Multifunctional Silica-Silicone Nanocomposite with Regenerative Superhydrophobic Capabilities

Batch Fabrication of Paper-Based Waterproof Flexible Pressure Sensors Enabled by Roll-to-Roll Lamination

Paper is a green and porous material that has been widely used in flexible pressure sensors due to its flexibility, renewability, and lightness. However, these sensors are often susceptible to environmental factors such as moisture and chemicals, leading to degradation or failure of their reliability for practical applications. Herein, we present a roll-to-roll lamination strategy for batch fabrication of paper-based waterproof flexible pressure sensors with good consistency based on single-walled carbon nanotube (SWCNT) coated tissue paper pieces. The pieces are sandwiched between poly(ethylene glycol) terephthalate (PET) films with a hot melt adhesive and screen-printed electrodes, and the layers are bonded reliably using roll-to-roll lamination. This process allows for the rapid fabrication of a batch of waterproof, flexible pressure sensors with high stability over 5000 loading/unloading cycles, an ultrashort response time of 8 ms, and a wide measurement range (450 kPa). These features enable our sensor to be utilized for human physiological signal detection, motion tracking, and drowning detection. Furthermore, the process also allows for the fabrication of sensor arrays for spatial pressure mapping and real-time human-machine interaction, expanding the application field of paper-based pressure sensors. This proposed batch fabrication strategy greatly enhances the consistency and reliability of paper-based pressure sensors, demonstrating endless possibilities for paper-based pressure sensors to be used for various applications.

Scalable Fabrication of Superhydrophobic Coating with Rough Coral Reef-Like Structures for Efficient Self-Cleaning and Oil-Water Separation: An Experimental and Molecular Dynamics Simulation Study

Superhydrophobic coating has a great application prospect in self-cleaning and oil-water separation but remains challenging for large-scale preparation of robust and weather-resistant superhydrophobic coatings via facile approaches. Herein, this work reports a scalable fabrication of weather-resistant superhydrophobic coating with multiscale rough coral reef-like structures by spraying the suspension containing superhydrophobic silica nanoparticles and industrial coating varnish on various substrates. The coral reef-like structures effectively improves the surface roughness and abrasion resistance. Rapid aging experiments (3000 h) and the outdoor building project application (3000 m2 ) show that the sprayed superhydrophobic coating exhibits excellent self-cleaning properties, weather resistance, and environmental adaptability. Moreover, the combined silica-coating varnish-polyurethane (CSCP) superhydrophobic sponge exhibits exceptional oil-water separation capabilities, selectively absorbing the oils from water up to 39 times of its own weight. Furthermore, the molecular dynamics (MD) simulation reveals that the combined effect of higher surface roughness, smaller diffusion coefficient of water molecules, and weaker electrostatic interactions between water and the surface jointly determines the superhydrophobicity of the prepared coating. This work deepens the understanding of the anti-wetting mechanism of superhydrophobic surfaces from the perspective of energetic and kinetic properties, thereby paving the way for the rational design of superhydrophobic materials and their large-scale applications.

Research Progress of Superhydrophobic Materials in the Field of Anti-/De-Icing and Their Preparation: A Review

Accumulated ice has brought much damage to engineering and people's lives. The accumulation of ice can affect the flight safety of aircraft and lead to the failure of cables and power generation blades; it can even cause damage to human life. Traditional anti-icing and de-icing strategies have many disadvantages such as high energy consumption, low efficiency, or pollution of the environment. Therefore, inspired by animal communities, researchers have developed new passive anti-icing materials such as superhydrophobic material. In this paper, the solid surface wetting phenomenon and superhydrophobic anti-icing and de-icing mechanism were introduced. The methods of fabrication of superhydrophobic surfaces were summarized. The research progress of wear-resistant superhydrophobic coatings, self-healing/self-repairing superhydrophobic coatings, photothermal superhydrophobic coatings, and electrothermal superhydrophobic coatings in the field of anti-icing and de-icing was reviewed. The current problems and challenges were analyzed, and the development trend of superhydrophobic materials was also prospected in the field of anti-icing and de-icing. The practicality of current superhydrophobic materials should continue to be explored in depth.

3D Printed Silicones with Shape Morphing and Low-Temperature Ultraelasticity

3D printed silicones have demonstrated great potential in diverse areas by combining the advantageous physiochemical properties of silicones with the unparalleled design freedom of additive manufacturing. However, their low-temperature performance, which is of particular importance for polar and space applications, has not been addressed. Herein, a 3D printed silicone foam with unprecedented low-temperature elasticity is presented, which is featured with extraordinary fatigue resistance, excellent shape recovery, and energy-absorbing capability down to a low temperature of -60 °C after extreme compression (an intensive load of over 66000 times its own weight). The foam is achieved by direct writing of a phenyl silicone-based pseudoplastic ink embedded with sodium chloride as sacrificial template. During the water immersion process to create pores in the printed filaments, a unique osmotic pressure-driven shape morphing strategy is also reported, which offers an attractive alternative to traditional 4D printed hydrogels in virtue of the favorable mechanical robustness of the silicone material. The underlying mechanisms for shape morphing and low-temperature elasticity are discussed in detail.

Fabrication of Superhydrophobic and Light-Absorbing Polyester Fabric Based on Caffeic Acid

Caffeic acid (CA) was treated on the surface of polyester fabric (PET), and Fe²⁺ was used as an intermediate to form chelates with CA to increase the roughness of the polyester surface. With the addition of n-octadecyl mercaptan (SH), the mercapto group reacted with the carbon-carbon double bond of CA on the PET surface through enol click chemical reaction. Meanwhile, CA was polymerized under UV radiation, and thus CA-Fe-SH-PET was prepared. The introduction of SH with a long carbon chain reduced the surface energy of the PET, in order to endow the polyester fabric with a superhydrophobic/lipophilic function. Combined with XPS and FTIR tests, the new carbon-carbon double bond's binding energy and vibration peak were found on the fabric surface, indicating that CA was adsorbed on the PET fabric's surface. After adding SH, the double bond disappeared, demonstrating that SH and CA occurred a click chemical reaction and were grafted onto the PET fabric's surface. The water contact angle (WCA) of CA-Fe-SH-PET was about 156 ± 0.6°, and the scrolling angle (SA) was about 3.298°. The results showed that the modified polyester had a robust superhydrophobic stability in washing, mechanical friction, sun aging, seawater immersion, organic reagent, and acid-base erosion derived from the good adhesion of polymerized CA (PCA). At the same time, the modified polyester fabric had good self-cleaning, antifouling, and oil-water separation performance. It was found that the CA-Fe-SH-PET fabric had unique photothermal conversion characteristics, which can convert the absorbed ultraviolet light into thermal energy, providing a local warming effect due to rapid heating and improving the transmission speed of heavy oil (engine oil and diesel). The CA-Fe-SH-PET fabric can further prevent the transmission of ultraviolet rays, and the UV resistance of CA-Fe-SH-PET fabric is far higher than the UV resistance standard. The preparation method is simple, fast, efficient, and environmentally friendly, and it has better a potential application value in the oil-water separation field.

A versatile "3M" methodology to obtain superhydrophobic PDMS-based materials for antifouling applications

Fouling, including inorganic, organic, bio-, and composite fouling seriously affects our daily life. To reduce these effects, antifouling strategies including fouling resistance, release, and degrading, have been proposed. Superhydrophobicity, the most widely used characteristic for antifouling that relies on surface wettability, can provide surfaces with antifouling abilities owing to its fouling resistance and/or release effects. PDMS shows valuable and wide applications in many fields, and due to the inherent hydrophobicity, superhydrophobicity can be achieved simply by roughening the surface of pure PDMS or its composites. In this review, we propose a versatile "3M" methodology (materials, methods, and morphologies) to guide the fabrication of superhydrophobic PDMS-based materials for antifouling applications. Regarding materials, pure PDMS, PDMS with nanoparticles, and PDMS with other materials were introduced. The available methods are discussed based on the different materials. Materials based on PDMS with nanoparticles (zero-, one-, two-, and three-dimensional nanoparticles) are discussed systematically as typical examples with different morphologies. Carefully selected materials, methods, and morphologies were reviewed in this paper, which is expected to be a helpful reference for future research on superhydrophobic PDMS-based materials for antifouling applications.

Advances in the development of superhydrophobic and icephobic surfaces

Superhydrophobicity and icephobicity are governed by surface chemistry and surface structure. These two features signify a potential advance in surface engineering and have recently garnered significant attention from the research community. This review aims to simulate further research in the development of superhydrophobic and icephobic surfaces in order to achieve their wide-spread adoption in practical applications. The review begins by establishing the fundamentals of the wetting phenomenon and wettability parameters. This is followed by the recent advances in modeling and simulations of the response of superhydrophobic surfaces to static and dynamic droplets contact and impingement, respectively. In view of their versatility and multifunctionality, a special attention is given to the development of these surfaces using nanocomposites. Furthermore, the review considers advances in icephobicity, its comprehensive characterization and its relation to superhydrophobicity. The review also includes the importance of the use of superhydrophobic surface to combat viral and bacterial contamination that exist in fomites.

A Novel Strategy for Creating an Antibacterial Surface Using a Highly Efficient Electrospray-Based Method for Silica Deposition

Adhesion of bacteria on biomedical implant surfaces is a prerequisite for biofilm formation, which may increase the chances of infection and chronic inflammation. In this study, we employed a novel electrospray-based technique to develop an antibacterial surface by efficiently depositing silica homogeneously onto polyethylene terephthalate (PET) film to achieve hydrophobic and anti-adhesive properties. We evaluated its potential application in inhibiting bacterial adhesion using both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) bacteria. These silica-deposited PET surfaces could provide hydrophobic surfaces with a water contact angle greater than 120° as well as increased surface roughness (root mean square roughness value of 82.50 ± 16.22 nm and average roughness value of 65.15 ± 15.26 nm) that could significantly reduce bacterial adhesion by approximately 66.30% and 64.09% for E. coli and S. aureus, respectively, compared with those on plain PET surfaces. Furthermore, we observed that silica-deposited PET surfaces showed no detrimental effects on cell viability in human dermal fibroblasts, as confirmed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyl tetrazolium bromide and live/dead assays. Taken together, such approaches that are easy to synthesize, cost effective, and efficient, and could provide innovative strategies for preventing bacterial adhesion on biomedical implant surfaces in the clinical setting.

Preparation strategy and evaluation method of durable superhydrophobic rubber composites

Superhydrophobic rubber composites have broad application prospects in national defense, industrial and agricultural production and daily life due to their special surface wettability. However, its poor durability at present seriously limits its practical application. Microstructure and low surface energy substances are the decisive factors to realize superhydrophobic surface. Therefore, three strategies to improve the durability of superhydrophobic surface were put forward, including improving the mechanical strength of microstructure, enhancing the adhesion between coating and substrate, and constructing self-repairing surface. On this basis, the preparation techniques of durable superhydrophobic rubber composites were summarized, and then the evaluation methods of durability of superhydrophobic rubber composites were introduced in detail from mechanical durability and chemical durability.

Toward nanotechnology-enabled face masks against SARS-CoV-2 and pandemic respiratory diseases

Wearing a face mask has become a necessity following the outbreak of the coronavirus (COVID-19) disease, where its effectiveness in containing the pandemic has been confirmed. Nevertheless, the pandemic has revealed major deficiencies in the ability to manufacture and ramp up worldwide production of efficient surgical-grade face masks. As a result, many researchers have focused their efforts on the development of low cost, smart and effective face covers. In this article, following a short introduction concerning face mask requirements, the different nanotechnology-enabled techniques for achieving better protection against the SARS-CoV-2 virus are reviewed, including the development of nanoporous and nanofibrous membranes in addition to triboelectric nanogenerators based masks, which can filter the virus using various mechanisms such as straining, electrostatic attraction and electrocution. The development of nanomaterials-based mask coatings to achieve virus repellent and sterilizing capabilities, including antiviral, hydrophobic and photothermal features are also discussed. Finally, the usability of nanotechnology-enabled face masks is discussed and compared with that of current commercial-grade N95 masks. To conclude, we highlight the challenges associated with the quick transfer of nanomaterials-enabled face masks and provide an overall outlook of the importance of nanotechnology in counteracting the COVID-19 and future pandemics.

Review on the recent development of durable superhydrophobic materials for practical applications

Biomimetic superhydrophobic surfaces show great potential in oil-water separation, anti-icing and self-cleaning. However, due to the instability caused by its fragile structure and non-durable superhydrophobicity, it is difficult to apply them in the actual field. Here, by introducing surface wettability and analysing the mechanism of superhydrophobic failure, it is concluded that the reason for the failure of the superhydrophobic surface comes from the transition of the surface energy and the hysteresis of the contact angle (CA). On the basis of this analysis, it is concluded that the principle of designing a durable superhydrophobic surface is to satisfy one of the following three points: improving the binding force between molecules, introducing durable materials and improving chemical durability. On this basis, a variety of preparation methods are proposed, such as assembly method and spray/dip coating method, and the design and preparation of a self-healing surface inspired by nature will also be included in the introduction. Last but not least, the preparation and application of a durable super-hydrophobic surface in oil-water separation, anti-icing and self-cleaning are also introduced in detail. This review reveals the conclusions and prospects of durable superhydrophobic surfaces, and aims to inspire more researchers to invest in this research.

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.

Robust Hierarchical Porous PTFE Film Fabricated via Femtosecond Laser for Self-Cleaning Passive Cooling

Passive cooling materials that spontaneously cool an object are promising choices for mitigating the global energy crisis. However, these cooling effects are usually weakened or lost when dust contaminates the surface structure, greatly restricting their applications. In this work, a robust hierarchical porous polytetrafluoroethylene (PTFE) film with coral-like micro/nanostructures is generated by a facile and efficient femtosecond laser ablation technique. Owing to its unique micro/nanostructures, the as-prepared surface exhibits an outstanding self-cleaning function for various liquids with ultralow adhesion. This self-cleaning characteristic enhances the durability of its passive cooling effect. It is demonstrated that the titanium (Ti) sheet covered with laser-ablated PTFE film can realize a maximum temperature decrease of 4 and 10 °C compared to the Ti sheet covered with pristine PTFE film and uncovered, respectively. This study reveals that femtosecond laser micromachining is a facile and feasible avenue to produce robust self-cleaning passive cooling devices.

Fight against COVID-19: The case of antiviral surfaces

The COVID-19 pandemic is the largest global public health outbreak in the 21st century so far. Based on World Health Organization reports, the main source of SARS-CoV-2 infection is transmission of droplets released when an infected person coughs, sneezes, or exhales. Viral particles can remain in the air and on the surfaces for a long time. These droplets are too heavy to float in air and rapidly fall down onto the surfaces. To minimize the risk of the infection, entire surrounding environment should be disinfected or neutralized regularly. Development of the antiviral coating for the surface of objects that are frequently used by the public could be a practical route to prevent the spread of the viral particles and inactivation of the transmission of the viruses. In this short review, the design of the antiviral coating to combat the spread of different viruses has been discussed and the technological attempts for minimizing the coronavirus outbreak have been highlighted.

Potential of combating transmission of COVID-19 using novel self-cleaning superhydrophobic surfaces: part II-thermal, chemical, and mechanical durability

In part I, we identified encapsulation, contamination suppression, and virus elimination as our three governing strategies for developing surfaces to combat the transmission and spread of COVID-19. We showed that our recent superhydrophobic nanocomposites has the potential of encapsulating and suppressing the virus so as to limit its transmission and spread. In this study, we examine the durability of the newly developed surfaces when subjected to elevated temperature, chemical attack and mechanical damage in the form of abrasion and compressive load. Extensive tests were conducted to reveal the effect of these parameters on the surface performance. Three aspects of the work were accordingly examined. The first was concerned with controlled thermal stability tests in which the surfaces were subjected to elevated temperatures approaching 350 °C for silicone-based nanocomposites and 150 °C for epoxy-based nanocomposites. The second was concerned with subjecting the surfaces to alkaline and acidic solutions with pH concentrations ranging between 1 and 13. Finally, the third involved surface damage by abrasion tests. Our results show clearly that the newly developed superhydrophobic surfaces are capable of resisting the adverse effects of thermal and chemical attacks as well as mechanical abrasion owing to the excellent structural stability and mechanical properties of the constituents of the nanocomposite. Moreover, our superhydrophobic monolith demonstrated exceptional regenerative capabilities even after being subjected to damaging compressive stresses of up to 10 MPa.

Potential of combating transmission of COVID-19 using novel self-cleaning superhydrophobic surfaces: part I-protection strategies against fomites

According to the World Health Organisation, one of the main concerns of COVID-19 virus is its tenacity to spread from droplets that either land directly on a surface or are transmitted to a surface by an infected person. In this study, we report the potential of using superhydrophobic surfaces to combat the transmission and spread of fomites infected by COVID-19 virus strand. Fomites include clothes, utensils, furniture, regularly touched objects and personal protective equipment used by Health Care Workers to act as barriers against fluid transmission and/or fluid penetration. In this effort, we propose three strategies to combat the transmission and the spread of the virus: encapsulation, contamination suppression, and elimination. We believe that this can be achieved by the use of our recently developed superhydrophobic coating and regenerative monolith to encapsulate and suppress the virus. The newly developed superhydrophobic coating and monolith are scalable, economical, and facile with the monolith capable of regeneration. The elimination of the virus will be through the use of antiviral and antibacterial copper nanoparticles or dedicated copper surfaces.

A Simple, Long-Lasting Treatment for Concrete by Combining Hydrophobic Performance with a Photoinduced Superhydrophilic Surface for Easy Removal of Oil Pollutants

Superhydrophobic surfaces present promising applications in the protection of building materials, such as the self-cleaning effect promoted by their high water-repellent properties. However, these surfaces easily lose their properties when exposed to oil contaminants. This is a critical weak point for their application in building facades, which are exposed to environmental pollutants such as hydrocarbons and vandalism (e.g., grafitti). A viable strategy to remove oils is to produce superhydrophilic surfaces, which present underwater superoleophobic behavior. In the case of buildings, the use of this strategy can be considered counterproductive because it promotes their interaction with water, the main vehicle of most decay agents. In this work, we have successfully combined the advantages of a superhydrophilic coating with a hydrophobic impregnation treatment, which prevents water ingress into the porous structure of the substrate. Specifically, a photoinduced superhydrophilic surface was produced on concrete by simple spraying of a starting sol containing TiO₂NPs, which create a Cassie-Baxter state, a silica oligomer, producing a compatible matrix promoting good adhesion to the substrate and polydimethylsiloxane as a hydrophobic agent. After being exposed to sunlight, the treated surfaces switched from superhydrophobic (SCA 160°) to superhydrophilic (SCA < 10°). These surfaces presented underwater superoleophobicity (SCA 152° with CHCl₃) and oil-contaminated dust was easily cleaned without employing detergents. The photoactivation does not alter the protection against water absorption (>85% reduction). The treatment showed suitable adhesion to the substrate and good resistance to rainfall and outdoor exposure due to the presence of the hydrophobic silica matrix in the concrete pore structure.

Template-Free Fabrication of Refractive Index Tunable Polysiloxane Coating Using Homogeneous Embedding Strategy: Application in High-Power Laser System

A refractive index (RI) tunable polysiloxane coating was fabricated based on the cross-linked network structure embedded with mesoporous silica nanoparticles (MSNs), in which the MSNs were utilized to modulate the RI as well as to support the interior structure of the polysiloxane coating. The Si-O-Si inorganic backbone structure in combination with characteristics from the photopolymerization of active bonds produced the main cross-linked network structure, and controllable embedding of MSNs constructed the network-sphere structure. This approach eliminated the high-temperature post-treatment that was needed to remove the template, which ensures the safe application for temperature-sensitive laser crystal substrates and avoids coating structure collapse. In addition, degradation of the resulting coating can be minimized due to the similar chemical formation between MSN and polysiloxane coating. Hereby, a polysiloxane coating with expected spectral and laser damage-resistant properties can be obtained. This will facilitate the fabrication and application of a laser component with both high-transmission and high-flux capability for a high-power laser system.