Water-repellent Films Research Articles

Transmittance Control of a Water-Repellent-Coated Layer on a Tensioned Web in a Roll-to-Roll Slot-Die Coating System.

Solar cells are important alternatives to fossil fuels for energy generation in today’s world, where the demand for alternative, renewable sources of energy is increasing. However, solar cells, which are installed outdoors, are susceptible to pollution by environmental factors. A solution to overcome this limitation involves coating solar cell surfaces with functional coatings. In this study, we propose a transmittance control method for a tensioned web in a roll-to-roll, transparent, water-repellent film coating. First, we analyzed the effects of process conditions on the transmittance and contact angle of the transparent water-repellent film during roll-to-roll slot-die coating. It was confirmed that the tension was the most dominant factor, followed by the coating gap. Through the tension control, the transmittance was changed by 3.27%, and the contact angle of the DI water was changed by 17.7°. In addition, it was confirmed that the transmittance was changed by 0.8% and the contact angle of DI water by 3.9° via the coating gap control. Based on these results, a transmittance prediction model was developed according to the tension and coating gap, and was then verified experimentally. Finally, a water-repellent film with a high transmittance of 89.77% was obtained using this model.

Preparation of Water-Repellent Film on a Plastic Plate by Unbalanced Radio-Frequency Magnetron Plasma Sputtering Using PTFE Target for a Next-Generation Automobile Window

Preparation of Water-Repellent Film on a Plastic Plate by Unbalanced Radio-Frequency Magnetron Plasma Sputtering Using PTFE Target for a Next-Generation Automobile Window

Wood films glow brightly

Researchers have converted natural wood into flexible, strong, water-repellent films that glow in different colors. The luminescent films could lead to more-sustainable alternatives to the glass an...

Ultra-low-voltage electrophoretic assembly of extremely water-repellent functional nano-Al films with long lifespan

It is still a bottleneck to design anti-wetting homogeneous metal films or coatings with great stability via by a high-efficiency and low-cost technique with applications in fields of battery, sensors, and electronics, etc. This paper proposed an environment-friendly ultra-low-voltage electrophoretic deposition (EPD) with facile modification post-processing method to fabricate a novel extremely water-repellent functional nano-Al films with evenly loose net-like structures and high purity. The optimized stable suspension consists of water–ethanol with trace nitric acid and polyethyleneimine. Product with an ultra-high contact angle of ~ 171° and extreme low sliding angle of 3 years) with great potential applications. These results provide a novel approach with low-cost and less energy consumption for preparing other functional ant-wetting metal coatings with wide potential applications.

Covalent and noncovalent films made up of sulfonimide-based dendrimers

Dendrimers are unique macromolecules composed of branched monomers that are characterized by monodispersity, biocompatibility, and multivalent surfaces and are synthesized by the stepwise addition of repetitive units. Over recent years, dendrimers have been attractive materials as detecting agents, targeting components, imaging agents, or pharmaceutically active compounds. This study demonstrates the possibility of the formation and transfer of thin sulfonimide dendrimer films of different generations to solid surfaces using the Langmuir-Blodgett technique. The surface of sulfonimide dendrimers was functionalized with naphthalene end groups (from 4 to 64 groups). The developed noncovalent and covalent films showed the expected different contact angles due to the presence of the naphthyl groups attached to the dendrimer side, which can bond intramolecularly or intermolecularly. Changing the number of naphthyl groups allows control of the hydrophobic properties of the films, providing an opportunity to create two types of films with covalent and noncovalent bonding. The difference in contact angle between the 2nd and 5th generations of dendrimers was approximately 33°. The low-cost formation of such transparent water-repellent film imparting water repellency to a substrate while maintaining its inherent properties, such as color and morphology, can protect glass and painted surfaces from excessive humidity.

Investigating the influence of volumetric hydrophobization on the formation of phase composition of cement stone and its physical-mechanical properties

We have examined the influence of the most widely used silicon-organic surface water repellent GKZH-11K on the physical-mechanical properties and the phase structure formation of cement is the fact that the introduction of the surface water repellent GKZH-11K to the composition of cement slurry leads to the formation of dispersive water-repellent films of various levels (size). These films adsorb at the surface of cement grains, as well as at the surface of hydrated components of cement particles, Са(ОН)2, calcium sulphoaluminates. It was determined that the disperse hydrophobic films partially block the penetration of water into the surface of cement grains and alter the kinetics of hydration.This leads to a decrease in the degree of hydration and the content of Са(ОН)2 in cement stone, resulting in the reduced shrinkage at hardening. At the same time, the disperse films adsorbed on neighboring hydrated cement particles within the contacts occurred in the process of their condensation can form hydrogen and chemical relationships. This interaction between the particles' films, despite the reduction in the degree of hydration, leads to a decrease in water absorption, improving the strength of cement stone, which in this case is also determined by the number and area of contacts per unit volume of cement stone. The overlap of pores with hydrophobic chains decreases the permeability of cement stone throughout its entire volume, which contributes to the growth of operational reliability and durability of structures, particularly thin-walled. Using this admixture for volumetric hydrophobization could greatly prolong repair-free operation of thin-walled products and structures, as well as bring down cost as there is no need to apply materials to protect the surface of concrete.

Low-cost fabrication of flexible water-repellent film by spray coating of a hydrophobic nanoparticle dispersion

In this study, a low-cost fabrication method based on colloidal deposition was developed to prepare water-repellent coatings on PDMS-based flexible films. For this purpose, a lotus effect was induced by transferring micron-sized surface protrusions of commercial paper onto PDMS films by curing PDMS monomer on the paper and subsequently detaching the film after curing. The resulting rough PDMS surfaces were spray coated with hydrophobic silica nanoparticles to increase the contact angle of water droplets via the lotus effect. The surface roughness of the rough PDMS film after spray deposition of hydrophobic nanoparticles was confirmed using a surface profile tester. The hydrophobic nanoparticles were prepared by surface modification of silica nanopowder using a silane or titanate coupling agent and subsequent redispersion in an alcohol medium by sonication. Chemisorption of the coupling agents onto the nanoparticle surface was confirmed by Fourier transform infrared analysis. The maximum contact angle of water droplets in this study was greater than 145°, indicating a nearly superhydrophobic property of silica nanoparticle surfaces modified with the coupling agents with long-chain hydrocarbons or a perfluoroalkyl group redispersed in alcohol with low polarity.

Realizing the flexible and transparent highly-hydrophobic film through siloxane functionalized polyurethane-acrylate micro-pattern

The superhydrophobic surface has received significant attention in both academic research and industrial applications. Several polymer-based functional films have been reported to produce superhydrophobic water-repellent films with optical transmittance over the years. However, most polymer materials have an aging issue when they exposed to sunlight for a long time. Herein, we propose a facile and cost-effective fabrication method for the preparation of a flexible and transparent highly hydrophobic PUA film. The intrinsic hydrophilicity of PUA has been successfully modified by forming the microstructures and surface modifications with low surface energy siloxane. The siloxane functionalized µ-patterned PUA film was investigated in detail by various material characterization techniques. The obtained results are consistent and confirm the successful formation of the siloxane functionalized µ-patterned PUA film. The siloxane functionalized PUA film achieved the highest water contact angle (WCA) of ∼146°. Also, the fabricated PUA film maintained the WCAs more than 140° even after 50 times bending motions at the bending angle of ∼60° demonstrating the high flexibility of the proposed hydrophobic structure. Furthermore, the suitability of the as-fabricated siloxane functionalized PUA film as a protection layer for a solar cell, and CMOS camera was also systematically proved by the almost unchanged photovoltaic conversion efficiency (PCE) of the solar panel and the high fidelity of the recorded video.

Comparison of Charge-Discharge Performance of Sealed and Unsealed Metal Hydride/Air Secondary Batteries

A metal hydride (MH)/air secondary battery using an alkaline aqueous solution as the electrolyte operates with water generation during discharge and water decomposition during charge. This battery has a potential that high energy density and high safety are compatible, since one of the active masses is oxygen in air and the materials of the electrolyte and the electrodes are non-flammable. In this unique system, the metal hydride electrode works for hydrogen supply and storage and the air electrode provides the reaction sites for OER and ORR. The discharge product is water so that no solid product is generated during discharge and no plugging of the air electrode occurs, which are quite different from the lithium/air and other air batteries producing solid discharge product in the air electrode. We have been developing the MH/air secondary battery, in which super lattice structure (A2B7) of hydrogen storage alloy is used in the negative electrode, and the air electrode comprising pyrochlore type oxide, e.g., bismuth ruthenium oxide, as the bi-functional oxygen catalyst, loaded on the conductive material, e.g., graphite particles, mixed with PTFE [1]. The materials, composition, structure, and preparation procedure of the air electrode and the lab-scale cell have been modified to reduce the polarization of charge and discharge and to improve the cell capacity, the power density, the energy density, and the cycling performance. In this paper, we present and compare the charge-discharge performance of two types of MH/air secondary batteries, i.e., sealed and unsealed types of cells. The unsealed cell was assembled in a PTFE container, in which from the bottom to the top, there were an MH electrode, a separator with 6 mol/L KOH solution, and an air electrode, as those described elsewhere [1]. In the sealed cell, the electrodes and the separator with the electrolyte were thermally sealed and packed in polyethylene film having an open area on the air electrode. A water repellent film was attached to the air electrode to prevent the flooding of the electrolyte. The sealed and unsealed types of cells were operated with constant current at room temperature without air or oxygen flow to the air electrode. The test results of the unsealed cell demonstrated that the cell capacity, the output power, and the energy density were 2.48 Ah, 368 mW (232 W/L), and 897 Wh/L, in which the energy density is higher than the theoretical one of lithium ion secondary batteries, and the maximum current for discharge was 1600 mA (136 mA/cm2). The unsealed cell using the air electrode attached with the water repellent film was operated over 250 cycles for charge and discharge. The sealed cell showed very stable charge and discharge voltages for 15 hours and the energy density of 772 Wh/L in the data of 20 charge-discharge cycles. More results on the performance of two types of MH/air batteries will be shown in this paper. This work was supported by “Advanced Low Carbon Technology Research and Development Program (ALCA), Grant No. JPMJAL 1204” of Japan Science and Technology Agency (JST). The authors acknowledge FDK Corporation for supplying the MH negative electrode. Reference1. C. Baba, K. Kawaguchi, and M. Morimitsu, Electrochemistry, 83, 855 (2015).

Improvement in Cycling Performance of Rechargeable Metal Hydride/Air Laminate Cell

A metal hydride (MH)/air secondary battery is one of the next generation energy storage devices, since a high energy density and a high power density are expected from its unique property that the active mass of the positive electrode is oxygen in air. We have developed this type of battery and demonstrated that a non-packaged cell fabricated using PTFE container has about 900 Wh/L [1] and a laminate cell using polyethylene film about 772 Wh/L [2], which are beyond the energy density of lithium ion secondary batteries. However, the laminate cell also indicated some issues on the structure and components of the cell, causing the electrolyte’s leakage and a poor cycleability. This work was done to improve the charge-discharge performance of the MH/air laminate cell, especially the cycling performance, and evaluated the charge-discharge behaviors of the cell obtained with some modification in the process and materials. The laminate cell consisted of an MH electrode (23 mm x 23 mm), an air electrode (23 x 23 mm), and a separator with 6 mol/L KOH solution between the electrodes, which were thermally sealed and packed in polyethylene (PE) film having an open area (13 x 13 mm) on the air electrode. All the components were the same as those used in our previous work [1]. We examined the design, size, and thickness of PE film to improve the adhesion to the electrode and between PE films and to inhibit the leakage of the alkaline solution. A water repellent film attached to the air electrode to prevent the flooding of the solution was also modified to suppress the increase in internal pressure by oxygen generated during charge. The cell was operated with constant current (0.05 C) at room temperature in a desiccator, and the cell voltages during charge and discharge were measured, in which charge was limited for 2 hours and the cut-off voltage of discharge was 0.5 V. Some modifications in the structure and components of the laminate cell, e.g., the change in the electrode’s tab from Ni ribbon to Ni mesh and the optimization on the thickness of PE film and the thermal bonding conditions such as heating temperature and time, resulted in no leakage of the electrolyte during charge-discharge cycles and no expansion of the laminate package by oxygen, and the cycling performance was significantly enhanced compared to our previous cell [2]. The cell presented very stable charge and discharge voltages for 20 cycles and the current efficiency was more than 90 %. More detailed results will be shown in this paper. This work was financially supported by “Advanced Low Carbon Technology Research and Development Program (ALCA)” of Japan Science and Technology Agency (JST). The authors acknowledge FDK Corporation for supplying the MH negative electrode. Reference [1] T. Gejo, K. Kawaguchi, M. Morimitsu, 2017 TMS Annual Meeting & Exhibition, Pan American Materials Congress, San Diego, USA (2017). [2] S. Kino, M. Morimitsu, The 232th ECS Meeting, Abs#104870, Washington, D. C., USA (2015).

Repeatable replication method with liquid infiltration to fabricate robust, flexible, and transparent, anti-reflective superhydrophobic polymer films on a large scale

Flexible superhydrophobic films that can be adapted to any target object for practical applications have drawn much attention in recent years. In this paper, we propose a simple method to fabricating highly flexible superhydrophobic polydimethylsiloxane (PDMS) films, via a repeatable replication and nondestructive detachment from a superhydrophobic aluminum mold. Due to the hierarchical surface structures and intrinsic hydrophobicity of PDMS, the fabricated films exhibited superior water repellency without any further modifications using low surface energy materials. Moreover, these water repellent films exhibited excellent mechanical durability and flexibility without losing the anti-wetting property under harsh conditions. The use of a robust superhydrophobic mold and the easy detachment of the film using a solution with a low surface tension allow for the clean release of large-area replicas without any damages to the mold. This enables the repeated fabrication of superhydrophobic PDMS films without the deterioration of their wettability using a single mold. Furthermore, the superhydrophobic PDMS film exhibited an efficient anti-reflection property and high transparency, which allows an enhanced light collection and efficiency when applied to solar cells. Consequently, this simple and inexpensive method is appropriate for diverse applications that require films with superior mechanical and optical properties, and a special wetting behavior.

Study for Transmittance Changes with the Thicknesses of ITO and Water-repellent Films of Ophthalmic Lens

Study for Transmittance Changes with the Thicknesses of ITO and Water-repellent Films of Ophthalmic Lens

Assessment of morphology, topography and chemical composition of water-repellent films based on polystyrene/titanium dioxide nanocomposites

In this study, polystyrene (PS)/titanium dioxide (TiO2) films were fabricated through simple solution casting technique via a modified phase separation process. The presented approach resulted in a remarkable reduction in the required amount of nanoparticles for achieving superhydrophobicity. Scanning electron microscopy (SEM) and 3D confocal microscopy were utilized to characterize surface morphology and topography of samples, respectively. An attempt was made to give an in-depth analysis on the surface rough structure using 3D roughness profiles. It was found that high inclusions of non-solvent and nanoparticles resulted in a stable self-cleaning behavior due to the strong presence of hydrophobic TiO2 nanoparticles on the surface. Quite unexpectedly, low inclusions of nanoparticles and non-solvent also resulted in superhydrophobic property mainly due to the proper level of induced surface roughness. XPS analysis was also utilized to determine the chemical composition of the films’ surfaces. The results of falling drop experiments showed that the sample containing a higher level of nanoparticles had a much lower mechanical resistance against the induced harsh conditions. All in all, the presented method has shown promising potential in fabrication of superhydrophobic surfaces with self-cleaning behavior using the lowest content of nanoparticles.

Plasma Treatment for Preparing Durable Water Repellent and Anti-Stain Synthetic Fabrics for Automotive Applications

This paper describes the development of a plasma process to produce a durable water repellent and anti-stain thin film on synthetic textile, utilized for the upholstery in the automotive field. The coatings were deposited in non equilibrium low pressure plasmas fed with 1H, 1H, 2H-perfluo-ro- 1-decene employing, as substrates, polyethylene terephthalate and polyethylene terephthalate thermo-coupled to polyurethane foam. It was found that the XPS F/C ratio of the deposit was higher than 1.4 and that the treated textile was always very hydrophobic (WCA > 140˚) and oil re- sistant (motor oil CA > 110˚), even after wear.

A raincoat for Bacillus subtilis

The Bacillus subtilis protein BslA self-assembles into a water-repellent film that coats the surface of biofilms.

Analysis of nano-cluster formation in the PECVD process

In this paper, the ultra water-repellent thin films were prepared by RF PECVD. On the basis of surface morphology, chemical bonding states and plasma diagnostics, a formation model of clusters for the ultra water-repellent films was discussed from considerations of formation process and laser scattering results. Moreover, using laser scattering method, the relative change of quantity of nano-clusters or size of agglomerates could be confirmed. From the results, the films were deposited with nano-clusters and those of agglomerates, which formed in organosilicon plasma, and formation of agglomerates were depended on the deposition time.

活性メチレン基を有するカルボキシ基含有アクリルシリコーン/シリカ複合微粒子による超撥水性膜の作製と架橋による耐久性付与

活性メチレン基を有するカルボキシ基含有アクリルシリコーン/シリカ複合微粒子による超撥水性膜の作製と架橋による耐久性付与

Production of Low Electron Temperature Plasma and Coating of Carbon-Related Water-Repellent Films on Plastic Plate

Low electron temperature plasma with a value less than 2 eV was produced by the inductively coupled discharge with a three-turn spiral antenna and the radio-frequency-biased grid for hard coating of carbon-related water-repellent thin films on plastic plate. It was found that the electron temperature decreased with increasing a negative biasing voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> for V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> <; -100 V and, then, electron population becomes bicomponent with the higher temperature of about 10 eV and the lower temperature of less than 2 eV. The water-repellent thin films were also prepared on polycarbonate and silicon wafer substrates in the low electron temperature plasma using C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and Ar mixture gases. The wetting contact angle and the pencil hardness were discussed.

Superhydrophobic modification of TiO2 nanocomposite PVDF membranes for applications in membrane distillation

Abstract Superhydrophobic membrane for the application in membrane distillation was generated by creating a hierarchical structure with multilevel roughness via depositing TiO 2 nanoparticles on microporous PVDF membranes by means of a low temperature hydrothermal (LTH) process. The TiO 2 coated membranes were then fluorosilanized using a low surface energy material H, 1H, 2H, 2H-perfluorododecyltrichlorosilane. A variety of techniques such as capillary flow porometry, TEM, SEM, XPS, KI test, liquid entry pressure (LEP) measurement and contact angle goniometry were applied to explore the effects of surface modification on the surface chemistry, structure and performance of the membranes. The anti-fouling performance of virgin and modified membranes were examined in a direct contact membrane distillation (DCMD) process using sodium chloride and humic acid solution as a model feed. Results showed that the modification was mechanically and thermally robust and photoactive. The liquid entry pressure (LEP) and water contact angle were increased from 120 kPa and 125° to 190 kPa and 166°, respectively. The fluorosilanization of TiO 2 nanocomposite PVDF membranes did not compromise the mean pore size. It was also appeared that the TiO 2 coating not only contributes in engineering the hierarchical structure but also provides sites (OH functional groups) for the hydrolyzed silane coupling agent to be anchored forming a robust uniform water repellent film. The filtration results also showed that the pure water flux of the modified membrane was lower than that of the virgin membrane particularly at higher temperatures. However, the sodium chloride DCMD test showed that the permeate conductivity of the virgin membrane was increased sharply whereas it was not changed for the modified membrane over the period of the experiment. A 20 h fouling DCMD experiment with humic acid did not show a reduction in flux for virgin and modified membranes. However, a substantial reduction in flux was observed with the addition of 3.775 mM CaCl 2 into the solution due to the formation of complexes with humic acid and consequent particles coagulation and precipitation on the membrane surface. Although both virgin and modified membranes showed similar fouling behaviors, a significantly higher flux recovery was found for modified membrane compared to the virgin membrane.

Structure and surface properties of fluorinated organic–inorganic hybrid films

Fluorinated organic–inorganic hybrid films were prepared by sol–gel process from tridecafluoroctyltriethoxysilane (PFAS), 3-glycidoxypropyltrimethoxysilane, and tetraethoxysilane (TEOS). It has been found that the fluorinated hybrid films possessed fluorinated side chains originating from PFAS as top layer, and silica network as bottom layer, which had very low surface energy and could be used as water repellent functional coatings. The outermost layer of the water-repellent film may be fully covered by the perfluoroalkyl side chains as the molar ratio of PFAS/TEOS increases up to about 0.005:1. The addition of BPA can enhance the cross-link density of fluorinated hybrid films, and make more perfluoroalkyl groups enriching at the coating film-air interface to lower the surface free energy. However, the improvement of the cross-link density of fluorinated hybrid films tends to exhibit brittleness and micro-cracks. Consequently, it can be concluded that a small BPA additive content is preferred for the formation of fluorinated hybrid films with a smooth surface and less detectable cracks.