Novel Fluorinated Polymers Containing Short Perfluorobutyl Side Chains and Their Super Wetting Performance on Diverse Substrates

Antibacterial Superhydrophobic Cotton Fabric with Photothermal, Self-Cleaning, and Ultraviolet Protection Functionalities

Cotton fabrics with superhydrophobic, antibacterial, UV protection, and photothermal properties were developed using Ag/PDMS coatings, and the role of coating formulations on the obtained functionalities was studied. Specific attention was paid to understanding the relationships between the fabrics' superhydrophobicity and antibacterial activity against Escherichia coli (E. coli) bacteria. UV protection performance of Ag/PDMS coatings was thoroughly evaluated based on the variation of UV transmission rate through coated fabrics and photoinduced chemiluminescence spectra. Moreover, the effect of silver nanoparticles (Ag NPs) and PDMS on developing a photothermal effect on fabrics was discussed. It was found that the content of Ag NPs and PDMS played critical roles in determining the water contact angle (WCA) on modified fabrics. The largest WCA was 171.31°, which was durable even after numerous accelerated wash cycles and abrasions. Antibacterial activity of fabrics showed the positive effect of pure PDMS in bacterial growth inhibition. Moreover, it was found that the antibacterial performance was greatly affected by the content of Ag NPs loaded on fabrics rather than their superhydrophobic status. Moreover, increasing the content of Ag NPs boosted the UV protection level of fabrics, improved fabrics photostability, and reduced the UV transmission rate through fabrics. Testing the photothermal effect confirmed that the content of Ag NPs and PDMS both played prominent roles, where Ag acted as a photothermal agent and PDMS determined the NIR reflection rate from the coated surface. The modified fabrics were characterized using TGA, SEM, FTIR, and XRD techniques, and it was confirmed that using a higher amount of PDMS increased the amount of Ag NPs deposition on fabrics.

Electrospun Nanofibrous Membranes: A Versatile Medium for Waterproof and Breathable Application

Waterproof and breathable membranes that prevent liquid water penetration, while allowing air and moisture transmission, have attracted significant attention for various applications. Electrospun nanofiber materials with adjustable pore structures, easily tunable wettability, and good pore connectivity, have shown significant potential for constructing waterproof and breathable membranes. Herein, a systematic overview of the recent progress in the design, fabrication, and application of waterproof and breathable nanofibrous membranes is provided. The various strategies for fabricating the membranes mainly including one-step electrospinning and post-treatment of nanofibers are given as a starting point for the discussion. The different design concepts and structural characteristics of each type of waterproof and breathable membrane are comprehensively analyzed. Then, some representative applications of the membranes are highlighted, involving personal protection, desalination, medical dressing, and electronics. Finally, the challenges and future perspectives associated with waterproof and breathable nanofibrous membranes are presented.

Non-Fluorine Oil Repellency: How Low the Intrinsic Wetting Threshold Can Be for Roughness-Induced Contact Angle Amplification?

Surface chemistries for realizing oil repellency are mostly based on perfluoro compounds (PFCs) owing to their low surface energy. However, PFCs are not sustainable because of their persistent and bioaccumulative properties, and their usage, even short-chain ones, has begun to be phased out. To date, studies on non-fluorine oil repellency have been extremely rare, and the obtained oil repellency has been limited. Here, we report the non-fluorine oil repellency of a coating prepared on a tightly woven plain-weave fabric through hydrolysis and polycondensation of difunctional chlorosilane. The coated fabric exhibited a contact angle of 119.0° for castor oil and 81.4° for hexadecane, as well as a contact angle of 51.9° for decane with a surface tension as low as γ_LV = 23.5 mN m^-1. According to the standard ISO 14419:2010, oil repellency was rated Grade 6. The solid surface tension of the coating was calculated to be γ_SV = 22.1 mN m^-1. Through the test of the difference in contact angles between rough and smooth surfaces, the intrinsic wetting threshold (θ_IWT) for such a surface chemistry was determined to be ranging from 8.9 to 14.5°. A study on the effects of surface morphologies suggests that the realization of an oil-repellency rating of 6 and a θ_IWT as low as 8.9-14.5° strongly depends on the roughness topographies. We hope that this study will be useful for the design─and our understanding─of non-fluorine oil repellency for applications including stain-resistant textiles and grease-resistant food packaging.

Improvement of Oil and Water Barrier Properties of Food Packaging Paper by Coating with Microcrystalline Wax Emulsion

Studies have shown that fluorinated oil repellents are potentially harmful to humans and the environment, and therefore, the development of non-toxic, green, and environmentally friendly oil repellents has become inevitable. Microcrystalline wax is a branched saturated alkane with a molecular weight of 580–700 Da, which has a lower surface tension than edible oil. Herein, microcrystalline wax emulsion (fluorine-free oil repellent) was prepared by mechanical stirring–homogenization, the effects of emulsifier ratio and dosage on the emulsion performance were systematically investigated, and the resultant stable microcrystalline wax emulsions were applied to the paper surface to explore the oil and water resistance and water vapor barrier performance. The results showed that stabilized microcrystalline wax emulsion was obtained at the emulsifier Span-80/Tween-80 ratio of 5:5, and the emulsifier dosage was 20% (relative to the microcrystalline wax). When 6 g/m² of microcrystalline wax was applied to the surface of starch pretreated paper, the kit rating value of the paper was high, at up to 10/12, the Cobb₆₀ value decreased to 12.5 g/m², the overall migration of paper was less than 10 mg/dm², and the water vapor permeability was reduced by 81.9%, which met the requirements of oil and water resistance performance of food packaging paper.

Persistent Water Repellency of Syndiotactic Polymethylene with Perfluoroethyl Hexyloxycarbonyl Side Chains

Polyacrylates bearing long fluoroalkyl (Rf) side chains are known to have ultralow surface energies that are appropriate for functional coating and fabric finishing. However, these long Rf chains cause health concerns because of the risk of toxic and bioaccumulative perfluoroalcanoic acid emission via oxidative degradation. This work demonstrates that incorporating a short Rf chain of perfluoroethylene at the end of the side chains of syndiotactic poly(substituted methylene) (PM) produces hydrophobicity. A contact angle of 105° of PM remains constant for more than 50 s, whereas that of the polyacrylate (PA) with the same side chain rapidly decreases from 85° to 44° over the same period. Such persistent water repellency of the PM is ascribed to a liquid crystal structure comprised the main chains arranged in a 2D hexagonal lattice and side chains that extend perpendicularly from these main chains.

Fluorinated Metal-Organic Coatings with Selective Wettability

Surface chemistry is a major factor that determines the wettability of materials, and devising broadly applicable coating strategies that afford tunable and selective surface properties required for next-generation materials remains a challenge. Herein, we report fluorinated metal-organic coatings that display water-wetting and oil-repelling characteristics, a wetting phenomenon different from responsive wetting induced by external stimuli. We demonstrate this selective wettability with a library of metal-organic coatings using catechol-based coordination and silanization (both fluorinated and fluorine-free), enabling sensing through interfacial reconfigurations in both gaseous and liquid environments, and establish a correlation between the coating wettability and polarity of the liquids. This selective wetting performance is substrate-independent, spontaneous, durable, and reversible and occurs over a range of polar and nonpolar liquids (60 studied). These results provide insight into advanced liquid-solid interactions and a pathway toward tuning interfacial affinities and realizing robust, selective superwettability according to the surrounding conditions.

Robust, Multiresponsive, Superhydrophobic, and Oleophobic Nanocomposites via a Highly Efficient Multifluorination Strategy

Artificial superhydrophobic surfaces are garnering constant attention due to their wide applications. However, it is a great challenge for superhydrophobic materials to simultaneously achieve good oil repellency, mechanochemical robustness, adhesion, thermomechanical properties, and multiresponsive ability. Herein, we propose a highly efficient multifluorination strategy to prepare superhydrophobic nanocomposites with the above features, which can be used as monoliths or coatings on various substrates. In this strategy, long-chain perfluorinated epoxy (PFEP) provides outstanding water/oil repellency, tetrafluorophenyl-based epoxy (FEP) possesses good thermodynamic compatibility with PFEP and increases the mechanical performance of the matrix, and carbon nanotubes grafted with perfluorinated segments and flexible spacers (FCNTs) tailor the surface roughness as well as impart multiple functions and ensure good binding interfaces. Notedly, all of the applications of constrained long-chain perfluorinated compounds are achieved via thiol-ene click chemistry, following the ethos of atom economy. The resultant PFEP₃₀/FCNTs₄₀ exhibits superhydrophobicity and oleophobicity, thermal conductivity (1.33 W·m^-1·K^-1), electronic conductivity (232 S m^-1), and electromagnetic interference shielding properties (∼30 dB at 8.2-12.4 GHz, 200 μm). Importantly, after different extreme physical/chemical tests, the PFEP₃₀/FCNTs₄₀ coating still shows outstanding water/oil repellency. In addition, the coating exhibits good photo/electrothermal conversion ability and shows the potential for sensor application. Moreover, the novel strategy provides an efficient guideline for large-scale preparation of robust, multiresponsive, superhydrophobic, and oleophobic materials.

Short-Branched Fluorinated Polyurethane Coating Exhibiting Good Comprehensive Performance and Potential UV Degradation in Leather Waterproofing Modification

In the current leather market, waterproof leather occupies a large proportion, where waterproofness has become one of the important standards for leather selection. However, the most advanced fluorine-containing waterproofing agents on the market always have long chains of over eight carbons (C8), whose use has been restricted due to their bioaccumulation and recalcitrance in natural environment. Consequently, creating waterproof materials characterized by their environmentally friendly qualities and high performance is of great significance. Herein, we report a novel strategy for preparation of the fluorinated polyurethanes containing short branched fluorocarbon chains, and apply it in leather waterproofing. Because the fluorine-containing chain segments are enriched on the coating surface, the waterproof agent coating shows good hydrophobicity, low water absorption, high wear resistance and potential photodegradation of performances. Additionally, the water and oil proof performances of the coating are comparable to that of the marketed C8 waterproofing agent. Its solvent-resistant and antifouling performances are also outstanding. Therefore, the coating can meet the property requirements for daily use and has broad application prospects.

The effect of Surface energy characterized functional group of self-assembled monolayer for enhancing electrical stability of oxide semiconductor thin film transistor

The exact direction, of the surface energy characterized functional group of self-assembled monolayer (SAM), is proposed for achieving the enhanced electrical stability of indium gallium zinc oxide (IGZO) semiconductor thin film transistor (TFT). The SAM treatment, particularly at the SAM functional group having lower surface energy, makes oxygen molecules difficult to be adsorbed onto IGZO. And such an effect much improves positive bias stability (PBS) and clockwise hysteresis stability to the same tendency. For NH2 and CF3 functional group SAMs with surface energies of 49.4 mJ/m2 and 23.5 mJ/m2, respectively, the IGZO TFT PBS was improved from 2.47 V to 0.32 V after the SAM treatment and the IGZO TFT clockwise hysteresis was also enhanced from 0.23 V to 0.11 V without any deterioration of TFT characteristics. Employing lower surface energy functional group to the SAM, of same head group and body group, does passivate and protect the IGZO backchannel region from oxygen molecules in the atmosphere. Consequently, the enhanced electrical stability of IGZO TFT can be achieved by the simple and economic SAM treatment.

Advances in photocatalytic self-cleaning, superhydrophobic and electromagnetic interference shielding textile treatments

The use of nanomaterials in textiles provides many new opportunities and advantages for users and manufacturers; however, it comes with some of its downsides and challenges which need to be understood and overcome for enhancing the applicability of these products. This review article discusses the recent progress in developing self-cleaning and conductive textiles as two of the leading research fields of smart textiles. In particular, different aspects of fabricating nanocoatings for photocatalytic self-cleaning, superhydrophobic and electromagnetic interference (EMI) shielding effect will be brought to light. The theoretical concepts, mechanisms, latest fabrication methods along with their potential applications will be discussed. Moreover, the current drawbacks of these fields will be underlined and some recommendations for future research trajectories in terms of performance, current limitations, sustainability and safety will be proposed. This review article provides a comprehensive review on the state-of-the-art achievements in the field, which will be a valuable reference for researchers and decision makers.

Fluorine-Free Waterborne Coating for Environmentally Friendly, Robustly Water-Resistant, and Highly Breathable Fibrous Textiles

Waterproof and breathable membranes (WBMs) with simultaneous environmental friendliness and high performance are highly desirable in a broad range of applications; however, creating such materials still remains a tough challenge. Herein, we present a facile and scalable strategy to fabricate fluorine-free, efficient, and biodegradable WBMs via step-by-step dip-coating and heat curing technology. The hyperbranched polymer (ECO) coating containing long hydrocarbon chains provided an electrospun cellulose acetate (CA) fibrous matrix with high hydrophobicity; meanwhile, the blocked isocyanate cross-linker (BIC) coating ensured the strong attachment of hydrocarbon segments on CA surfaces. The resulting membranes (TCA) exhibited integrated properties with waterproofness of 102.9 kPa, breathability of 12.3 kg m^-2 d^-1, and tensile strength of 16.0 MPa, which are much superior to that of previously reported fluorine-free fibrous materials. Furthermore, TCA membranes can sustain hydrophobicity after exposure to various harsh environments. More importantly, the present strategy proved to be universally applicable and effective to several other hydrophilic fibrous substrates. This work not only highlights the material design and preparation but also provides environmentally friendly and high-performance WBMs with great potential application prospects for a variety of fields.

Suppressed Surface Reorganization in a High-Density Poly(methyl methacrylate) Brush

A high-density poly(methyl methacrylate) (PMMA) brush (σ = 0.77 chain/nm²) with a lower molecular weight distribution was prepared onto a silicon wafer by surface-initiated atom transfer radical polymerization. The surface of the PMMA brush chains was characterized upon the process of the environmental change, from air to water, using contact angle measurements in conjunction with sum-frequency generation spectroscopy. The surface structure and properties altered less with the changing environment from air to water for the PMMA brush than for a spin-coated film; that is, the extent of surface reorganization could be suppressed by grafting densely-packed chains onto a substrate. Also, the water penetration into the brush surface was inhibited because of the densely packed chain structure.

Facile fabrication of fluorine-free breathable poly(methylhydrosiloxane)/polyurethane fibrous membranes with enhanced water-resistant capability

HYPOTHESIS

Ideal breathable and waterproof materials contain two key elements: hydrophobic matrix and small pore size. Current high-performing breathable waterproof membranes usually employ fluorinated materials to construct hydrophobic surface, which possess alarming potential environmental hazards. Fluorine-free waterproof agents through coating treatment to obtain hydrophobicity suffer from complicated fabrication process and poor durability. Hence, non-fluorinated chemicals incorporated into fibers via a facile one-step electrospinning may be an effective approach to attain durable hydrophobic membranes.

EXPERIMENTS

Poly(methylhydrosiloxane)/polyurethane (PMHS/PU) solution with various PMHS concentration was formulated and electrospun to fibrous membranes, followed by a facile thermal treatment process. A systematic study including morphologies, porous structure, and surface wettability was performed. Breathable waterproof performance and tensile strength were also investigated.

FINDINGS

Added PMHS imparted mighty hydrophobicity to the membranes with a water contact angle of 130.2°, and the subsequent heat treatment greatly improved waterproofness, meanwhile doubled the tensile strength. The resultant membranes exhibited robust hydrostatic pressure of 54.1 kPa, medium breathability of 9.5 kg m^-2 d^-1, and excellent stretching stress of 14.1 MPa, which can meet the requirements of general use. The presented strategy on membrane fabrication is feasible and scalable, which may be considered as an effective remedy for environmental protection.

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.

Phosphate-Based Cross-Linked Polymers from Iodo-ene Photopolymerization: Tuning Surface Wettability through Thiol-ene Chemistry

Motivated by the various reported potential applications of poly(phosphine oxide) materials, a visible light photoinitiated iodo-ene reaction was successfully employed in network polymerization between the phosphorus-containing multifunctional monomer, tris(allyloxymethyl)phosphine oxide (TAOPO), and diiodoperfluorobutane. The cross-linked poly(phosphine oxide) network exhibited a higher glass transition temperature than a similarly cross-linked polymer formulated with trimethylolpropane triallyl ether (TMPTAE). Interestingly, the TMPTAE/DIPFB cross-linked polymer, changed color from clear to yellow within 10 min of exposure to air, whereas the cross-linked poly(phosphine oxide) underwent a similar change only upon heating. Upon investigation, it was determined that alkenes were generated within the polymer network, presumably via elimination, accounting for the observed color. These double bonds, formed in the polymer matrix, permitted surface modification via radical thiol-ene reaction. The successful surface functionalization with PEG-SH resulted in increasing the surface wettability. Additionally, the phosphorus-containing network polymer with double bonds in the polymer matrix showed shape memory capability, this representing an exciting and versatile materials platform.

Fluoropolymer-Containing Opals and Inverse Opals by Melt-Shear Organization

The preparation of highly ordered colloidal architectures has attracted significant attention and is a rapidly growing field for various applications, e.g., sensors, absorbers, and membranes. A promising technique for the preparation of elastomeric inverse opal films relies on tailored core/shell particle architectures and application of the so-called melt-shear organization technique. Within the present work, a convenient route for the preparation of core/shell particles featuring highly fluorinated shell materials as building blocks is described. As particle core materials, both organic or inorganic (SiO₂) particles can be used as a template, followed by a semi-continuous stepwise emulsion polymerization for the synthesis of the soft fluoropolymer shell material. The use of functional monomers as shell-material offers the possibility to create opal and inverse opal films with striking optical properties according to Bragg’s law of diffraction. Due to the presence of fluorinated moieties, the chemical resistance of the final opals and inverse opals is increased. The herein developed fluorine-containing particle-based films feature a low surface energy for the matrix material leading to good hydrophobic properties. Moreover, the low refractive index of the fluoropolymer shell compared to the core (or voids) led to excellent optical properties based on structural colors. The herein described fluoropolymer opals and inverse opals are expected to pave the way toward novel functional materials for application in fields of coatings and optical sensors.

Human Skin-Like, Robust Waterproof, and Highly Breathable Fibrous Membranes with Short Perfluorobutyl Chains for Eco-Friendly Protective Textiles

Flexible smart membranes with superior waterproofness and extreme breathability are highly desirable for wearable uses. However, present waterproof and breathable materials suffer from limited performance efficiency, alarming environmental risks, and complicated fabrication procedures. We report on eco-friendly fibrous membranes with human skin-like, robust waterproof, and highly breathable capabilities that can be prepared via a facile electrospinning strategy. A novel polyurethane elastomer (C4FPU) possessing double-terminal short perfluorobutyl (-C₄F₉) chain is synthesized for the first time and incorporated into the polyurethane (PU) fiber matrix, endowing the membrane with mighty and durable hydrophobicity. Additionally, the employment of AgNO₃ greatly decreased the maximum pore size ( d_max), contributing to the dramatically enhanced waterproofness. The resulting PU/C4FPU/AgNO₃ fibrous membranes exhibit comprehensive properties of exceptional hydrostatic pressure (102.8 kPa), excellent water vapor transmission rate (12.9 kg m^-2 d^-1), high mechanical property (9.8 MPa), and significant antibacterial efficacy against Escherichia coli and Staphylococcus aureus. The successful synthesis of these intriguing membranes may provide a promising candidate for the new generation of key building blocks of the upscale protective garments.

Bioinspired Surfaces with Superwettability for Anti-Icing and Ice-Phobic Application: Concept, Mechanism, and Design

Ice accumulation poses a series of severe issues in daily life. Inspired by the nature, superwettability surfaces have attracted great interests from fundamental research to anti-icing and ice-phobic applications. Here, recently published literature about the mechanism of ice prevention is reviewed, with a focus on the anti-icing and ice-phobic mechanisms, encompassing the behavior of condensate microdrops on the surface, wetting, ice nucleation, and freezing. Then, a detailed account of the innovative fabrication and fundamental research of anti-icing materials with special wettability is summarized with a focus on recent progresses including low-surface energy coatings and liquid-infused layered coatings. Finally, special attention is paid to a discussion about advantages and disadvantages of the technologies, as well as factors that affect the anti-icing and ice-phobic efficiency. Outlooks and the challenges for future development of the anti-icing and ice-phobic technology are presented and discussed.

Environmentally Friendly and Breathable Fluorinated Polyurethane Fibrous Membranes Exhibiting Robust Waterproof Performance

Waterproof and breathable membranes that provide a high level of protection and comfort are promising core materials for meeting the pressing demand for future upscale protective clothing. However, creating such materials that exhibit environmental protection, high performance, and ease of fabrication has proven to be a great challenge. Herein, we report a novel strategy for synthesizing fluorinated polyurethane (C6FPU) containing short perfluorohexyl (-C₆F₁₃) chains and introduced it as hydrophobic agent into a polyurethane (PU) solution for one-step electrospinning. A plausible mechanism about the dynamic behavior of fluorinated chains with an increasing C6FPU concentration was proposed. Benefiting from the utilization of magnesium chloride (MgCl₂), the fibrous membranes had dramatically decreased maximum pore sizes. Consequently, the prepared PU/C6FPU/MgCl₂ fibrous membranes exhibited an excellent hydrostatic pressure of 104 kPa, a modest water vapor transmission rate of 11.5 kg m^-2 d^-1, and a desirable tensile strength of 12.4 MPa. The facile fabrication of PU/C6FPU/MgCl₂ waterproof and breathable membranes not only matches well with the tendency to be environmentally protective but also fully meets the requirements for high performance in extremely harsh environments.

Strategies for anti-icing: low surface energy or liquid-infused?

Recent progress on the preparation and surface characteristics of polymeric anti-icing coatings from low surface energy or liquid-infused slippery surfaces is reviewed and illustrated.