and then reached a saturated state in the tree species, excluding M. kobus. In the 4 evergreen broad-leaved trees, the seasonal variation was positively correlated with the atmospheric concentration of BC particle. In the 5 deciduous broad-leaved trees, the seasonal variation was negatively and positively correlated with the water-repellence (water droplet contact angle) and the amount of epicuticular wax on the leaf surface, respectively. Therefore, the BC amounts on the leaves of evergreen and deciduous broad-leaved urban tree species are considered to be mainly regulated by environmental factors and leaf surface characteristics, respectively.

Nanometric CrN/CrAlN and CrN/ZrN multilayer physical vapor deposited coatings on 316L stainless steel as bipolar plate for proton exchange membrane fuel cells

Nanometric CrN/ZrN and CrN/CrAlN multilayer coatings were deposited on 316L stainless steel as metallic bipolar plates (BPs) for proton exchange membrane fuel cells (PEMFCs) by the cathodic arc evaporation-physical vapor deposition technique. The coatings were evaluated using X-ray diffraction, field emission scanning electron microscopy, surface roughness determination, and water droplet contact angle measurement. In order to study the electrochemical behavior of the coatings, potentiodynamic polarization and electrochemical impedance spectroscopy examinations were conducted at the simulated cathodic PEMFC media (0.5 M H2SO4 purging O2, 70°C). Also, the interfacial contact resistance (ICR) of the coated and uncoated 316L BPs was evaluated in different compaction forces before and after the potentiostatic polarization test. The current density at 0.644 V vs. Ag/AgCl of 0.16 and 0.76 μA cm−2 was recorded for CrN/ZrN and CrN/CrAlN, respectively. Moreover, it was found that after the potentiostatic polarization tests, the ICR values of the 316L BPs were decreased from 276 to 8.3 and 9.4 mΩ cm2 by the deposition of the CrN/ZrN and CrN/CrAlN coatings, respectively. The enhancement in the ICR and corrosion behavior of both CrN/ZrN and CrN/CrAlN multilayer coatings indicated that these coatings can be potentially suitable for PEMFCs application, according to the United States Department of Energy's targets.

Surface Characteristics of Ageing Asphalt Binder Coupling Thermal Oxidation and Ultraviolet Radiation

In this study, styrene-butadiene-styrene (SBS) modified asphalt binder was aged by thermal oxidation coupled with ultraviolet (UV) radiation. Fluorescence microscopy (FM), scanning electron microscopy (SEM) with energy dispersive x-ray (EDX) detector, surface free energy, optical technology, Fourier transform infrared spectroscopy, and dynamic shear rheometer were used to explore the surface characteristics and trace the chemo-rheological evolution of the asphalt binder at various durations of aging. Both FM and SEM could observe two phases of degradation of the polymer under thermo-oxidation. The surface of UV-aged asphalt binder produced more cracks, observed by FM and SEM, and bulged along these cracks and some fragmented blocks appeared. EDX results indicated that the oxygen content of the surface of the asphalt binder increased with increasing aging duration, leading to more oxygen-containing compounds, more carbonyl and sulfoxide groups, increasing polarity, and decreasing contact angle of water droplets on the surface of the asphalt binder. Coupled aging increased the reflectance in all regions from 200 nm to 2,500 nm, while thermo-oxidative aging alone increased the reflectance from 200 to 400 nm and produced the opposite result in the other region. With increased aging duration, UV-aged asphalt binder becomes brighter and thermo-oxidative aged asphalt binder becomes darker. The asphalt binder samples did not discolor much with varying aging duration, and the color difference was more similar than opposite. The results of testing chemo-rheological properties indicated that the addition of UV radiation significantly increased the stiffness and elasticity and produced more obvious effects on the surface characteristics of variously aged binders.