Recent Progress in Fabrication and Applications of Superhydrophobic Coating on Cellulose-Based Substrates

A One-Step Approach for a Durable and Highly Hydrophobic Coating for Flax Fabrics for Self-Cleaning Application

Highly hydrophobic flax fabrics with durable properties were prepared using the "dip-coating" method for self-cleaning application. Flax fabrics were coated with a polysiloxane coating via a hydrosilylation reaction with a Karstedt catalyst at room temperature. The coated fabrics displayed highly and durable hydrophobic properties (contact angle and sliding angle of about 145° and 23°, respectively) with good self-cleaning ability for certain pollutants and excellent durability. Moreover, the influence of the coating process on the mechanical properties of fabrics was investigated. A decrease in E modulus and an increase in tensile stress at maximum force and elongation at maximum force has been observed. Furthermore, this influence of the coating process can be easily controlled by adjusting the proportion of curing agent in the treatment solution.

Effect of Oxygen Plasma Pre-Treatment on the Surface Properties of Si-Modified Cotton Membranes for Oil/Water Separations

Hydrophobic and oleophilic Si-based cotton fabrics have recently gained a lot of attention in oil/water separation due to their high efficiency. In this study, we present the effect of O₂ plasma pre-treatment on the final properties of two Si-based cotton membranes obtained from dip coating and plasma polymerization, using polydimethylsiloxane (PDMS) as starting polymeric precursor. The structural characterizations indicate the presence of Si bond on both the modified cotton surfaces, with an increase of the carbon bond, assuring the success in surface modification. On the other hand, employing O₂ plasma strongly changes the cotton morphology, inducing specific roughness and affecting the hydrophobicity durability and separation efficiency. In particular, the wettability has been retained after 20 laundry tests at 40 °C and 80 °C, and, for separation efficiency, even after 30 cycles, an improvement in the range of 10-15%, both at room temperature and at 90 °C can be observed. These results clearly demonstrate that O₂ plasma pre-treatment, an eco-friendly, non-toxic, solvent-free, and one-step method for inducing specific functionalities on surfaces, is very effective in enhancing the oil/water separation properties for Si-based cotton membranes, especially in combination with plasma polymerization procedure for Si-based deposition.

Smart Superhydrophobic Filter Paper for Water/Oil Separation and Unidirectional Transportation of Liquid Droplet

Water/oil separation from their mixture and emulsion has been a prominent topic in fundamental research and in practical applications. In this work, a smart superhydrophobic membrane (SHP) was obtained by dipping an off-the-shelf laboratory filter paper in an ethanol suspension of trichloro (1H,1H,2H,2H-tridecafluoro-n-octyl) silane, tetraethyl orthosilicate, and titanium dioxide nanoparticles with different dimensions of 20 and 100 nm. The selection of membrane substrates was optimized including different quantitative and quantitative filter papers with different filtration velocity (slow, intermediate, and fast). The as-prepared SHP was demonstrated to be superhydrophobic and photosensitive, which was used in the separation of carbon tetrachloride and water from their mixture and emulsion. Moreover, orderly aligned micropores were formed for the modified superhydrophobic filter papers by using nanosecond laser. Unidirectional penetration was obtained for the UV-irradiated paper with a bored pore in the range of 50-500 μm in the systems of air/water and water/oil. This study may promote the understanding of unidirectional transportation of liquid droplet and facilitate the design of interfacial materials with Janus-type wettability.

Surface Modification of Polyester/Viscose Fabric with Silica Hydrosol and Amino-Functionalized Polydimethylsiloxane for the Preparation of a Fluorine-Free Superhydrophobic and Breathable Textile

This work attempted to fabricate superhydrophobic fabric via a simple immersion technique. Textile fabrics were coated with silica nanoparticles prepared from tetraethoxysilane (TEOS) to obtain sufficient roughness with hydrophobic surface chemistry. Then, the coated fabrics were treated with polydimethylsiloxane (PDMS) and aminopropyltriethoxysilane (APTES) to reduce the surface energy. The effects of the PDMS concentration on the surface morphology and superhydrophobicity of as-prepared fabric were investigated. The morphology and the composition of superhydrophobic fabric were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDS), and Fourier transform infrared (FTIR) spectroscopy. The results revealed the formation of spherical silica nanoparticles with an average particle size of 250 nm throughout the fabric surface. The possible interactions between silica nanoparticles and APTES, as well as the fabrics, were elucidated. Investigating the hydrophobicity of fabrics via water contact angle (WCA) measurement showed that the treated fabric exhibits excellent water repellency with a water contact angle as high as 151° and a very low water sliding angle. It was also found that the treated fabric maintained most of its hydrophobicity against repeated washing, as the WCA of superhydrophobic fabrics decreased to 141° after 25 repeated washing cycles. The comfort properties of the obtained superhydrophobic fabrics in terms of air permeability and bending length did not reveal any significant changes.

Degradable collagen/sodium alginate/polyvinyl butyral high barrier coating with water/oil-resistant in a facile and effective approach

Degradable bio-based materials have been widely considered as functional coatings, however, it is a great challenge to fabricate biodegradable coatings with high barrier, water- and oil- resistance. In this work, such coatings were fabricated by using collagen fibers (CF), sodium alginate (SA), and polyvinyl butyral (PVB). CF and SA were mixed evenly and coated on Ca²⁺ pretreated filter paper. It was mainly due to the electrostatic adsorption between collagen fibers and sodium alginate, and the crosslinking between the adsorption products and Ca²⁺. By coating PVB solution, the barrier performance was further improved. Notably, the composite exhibited excellent water vapor resistance (48 g/m²·24 h), water resistance (31 g/m²), oil resistance (kit rating: 12/12) and good mechanical properties. This degradable, environmentally friendly, and simple composite paper method has excellent barrier properties, mechanical properties and fluorine-free properties, and will have many applications in the food and packaging fields.

Three-Dimensional Multilayer Vertical Filament Meshes for Enhancing Efficiency in Fog Water Harvesting

Novel types of vertical filament mesh (VFM) fog harvesters, 3D VFM fog harvesters, and multilayer 3D VFM fog harvesters were developed by mimicking the water-harvesting nature of desert beetles and the spider silks from fog. Four different types of polymer filaments with different hydrophilic-hydrophobic properties were used. The polymer filaments were modified with the polyurethane-sodium alginate (PU-SA) mixture solution, and a simple spraying method was used to form alternating 3D PU-SA microbumps. Polymer VFMs exhibited a higher fog-harvesting efficiency than the vertical metal meshes. Moreover, the hydrophobic VFM was more efficient in fog harvesting than the hydrophilic VFM. Notably, the fog-harvesting efficiency of all VFMs increased by 30-80% after spraying with the mixed PU-SA solution to form a 3D geometric surface structure (3D PU-SA microbumps), which mimicked the desert beetle back surface. This modification caused the fog-harvesting efficiency of PTFE 3D VFM to be thrice higher than that of Fe VFM. This increase was attributed to the improved synergistic effects of fog capturing, droplet growing, and droplet shedding. The multilayer VFMs were more efficient in fog harvesting than the single-layer VFMs because of a larger droplet capture area. The fog-harvesting efficiency of two-layer and four-layer polymer VFMs was approximately 35% and about 45% higher than that of the single-layer polymer VFMs, respectively. The four-layer PTFE 3D VFM with the type B PU-SA bump surface (bump/PU-SA) had the highest efficiency of 287.6 mL/m²/h. Besides the high fog-harvesting efficiency, the proposed polymer VFMs are highly stable, cost-effective, rust-free, and easy to install in practical applications. These advantages are ascribed to the elasticity of the polymer filaments. This work provides new ideas and methods for developing high-performance fog harvesters such as the 3D VFM.

Rapid and Stable Plasma Transformation of Polyester Fabrics for Highly Efficient Oil-Water Separation

Fabrics with special wettability have drawn growing attention in recent years in the area of oil-water separation due to their low cost, good flexibility, and ease of handling. However, an efficient and fast method to enable the required wetting state on fabrics still remains a challenge. In this work, a one-step, rapid, and chemical-free hydrogen plasma treatment is reported to prepare a superhydrophobic and oleophilic polyester fabric. The as-prepared fabrics display a static water contact angle of 153.2° with excellent oil-water separation capability. The mechanism of surface transformation is discussed through chemical analyses, which indicate a significant removal of carboxyl group from the pristine hydrophilic surface. This developed method is envisaged to be used for on-demand large-scale production of materials for emergency oil cleanup through either separation or selective adsorption.

Bioinspired Hydrophobic Cellulose Nanocrystal Composite Films as Organic-Solvent-Responsive Structural-Color Rewritable Papers

Lots of beetles, moths, and birds in the natural world present stunning unique structural colors as well as excellent hydrophobic performances. Herein, a novel bioinspired variable structural-color film with organic-solvent responsiveness and surface hydrophobicity was fabricated. Cellulose nanocrystals (CNCs) provided structural color with left-handed helicity. PEG-PPG-PEG triblock copolymers (PPPTCs) were blended with CNCs, giving rise to the organic-solvent-responsive structural color and wider red-shift window of the reflectance peak. The color of the film could be regulated repeatedly under the stimulus of cyclohexanone with an obvious red shift up to 107 nm, corresponding to a macroscopic color change from blue to yellow. Low-surface-energy compound hexadecyltrimethoxysilane (HDTMS) was covalently grafted on the surface in a one-step method to introduce hydrophobicity, successfully preventing the effect of water on the ordered nanostructure. Based on the bionics principle, the as-prepared CNC/PPPTC nanocomposite films with variable structural colors and hydrophobicity are beneficial to their prospective applications in display screens, rewritable hydrophobic structural-color-changing paper, biomimetic sensors, and so forth.

Facile Approach for Ecofriendly, Low-Cost, and Water-Resistant Paper Coatings via Palm Kernel Oil

Paper-based packaging is widely employed in industries ranging from food to beverages to pharmaceuticals because of its attractive advantages of biodegradability, recyclability, good strength, low cost, and lightweight. However, paper products usually have poor water barrier resistance properties because of paper and fibers porous microstructure. In this study, an ecofriendly water-resistant (hydrophobic) oil from biological origin, namely, palm kernel oil (PKO) was used to coat paper by using a facile and cost-effective dip-casting approach. PKO formulation was prepared by mixing with a solvent and furfuryl alcohol (FA). The water resistance, structural properties, and thermal and mechanical properties of the coated papers obtained under different processing conditions were reported and compared to understand the performance of coated paper. Contact angle (CA), Fourier transform infrared (FTIR), and thermal gravimetry (TGA) were used for analysis and characterization of coated papers. Data from contact angle measurements showed that the PKO formulation could considerably improve the liquid water barrier property of the paper, with a measured water contact angle (CA) of ∼120° and reduce the water vapor transmission rate (WVTR) by 22%. This novel, green, low-cost, and water-resistant paper coating made with biological and biodegradable oil is a potential candidate for replacing petroleum-based coatings used in a broad range of applications and will also be able to make an additional full use of the palm kernel oil.

Design of SiO2/TiO2 that Synergistically Increases The Hydrophobicity of Methyltrimethoxysilane Coated Glass

This research work presents the design of a mixture of SiO2/TiO2 that increases the surface roughness and hydrophobicity of methyltrimethoxysilane (MTMS) coated glass. The deposition of SiO2, TiO2, and MTMS were conducted using a layer by layer dip coating technique. The SiO2/TiO2 coating was derived from complete hydrolysis of tetraethylorthsilicate and titanium tetraisopropoxide. In order to evaluate and compare the performance of SiO2/TiO2/MTMS coated glass, the SiO2/SiO2/MTMS and TiO2/TiO2/MTMS were also fabricated. SiO2/TiO2/MTMS samples displayed the highest water contact angle. The topography of surfaces showed that SiO2/TiO2/MTMS exposed higher surface roughness with micro-nanoscale structures. The sequence of SiO2 and TiO2 influenced the water contact angle and the stability of the coatings. SiO2/TiO2/MTMS produced higher contact angle and stability than TiO2/SiO2/MTMS.

Environmentally benign non-wettable textile treatments: A review of recent state-of-the-art

Among superhydrophobic materials, non-wettable textiles are probably the ones that come in contact or interact with the human body most frequently. Hence, textile treatments for water or oil repellency should be non-toxic, biocompatible, and comply with stringent health standards. Moreover, considering the volume of the worldwide textile industry, these treatments should be scalable, sustainable, and eco-friendly. Due to this awareness, more and more non-wettable textile treatments with eco-friendly processes and green or non-toxic chemicals are being adopted and reported. Although fluorinated alkylsilanes or fluorinated polymers with C8 chemistry (with ≥ 8 fluorinated carbon atoms) are the best performing materials to render textiles water or oil repellent, they pose substantial health and environmental problems and are being banned. For this reason, water/solvent-borne, C8-free vehicles for non-wettable treatment formulations are probably the only ones that can have commercialization prospects. Hence, researchers have come up with a variety of new, non-toxic, green formulations and materials to render fabrics liquid repellent that constitute the focus of this review paper. As such, this review article discusses and summarizes recent developments and techniques on various sustainable superhydrophobic treatments for textiles, with comparable performance and durability to formulations based on fluorinated C8 compounds. The current state-of-the-art technologies, potential commercialization prospects, and relevant limitations are discussed and summarized with examples. The review also attempts to indicate promising future strategies and new materials that can transform the process for non-wettable textiles into an all-sustainable technology.

Superhydrophobic and flame retardant cotton modified with DOPO and fluorine-silicon-containing crosslinked polymer

Modification of cotton fabric to achieve superhydrophobic, self-cleaning and heat resistance is of particular interest for practical applications. Herein, a simple surface modification route is designed to introduce flame retardant component 9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) and low surface energy crosslinked polymer network comprising both fluorine and silicon elements on the surface of cotton fabric. The modified cotton fabric shows characteristic of superhydrophobic property with water contact angle of 154.8°, and exhibits promising self-cleaning performance. With the characters of hydrophobicity and lipophilicity, the modified cotton fabric can efficiently separate oil-water mixture and even emulsion. Moreover, the introduction of DOPO and fluorine-silicon-containing coating not only enhances the heat resistance of cotton, but also improves the flame retardant property.

Fabrication of Food-Safe Water-Resistant Paper Coatings Using a Melamine Primer and Polysiloxane Outer Layer

Paper-based materials are highly desirable as packaging materials due to their numerous advantages that include low cost, renewability, and biodegradability. However, their hydrophilicity has limited their range of applications. Reported herein is a facile and economical approach for the preparation of biodegradable water-resistant paper for food-contact applications. Commercial printing paper and cup papers are coated with melamine, which is FDA approved for food-contact applications. Subsequently, a water-repellent outer layer is applied using poly(dimethylsiloxane) (PDMS)-isocyanate. A relationship between the PDMS concentration and water contact angles (WCAs) of the obtained coating was studied. Typically, the coated cup paper and printing paper had coating loadings of 1.61 ± 1.10 and 0.93 ± 0.74 wt %, respectively. After the coatings had been applied, the WCAs were very high (>125°), and water absorption had decreased by 70% for printing paper and by 35% for cup paper. Considering the facile fabrication method and the low-cost food-safe raw materials, herein, this approach will have great potential for the large-scale production of materials for use in food- and nonfood contact applications.

Dimensionally stable cellulosic aerogels functionalized by titania

The study is aimed at imparting dimensional stability and some functionalities to cellulosic aerogels. The polysaccharide suffers from mechanical strength loss in wetted state that restricts its application. Improvement is achieved by mean of microfibrillation of cellulosic fibers combining intense mechanical treatment with freeze-thawing. Addition of the latter decreases the number of cycles. Aerogels prepared from microfibrillated cellulose by freeze-drying hold their dimensional stability in solutions that makes possible treating them chemically without loss in shape. Here a method of directional sol-gel processing is applied to mineralize such aerogels by titania. Owing to covalent bonds to cellulose macromolecules formed via the condensation reactions, titania coating possesses good adhesion, not separating at heating when it is transferred in anatase form. Its photocatalytic activity results in self-cleaning of cellulose aerogels under outdoor sunlight irradiation. Calcination in air or carbonization in an inert gas atmosphere can serve to prepare metal oxide or composites with carbon of various shape and dimensionality.

Bacterial cellulose as a potential bioleather substitute for the footwear industry

Shoe patterns and a sole made of BC, baby shoe made of BC and, on the right BC material dyed in red. (prototype made by www.patent-shoes.com).

Superhydrophobic surfaces generated by one-pot spray-coating of chitosan-based nanoparticles

Superhydrophobic surfaces have attracted great attention due to their attractive properties. Biopolymer-based low-cost and environmentally-friendly superhydrophobic coatings with easy-to-perform fabrication methods are always desirable. Herein, we report superhydrophobic surfaces using a one-step spray-coating of chitosan-based nanoparticles. The particles were easily prepared by a nanoprecipitation strategy using synthesized organosoluble chitosan stearoyl ester (CSSE). The resulting particles had an average size of 165 ∼ 235 nm depending on the applied concentration. Subsequently, spray-coating of such particles onto silicon wafer generated a surface with a water contact angle of 155 ± 1°. SEM and AFM images exhibited a nano/microscaled roughness appeared on the coated surface. The superhydrophobic surfaces showed a stable superhydrophobic performance even after storage for 15 days, pH stability between pH 1 to pH 11 and thermal stability until a temperature no more than 50 °C. These properties would broaden the application fields of superhydrophobic surfaces as well as the chitosan itself.

Facile Preparation of a Robust and Durable Superhydrophobic Coating Using Biodegradable Lignin-Coated Cellulose Nanocrystal Particles

It is a challenge for a superhydrophobic coating to overcome the poor robustness and the rough surface structure that is usually built using inorganic particles that are difficult to degrade. In this study, a robust superhydrophobic coating is facilely prepared by using commercial biodegradable lignin-coated cellulose nanocrystal (L-CNC) particles after hydrophobic modification to build rough surface structures, and by choosing two different adhesives (double-sided tape and quick-setting epoxy) to support adhesion between the L-CNC particles and the substrates. In addition to excellent self-cleaning and water repellence properties, the resulting coatings show outstanding mechanical strength and durability against sandpaper abrasion, finger-wipe, knife-scratch, water jet, UV radiation, high temperature, and acidic and alkali solutions, possessing a wide application prospect.

Durable antibacterial and UV-protective Ag/TiO2@ fabrics for sustainable biomedical application

A facile method was developed to endow cotton fabric with remarkable antibacterial and ultraviolet (UV)-protective properties. The flower-like TiO₂ micro-nanoparticles were first deposited onto cotton fabric surface via hydrothermal deposition method. Then, the Ag NPs with a high deposition density were evenly formed onto TiO₂@cotton surface by sodium hydroxide solution pretreatment and followed by in situ reduction of ANO₃. This work focused on the influence of different hydrothermal reaction durations and the concentration of AgNO₃ on antibacterial activity against relevant microorganisms in medicine as well as on the UV-blocking property. Ag NPs-loaded TiO₂@cotton exhibited high antibacterial activity with an inhibition rate higher than 99% against Staphylococcus aureus and Escherichia coli bacteria. Moreover, the as-prepared cotton fabric coated with Ag NPs and TiO₂ NPs demonstrated outstanding UV protective ability with a high ultraviolet protection factor value of 56.39. Morphological image of the cells revealed a likely loss of viability as a result of the synergistically biocidal effects of TiO₂ and Ag on attached bacteria. These results demonstrate a facile and robust synthesis technology for fabricating multifunctional textiles with a promising biocidal activity against common Gram-negative and Gram-positive bacteria.

Nature-Inspired Strategy toward Superhydrophobic Fabrics for Versatile Oil/Water Separation

Phytic acid, which is a naturally occurring component that is widely found in many plants, can strongly bond toxic mineral elements in the human body, because of its six phosphate groups. Some of the metal ions present the property of bonding with phytic acid to form insoluble coordination complexes aggregations, even at room temperature. Herein, a superhydrophobic cotton fabric was prepared using a novel and facile nature-inspired strategy that introduced phytic acid metal complex aggregations to generate rough hierarchical structures on a fabric surface, followed by PDMS modification. This superhydrophobic surface can be constructed not only on cotton fabric, but also on filter paper, polyethylene terephthalate (PET) fabric, and sponge. Ag^I, Fe^III, Ce^III, Zr^IV, and Sn^IV are very commendatory ions in our study. Taking phytic acid-Fe^III-based superhydrophobic fabric as an example, it showed excellent resistance to ultraviolet (UV) irradiation, high temperature, and organic solvent immersion, and it has good resistance to mechanical wear and abrasion. The superhydrophobic/superoleophilic fabric was successfully used to separate oil/water mixtures with separation efficiencies as high as 99.5%. We envision that these superantiwetting fabrics, modified with phytic acid-metal complexes and PDMS, are environmentally friendly, low cost, sustainable, and easy to scale up, and thereby exhibit great potentials in practical applications.

Plasma Processing with Fluorine Chemistry for Modification of Surfaces Wettability

Using plasma in conjunction with fluorinated compounds is widely encountered in material processing. We discuss several plasma techniques for surface fluorination: deposition of fluorocarbon thin films either by magnetron sputtering of polytetrafluoroethylene targets, or by plasma-assisted chemical vapor deposition using tetrafluoroethane as a precursor, and modification of carbon nanowalls by plasma treatment in a sulphur hexafluoride environment. We showed that conformal fluorinated thin films can be obtained and, according to the initial surface properties, superhydrophobic surfaces can be achieved.