Liquidlike, Low-Friction Polymer Brushes for Microfibre Release Prevention from Textiles.

During synthetic textile washing, rubbing between fibres or against the washing machine, exacerbated by the elevated temperature, initiates the release of millions of microplastic fibres into the environment. A general tribological strategy is reported that practically eliminates the release of microplastic fibres from laundered apparel. The two-layer fabric finishes combine low-friction, liquidlike polymer brushes with "molecular primers", that is, molecules that durably bond the low-friction layers to the surface of the polyester or nylon fabrics. It is shown that when the coefficient of friction is below a threshold of 0.25, microplastic fibre release is substantially reduced, by up to 96%. The fabric finishes can be water-wicking or water-repellent, and their comfort properties are retained after coating, indicating a tunable and practical strategy toward a sustainable textile industry and plastic-free oceans and marine foodstuffs.

Molecularly Capped Omniphobic Polydimethylsiloxane Brushes with Ultra-Fast Contact Line Dynamics.

Droplet friction is common and significant in any field where liquids interact with solid surfaces. This study explores the molecular capping of surface-tethered, liquid-like polydimethylsiloxane (PDMS) brushes and its substantial effect on droplet friction and liquid repellency. By exchanging polymer chain terminal silanol groups for methyls using a single-step vapor phase reaction, the contact line relaxation time is decreased by three orders of magnitude-from seconds to milliseconds. This leads to a substantial reduction in the static and kinetic friction of both high- and low-surface tension fluids. Vertical droplet oscillatory imaging confirms the ultra-fast contact line dynamics of capped PDMS brushes, which is corroborated by live contact angle monitoring during fluid flow. This study proposes that truly omniphobic surfaces should not only have very small contact angle hysteresis, but their contact line relaxation time should be significantly shorter than the timescale of their useful application, i.e., a Deborah number less than unity. Capped PDMS brushes that meet these criteria demonstrate complete suppression of the coffee ring effect, excellent anti-fouling behavior, directional droplet transport, increased water harvesting performance, and transparency retention following the evaporation of non-Newtonian fluids.

Ultrasmall Volume Single-Droplet Viscometry: Monitoring Cornering Instabilities on Omniphobic Polydimethylsiloxane Brushes.

Viscosity is an essential fluid property that is important for industrial and laboratory applications. For biological, complex, and/or precious liquid samples, the available volume of fluid is limited, yet there are few existing techniques to measure the viscosity of small volumes of liquids. We report a facile method to measure the viscosity of liquids by monitoring the sliding of single-cornered droplets on surfaces coated with an omniphobic film that minimizes the contact-angle hysteresis. The developed measurement method was capable of accurately characterizing the viscosity of various liquids and showed statistically equivalent values when compared to the literature, for fluids with viscosities ranging from 0.35 to ∼800 mPa s (acetone to castor oil). Using the developed single-droplet viscometer, the minimum volume required to measure the viscosity of hexadecane, dodecane, toluene, and ethanol was <5 µL and was <1 µL for decane and isopropyl alcohol, respectively. Further, the viscosity of hexadecane measured from 22 to 70 °C matched literature values precisely. The single-droplet, small-volume viscometer also requires minimal cleaning due to the omniphobic surface, meaning the fluid may be reused for other purposes with no liquid loss occurring due to the viscosity measurement.

Statistical Heuristic Wettability Analysis of Randomly Textured Surfaces.

The liquid repellency enabled by air bubbles trapped within surface roughness features has drawn the attention of many researchers over the past century. The effects of surface roughness on superhydrophobicity have been extensively studied, mainly using regularly textured, idealized geometries. In comparison, fewer works have investigated the wettability of randomly textured surfaces, although they are much more similar to scalable and bioinspired surfaces. In this work, we investigated whether prior theories developed for understanding the wettability of regularly structured surfaces may be extended to randomly rough surfaces. Sandpapers of varying grit size, when hydrophobized, served as model randomly rough surfaces. Two analyses were conducted. In the first, termed the nonstatistical approach, direct imaging of the surfaces was used to extract an effective texture size and spacing, based on particle analysis and Delaunay triangulation. In the second, termed the statistical approach, two metrology parameters, sample autocorrelation length and mean periodicity, served as the effective texture size and spacing. Overall, the statistical method predicted water contact angles better than the nonstatistical approach, especially for surfaces in the fully wetted Wenzel state or fully nonwetted Cassie state. For surfaces exhibiting a mixed Cassie state of wetting, neither approach was able to predict the apparent contact angles precisely, likely due to the propagation of wetting in three dimensions, as two-dimensional analysis was used to derive the theories of wetting investigated. Estimates on the pressure stability of the nonwetted states were underpredicted when using the statistical parameters. In summation, when randomly rough surfaces exhibit a distribution of texture sizes and spacings, current theories of wettability cannot be directly implemented by a simple mapping using statistical metrology parameters.

Bioinspired surfaces for turbulent drag reduction.

In this review, we discuss how superhydrophobic surfaces (SHSs) can provide friction drag reduction in turbulent flow. Whereas biomimetic SHSs are known to reduce drag in laminar flow, turbulence adds many new challenges. We first provide an overview on designing SHSs, and how these surfaces can cause slip in the laminar regime. We then discuss recent studies evaluating drag on SHSs in turbulent flow, both computationally and experimentally. The effects of streamwise and spanwise slip for canonical, structured surfaces are well characterized by direct numerical simulations, and several experimental studies have validated these results. However, the complex and hierarchical textures of scalable SHSs that can be applied over large areas generate additional complications. Many studies on such surfaces have measured no drag reduction, or even a drag increase in turbulent flow. We discuss how surface wettability, roughness effects and some newly found scaling laws can help explain these varied results. Overall, we discuss how, to effectively reduce drag in turbulent flow, an SHS should have: preferentially streamwise-aligned features to enhance favourable slip, a capillary resistance of the order of megapascals, and a roughness no larger than 0.5, when non-dimensionalized by the viscous length scale.This article is part of the themed issue 'Bioinspired hierarchically structured surfaces for green science'.

Advancing Antimicrobial Textiles: A Comprehensive Study on Combating ESKAPE Pathogens and Ensuring User Safety.

Antibiotic-resistant bacteria, ESKAPE pathogens, present a significant and alarming threat to public health and healthcare systems. This study addresses the urgent need to combat antimicrobial resistance by exploring alternative ways to reduce the health and cost implications of infections caused by these pathogens. To disrupt their transmission, integrating antimicrobial textiles into personal protective equipment (PPE) is an encouraging avenue. Nevertheless, ensuring the effectiveness and safety of these textiles remains a persistent challenge. To achieve this, we conduct a comprehensive study that systematically compares the effectiveness and potential toxicity of five commonly used antimicrobial agents. To guide decision making, a MULTIMOORA method is employed to select and rank the optimal antimicrobial textile finishes. Through this approach, we determine that silver nitrate is the most suitable choice, while a methoxy-terminated quaternary ammonium compound is deemed less favorable in meeting the desired criteria. The findings of this study offer valuable insights and guidelines for the development of antimicrobial textiles that effectively address the requirements of effectiveness, safety, and durability. Implementing these research outcomes within the textile industry can significantly enhance protection against microbial infections, contribute to the improvement of public health, and mitigate the spread of infectious diseases.

Transparent, flexible, superomniphobic surfaces with ultra-low contact angle hysteresis.

See-through surfaces: High transparency is required to use superomniphobic surfaces, which can be self-cleaning, stain-proof, anti-bio-fouling, drag-reducing, or anti-fogging, for smartphone screens, eye glasses, windshields, or flat panel displays. A spray-based method has now been developed that can fabricate transparent, flexible, and highly superomniphobic surfaces. HD=hexadecane.

Comment on "Vapor Lubrication for Reducing Water and Ice Adhesion on Poly(dimethylsiloxane) Brushes": Vapor Alteration Alone Reduces Water Droplet Adhesion.

A reduction in lateral adhesion of water droplets on poly(dimethylsiloxane) (PDMS) brush surfaces exposed to various vapor conditions was recently reported. It was suggested that the mobility of droplets is due to swelling of the PDMS brushes. When changing the vapor surrounding sliding droplets on bare surfaces, a similar phenomenon is observed, presenting a much simpler explanation of the observed results.

Erosion-resistant materials demonstrate low interfacial toughness with ice and superior durability.

The strong adhesion of ice to surfaces results in unwanted effects in various industrial activities. However, current strategies for passive ice-phobic purposes lack either scalability or durability, or both, in industrial applications. In this study, erosion-resistant materials, including ceramic-based (WC, SiC, and alumina) and metal-based (a quasicrystalline coating, QC), were studied for their ice-phobic properties via push-off tests with bulk-water ice from -5 to -20 °C. Although their ice adhesion strengths were high (>400 kPa), their interfacial toughness with ice was quite low (1.1 to 2.6 J m-2) and comparable to polymeric surfaces. The force per width required to remove ice on the QC surface was even lower than that of a silicone (Sylgard 184) surface for an ice length of 7.0 cm. The low interfacial toughness of the erosion-resistant materials with ice was also retained after 1000 cycles of linear abrasion under a pressure of 27.0 kPa. The findings of this work expand the material selection options for durable large-scale ice-phobic applications and could enlighten the use of erosion-resistant materials in harsh industrial environments requiring effective de-icing.

Surface-engineered double-layered fabrics for continuous, passive fluid transport.

Textiles with a wicking finish transport moisture away from the skin, such that it is exposed to the environment for fast evaporation, aiding in thermophysiological comfort. Once saturated, such as in highly humid environments or if the wearer dons multiple layers, the efficacy of such a finish is substantially reduced. Here, we develop a new type of fluid transport textile design by combining physical and chemical wettability patterns to transport and remove liquids like sweat. First, a non-toxic, superhydrophobic fabric finish is developed that retains the air permeability of the fabric. Next, two superhydrophobic fabric layers are threaded together, containing wettability channels patterned at the inner/interior side of the fabrics. This design allows for liquid transport through the stitches to the interior channels and keeps both external faces dry. The developed strategy enables directional fluid transport under highly humid conditions, resulting in a ∼20 times faster transport rate than evaporation-based methods. The design principles described here can be used to provide thermophysiological comfort for users in extreme conditions, such as firefighters, law enforcement personnel, and health workers wearing personal protective ensembles.

Non-destructive erosive wear monitoring of multi-layer coatings using AI-enabled differential split ring resonator based system.

Unprotected surfaces where a coating has been removed due to erosive wear can catastrophically fail from corrosion, mechanical impingement, or chemical degradation, leading to major safety hazards, financial losses, and even fatalities. As a preventive measure, industries including aviation, marine and renewable energy are actively seeking solutions for the real-time and autonomous monitoring of coating health. This work presents a real-time, non-destructive inspection system for the erosive wear detection of coatings, by leveraging artificial intelligence enabled microwave differential split ring resonator sensors, integrated to a smart, embedded monitoring circuitry. The differential microwave system detects the erosion of coatings through the variations of resonant characteristics of the split ring resonators, located underneath the coating layer while compensating for the external noises. The system's response and performance are validated through erosive wear tests on single- and multi-layer polymeric coatings up to a thickness of 2.5 mm. The system is capable of distinguishing which layer is being eroded (for multi-layer coatings) and estimating the wear depth and rate through its integration with a recurrent neural network-based predictive analytics model. The synergistic combination of artificial intelligence enabled microwave resonators and a smart monitoring system further demonstrates its practicality for real-world coating erosion applications.

An improved plastination method for strengthening bamboo culms, without compromising biodegradability.

Biomaterials are increasingly being designed and adapted to a wide range of structural applications, owing to their superior mechanical property-to-weight ratios, low cost, biodegradability, and CO2 capture. Bamboo, specifically, has an interesting anatomy with long tube-like vessels present in its microstructure, which can be exploited to improve its mechanical properties for structural applications. By filling these vessels with a resin, e.g. an applied external loading would be better distributed in the structure. One recent method of impregnating the bamboo is plastination, which was originally developed for preserving human remains. However, the original plastination process was found to be slow for bamboo impregnation application, while being also rather complicated/methodical for industrial adaptation. Accordingly, in this study, an improved plastination method was developed that is 40% faster and simpler than the original method. It also resulted in a 400% increase in open-vessel impregnation, as revealed by Micro-X-ray Computed Tomography imaging. The improved method involves three steps: acetone dehydration at room temperature, forced polymer impregnation with a single pressure drop to - 23 inHg, and polymer curing at 130 °C for 20 min. Bamboo plastinated using the new method was 60% stronger flexurally, while maintaining the same modulus of elasticity, as compared to the virgin bamboo. Most critically, it also maintained its biodegradability from cellulolytic enzymes after plastination, as measured by a respirometric technique. Fourier transform infrared-attenuated total reflection, and thermogravimetric analyses were conducted and showed that the plastinated bamboo's functional groups were not altered significantly during the process, possibly explaining the biodegradability. Finally, using cone calorimetry, plastinated bamboo showed a faster ignition time, due to the addition of silicone, but a lower carbon monoxide yield. These results are deemed as a promising step forward for further improvement and application of this highly abundant natural fiber in engineering structures.

Thermal Insulation and Superhydrophobicity Synergies for Passive Snow Repellency.

The adhesion mechanisms and fracture mechanics of snow on solid surfaces are complex, making the design of an all-purpose snow-repellent surface that is applicable to multiple real-life situations a considerable and unsolved challenge. In this study, we focus on the most difficult-to-remove snow accretion scenario─the formation of a highly adhesive meltwater ice layer at the snow-solid interface. This ice layer originates from snow melting on an initially above 0 °C surface, followed by refreezing in a subzero environment. The complete removal of this ice layer is especially challenging and usually requires active and energy-intensive methods. By combining the characteristics of thermal insulation and superhydrophobicity on solid surfaces, we successfully prevent snow melting and its subsequent refreezing to this highly adhesive ice layer, enabling the complete passive removal of snow from solid surfaces. Our snow-repellent platform is designed using thin superhydrophobic sheets covering solid surfaces, separated by a thermally insulative layer (air gap or aerogel). In contrast to conventional icephobic surfaces, the synergies between thermal insulation and superhydrophobicity provide a tailored route specifically toward the design of passive snow-repellent surfaces.

Suspended Kirigami Surfaces for Multifoulant Adhesion Reduction.

High foulant adhesion remains a critical issue in a wide range of industries, such as ice accretion on aircraft, biofoulants on ships, wax build-up within pipelines, and scale formation in water remediation. Previous anti-fouling surfaces have only shown promise for reducing the adhesion of a single foulant system; a multi-foulant anti-fouling technology remains elusive. Here, we introduce a mechanical metamaterial-based approach to develop anti-fouling surfaces applicable to a wide range of fouling substances. The suspended kirigami inverted nil-adhesion surfaces, or SKINS, show significantly reduced adhesion of ice, different waxes, dried mud, pressure-sensitive adhesive tape, and a marine hard foulant simulant. SKINS mimic the wrinkling of hard films adhered to soft substrates. Foulant adhesion can be minimized by this wrinkling, which may be controlled by tuning the kirigami motif, sheet material, and foulant dimensions. SKINS reduce adhesion mechanically and were found to be independent of surface energy, enabling their fabrication from commonplace hydrophilic polymers like cellulose acetate. Optimized SKINS exhibited extremely low foulant adhesion, for example, ice adhesion strengths less than 5 kPa (a >250-fold reduction from aluminum substates), and were found to maintain their performance on curved surfaces like transmission cables. The low foulant adhesion persisted over 30 repeated foulant deposition and removal cycles, demonstrating the anti-fouling durability of SKINS. Overall, SKINS offers a previously unexplored route to achieving low foulant adhesion that is highly tunable in both geometry and material selection, is applicable to many different fouling substances, and maintains extremely low foulant adhesion even on complex substrates over large fouled interfaces.

Complete Inhibition of Vertical Mosquito Landing through Topographical Surface Design.

Mosquito-borne diseases such as dengue, chikungunya, and malaria have long been a health and economic burden in our society. Such illnesses develop after the pathogen, here arboviruses, are transmitted to humans by female mosquitoes during blood meals. In the case of dengue and chikungunya, such pathogens are transmitted to humans by infected Aedes aegypti females. Prior to feeding the insects rest on vertical surfaces. In this work, a surface roughness threshold was observed for live Aedes aegypti colonies, and below a root-mean-squared roughness of Sq < 0.124 µm the mosquitoes were physically incapable of gripping vertical substrates. This roughness threshold was unaffected by surface wettability or relative humidity. The importance of topographical feature height was understood using a claw-hooking model considering friction. Local defects above this threshold allowed claw hooking to take place, emphasizing the importance of surface uniformity. An antimosquito coating was developed that reduced surface roughness below this threshold when it was applied to realistic surfaces such as wood, brick, wall laminates, and tile. Lowering the surface roughness below the threshold reduced the number of mosquitoes capable of landing on the surfaces by 100%: i.e., no mosquitoes were able to adhere to the treated surfaces. The ability to completely inhibit Aedes aegypti females from landing on surfaces represents a new vector-borne disease control strategy that does not suffer from the nontarget toxicity, resistance, or ecosystem disruption associated with conventional chemical control strategies.

Enhanced protection face masks do not adversely impact thermophysiological comfort.

The World Health Organization has advocated mandatory face mask usage to combat the spread of COVID-19, with multilayer masks recommended for enhanced protection. However, this recommendation has not been widely adopted, with noncompliant persons citing discomfort during prolonged usage of face masks. And yet, a scientific understanding on how face mask fabrics/garment systems affect thermophysiological comfort remains lacking. We aimed to investigate how fabric/garment properties alter the thermal and evaporative resistances responsible for thermophysiological strain. We constructed 12 different layered facemasks (D1-D5, T1-T6, Q1) with various filters using commercially available fabrics. Three approaches were employed: (1) the evaporative and thermal resistances were measured in all the test face masks using the medium size to determine the effect of fabric properties; (2) the effect of face mask size by testing close-fitted (small), fitted (medium) and loose fitted (large) face mask T-6; (3) the effect of face mask fit by donning a large size face mask T-6, both loose and tightened using thermal manikin, Newton. ANOVA test revealed that the additional N95 middle layer filter has no significant effect on the thermal resistances of all the face masks, and evaporative resistances except for face masks T-2 and T-3 (P-values<0.05) whereas size significantly affected thermal and evaporative resistances (P-values<0.05). The correlation coefficient between the air gap size and the thermal and evaporative resistance of face masks T-6 were R2 = 0.96 and 0.98, respectively. The tight fit large face mask had superior performance in the dissipation of heat and moisture from the skin (P-values <0.05). Three-layer masks incorporating filters and water-resistant and antimicrobial/antiviral finishes did not increase discomfort. Interestingly, using face masks with fitters improved user comfort, decreasing thermal and evaporative resistances in direct opposition to the preconceived notion that safer masks decrease comfort.

Smart low interfacial toughness coatings for on-demand de-icing without melting.

Ice accretion causes problems in vital industries and has been addressed over the past decades with either passive or active de-icing systems. This work presents a smart, hybrid (passive and active) de-icing system through the combination of a low interfacial toughness coating, printed circuit board heaters, and an ice-detecting microwave sensor. The coating's interfacial toughness with ice is found to be temperature dependent and can be modulated using the embedded heaters. Accordingly, de-icing is realized without melting the interface. The synergistic combination of the low interfacial toughness coating and periodic heaters results in a greater de-icing power density than a full-coverage heater system. The hybrid de-icing system also shows durability towards repeated icing/de-icing, mechanical abrasion, outdoor exposure, and chemical contamination. A non-contact planar microwave resonator sensor is additionally designed and implemented to precisely detect the presence or absence of water or ice on the surface while operating beneath the coating, further enhancing the system's energy efficiency. Scalability of the smart coating is demonstrated using large (up to 1 m) iced interfaces. Overall, the smart hybrid system designed here offers a paradigm shift in de-icing that can efficiently render a surface ice-free without the need for energetically expensive interface melting.

Modeling and Prediction of Thermophysiological Comfort Properties of a Single Layer Fabric System Using Single Sector Sweating Torso.

Thermophysiological comfort is known to play a primary role in maintaining thermal balance, which corresponds to a person's satisfaction with their immediate thermal environment. Among the existing test methods, sweating torsos are one of the best tools to provide a combined measurement of heat and moisture transfer using non-isothermal conditions. This study presents a preliminary numerical model of a single sector sweating torso to predict the thermophysiological comfort properties of fabric systems. The model has been developed using COMSOL Multiphysics, based on the ISO 18640-1 standard test method and a single layer fabric system used in sportswear. A good agreement was observed between the experimental and numeral results over different exposure phases simulated by the torso test (R2 = 0.72 to 0.99). The model enables a systematic investigation of the effect of fabric properties (thickness, porosity, thermal resistance, and evaporative resistance), environmental conditions (relative humidity, air and radiant temperature, and wind speed), and physiological parameters (sweating rate) to gain an enhanced understanding of the thermophysiological comfort properties of the fabric system.

Designing scalable elastomeric anti-fouling coatings: Shear strain dissipation via interfacial cavitation.

HYPOTHESIS: Soft elastomers are promising anti-fouling materials and this has been demonstrated for many small elastomer/foulant interfaces. Toughness should control the adhesive fracture of large interfaces, although this has never been shown for elastomers. We hypothesized that energy-dissipative processes like interfacial cavitation are largely responsible for the absence of toughness-mediated fracture for larger elastomer/foulant interfaces. EXPERIMENTS: Rigid and transparent model foulants of various length were adhered to elastomers exhibiting three different moduli. The length of the foulant and the height above the interfacial plane of the applied force were systematically varied. A phase diagram was established for designing low-modulus, anti-fouling materials as a function of foulant thickness and length. FINDINGS: A new regime of interfacial detachment was observed, where foulants remained partially attached to the surface and interfacial cavitation initiated from the edge of the detached region. Interfacial cracks were arrested before de-bonding the foulant and the majority of the applied energy was dissipated as cavitation bubbles. Our analysis showed that the use of elastomers as anti-fouling materials is limited for large scale applications. Foulant dimensions constrain the design of anti-fouling elastomeric coatings as an applied shear stress can only be exerted at a height above the interface that is less than the foulant thickness. Design rules are presented for the correct fabrication of elastomers to be used as anti-fouling coatings over large interfacial areas.

Patch antenna sensor for wireless ice and frost detection.

A patch antenna sensor with T-shaped slots operating at 2.378 GHz was developed and investigated for wireless ice and frost detection applications. Detection was performed by monitoring the resonant amplitude and resonant frequency of the transmission coefficient between the antenna sensor and a wide band receiver. This sensor was capable of distinguishing between frost, ice, and water with total shifts in resonant frequency of 32 MHz and 36 MHz in the presence of frost and ice, respectively, when compared to the bare sensor. Additionally, the antenna was sensitive to both ice thickness and the surface area covered in ice displaying resonant frequency shifts of 2 MHz and 8 MHz respectively between 80 and 160 µL of ice. By fitting an exponential function to the recorded data, the freezing rate was also extracted. The analysis within this work distinguishes the antenna sensor as a highly accurate and robust method for wireless ice accretion detection and monitoring. This technology has applications in a variety of industries including the energy sector for detection of ice on wind turbines and power lines.