Lubricant-infused slippery surfaces: Facile fabrication, unique liquid repellence and antireflective properties

Antifouling applications and fabrications of biomimetic micro-structured surfaces: A review

BACKGROUND

Since the inception of the term "Biomimetics" in 1991, the concept of utilizing natural solutions or deriving inspiration from nature to address contemporary engineering challenges has gained significant attention within the scientific community. Organisms, in order to thrive in harsh environments, have evolved a wide range of micro/nanostructured surfaces, which serve as a rich source of inspiration for the development of artificial micro/nano-structured surfaces. These natural adaptations provide valuable insights and novel pathways for fabricating such surfaces.

AIM

To conclude recent advances in micro/nano-structured surfaces from four aspects: biomimetic micro-structured surfaces of plants and animals, properties and applications of biomimetic surfaces, methods of preparations, and their limitation.

KEY SCIENTIFIC CONCEPTS

Artificial micro/nano-structured surfaces inspired by animals and plants are classified and demonstrated according to their living environment. The performances, principles and preparation techniques of natural superhydrophobic surfaces, slippery liquid-infused porous surfaces (SLIPS), anisotropic surfaces, etc. are described in detail. Moreover, the pros and cons of each preparation measures are compared and the challenges developing large-scale, cost-effective surface microstructure preparation processes are pointed out. In the end, the development trends of artificial micro/nano-structured surface are forecasted.

Fabrication and Functional Regulation of Biomimetic Interfaces and Their Antifouling and Antibacterial Applications: A Review

Biomimetic synthesis provides potential guidance for the synthesis of bio-nanomaterials by mimicking the structure, properties and functions of natural materials. Behavioral studies of biological surfaces with specific micro/nano structures are performed to explore the interactions of various molecules or organisms with biological surfaces. These explorations provide valuable inspiration for the development of biomimetic surfaces with similar effects. This work reviews some conventional preparation methods and functional modulation strategies for biomimetic interfaces. It aims to elucidate the important role of biomimetic interfaces with antifouling and low-pollution properties that can replace non-environmentally friendly coatings. Thus, biomimetic antifouling interfaces can be better applied in the field of marine antifouling and antimicrobial. In this review, the commonly used fabrication methods for biomimetic interfaces as well as some practical strategies for functional modulation is present in detail. These methods and strategies modify the physical structure and chemical properties of the biomimetic interfaces, thus improving the wettability, adsorption, drag reduction, etc. that they exhibit. In addition, practical applications are presented of various biomimetic interfaces for antifouling and look ahead to potential biomedical applications. By continuously discovering functional surfaces with biomimetic properties and studying their microstructure and macroscopic properties, more biomimetic interfaces will be developed.

Multifunctional Anti-Icing Gel Surface with Enhanced Durability

Materials with low ice adhesion and long-lasting anti-icing properties remain an ongoing challenge in ultralow temperature environments (≤-30 °C). This study presents a gel material consisting of a polymer matrix (copolymer of polyurethane and acrylamide) and an anti-icing agent, ethylene glycol (EG), designed for anti-icing applications at ultralow temperatures. The surface shows a prolonged droplet freezing delay of ca. 322 s at -30 °C and frost resistance properties. It also exhibits an ice adhesion strength of 1.1 kPa at -10 °C and 39.8 kPa at -50 °C, resulting from the interaction between EG and water molecules that hinders the crystallization of ice as well as the significant mismatch between elastic gel and ice. In addition, the gel surface exhibits favorable anti-icing durability, with an ice adhesion strength below 20.0 kPa after 25 icing/deicing cycles and mechanical scratch tests. The gel demonstrates remarkable thermal durability, achieved through the H-bonds between the EG and polymer matrix. The H-bonds further enhance the anti-icing performance, thereby remarkably decreasing EG depletion and improving anti-icing durability. Overall, these properties suggest the potential application of this gel material in harsh environments including polar regions.

Multifunctional slippery photothermal coating

Slippery liquid-infused porous surface (SLIPS) has shown significant application values in various areas and has been commonly obtained by injecting the water-immiscible lubricant into a low-surface-energy modified micro/nano-structured surface. Constrained by the availability of desirable structured substrates or simple preparation schemes, the exploration of SLIPS with multifunctionality and universality that is facile to fabricate and robust in realistic applications remains challenging. Herein, we propose a one-step, fluoride-free and unconventional protocol based on a one-pot reaction of polysilazane (PSZ), silicone oils and multiwalled carbon nanotubes (MWCNT), which creates not only the favorable micro/nano-scale physical structures and surface chemistry for the excellent slippery property (sliding angle < 3°) and robust lubricant retention, but also the superior photothermal responsiveness for the potential multifunctional applications. It has been demonstrated that the proposed multifunctional slippery photothermal coating (MSPC) displayed outstanding potential in corrosion resistance, droplet manipulation and anti/de-icing. We envision that the proposed strategy could be realized in the real-life applications.

Silane coupling agent in biomedical materials

Medical devices are becoming more and more significant in our daily life. For implantable medical devices, good biocompatibility is required for further use in vivo. Thus, surface modification of medical devices is really important, which gives a wide application scene for a silane coupling agent. The silane coupling agent is able to form a durable bond between organic and inorganic materials. The dehydration process provides linking sites to achieve condensation of two hydroxyl groups. The forming covalent bond brings excellent mechanical properties among different surfaces. Indeed, the silane coupling agent is a popular component in surface modification. Metals, proteins, and hydrogels are using silane coupling agent to link parts commonly. The mild reaction environment also brings advantages for the spread of the silane coupling agent. In this review, we summarize two main methods of using the silane coupling agent. One is acting as a crosslinker mixed in the whole system, and the other is to provide a bridge between different surfaces. Moreover, we introduce their applications in biomedical devices.

Slippery Alkoxysilane Coatings for Antifouling Applications

Herein, we report the wettability and antifouling behavior of a range of different siloxane coatings on plastic and glass substrates. The films investigated are prepared using trimethoxysilane precursors with different alkyl chain lengths (1-18 C atoms) in order to study how the nature of the hydrophobic group affects the different parameters used to characterize wettability (contact angles, sliding angles, and contact angle hysteresis). Atomic force microscopy analysis shows that the coatings possess low surface topography [root mean squared roughness (rms) < 50 nm] and are highly transparent as studied using UV-vis spectroscopy. The sliding properties of H₂O, CH₂I₂, methanol, and ethylene glycol were observed to be strongly influenced by the chain length of the alkoxysilane precursor used. The coatings formed from the longer chain analogues show comparable water sliding angles to superhydrophobic surfaces. These coatings show similar performance to analogous alkoxysilane coating-bearing fluorinated groups, indicating that they could act as viable environmentally friendly alternatives to some of the fluorinated films that have been widely adopted. Furthermore, these surfaces are highly durable toward common forms of abrasion and are observed to show low adhesion toward synthetic feces, indicating that their utility extends further than repelling liquids alone. Consequently, these coatings could show promise for potential use in applications in the medical sector where fouling by biological mixtures leads to an unsustainable use of materials.

Infusing Silicone and Camellia Seed Oils into Micro-/Nanostructures for Developing Novel Anti-Icing/Frosting Surfaces for Food Freezing Applications

Undesired ice/frost formation and accretion often occur on food freezing facility surfaces, lowering freezing efficiency. In the current study, two slippery liquid-infused porous surfaces (SLIPS) were fabricated by spraying hexadecyltrimethoxysilane (HDTMS) and stearic acid (SA)-modified SiO₂ nanoparticles (NPs) suspensions, separately onto aluminum (Al) substrates coated with epoxy resin to obtain two superhydrophobic surfaces (SHS), and then infusing food-safe silicone and camellia seed oils into the SHS, respectively, achieving anti-frosting/icing performance. In comparison with bare Al, SLIPS not only exhibited excellent frost resistance and defrost properties but also showed ice adhesion strength much lower than that of SHS. In addition, pork and potato were frozen on SLIPS, showing an extremely low adhesion strength of <10 kPa, and after 10 icing/deicing cycles, the final ice adhesion strength of 29.07 kPa was still much lower than that of SHS (112.13 kPa). Therefore, the SLIPS showed great potential for developing into robust anti-icing/frosting materials for the freezing industry.

Transparent Oil-Water Separating Spiky SiO2 Nanoparticle Supramolecular Polymer Superhydrophobic Coatings

A potential application of spiky SiO₂ nanoparticles (NPs) with tubular and rough surfaces is investigated as superhydrophobic coatings, for their unique transparent, fluorinate-free, and environmentally friendly properties. This study demonstrates a facile method for the successful fabrication of superhydrophobic coatings and SiO₂ @polydimethylsiloxane (PDMS) using spiky SiO₂ NPs, N-coordinated boroxines, and PDMS. Combined with spray coating technology, this method of superhydrophobic coating can be simply applied to both hydrophilic and hydrophobic surfaces, including wood, fabric, glass, metal, sponge, and paper. The nanocomposite coating on the glass surface showed both excellent superhydrophobicity and high transparency, with a contact angle of 165.4 ± 1.0° and 96.93% transmittance at 550 nm, respectively. SiO₂ @PDMS-modified glass substrate is found to be resilient to UV irradiation, water, and high temperature treatments at ambient conditions. Experimental data demonstrated that the simple but effective combination of N-boroxine-PDMS and spiky SiO₂ NPs produces a layered coating material that exhibits many good integrated surface properties, including stability, transparency, superhydrophobicity, and oil-water separation.

Tribological Behavior of Bioinspired Surfaces

Energy losses due to various tribological phenomena pose a significant challenge to sustainable development. These energy losses also contribute toward increased emissions of greenhouse gases. Various attempts have been made to reduce energy consumption through the use of various surface engineering solutions. The bioinspired surfaces can provide a sustainable solution to address these tribological challenges by minimizing friction and wear. The current study majorly focuses on the recent advancements in the tribological behavior of bioinspired surfaces and bio-inspired materials. The miniaturization of technological devices has increased the need to understand micro- and nano-scale tribological behavior, which could significantly reduce energy wastage and material degradation. Integrating advanced research methods is crucial in developing new aspects of structures and characteristics of biological materials. Depending upon the interaction of the species with the surrounding, the present study is divided into segments depicting the tribological behavior of the biological surfaces inspired by animals and plants. The mimicking of bio-inspired surfaces resulted in significant noise, friction, and drag reduction, promoting the development of anti-wear and anti-adhesion surfaces. Along with the reduction in friction through the bioinspired surface, a few studies providing evidence for the enhancement in the frictional properties were also depicted.

Novel Slippery Liquid-Infused Porous Surfaces (SLIPS) Based on Electrospun Polydimethylsiloxane/Polystyrene Fibrous Structures Infused with Natural Blackseed Oil

Hydrophobic fibrous slippery liquid-infused porous surfaces (SLIPS) were fabricated by electrospinning polydimethylsiloxane (PDMS) and polystyrene (PS) as a carrier polymer on plasma-treated polyethylene (PE) and polyurethane (PU) substrates. Subsequent infusion of blackseed oil (BSO) into the porous structures was applied for the preparation of the SLIPS. SLIPS with infused lubricants can act as a repellency layer and play an important role in the prevention of biofilm formation. The effect of polymer solutions used in the electrospinning process was investigated to obtain well-defined hydrophobic fibrous structures. The surface properties were analyzed through various optical, macroscopic and spectroscopic techniques. A comprehensive investigation of the surface chemistry, surface morphology/topography, and mechanical properties was carried out on selected samples at optimized conditions. The electrospun fibers prepared using a mixture of PDMS/PS in the ratio of 1:1:10 (g/g/mL) using tetrahydrofuran (THF) solvent showed the best results in terms of fiber uniformity. The subsequent infusion of BSO into the fabricated PDMS/PS fiber mats exhibited slippery behavior regarding water droplets. Moreover, prepared SLIPS exhibited antibacterial activity against Staphylococcus aureus and Escherichia coli bacterium strains.

A fabric-based superhydrophobic ACNTs/Cu/PDMS heater with an excellent electrothermal effect and deicing performance

The fabric not only has good electrical conductivity, chemical stability and mechanical durability, but also exhibits excellent electrothermal effects and de-icing properties. In addition, it can be used to monitor various movements of the human body.

Non-wetting Liquid-Infused Slippery Paper

Liquid-infused slippery surfaces have replaced structural superhydrophobic surfaces in a plethora of emerging applications, hallmarked by their favorable self-healing and liquid-repelling characteristics. Their ease of fabrication on different types of materials and increasing demand in various industrial applications have triggered research interests targeted toward developing an environmental-friendly, flexible, and frugal substrate as the underlying structural and functional backbone. Although many expensive polymers such as polytetrafluoroethylene have so far been used for their fabrication, these are constrained by their compromised flexibility and non-ecofriendliness due to the use of fluorine. Here, we explore the development and deployment of a biodegradable, recyclable, flexible, and an economically viable material in the form of a paper matrix for fabricating liquid-infused slippery interfaces for prolonged usage. We show by controlled experiments that a simple silanization followed by an oil infusion protocol imparts an inherent slipperiness (low contact angle hysteresis and low tilting angle for sliding) to the droplet motion on the paper substrate and provides favorable anti-icing characteristics, albeit keeping the paper microstructures unaltered. This ensures concomitant hydrophobicity, water adhesion, and capillarity for low surface tension fluids, such as mustard oil, with an implicit role played by the paper pore size distribution toward retaining a stable layer of the infused oil. With demonstrated supreme anti-icing characteristics, these results open up new possibilities of realizing high-throughput paper-based substrates for a wide variety of applications ranging from biomedical unit operations to droplet-based digital microfluidics.

Lubricant-Infused Three-Dimensional Frame Composed of a Micro/Nanospinous Ball Cluster Structure with Salient Durability and Superior Fog Harvesting Capacity

Due to the limitation of the special wettability surface in the water collection field, the smooth surface injected by the lubricant has attracted wide attention. In this study, a simple two-step electrochemical reaction was used to successfully design a micro/nanospinous ball cluster structure on the surface of a frame. Subsequently, after low-surface-energy treatment and lubricant immersion, a lubricant-infused three-dimensional frame is prepared. The three-dimensional grid system of the frame and the micro/nanospinous ball cluster structure on the surface exert synergistic capillary force, which helps to maintain a stable lubricant-infused smooth surface. This interface system, which exhibits superior water collection efficiency, can achieve efficient droplet capture, coagulation, and removal. The prepared lubricant-infused frame also has remarkable corrosion resistance and anti-icing performance. After high-shear rate rotation and long-term storage, it still maintains a stable and smooth surface. The reported lubricant-infused three-dimensional frame has great potential in water condensation, droplet transport, and phase-to-heat transition.

Innovative fouling-resistant materials for industrial heat exchangers: a review

Fouling of heat exchangers (HEs) has become a major concern across the industrial sector. Fouling is an omnipresent phenomenon but is particularly prevalent in the dairy, oil, and energy industries. Reduced energy performance that results from fouling represents significant operating loss in terms of both maintenance and impact on product quality and safety. In most industries, cleaning or replacing HEs are currently the only viable solutions for controlling fouling. This review examines the latest advances in the development of innovative materials and coatings for HEs that could mitigate the need for costly and frequent cleaning and potentially extend their operational life. To better understand the correlation between surface properties and fouling occurrence, we begin by providing an overview of the main mechanisms underlying fouling. We then present selected key strategies, which can differ considerably, for developing antifouling surfaces and conclude by discussing the current trends in the search for ideal materials for a range of applications. In our presentation of all these aspects, emphasis is given wherever possible to the potential transfer of these innovative surfaces from the laboratory to the three industries most concerned by HE fouling problems: food, petrochemicals, and energy production.

Slippery Antifouling Polysiloxane-Polyurea Surfaces with Matrix Self-Healing and Lubricant Self-Replenishing

The inferior mechanical properties and the difficulty in repairing damaged substrates and lubricant films of slippery liquid-infused porous surfaces significantly hampered their practical applications. To solve this problem, we fabricated a polysiloxane-polyurea slippery elastomer with lubricant self-replenishing and matrix self-healing properties by encapsulating silicone oil into the thermoplastic elastomers. By optimizing the chemical compositions and molecular interactions, the obtained slippery elastomer exhibits unique mechanical properties with a maximum breaking strength of 0.12 MPa, elongation of 1600%, and self-healing efficiency of 98%. Moreover, the lubricant stored in the capsule of the slippery elastomer can be controlled released under mechanical stimulation, further realizing surfaces' self-lubricating and liquid manipulation switching between slippery and pinning states. Furthermore, the textile-reinforced slippery elastomer with superior mechanical strength also exhibited liquid repellency, anti-biofouling, and drag reduction properties. Therefore, this textile-reinforced omniphobic surface with high mechanical property, matrix self-healing, and lubricant self-replenishing property shows a broad application prospect in surface protection, underwater antifouling, and drag reduction.

How to Efficiently Prepare Transparent Lubricant-Infused Surfaces: Inspired by Candle Soot

Poly(dimethylsiloxane) is a common dispersant, modifier, and binder in the field of bioinspired wettability. Herein, the soot production when poly(dimethylsiloxane) was burning was used to directly construct a superhydrophobic coating with the water contact angle reaching 159.7°. After the lubricant was infused, its transparency was greater than 80% of air in the visible light range of the human eye. In addition, the sliding angle and contact angle of the coating were stable for 15 days. It showed excellent oil-locking ability and stability. Even if the superhydrophobic coating was immersed in various organic solvents for 15 days, its hydrophobicity did not change. Moreover, the coating had an excellent anti-fouling ability and self-cleaning ability to meet actual application conditions. Furthermore, the preparation method was simple and rapid, without the participation of fluorine-containing modifiers, and provides a brand-new method for preparing transparent lubricant-infused surfaces.

The growth and shrinkage of water droplets at the oil-solid interface

HYPOTHESIS

The mechanism for the spontaneous formation of water droplets at oil/solid interfaces immersed in water is currently unclear. We hypothesize that growth and shrinkage of droplets are kinetically controlled by diffusion of water through the oil, driven by differences in chemical potential between the solid substrate and the aqueous reservoir.

EXPERIMENTS

The formation, growth and shrinkage of water droplets at an immersed oil/solid interface are investigated theoretically and experimentally with three silicone oils. The surface is hydrophobic and the droplets formed are truncated spheres with radius, a, less than 10 μm. The expansion and contraction of the droplets can be controlled by adjusting the difference in chemical potential. The growth kinetics are modelled in terms of water migration through the oil layer which predicts a²∝t.

FINDINGS

This is the first study of possible mechanisms for the formation of such interfacial droplets. Several possible causes are shown to be unfavourable, negligible, or are eliminated by careful experiments controlling key parameters (such as oil viscosity, substrate chemistry). The rate constant for mass transport is proportional to difference in chemical potential and an estimate shows dissociation of surface groups on the substrate provides a driving chemical potential of the right magnitude.

Designing Flexible but Tough Slippery Track for Underwater Gas Manipulation

Lubricant-infused slippery surface exhibits a series of superior properties such as pressure tolerance, self-healing, oil-repellence, etc. Especially when being applied in an aqueous environment, the reliable bubble manipulating ability of slippery surface offers great opportunities to develop advanced systems in the field of gas transport, water splitting, etc. To improve the strength and the functionality of slippery surfaces, a sliced lubricant-infused slippery (SLIS) track is presented here, possessing both flexibility and toughness for underwater bubble manipulation. The rigid slippery slices with hydrophobic porous structure are linked by the liquid bridge of silicone oil, resulting in a continuous lubricant layer for bubble transfer. Taking advantage of this unique assembled structure, the in situ bubble controlling process, that is, pinning and moving, is achieved via the stretching/releasing of an elastic SLIS track. Besides, on the basis of the integrated design, a hypothesis of underwater gas mining is proved in the all-in-one process including the micro-bubble generation, bubble collection, and gas transport. The current design paves an avenue to reinforce the structure of slippery surfaces, and should promote the function of underwater bubble manipulation toward real-world applications.

Stable and biocompatible slippery lubricant-infused anode-oxidated titanium nanotube surfaces via a grafted polydimethylsiloxane brush

This work aims at optimizing the structure and enhancing the interaction force between the substrate and the lubricant to prepare a slippery lubricant-infused TiO2 NT surface that maintains stable omniphobic performance in extreme environments.

Bionic smart recycled paper endowed with amphiphobic, photochromic, and UV rewritable properties

The single-use of large volumes of paper has become a serious issue which is depleting our resources and damaging the environment. It is of great significance and challenging to adopt simple, reasonable and practical methods to prepare functional recyclable paper. In this article, inspired by pleochromatic creatures and plant leaves' special wettability, a series of photochromic amphiphobic recycled paper (PAR _i ) products was successfully prepared by adding gourd-like modified tungsten trioxide (MTT) to waste paper pulp. The results show that PAR_2-7 has excellent lyophobic performance and amazing photochromic properties. It is worth noting that PAR₇ has an impressive amphiphobic behavior, and its surface water contact angle (WCA) and oil contact angle (OCA) are 146 ± 1° and 137 ± 1°, respectively. It can withstand continuous ultraviolet light irradiation for 60 h, indicating excellent resistance to ultraviolet radiation. Most importantly, the reversible photochromic properties of PAR₇ make it possible to write repeatedly on the surface by using ultraviolet light. In short, the performance of the prepared PAR is stable and superior, which can not only alleviate paper waste, but also means it has great potential in the fields of decoration, packaging, and banknote anti-counterfeiting technology.

On the Role of γ-Fe2O3 Nanoparticles and Reduced Graphene Oxide Nanosheets in Enhancing Self-Cleaning Properties of Composite TiO2 for Cultural Heritage Protection

The durability of novel metallic artifacts and buildings is an open issue, and the role of smart protecting coatings in extending these artifacts’ lifetimes is crucial. In this paper, the role of γ-Fe2O3 nanoparticles and reduced graphene oxide (rGO) nanosheets on enhancing the self-cleaning properties of composite TiO2 films and reducing metal alterations due to contact with acid rain and pollutants is investigated. The photocatalytic assessment of the TiO2 based films indicates that there are optimum contents for γ-Fe2O3 and rGO, which confer the film lower bandgap and tune the TiO2 anatase/rutile ratio. By adding a proper content of γ-Fe2O3, wettability is reduced both in dark and under illumination, which could be related to higher roughness. γ-Fe2O3 overloading causes increasing crack density and eventually a fully cracked structure. Adding an appropriate amount of rGO causes a sharp increase in roughness, due to the stacking of rGO nanosheets, while simultaneously avoiding cracking. At higher contents of rGO, wettability further decreases due to higher amounts of hydroxyl groups bound onto rGO; also in this case, overloading causes film cracking. Evaluation of self-cleaning performance and discoloration resistance under soiling and acid rain simulated tests demonstrates that proper loadings of γ-Fe2O3 and rGO present higher efficiency thanks to higher superhydrophilic tendency and higher photocatalytic activities, as well as an efficient barrier effect.

Facile Fabrication of Slippery Lubricant-Infused CuO-Coated Surfaces with Different Morphologies for Efficient Water Collection and Excellent Slippery Stability

How to prepare multifunctional surfaces with high nucleation density and fast droplet removal during droplet condensation remains a challenge. It is believed that a water droplet on a superhydrophobic surface (SHS) in the Cassie state is inclined to convert to the Wenzel state under high-pressure or high-humidity conditions, which results in the pinning effect. Hence, it is necessary to form thermodynamically stable lubricant-infused surfaces (LISs) to be applied in water condensation, especially under extreme working conditions. In this work, CuO LISs with two different morphologies (chrysanthemum-like and dandelion-like structures) in the slippery state were prepared and the effect of surface morphology on water harvesting behavior was investigated. The results indicated that dandelion-like CuO consisting of nanoneedles exhibited inferior water harvesting behavior compared to chrysanthemum-like CuO consisting of nanolamellas due to worse lubricating oil loss. Furthermore, the strong intermolecular forces between the perfluoropolyether (PFPE) lubricating oil and perfluorodecanethiol (PFDT)-modified coating resulted in a durable lubricating layer, which exhibited favorable anti-icing, anticorrosion, and liquid repellency even under strong acid and alkali conditions, high shear force rate up to 7000 rpm, and long-time ultraviolet light irradiation for 12 h. This work paves the path for efficient droplet nucleation and removal, which has potential in water harvesting in arid regions and water condensation for power generation.

Heterostructured TiO2/SiO2/γ-Fe2O3/rGO Coating with Highly Efficient Visible-Light-Induced Self-Cleaning Properties for Metallic Artifacts

A novel nanohybrid composite of TiO₂, SiO₂, γ-Fe₂O₃, and reduced graphene oxide (TiO₂@Si:Fe:rGO) is fabricated by the sol-gel method. The properties of the coated film were examined by structural and self-cleaning analyses using simulated discoloration/soiling and roofing tests. The fabricated transparent TiO₂@Si:Fe:rGO composite showed excellent photoactivity and wettability, behaving well in self-cleaning applications. The addition of SiO₂ improved the crystalline structure and surface hydroxylation of TiO₂ nanoparticles. γ-Fe₂O₃ decreased the recombination rate of e^-/h⁺ pairs, and significantly improved photocatalytic activity under visible light. Moreover, rGO sheets as excellent electron acceptors and transporters also reduced recombination, as well as affected wettability, achieving superhydrophilicity under irradiation. The coated substrate showed excellent resistance to simulated acid rain and significantly preserved the substrate from soiling in roofing tests.

Mechanically durable and long-term repairable flexible lubricant-infused monomer for enhancing water collection efficiency by manipulating droplet coalescence and sliding

Lubricant-infused surfaces have attracted widespread attention due to their excellent liquid and organic solution repellency. On account of their high condensation heat transfer coefficient and low nucleation energy barrier, many lubricant-infused surfaces have been applied in water collection. However, they have a number of shortcomings, such as an unstable lubricating layer, poor mechanical/chemical stability and hard shedding, which severely limit the application of slippery surfaces. In this work, the silicone oil was infused into a superhydrophobic monomer (SHM) to form a flexible lubricant-infused monomer (FLIM) with outstanding sliding ability and omniphobicity for low surface energy liquids. Because the silicone oil is similar to the base molecule, there is a strong interacting force to hold the lubricant layer to the surface of the SHM. In addition, the high viscosity of the silicone oil further strengthens the lubricant layer adhesion. Therefore, the FLIM could resist hot liquid and high shear stress (up to 5000 rpm). In addition, the FLIM substrate possessed a self-similar low surface energy structure, which could endure various physical and chemical damages, such as abrasion, scratching, stretching, strong acid and alkali. Finally, pinned droplets could coalesce into large droplets to slide down its surface, resulting from the strain/release due to the high degree of deformation of the surface, which highly enhanced water/liquid coalescence and collection. The preparation of the FLIM was green and the chemicals involved were inexpensive and environmentally friendly, and thus it can be applied for large-scale water collection.

Durable lubricant-infused coating on a magnesium alloy substrate with anti-biofouling and anti-corrosion properties and excellent thermally assisted healing ability

Inspired by lotus leaves, superhydrophobic surfaces (SHS) have been fabricated by many methods due to their various properties such as self-cleaning, anti-corrosion, and anti-biofouling properties. In recent years, inspired by Nepenthes pitcher plants, the 'slippery liquid-infused porous surface' (SLIPS) has attracted numerous researchers' attention because it not only shows ability corresponding to SHS but also exhibits durability in some aspects due to the continuous and homogeneous liquid-infused surfaces. In this paper, we firstly used a facile hydrothermal method and modification to fabricate SHS on a Mg alloy substrate. After the infusion of a lubricant by a spin-coating method, the transformation from the SHS to SLIPS can be achieved. The SLIPS exhibits an excellent self-cleaning property compared to the SHS, except that the water droplet rolls on the SHS and slides on the SLIPS. Moreover, the SLIPS demonstrates better anti-corrosion and anti-biofouling properties, and is obviously superior to SHS for use on the Mg alloy substrate. The enhanced anti-corrosion and anti-biofouling properties of the SLIPS are because the continuously infused lubricant replaces the air trapped in the micro-pores. Importantly, compared with SHS, the SLIPS shows excellent thermally assisted healing properties. The results of this work indicate that the SLIPS is expected to be an efficient method for improving the water-repellent, self-cleaning, anti-biofouling and anti-corrosion properties of magnesium alloys.

Life and death of liquid-infused surfaces: a review on the choice, analysis and fate of the infused liquid layer

We review the rational choice, the analysis, the depletion and the properties imparted by the liquid layer in liquid-infused surfaces – a new class of low-adhesion surface.

Liquid infused surfaces with anti-icing properties

Ice accretion on solid surfaces, a ubiquitous phenomenon that occurs in winter, brings much inconvenience to daily life and can even cause serious catastrophes. Icephobic surfaces, a passive way of processing surfaces to prevent surface destruction from ice accumulation, have attracted much attention from scientists because of their special ice-repellent properties, and many efforts have been made to rationally design durable icephobic coatings. This review is aimed at providing a brief and crucial overview of ice formation processes and feasible de-icing strategies. Here, the excellent anti-icing performance of liquid infused surfaces (LIS) inspired from Nepenthes is emphatically introduced. After a short introduction, the recent progresses in ice nucleation theory and ice adhesion decrease mechanism are comprehensively reviewed to gain a general understanding of the long freeze process and low ice adhesion on LIS. Subsequently, the anti-icing performance of LIS is systematically evaluated from four aspects regarding water repellence, condensation-frosting, long freeze process, and low ice adhesion. Finally, this review focuses on discussing the advantages and disadvantages of LIS and the potential measures to eliminate and alleviate these drawbacks.

Durable and Multifunctional Superhydrophobic Coatings with Excellent Joule Heating and Electromagnetic Interference Shielding Performance for Flexible Sensing Electronics

Superhydrophobic coatings have wide applications in many fields. However, superhydrophobic and smart coatings with multifunctionality and their applications in flexible sensing electronics are seldom reported. In this work, durable, superhydrophobic, and anticorrosive coatings with excellent Joule heating and electromagnetic interference (EMI) shielding performance are prepared on the basis of Ag precursor reduction and synchronous nonsolvent induced phase separation. Silver nanoparticles (AgNPs) coated with the copolymer (polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene: SEBS) are uniformly distributed on the target substrate, forming mechanically durable conductive network. SEBS could not only endow the surface coating with superhydrophobicity but also improve the interaction among individual Ag nanoparticles and the interfacial adhesion between AgNPs and the substrate. The multifunctional coating possesses excellent anticorrosive, self-cleaning, and deicing properties. The high conductivity endows the coatings with excellent Joule heating and EMI shielding performance. The multifunctional coating can be applied to a variety of different substrates with outstanding surface stability and reliability. The conductivity for the smart coating can reach as high as 107 S/cm with the EMI shielding effectiveness up to 37.8 dB. At a low applied voltage of 1 V, the conductive fabric can be heated up to over 80 °C in 60 s and displays good recyclability during dozens of heating and cooling cycles. The Joule heating-induced temperature increase could be used for efficient surface deicing. When used for the flexible and wearable strain sensors, the multifunctional coating has a very low strain detection limit of 0.5% and large sensitivity (with the gauge factor as high as 1075) and excellent repeatability. In addition, it can be used for precisely monitoring different body motions, including both large and subtle joint movement.

Drop/bubble transportation and controllable manipulation on patterned slippery lubricant infused surfaces with tunable wettability

Directional transportation and manipulation of liquid droplets, which are of great significance for science and technologies, are mainly dependent on special surface wettability. Inspired by the carnivorous nepenthes, we fabricate a paraffin infused hybrid porous hydroxyapatite nanowires/carbon nanofibers film (PIHPHCF). The inorganic hydroxyapatite nanowires (HAPNWs) firmly intertwine with the carbon nanofibers (CNTs) to form a three-dimensional porous network after the self-assembly process. On account of the CNTs' photothermal effect, the infused paraffin in PIHPHCF can transform from the solid state to a liquid state in response to near-infrared light irradiation (NIRLI, 808 nm), causing the wettability of the film to convert from hydrophobic to slippery. Through inducting variform mask layers, the slippery pathways melting from the lubricating paraffin are adjusted to different shapes such as 'S' and 'Y', where liquid droplets are able to be directionally transported. Additionally, potential application of the as-prepared patterned slippery film is explored as a microreactor and microfluidics device. Moreover, such a patterned slippery surface is successfully utilized to explore bubbles capture, manipulation and release under a warm-water environment. We anticipate that this work is poised to broaden the application of patterned slippery surfaces, as an example of which is liquid or bubble controllable transportation and manipulation.

PDMS-Infused Poly(High Internal Phase Emulsion) Templates for the Construction of Slippery Liquid-Infused Porous Surfaces with Self-cleaning and Self-repairing Properties

Advanced liquid-repelling materials that resist both water-based and oil-based contaminants have significant applications in many fields. Herein, a novel protocol for the fabrication of a robust poly(high internal phase emulsion) (polyHIPE)-based slippery liquid-infused porous surface (SLIPS) system with combined self-repairing and self-cleaning properties is developed. Specifically, polystyrene-based polyHIPE (PS-HIPE) membranes with an interconnected porous structure were prepared from polymerization of the continuous oil phase in the water-in-oil HIPE templates. These polyHIPE membranes were used, for the first time, as porous substrates for loading low surface tension silicone oils as lubricating liquids for the fabrication of polyHIPE-based SLIPS membranes. These polyHIPE-based SLIPS membranes could easily repel both water- and oil-based contaminants (e.g., ink, milk, and coffee) with very low sliding angles (3.0 ? 1.3?) and could even repel solid contaminants (e.g., dust) upon washing with water. Meanwhile, such membranes exhibit excellent self-repairing properties so that physical scratching damage, such as cutting a trench, does not affect the liquid-repelling performance. The liquid-repelling ability could be recovered completely within 10 s. More significantly, such a SLIPS membrane shows excellent durability so that the water sliding angle of the SLIPS could be maintained at less than 5.0? for about 80 cycles owing to the regenerated poly(dimethylsiloxane) layer on the surface. This work represents a robust methodology to enrich the development of hydrophobic and oleophobic slippery surfaces, which is promising for many areas, such as biomedical, self-cleaning, antifouling, and self-repairing materials.

Wettability of graphene: from influencing factors and reversible conversions to potential applications

As a member of the carbon material family, graphene has long been the focus of research on account of its abundant excellent properties. Nevertheless, many previous research works have attached much importance to its mechanical capacity and electrical properties, and not to its surface wetting properties with respect to water. In this review, a series of methods are put forward for characterization of the water contact angle of graphene, such as experimental measurements, classic molecular dynamics simulations, and formula calculations. A series of factors that affect the wettability of graphene, including defects, controllable atmosphere, doping, and electric field, are also discussed in detail, and have rarely have been covered in other review articles before. Finally, with the developments of smart surfaces, a reversible wettability variation of graphene from hydrophobic to hydrophilic is important in the presence of external stimulation and is discussed in detail herein. It is anticipated that graphene could serve as a tunable wettability coating for further developments in electronic devices and brings a new perspective to the construction of smart material surfaces.