Hydrophobic Thin Films Research Articles

Spray synthesized hydrophobic α-Fe2O3 thin film electrodes for supercapacitor application

α-Fe2O3 thin films were deposited through spray pyrolysis technique with different precursor solution concentrations i.e. (0.05, 0.1 and 0.2 M) of iron nitrate at optimized 400 °C temperature. The effect of precursor concentrations on material properties such as structural, morphological, contact angle and electrochemical supercapacitive were explored. Structural analysis, using X-ray diffraction confirmed the hexagonal phase of the films polycrystalline in nature. The Scanning electron microscopy showed large area grannual morphology. Contact angle analysis of α-Fe2O3 thin films illustrated hydrophobic in nature. The supercapacitive performance of Fe2O3 thin film electrodes were explored in 1M NaOH aqueous electrolyte. The specific capacitance was decreased from 277 F g−1 to 196 F g−1 as the concentrations of precursor solution varied from 0.05 to 0.2 M.

Overcoming the Intrinsic Difference between Hydrophilic CH₃NH₃PbI₃ and Hydrophobic C60 Thin Films to Improve the Photovoltaic Performance.

Dimethylformamide/dimethyl sulfoxide solvent mixtures were used as the CH3NH3PbI3 (MAPbI3) precursor solvent in a one-step spin coating method to fabricate smooth and hydrophilic crystalline MAPbI3 thin films on top of hydrophobic carbon-60 (C60) thin film for highly efficient photovoltaics. The structural, optical, and excitonic characteristics of the resultant MAPbI3 thin films were analyzed using X-ray diffraction (XRD), atomic-force microscopy, absorbance spectroscopy, photoluminescence (PL) spectrometry, and nanosecond time-resolved PL. There was a trade-off between the crystallinity and surface roughness of the MAPbI3 thin films, which strongly influenced the device performance of MAPbI3-based photovoltaics. The high power conversion efficiency (PCE) of 17.55% was achieved by improving the wettability of MAPbI3 precursor solutions on top of the C60 thin films. In addition, it was predicted that the fill factor and PCE could be further improved by increasing the crystallinity of the MAPbI3 thin film while keeping it smooth.

Design and fabrication of highly hydrophobic Mn nano-sculptured thin films and evaluation of surface properties on hydrophobicity

The wettability of solid surfaces is important from the aspects of both science and technology. The Mn nano-sculptured thin films were designed and fabricated by oblique angle deposition of Mn on glass substrates at room temperature. The obtained structure was characterized by field emission scanning electron microscopy and atomic force microscopy. The wettability of thin films samples was investigated by water contact angle (WCA). The 4-pointed helical star-shaped structure exhibits hydrophobicity with static WCAs of more than 133° for a 10-mg distilled water droplet. This sample also shows the rose petal effect with the additional property of high adhesion. The Mn nano-sculptured thin films also act as a sticky surface which is confirmed by hysteresis of the contact angle obtained from advancing and receding contact angles measurements. Physicochemical property of liquid phase could effectively change the contact angle, and polar solvents in contact with hydrophobic solid surfaces do not necessarily show high contact angle value.

Ambient aging of rhenium filaments used in thermal ionization mass spectrometry: Growth of oxo-rhenium crystallites and anti-aging strategies.

Degassing is a common preparation technique for rhenium filaments used for thermal ionization mass spectrometric analysis of actinides, including plutonium. Although optimization studies regarding degassing conditions have been reported, little work has been done to characterize filament aging after degassing. In this study, the effects of filament aging after degassing were explored to determine a “shelf-life” for degassed rhenium filaments, and methods to limit filament aging were investigated. Zone-refined rhenium filaments were degassed by resistance heating under high vacuum before exposure to ambient atmosphere for up to 2 months. After degassing the nucleation and preferential growth of oxo-rhenium crystallites on the surface of polycrystalline rhenium filaments was observed by atomic force microscopy and scanning electron microscopy (SEM). Compositional analysis of the crystallites was conducted using SEM-Raman spectroscopy and SEM energy dispersive X-ray spectroscopy, and grain orientation at the metal surface was investigated by electron back-scatter diffraction mapping. Spectra collected by SEM-Raman suggest crystallites are composed primarily of perrhenic acid. The relative extent of growth and crystallite morphology were found to be grain dependent and affected by the dissolution of carbon into filaments during annealing (often referred to as carbonization or carburization). Crystallites were observed to nucleate in region specific modes and grow over time through transfer of material from the surface. Factors most likely to affect the rates of crystallite growth include rhenium substrate properties such as grain size, orientation, levels of dissolved carbon, and relative abundance of defect sites; as well as environmental factors such as length of exposure to oxygen and relative humidity. Thin (∼180 nm) hydrophobic films of poly(vinylbenzyl chloride) were found to slow the growth of oxo-rhenium crystallites on the filament surfaces and may serve as an alternative carbon source for filament carburization.

Structure and Hydrophobicity of Fe<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub> Coatings

Fe2O3–TiO2 coatings were successfully prepared on glass slide substrates using sol–gel method for wettability applications. The microstructure and surface properties of the coatings were extensively characterized by using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Different solutions were prepared by adding distilled water to sol solution. Glass substrates were coated by solutions of Ti-alkoxide, Fe-chloride hexahydrate, ethylene glycol, acetic acid, isopropanol and glycerol. The obtained gel films were dried at room temperature for 15 min in air. The oxide thin films were annealed at 500 ºC for 1h. The influence of distilled water concentration and withdraw speed on contact angle of the films was established. In addition, XRD results revealed that Fe2O3–TiO2 films composed of anatase, rutile, brookite and hematite phases. The purpose of this contribution was the investigation of different preparation parameters during the synthesis of iron oxide rich Fe2O3–TiO2 thin hydrophobic films on glass substrate. SEM and AFM observations revealed leaf-like structure formation on a coating surface.

Intrinsic Hydrophobic Antibacterial Thin Film from Renewable Resources: Application in the Development of Anti-Biofilm Urinary Catheters

The use of renewable resources to develop functional materials is increasing in order to meet the sustainability challenges. In an era of inexorable evolution of antimicrobial resistance, there is a substantial increase in demand for the development of efficient antimicrobial thin film coating from renewable resources for public bacterial threats, food, biomedical, and industrial applications. In the present investigation, we have used cardanol, a phenolic compound having unsaturated hydrophobic tail isolated from cashew fruits, and linseed oil, a vegetable oil and an important biobased building block, which are cheap and easy to regenerate. This study reports the synthesis of cardanol based metal complexes having unsaturated hydrophobic unit and acrylated epoxidized linseed oil (AELO) prepared via epoxidation of double bonds followed by acrylation. The double bond present in the metal complexes and AELO is prone to form assembled thin film under atmospheric conditions, without the need of any initiators....

Effects of seed layers on controlling of the morphology of ZnO nanostructures and superhydrophobicity of ZnO nanostructure/stearic acid composite films

Hydrophobic ZnO self-cleaning thin films with the nanobundles and nanocarpets structures fabricated on indium tin oxides (ITO) glass substrate are reported. The water contact angle of ZnO nanobundles and nanocarpets structures (79° and 67° respectively) is higher than that of unmodified ZnO nanorods. A subsequent chemcial treatment with stearic acid (SA) contributed to a superhydrophobic surface with a water contact angle of 159°. Its superhydrophobic property is originated from the nanobundles or nanocarpets structures and surface energy of SA/ZnO nanobundles and SA/ZnO nanocarpets composite nanostructures. Moreover, this promising ZnO nanostructured materials show an important application in self-cleaning smart coatings.

Detection of chemical substances in water using an oxide nanowire transistor covered with a hydrophobic nanoparticle thin film as a liquid-vapour separation filter

We have developed a method to detect the presence of small amounts of chemical substances in water, using a Al2O3 nanoparticle thin film covered with phosphonic acid (HDF-PA) self-assembled monolayer. The HDF-PA self-assembled Al2O3 nanoparticle thin film acts as a liquid-vapour separation filter, allowing the passage of chemical vapour while blocking liquids. Prevention of the liquid from contacting the SnO2 nanowire and source-drain electrodes is required in order to avoid abnormal operation. Using this characteristic, the concentration of chemical substances in water could be evaluated by measuring the current changes in the SnO2 nanowire transistor covered with the HDF-PA self-assembled Al2O3 nanoparticle thin film.

Ethanol–water co-condensation into hydrophobic mesoporous thin films: example of a photonic ethanol vapor sensor in humid environment

In this work, we report a new generation of sol–gel photonic vapor sensor based on water-repellent methyl-functionalized mesoporous silica thin films for the detection of alcohol vapors. Relative humidity, generally accountable for sensor performance deterioration, was demonstrated as a key parameter to detect and enhance sensor sensitivity concerning ethanol. The ethanol-assisted water vapor capillary condensation into hydrophobic mesopores was observed and investigated as an innovative sensing mechanism. We showed that water condensation was triggered by the surfactant-like behavior of alcohol molecules whose alkyl moieties preferentially interact with the hydrophobic walls and reversibly switch the surface energy from hydrophobic to hydrophilic. Influence of the ethanol and water pressure conditions for which the capillary condensation occurs were studied by in situ ellipsometry. This study revealed a synergic mechanism of co-adsorption where the minimum ethanol concentration allowing water capillary adsorption decreases when humidity increases. Nanopatterned diffraction gratings films, fabricated via a nanoimprinting process, were demonstrated to be efficient transductor to transform the capillary-induced nanoscale variations of refractive index of the porous materials into optical signals easily measurable by conventional camera. Sensing results exhibited an ethanol vapor pressure threshold limit of detection of P/P 0 EtOH = 0.07 at 100 % relative humidity and typical response and regeneration times are below one minute.

A fast response/recovery of hydrophobic Pd/V2O5 thin films for hydrogen gas sensing

We have developed a fast and highly sensitive gas sensor based on the Pd/V2O5 thin films for the low temperature detection of hydrogen in the range 2–500ppm in air. Sensor response, selectivity, and stability studies reveal excellent sensing of the thin films. The formation of vanadium bronze was studied by spectroscopic ellipsometry. The low temperature operation under ambient conditions and the wide range sensing indicates that these hydrophobic nanocrystalline thin films can be explored for optical as well as chemiresistive gas sensing applications.

Analysis on superhydrophobic silver decorated copper Oxide nanostructured thin films for SERS studies

The present work demonstrates the superhydrophobic and Surface Enhanced Raman Spectroscopy (SERS) active substrate performance of silver coated copper oxide (Ag@CuO) nanostructured thin films prepared by the SILAR process. Super hydrophobic substrates that combine super hydrophobic condensation effect and high enhancement ability of Ag@CuO nanoflowers are investigated for SERS studies. The possible growth mechanism for the formation of nanoflower arrays from nanospindles has been discussed. Morphology and crystallinity of the Ag@CuO thin films are confirmed using FESEM and XRD. The results obtained in the present study indicate that the as-deposited hydrophobic nanospindles structure converts to super hydrophobic nanoflower arrays on annealing at 200°C. The Ag@CuO super hydrophobic nanoflowers thin film based SERS substrates show highly enhanced Raman spectra with an EF value of 2.0×107 for (Rhodamine 6G) R6G, allowing a detection limit from a 10−10molL−1 solution. The present study may provide a new perception in fabricating efficient super hydrophobic substrates for SERS, suggesting that the fabricated substrates are promising candidates for trace analysis of R6G dye and are expected to be widely used as highly sensitive SERS active substrates for various toxic dyes in the future.

Effects of moisture ingressions on mechanical properties of honeycomb-structured fiber composites for aerospace applications

Composite structures are usually subjected to a wide range of environmental conditions whereby they can absorb a substantial amount of moisture, oil, or solvent from the environment, thus reducing their mechanical, thermal, electrical, and other physical properties and service times. In this study, hydrophobic barrier films used to prevent moisture ingression into sandwich structures are investigated. Four different hydrophobic thin barrier films—polyvinyl fluoride (PVF), polyether ether ketones (12.5 and 25 μm), polyimide, and polytetrafluoroethylene—were co-bonded to the surfaces of fiber composite sandwich structures to study the changes in mechanical properties of the sandwich structures before and after immersing them into deionized (DI) water and aviation hydraulic fluid (Skydrol®). For comparison and evaluation purposes, the composite coupons underwent two different mechanical tests: sandwich flexure and compression strength compression. Test results confirmed that using barrier films as the outermost ply on composite sandwich structures significantly reduced moisture ingression, and as a result, mechanical properties were considerably increased compared to those coupons without any barrier films.

Hydrophilic Domains Enhance Nanobubble Stability.

Highly stable nanoscale gas states at solid/liquid interfaces, referred to as nanobubbles, have been widely studied for over a decade. In this study, nanobubbles generated on a hydrophobic Teflon amorphous fluoroplastic thin film in the presence and absence of hydrophilic carbon domains are investigated by peak force quantitative nanomechanics. On the hydrophobic surface without hydrophilic domains, a small number of nanobubbles are generated and then rapidly decrease in size. On the hydrophobic surface with hydrophilic domains, the hydrophilic domains have a significant effect on the generation and stability of nanobubbles, with bubbles remaining on the surface for up to three days.

Bionic micro-nano-bump-structures with a good self-cleaning property: The growth of ZnO nanoarrays modified by polystyrene spheres

Hydrophobic ZnO self-cleaning thin films with the bionic micro-nano-bump-structures are prepared on ITO glass by growing ZnO nanoarrays supported by polystyrene spheres. The mechanism of the polystyrene spheres on ZnO nanoarrays structure formation is discussed and its superhydrophobic property is originated from the micro-nano-bump-structures of ZnO nanoarrays and surface roughness. Interestingly, the hydrophobic property of ZnO nanoarrays can switch to superhydrophilic by depositing TiO2 on ZnO nanoarrays structure confirmed by water contact angle test. Water contact angle changed from previous 152° with ZnO nanoarrys to 4° with TiO2 on ZnO nanoarrays. These promising ZnO nanostructured materials show an important application in self-cleaning smart coatings.

Organo-layered double hydroxides composite thin films deposited by laser techniques

We used laser techniques to create hydrophobic thin films of layered double hydroxides (LDHs) and organo-modified LDHs. A LDH based on Zn-Al with Zn2+/Al3+ ratio of 2.5 was used as host material, while dodecyl sulfate (DS), which is an organic surfactant, acted as guest material. Pulsed laser deposition (PLD) and matrix assisted pulsed laser evaporation (MAPLE) were employed for the growth of the films. The organic anions were intercalated in co-precipitation step. The powders were subsequently used either as materials for MAPLE, or they were pressed and used as targets for PLD. The surface topography of the thin films was investigated by atomic force microscopy (AFM), the crystallographic structure of the powders and films was checked by X-ray diffraction. FTIR spectroscopy was used to evidence DS interlayer intercalation, both for powders and the derived films. Contact angle measurements were performed in order to establish the wettability properties of the as-prepared thin films, in view of functionalization applications as hydrophobic surfaces, owing to the effect of DS intercalation.

Preparation and Properties of Superhydrophobizted Sprayed Zn-Al Coating

A superhydrophobic ZnAl coating was prepared by the electric arc spraying technology and then surface modification by stearic acid/ethanol. The surface wettability, morphology and chemical structure of the ZnAl coating before and after modification were characterized by contact angle measurement(OCA-20), scanning electron microscope(SEM) and artificial FTIR spectrometer(ATR), respectively. The impedance spectrum and polarization curves of the coatings were measuared by electrochemical workstation(Solartron Analytical) with three electrodes system. The results show that the as sprayed ZnAl coating consists of irregular micro-and nano-sized alloy particles and pores, and exhibits clear hydrophilicity, which may be ascribed to the high surface energy of metallic coating. After the surface modification with stearic acid, the static contact angle of the coating reached 153.8° with a rolling angle less than 10°, because there exsited a large number of hydrophobic long alkyl chains on the surface of the modified Zn Al coating. In addition, the surface modification could significantly enhance the corrosion resistance of ZnAl coating due to that the thin hydrophobic film plays an important role in supression of the fall off and dissolution of corrosion products on the ZnAl coating, leading to the increase of charge transfer resistance and the corrosion current density.

SiCxHy-based hydrophobic thin films with good chemical and mechanical properties synthesized by PECVD at various substrate temperatures

This work investigates on chemical and mechanical resistance of hydrophobic films; prepared using radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) method, by varying substrate temperature. For this work, Hexamethyldisilane (HMDS) is used as the precursor, with hydrogen gas as the reactive agent. The surface energy and surface morphology are studied by measuring water contact angle (WCA) and atomic force microscopy (AFM), respectively. Measurement reveals that WCA does not change much and acquires the value in between 105 and 110°. FT–IR analysis shows that the films are well-covered with “–CHx” groups, which can provide the hydrophobicity. The pencil hardness test of the deposited films at higher substrate temperature (>160 °C), have shown a high stability up to 6H. Also, the films show good chemical resistance against boiling salt water and cosmetics in the chemical reliability test due to their much denser structure with reduced defects. Additionally, XPS analysis shows that there is the shift in the peak position of the C–C bond to lower binding energy that is attributed to a highly cross-linked carbon structure formation in the film. The films are chemically inert and have shown good adhesion and durability.

Deposition and characterization of AlN thin films on ceramic electric insulators using pulsed DC magnetron sputtering

Abstract Porcelain electric insulators are fundamental support devices to act as holders for transmission lines. The exposition to pollutants environments such as industrial areas, deserts and sea air, containing carbon, sand and salt are examples that can reduce the devices dielectric property. The present investigation aims to develop and characterize hydrophobic aluminum nitride thin films, deposited on porcelain insulators surfaces, using a pulsed direct current magnetron sputtering (PDMS). An aluminum target with 99.999% purity was used as precursor and nitrogen 99.999% purity was employed. The film characterization was performed using AFM, FEG and FTIR. The surface resistivity was evaluated by four-point probe method. Different deposition times lead to different wettability characteristics, verified by the sessile drop method using a goniometer. The experimental results show the formation of a low roughness aluminum nitride film with hydrophobic properties over the glazed surface of a commercial porcelain electrical insulator.

Versatile Self‐Cleaning Coating Production Through Sol–Gel Chemistry

The performance of optical devices is dependent on their optical transparency (OT). This is evident when such devices are exposed to environmental conditions that can reduce OT. The development of a robust, transparent and self‐cleaning coating is highly desirable, for applications likeoptical windows and solar panels. This work reports the design of such coatings based on a hydrophobic thin film fabricated using a sol‐gel process. Coating properties were optimised by modification of the surface topography of the coatings, achieved by the incorporation of silica nanoparticles(NPs). The coating was characterised by water contact angle(WCA), scanning electron microscopy(SEM) and white light interferometry (WLI). The efficacy and robustness of the coating foroptical application was assessed.

Fusion peptide P15-CSP shows antibiofilm activity and pro-osteogenic activity when deposited as a coating on hydrophilic but not hydrophobic surfaces.

In the context of porous bone void filler for oral bone reconstruction, peptides that suppress microbial growth and promote osteoblast function could be used to enhance the performance of a porous bone void filler. We tested the hypothesis that P15-CSP, a novel fusion peptide containing collagen-mimetic osteogenic peptide P15, and competence-stimulating peptide (CSP), a cationic antimicrobial peptide, has emerging properties not shared by P15 or CSP alone. Peptide-coated surfaces were tested for antimicrobial activity toward Streptoccocus mutans, and their ability to promote human mesenchymal stem cell (MSC) attachment, spreading, metabolism, and osteogenesis. In the osteogenesis assay, peptides were coated on tissue culture plastic and on thin films generated by plasma-enhanced chemical vapor deposition to have hydrophilic or hydrophobic character (water contact angles 63°, 42°, and 92°, respectively). S. mutans planktonic growth was specifically inhibited by CSP, whereas biofilm formation was inhibited by P15-CSP. MSC adhesion and actin stress fiber formation was strongly enhanced by CSP, P15-CSP, and fibronectin coatings and modestly enhanced by P15 versus uncoated surfaces. Metabolic assays revealed that CSP was slightly cytotoxic to MSCs. MSCs developed alkaline phosphatase activity on all surfaces, with or without peptide coatings, and consistently deposited the most biomineralized matrix on hydrophilic surfaces coated with P15-CSP. Hydrophobic thin films completely suppressed MSC biomineralization, consistent with previous findings of suppressed osteogenesis on hydrophobic bioplastics. Collective data in this study provide new evidence that P15-CSP has unique dual capacity to suppress biofilm formation, and to enhance osteogenic activity as a coating on hydrophilic surfaces.