Hydrophobic Thin Films Research Articles

Ultra-Pressurized Deposition of Hydrophobic Chitosan Surface Coating on Wood for Fungal Resistance.

Fungi (Neolentinus lepideus, Nl, and Trametes versicolor, Tv) impart wood rot, leading to economic and environmental issues. To overcome this issue, toxic chemicals are commonly employed for wood preservation, impacting the environment and human health. Surface coatings based on antimicrobial chitosan (CS) of high molar mass (145 × 105 Da) were tested as wood preservation agents using an innovative strategy involving ultra-pressurizing CS solutions to deposit organic coatings on wood samples. Before coating deposition, the antifungal activity of CS in diluted acetic acid (AcOOH) solutions was evaluated against the rot fungi models Neolentinus lepideus (Nl) and Trametes versicolor (Tv). CS effectively inhibited fungal growth, particularly in solutions with concentrations equal to or higher than 0.125 mg/mL. Wood samples (Eucalyptus sp. and Pinus sp.) were then coated with CS under ultra-pressurization at 70 bar. The polymeric coating deposition on wood was confirmed through X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM) images, and water contact angle measurements. Infrared spectroscopy (FTIR) spectra of the uncoated and coated samples suggested that CS does not penetrate the bulk of the wood samples due to its high molar mass but penetrates in the surface pores, leading to its impregnation in wood samples. Coated and uncoated wood samples were exposed to fungi (Tv and Nl) for 12 weeks. In vivo testing revealed that Tv and Nl fungi did not grow on wood samples coated with CS, whereas the fungi proliferated on uncoated samples. CS of high molar mass has film-forming properties, leading to a thin hydrophobic film on the wood surface (water contact angle of 118°). This effect is mainly attributed to the high molar mass of CS and the hydrogen bonding interactions established between CS chains and cellulose. This hydrophobic film prevents water interaction, resulting in a stable coating with insignificant leaching of CS after the stability test. The CS coating can offer a sustainable strategy to prevent wood degradation, overcoming the disadvantages of toxic chemicals often used as wood preservative agents.

High temperature long-lasting corrosion inhibition mechanism of sodium dodecyldiphenyl ether disulfonate on ADC12 aluminum alloy in oxalic acid solution

The high temperature corrosion inhibition mechanism of sodium dodecyl diphenyl ether disulfonate (MADS) on ADC12 aluminum alloy in oxalic acid solution at 80 °C was investigated using electrochemical measurements, surface characterization and theoretical computations. The results manifested that MADS still had excellent performance in high-temperature oxalic acid solution, and was a highly efficient and long-lasting corrosion inhibitor with an optimal corrosion inhibition efficiency (ƞ) of 90.90 %. With increasing soaking time, the ƞ increased to 98.70 %. MADS molecule adsorbed on the aluminum alloy surface in an L-shaped walking scooter configuration through physicochemical adsorption to form a dense, thin and stable hydrophobic film, inhibiting the formation of aluminum oxalate and Al2O3, and protecting it from corrosion.

Substrate controlled hydrophobicity of the Y2O3 films

The development of hydrophobic surfaces is an important factor for clean energy production from solar arrays, enabling their operation at the highest possible efficiencies for the longest possible time, without the need for physical intervention. This work reports the development of hydrophobic Y2O3 thin films on a range of transparent glass substrates. The growth of the Y2O3 films from the mono-hydrate yttrium (III) complex of 1,3-diphenyl-1,3-propanedione [Y(dbm)3(H2O)] is studied using the aerosol-assisted chemical vapor deposition (AACVD) technique. The qualitative evaluation of the deposited films and their hydrophobicity is assessed using several materials characterization techniques, such as scanning electron microscopy, grazing incident X-ray diffraction, Fourier-transform infrared, X-Ray photoelectron spectroscopy, in addition to a surface free energy and water contact angle measurements. This work demonstrates experimentally a relationship between the Y2O3 wettability and its physico-chemical characteristics in terms of surface energy, chemical composition, and morphology which is controlled by the type of glass support used. The water contact angle of the hydrophobic Y2O3 coating grown on the F-doped tin oxide glass reached 128°; currently the first deposited on transparent glass. This film exhibits the highest WCA reported up to date without the need for performing post-reaction surface treatment processes. The hydrophobic nature of the transparent Y2O3 films marks a significant leap forward in the field of anti-soiling coatings suitable for photovoltaic technology.

Synthesis, characterization, and application of silica aerogel thin films prepared via surface derivatization: A comprehensive study on micro-silica nanofilms for enhanced photoelectric conversion efficiency in photovoltaic solar cells

Silica aerogels are nanoporous materials with exceptional optical and physical properties, making them promising candidates to enhance solar cell efficiency as antireflective coatings. This study synthesized hydrophobic silica aerogel thin films under ambient conditions and characterized their porous structure, surface morphology, and optical performance. The films were deposited on monocrystalline silicon solar cells to assess their impact on photovoltaic properties. A two-step acid/base catalyzed sol-gel process was utilized, followed by solvent exchange and surface modification with trimethylchlorosilane. Structural analysis via SEM revealed successful deposition of crack-free films when aging occurred in an ethanol environment. The aerogel displayed considerable specific surface area (115 m2/g), porosity (77.92%) and surface roughness (55-78%) along with a low refractive index (1.05), benefiting light harvesting. Preliminary solar testing showed increased output voltage with a 0.2 mm aerogel coating versus a bare cell. Further IV measurements demonstrated enhanced charge transport and conversion efficiency for the treated cell. The aerogels antireflective and light-trapping effects appear to improve photon absorption. This initial research validates the potential of ambient pressure-synthesized hydrophobic silica aerogels to increase the performance of silicon photovoltaics cost-effectively. Further optimization of film thickness and morphology could realize higher efficiency gains.

Characterization of nanoscale pinhole defects in hydrophobic coatings using copper electrodeposition

Thin (∼ 100 nm thick) hydrophobic polymer films are used in a plethora of applications where water repellency is required. However, hydrophobic film implementation in industry is limited due to poor durability. Thin hydrophobic film blistering during condensation has been identified as one of the main mechanisms associated with failure. Yet, disagreement exists about the source of blister initiation. Furthermore, there is a lack of understanding about the physical defects or pinholes that facilitate vapor penetration pathways through thin hydrophobic films. These pinholes govern the nucleation of blisters on the interface between the hydrophobic polymer and metal substrate. Here, we use metal electrodeposition as a means to characterize these intrinsic pinholes in thin hydrophobic polymers. A facile method is demonstrated to locate pinholes and measure pinhole density on CFx and poly(2-chloro-p-xylylene) (Parylene C) films. Our work not only helps to understand the intrinsic defects associated with film deposition, it also provides design guidelines for the selection and development of efficient thin film hydrophobic coatings.

Novel hydrophobic Ti-PVDF energetic thin films with excellent mechanical and ignition properties and their reaction mechanisms

With the development of traditional aluminum(Al)-based nanothermites, some problems on account of the metal Al powder gradually emerged. Therefore, extensive research is devoted to exploring novel metal fuels to achieve better energy release effects. Titanium (Ti) powder is a potential metal fuel theoretically considering of reducibility and calorific value, but it has rarely been reported in the field of nanothermites. This paper put forward the design strategy by selecting as the metal fuel and polyvinylidene fluoride (PVDF) as oxidant. According to the hydrophilicity of Ti powders, the PVDF film encapsulation can effectively improve hydrophobicity and storage stability. Another advantage of PVDF film state is that it imparts excellent mechanical properties (yield strength of 30.5 MPa and elongation at break of 202.8 %). According to the results of thermal analysis, Ti increased the thermal stability of PVDF while accelerated its thermal decomposition rate. In ignition properties, Ti-PVDF films have the shortest ignition delay time (217 ms) lower than results reported in the literature of other nanothermites under the same conditions. In addition, the energy release process of ignition combustion is analyzed and verified in this paper. Therefore, Ti-PVDF energetic ignition material with diverse properties is expected to be applied in more fields not limited to nanothermites.

Surface treatment of large-area epoxy resin by water-perforated metal plate electrodes dielectric barrier discharge: Hydrophobic modification and uniformity improvement

Wind power plays a vital role in the field of renewable energy. However, a significant challenge arises when operating wind turbines with epoxy resin blades in temperatures below 0℃, as they tend to ice up, causing unexpected shutdowns. Low-temperature plasma technology emerges as a promising solution that can produce hydrophobic thin films with excellent mechanical properties in an eco-friendly way, but its application is currently limited to small objects. This paper presents a novel design for a large-scale DBD (Dielectric Barrier Discharge) water-perforated metal electrode plasma treatment device that was optimized through simulations to achieve uniform gas discharge at low flow rates. The device successfully deposited a hydrophobic thin film uniformly on the surface of an epoxy resin plate with an average water contact angle of 139.5 ± 2.5°, which is an 87% improvement compared to the untreated surface. In addition, the device reduced the required working gas flow rate by 40–60% compared to existing large-area processing devices, and improved the effectiveness by 16%. Physical and chemical property tests demonstrated that the device’s design increased surface roughness and generated a dense film containing hydrophobic silicon groups (such as Si-O-Si and Si-(CH3)x), contributing to the improvement in hydrophobicity. Overall, the presented device offers an efficient, eco-friendly, and effective method for depositing hydrophobic thin films on large-scale materials, which can enhance wind turbine performance by preventing ice formation on epoxy resin blades.

Review on Hydrophobic Thin Films Prepared Using Magnetron Sputtering Deposition.

Hydrophobic thin films have gained significant attention due to their broad applications in self-cleaning, anti-corrosion, anti-icing, medicine, oil-water separation, and other fields. The target hydrophobic materials can be deposited onto various surfaces thanks to the scalable and highly reproducible nature of magnetron sputtering, which is comprehensively overviewed in this review. While alternative preparation methods have been extensively analyzed, a systematic understanding of hydrophobic thin films fabricated using magnetron sputtering deposition is still absent. After outlining the fundamental mechanism of hydrophobicity, this review briefly summarizes three types of sputtering-deposited thin films that originate from oxides, polytetrafluoroethylene (PTFE), and diamond-like carbon (DLC), respectively, primarily focusing on the recent advances in their preparation, characteristics, and applications. Finally, the future applications, current challenges, and development of hydrophobic thin films are discussed, and a brief perspective on future research directions is provided.

Autonomous Self-healable Scratch-free Bilayer Anti-corrosion Film

Thin hydrophobic polymer film, which physically prevents an approach of corrosive media, has been widely used as an anti-corrosion coating for metals. Though polymer film effectively passivates surface of metal, it loses its anti-corrosion property once the film is peeled off by physical damage, such as scratches. Corrosion can be propagated from the exposed area even if the area is small. Therefore, for long-term anti-corrosion, the film should be seamless and completely cover the entire metal surface without scratches. In this study, we introduce an autonomously self-healable hydrophobic coating with superior anti-corrosion property by a combination of self-healable/fluorinated polymers. Schiff-base linkages based polydimethylsiloxane (SC-PDMS) is used as a primary protection layer against corrosive media. The SC-PDMS matrix with the dynamic imine bonds allows scratch-free metal protection layer by reproducible damage healing property. In addition, we applied polytetrafluoroethylene (PTFE) thin film at the surface of the SC-PDMS, which suppresses the reaction of imine bond with water and helps to maintain long-term anti-corrosion property. Eventually, this simple coating of bilayer structure with SC-PDMS and PTFE shows an effective scratch-free corrosive resistance, providing a new way of long-term use of metals.

The Characterization of the Hydrophobic Surface of Nanocomposites Aloe vera/PS for Antimicrobial Pathogens

The spread of pathogenic microorganisms on a large scale creates a health disaster for the world. Modifying the surface of the fabric so that it is antimicrobial pathogens with hydrophobic properties is one solution to inhibit the spread of microorganisms. Surface modification was carried out using Aloe vera powder as filler and polystyrene matrix with Aloe vera:PS composition variations of 1:5, 2:5, and 3:5 using the dip coating method and drying temperatures of 10◦C, 50◦C, and 90◦C. The characterization results that have been carried out with the best composition variations are 3:5 and 50◦C with a layered morphology using Scanning Electron Microscopy (SEM), resulting in a surface particle size of 21.243 nm, large contact angle/WCA using a Canon D350 camera with a size of 150.23◦, Fourier Transmission Infrared Analysis (FTIR) with the dominant functional group in the vibration band 2629 cm−1 indicates the presence of a long hydroxyl chain, the vibration band 1500 cm−1 with C-H stretching of the aromatic ring is caused by the characteristics of the polystyrene polymer and the wave number is 1700 cm−1 with stretching C=O which shows the characteristics of the carbonyl group in the Aloe vera sample is a flavonoid compound. The resistance of Aloe vera/PS solution to Klebsiella pneumonia resulted in a 20.18 mm diameter barrier showing strong resistance against bacteria and X-Ray Diffraction analysis showed that the AV powder was amorphous. Thus, the AV/PS 3:5 composition with a calcination temperature of 50◦C represents the greatest variation in the synthesis and characterization of hydrophobic thin films for pathogenic antimicrobial organisms.

Highly Hydrophobic Films of Engineered Silk Proteins by a Simple Deposition Method.

Molecular engineering of protein structures offers a uniquely versatile route for novel functionalities in materials. Here, we describe a method to form highly hydrophobic thin films using genetically engineered spider silk proteins. We used structurally engineered protein variants containing ADF3 and AQ12 spider silk sequences. Wetting properties were studied using static and dynamic contact angle measurements. Solution conditions and the surrounding humidity during film preparation were key parameters to obtain high hydrophobicity, as shown by contact angles in excess of 120°. Although the surface layer was highly hydrophobic, its structure was disrupted by the added water droplets. Crystal-like structures were found at the spots where water droplets had been placed. To understand the mechanism of film formation, different variants of the proteins, the topography of the films, and secondary structures of the protein components were studied. The high contact angle in the films demonstrates that the conformations that silk proteins take in the protein layer very efficiently expose their hydrophobic segments. This work reveals a highly amphiphilic nature of silk proteins and contributes to an understanding of their assembly mechanisms. It will also help in designing diverse technical uses for recombinant silk.

NEW VAPOR DEPOSITED DIELECTRIC POLYMER THIN FILMS FOR ELECTRONIC APPLICATIONS

Dielectric materials are of great interest in a vast amount of applications ranging from cable insulation to advanced electronic devices. The emerging trend of device miniaturization is creating an increased demand for dielectric thin films that can be produced precisely on the nanometer scale. In addition, special mechanical properties are often required, for example in the field of flexible organic electronics. Polymers are first-choice materials for this purpose. However, it is extremely difficult to produce precise nanoscale thin films, which have a low defect density and are free of e.g. residual solvent, by wet chemistry approaches. Initiated chemical vapor deposition (iCVD) is a solvent-free polymer thin film deposition process which can be used to produce high quality dielectric thin films with nanoscale control and circumvents thus these problems. This work demonstrates the versatility of the iCVD process in the field of electrical applications by some new application examples of iCVD. By adding e.g. a hydrophobic organosiloxane thin film on columnar zinc oxide (ZnO:Fe) gas sensing structures there was a change in the selectivity from ethanol to hydrogen, as well as improved performance at high humidity level. The modified sensors can thus be used in humid ambient, especially for breathing tests, which can lead to the diagnosis of some diseases by cutting edge non-invasive approaches.

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%.

An improved surface enhanced Raman spectroscopic method using a paper-based grape skin-gold nanoparticles/graphene oxide substrate for detection of rhodamine 6G in water and food.

Organic toxins are persistent chemicals of global concern capable of accumulating in environment and food. Surface enhanced Raman spectroscopy (SERS) is a promising technique that facilitates onsite detection of organic toxins. However, the fabrication of a SERS substrate is complicated and difficult to provide flexibility, fastness and cost-effectiveness. This study aims to develop a paper-based SERS method using grape skin-gold nanoparticles/graphene oxide (GE-AuNPs/GO) as SERS substrate and evaluate its efficiency with rhodamine 6G (Rh6G) as a model organic toxin and a real water and food contaminant. GE-AuNPs synthesized by green method using grape skin waste extract and GE-AuNPs/GO showed a surface plasmon resonance at 536 and 539nm, particle size 18.6 and 19.5nm, and zeta potential -44.6 and -59.7mV, respectively. Paper-based SERS substrates were prepared by coating a hydrophobic thin-film of 30% polydimethylsiloxane solution in hexane on Whatman no. 1 filter paper, followed by drop-casting GE-AuNPs or GE-AuNPs/GO and drying. The SERS signals of Rh6G showed an enhancement factor of 5.8×104 for GE-AuNPs and 1.92×109 for GE-AuNPs/GO, implying that a combination of electromagnetic surface plasmon, charge transfer and molecular resonances may be responsible for a higher enhancement of signal by the latter. A low detection limit of 7.33×10-11M in the linear range of 10-11-10-5M was obtained for GE-AuNPs/GO, while the relative standard deviation of repeatability and reproducibility was 9.6 and 12.6%, respectively. Paper-based GE-AuNPs/GO SERS substrate was highly stable as <20% loss in efficiency was shown over a 60-day storage period. Application to real samples showed a high recovery of Rh6G from tap water (93.9-100.8%) as well as food samples such as red chilli powder (91.0-95.4%), red glutinous rice ball (96.6-98.3%) and tomato ketchup (98.9-102.3%) after QuEChERS extraction. Collectively, the developed paper-based GE-AuNPs/GO can be a potential substrate for sensitive onsite detection of rhodamine 6G by SERS method.

Long-lifetime, superhydrophobic, free-standing carbon infiltrated vertically aligned carbon nanotube structures

Long lifetime, free-standing, superhydrophobic, carbon infiltrated vertically aligned carbon nanotube structures (ct-VACNT) are prepared by VLS-assisted VACNT growth on photolithographic patterned catalyst wafers, followed by a carbon infiltration process creating c-VACNT precursor structures (made from a nanoporous carbon sponge material) which are subsequently released from the catalyst wafers, surface roughened on their top and bottom surface and then conformally overcoated with a few nm thick hydrophobic thin film of a hydrophobic amorphous fluoropolymer, thus resulting in free-standing superhydrophobic ct-VACNT structures. Longevity testing of the hydrophobic overcoating shows that the addition of a customized surface roughening step (especially in the form of low-pressure O2 plasma-assisted surface burning of the nanocarbon sponge material) for the bottom and top surfaces is key to extending the hydrophobic lifetime of such ct-VACNT structures from a few weeks to over a year.These long-lifetime ct-VACNT structures can now be used to develop novel fluid processing devices for a range of industrial and medical fluid processing applications requiring gas transfer into and/or out of aqueous liquids. Such novel fluid reactor devices are enabled by application-specific optimized components made from these novel nano-to macro ct-VACNT structures, in the form of Fluid channel Array Bricks (FABs).

Sodium dodecylbenzene sulfonate film absorbed on magnesium alloy surface: An electrochemical, SKPFM, and molecular dynamics study

Sodium dodecylbenzene sulfonate (SDBS) was used as an environmentally friendly corrosion inhibitor to alleviate the corrosion of magnesium alloys in 3.5 wt% NaCl solution. In this study, the corrosion inhibition impact of the SDBS inhibitor on AZ31 alloy surface was investigated by electrochemical, scanning Kelvin probe force microscopy (SKPFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), contact angle measurement and molecular dynamics (MD) simulation. Electrochemical results indicated that the maximum inhibition efficiency was 93.9% for 0.008 M SDBS after 72 h of immersion. The adsorption of SDBS on the Mg alloy surface obeyed Langmuir adsorption isotherm. The SKPFM and contact angle results show that a thin hydrophobic SDBS film formed on the Mg alloy surface, which isolated the alloy surface from electrolyte and then inhibited micro-galvanic corrosion. Furthermore, the MD simulation substantiated with the experiments and visualized adsorption behavior of the SDBS inhibitor under long-term immersion condition. The long-term corrosion resistance mechanism of the SDBS film is herein proposed.

Evaluation of cold plasma effect to achieve fullerene and zinc oxide-fullerene hydrophobic thin films

Evaluation of cold plasma effect to achieve fullerene and zinc oxide-fullerene hydrophobic thin films

Experimental study of pool boiling on hydrophilic and hydrophobic thin films deposited on copper surfaces using atmospheric cold plasma

Critical heat flux (CHF) is considered a safety constraint in various types of thermal systems. Enhancement of CHF threshold brings about noticeable improvements in safety measures and overall economic structures. In this study, SiO2-like hydrophilic and polymer-like SiOxCyHz hydrophobic thin films are deposited on copper surfaces using atmospheric pressure plasma enhanced chemical vapor deposition of Ar/HMDSO in the presence/non-presence of O2. Pool boiling experiments are performed on prepared surfaces under atmospheric saturation conditions. The aim is to investigate the effect of surface modifications on CHF and such other key parameters as the onset of nucleate boiling (ONB) as well as heat transfer coefficient (HTC). Scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX), and contact angle measurement are employed to determine the morphology and composition of the thin films. Experimental results demonstrate that the hydrophilic films deposited on surfaces give rise to significant increases in CHF and HTC compared to bare surfaces. Also observed was a reduction of up to 53% in the ONB of the hydrophobic films deposited on copper surfaces.

Investigation of Interfacial Water Accumulation between Polypropylene Thin Film and Si Substrate by Neutron Reflectivity.

We performed neutron reflectivity (NR) measurements of isotactic polypropylene (PP) thin films deposited on a Si substrate at the saturated vapor pressure of deuterated water to investigate interfacial water accumulation between the PP and metal surfaces in PP-based polymer/inorganic filler nanocomposites and metal/resin bonding materials. The PP thin films prepared on a Si substrate by a spin-coating technique were adequate as a model system for the PP/metal interface in these materials. A water-rich layer with a maximum water concentration of 0.5, which was considerably higher than those reported in previous studies of organic/inorganic interfaces, was observed within a width of approximately 3 nm at the interface under saturated vapor conditions. This could be attributed to the weak interaction between the PP thin film and the Si substrate. The pathway of moisture transport to the interfacial region was along the interface rather than through the PP film because the hydrophobic PP thin film does not entirely swell with water vapor.

Hydrophobic Thin Films from Sol-Gel Processing: A Critical Review.

Fabrication of hydrophobic thin films from a liquid phase is a hot topic with critical technological issues. Interest in the production of hydrophobic surfaces is growing steadily due to their wide applications in several industrial fields. Thin films from liquid phases can be deposited on different types of surfaces using a wide variety of techniques, while the design of the precursor solution offers the possibility of fine-tuning the properties of the hydrophobic coating layers. A general trend is the design of multifunctional films, which have different properties besides being hydrophobic. In the present review, we have described the synthesis through sol–gel processing of hydrophobic films enlightening the main achievements obtained in the field.