Self-healing of voids in the wax coating on plant surfaces

Multi-stimulus Response Behavior of Biomimetic Autocrine Waxy Materials for Potential Self-Constructing Surface Microstructures

Many functions of terrestrial plant leaves rely on the regenerable epidermal wax layer. Biomimetic autocrine waxy materials (AWMs) inspired by renewable epidermal waxes are attracting increasing attention. However, the growth properties of the wax layer remain unclear, limiting the development of this promising material. This work focuses on the stimulated growth characteristics and microstructural regulation methods of the waxy layers. It is found that the wax layers exhibit a corresponding behavior of changing their surface micromorphology under force, heat, solvents, and other stimuli during the self-growth process, and as a result of which, various types of fine surface microstructures such as grids, rings, stripes, pattern copying, and printing can be self-built on their surfaces. The composition of the surface autocrine wax layer changes with the autocrine time, and this finding may be useful for the separation and purification of alkane mixtures. In addition, the surface wax layer possesses the ability to self-heal and strengthen itself at the damage site after being stimulated by injury, similar to the damage-response behavior of a bark surface. Such multi-stimulus response behavior described here provides a platform for the discovery of more functional materials and microstructural self-construction techniques and can also serve as a basis for their applications.

Bio-inspired and metal-derived superwetting surfaces: Function, stability and applications

Due to their exceptional anti-icing, anti-corrosion, and anti-drag qualities, biomimetic metal-derived superwetting surfaces, which are widely employed in the aerospace, automotive, electronic, and biomedical industries, have raised significant concern. However, further applications in other domains have been hampered by the poor mechanical and chemical durability of superwetting metallic surfaces, which can result in metal fatigue and corrosion. The potential for anti-corrosion, anti-contamination, anti-icing, oil/water separation, and oil transportation on surfaces with superwettability has increased in recent years due to the advancement of research in biomimetic superwetting interface theory and practice. Recent developments in functionalized biomimetic metal-derived superwetting surfaces were summarized in this paper. Firstly, a detailed presentation of biomimetic metal-derived superwetting surfaces with unique capabilities was made. The problems with the long-term mechanical and chemical stability of biomimetic metal-derived superwetting surfaces were then examined, along with potential solutions. Finally, in an effort to generate fresh concepts for the study of biomimetic metal-derived superwetting surfaces, the applications of superwetting metallic surfaces in various domains were discussed in depth. The future direction of biomimetic metal-derived superwetting surfaces was also addressed.

Self-Healing of Biocompatible Superhydrophobic Coatings: The Interplay of the Size and Loading of Particles

The broad application potential of superhydrophobic coatings is limited by the usage of environment-threatening materials and poor durability. The nature-inspired design and fabrication of self-healing coatings is a promising approach for addressing these issues. In this study, we report a fluorine-free and biocompatible superhydrophobic coating that can be thermally healed after abrasion. The coating is composed of silica nanoparticles and carnauba wax, and the self-healing is based on surface enrichment of wax in analogy to the wax secretion in plant leaves. The coating not only exhibits fast self-healing, just in 1 min under moderate heating, but also displays increased water repellency and thermal stability after healing. The rapid self-healing ability of the coating is attributed to the relatively low melting point of carnauba wax and its migration to the surface of the hydrophilic silica nanoparticles. The dependence of self-healing on the size and loading of particles provides insights into the process. Furthermore, the coating exhibits high levels of biocompatibility where the viability of fibroblast L929 cells was ∼90%. The presented approach and insights provide valuable guidelines in the design and fabrication of self-healing superhydrophobic coatings.

Effect of Seasonal Variation on Leaf Cuticular Waxes’ Composition in the Mediterranean Cork Oak (Quercus suber L.)

Quercus suber L. (cork oak) leaves were analyzed along one annual cycle for cuticular wax content and chemical composition. This species, well adapted to the long dry summer conditions prevailing in the Mediterranean, has a leaf life span of about one year. The cuticular wax revealed a seasonal variation with a coverage increase from the newly expanded leaves (115.7 µg/cm2 in spring) to a maximum value in fully expanded leaves (235.6 µg/cm2 after summer). Triterpenoids dominated the wax composition throughout the leaf life cycle, corresponding in young leaves to 26 µg/cm2 (22.6% of the total wax) and 116.0 µg/cm2 (49% of the total wax) in mature leaves, with lupeol constituting about 70% of this fraction. The total aliphatic compounds increased from 39 µg/cm2 (young leaves) to 71 µg/cm2 (mature leaves) and then decreased to 22 µg/cm2 and slightly increased during the remaining period. The major aliphatic compounds were fatty acids, mostly with C16 (hexadecanoic acid) and C28 (octacosanoic acid) chain lengths. Since pentacyclic triterpenoids are located almost exclusively within the cutin matrix (intracuticular wax), the increase in the cyclic-to-acyclic component ratio after summer shows an extensive deposition of intracuticular waxes in association with the establishment of mechanical and thermal stability and of water barrier properties in the mature leaf cuticle.

Long-Lasting Self-Healing Surface Dewettability through the Rapid Regeneration of Surface Morphologies

The development of self-healing systems for artificial superhydrophobic materials/surfaces based on the reconstruction of surface topologies rather than chemical makeup has been much less established. In this article, we report for the first time a simple and straightforward method for self-repairing surface dewettability over a long period of time by rapidly regenerating surface microstructures. We selected paraffin wax as a matrix for methyltrichlorosilane (MTCS) having strong reactivity with moisture/water and simply mixed them. When the as-prepared MTCS-loaded paraffin wax surfaces were exposed to air for a few hours, they spontaneously became highly hydrophobic with water contact angles of about 150° due to the formation of disordered surface microstructures. The use of paraffin wax with a few angstrom-scale space as a matrix was found to be more effective than the use of poly(dimethylsiloxane) with nanometer-size porosity in preventing both evaporation and degradation of MTCS's chemical reactivity for a long period. Therefore, for about 1 month, even after the surface microstructures were completely destroyed, surface dewettability could be self-repaired by rapidly regenerating surface morphologies. In addition, chemical damage by UV/ozone exposure could also be repeatably self-healed by the reconstruction of surface chemical makeup. We thus expect that this simple approach could provide future insights to impart the self-healing ability of manmade superhydrophobic materials/surfaces against chemical and physical damages.

Robust and durable liquid-repellent surfaces

This review provides a comprehensive summary of characterization, design, fabrication, and application of robust and durable liquid-repellent surfaces.

Recent Advances in Plant Nanoscience

Plants have complex internal signaling pathways to quickly adjust to environmental changes and harvest energy from the environment. Facing the growing population, there is an urgent need for plant transformation and precise monitoring of plant growth to improve crop yields. Nanotechnology, an interdisciplinary research field, has recently been boosting plant yields and meeting global energy needs. In this context, a new field, "plant nanoscience," which describes the interaction between plants and nanotechnology, emerges as the times require. Nanosensors, nanofertilizers, nanopesticides, and nano-plant genetic engineering are of great help in increasing crop yields. Nanogenerators are helping to develop the potential of plants in the field of energy harvesting. Furthermore, the uptake and internalization of nanomaterials in plants and the possible effects are also worthy of attention. In this review, a forward-looking perspective on the plant nanoscience is presented and feasible solutions for future food shortages and energy crises are provided.

Fast Self-Healing Superhydrophobic Thermal Energy Storage Coatings Fabricated by Bio-Based Beeswax and Artificially Cultivated Diatom Frustules

Diatom frustules (DFs) with delicate hierarchical pores and a large specific surface area are extracted from artificially cultured diatoms, showing their utilization potential as shape-stabilized phase change materials (ss-PCMs). Herein, we successfully prepared a fully biomass-based ss-PCM, superhydrophobic thermal energy storage (STES) coating by employing beeswax (BW) as phase change materials (PCMs) and DFs as supporting materials via a facile spraying method. DFs can adsorb as much as 65 wt % BW without leakage, accompanied with a high heat storage capacity of 112.57 J/g. The thermal stability test demonstrates that the DF/BW coating can undergo 500 heating-freezing cycles with the reduction of the phase change enthalpy being less than 5%. Simultaneously, the DF also endows BW with a higher thermal degradation temperature (from ∼200 to ∼250 °C). In addition, the DF/BW coating shows superhydrophobicity due to the incorporation of the low surface energy of BW and the micro/nanostructures of DFs. This superhydrophobic surface can quickly and repeatedly recover its excellent water repellency through a simple heat treatment (80 °C, 20 min) after being damaged by a water impact or strong acid and alkali corrosion. This self-healing ability can effectively overcome the poor durability of traditional superhydrophobic materials. Our research can expand the application of DFs in the field of ss-PCMs and guide the preparation of durable superhydrophobic surfaces with rapid self-healing performance.

Nanomaterials and their applications on bio-inspired wearable electronics

Wearable electronics featuring conformal attachment, sensitive perception and intellectual signal processing have made significant progress in recent years. However, when compared with living organisms, artificial sensory devices showed undeniable bulky shape, poor adaptability, and large energy consumption. To make up for the deficiencies, biological examples provide inspirations of novel designs and practical applications. In the field of biomimetics, nanomaterials from nanoparticles to layered two-dimensional materials are actively involved due to their outstanding physicochemical properties and nanoscale configurability. This review focuses on nanomaterials related to wearable electronics through bioinspired approaches on three different levels, interfacial packaging, sensory structure, and signal processing, which comprehensively guided recent progress of wearable devices in leveraging both nanomaterial superiorities and biorealistic functionalities. In addition, opinions on potential development trend are proposed aiming at implementing bioinspired electronics in multifunctional portable sensors, health monitoring, and intelligent prosthetics.

Robust superhydrophobicity: mechanisms and strategies

Superhydrophobic surfaces hold great prospects for extremely diverse applications owing to their water repellence property. The essential feature of superhydrophobicity is micro-/nano-scopic roughness to reserve a large portion of air under a liquid drop. However, the vulnerability of the delicate surface textures significantly impedes the practical applications of superhydrophobic surfaces. Robust superhydrophobicity is a must to meet the rigorous industrial requirements and standards for commercial products. In recent years, major advancements have been made in elucidating the mechanisms of wetting transitions, design strategies and fabrication techniques of superhydrophobicity. This review will first introduce the mechanisms of wetting transitions, including the thermodynamic stability of the Cassie state and its breakdown conditions. Then we highlight the development, current status and future prospects of robust superhydrophobicity, including characterization, design strategies and fabrication techniques. In particular, design strategies, which are classified into passive resistance and active regeneration for the first time, are proposed and discussed extensively.

Does Acid Rain Alter the Leaf Anatomy and Photosynthetic Pigments in Urban Trees?

Megapolis such as Mexico City, have atmospheric pollutants that interact with the humidity and solar radiation. The topography of this city promotes air stagnation, generating atmospheric pollutants and episodes of acid rain, a phenomenon well recorded since the end of the 1980s. However, little we know about how urban trees respond to acid rain in the city. Here we present how simulated acid rain causes anatomical and changes in photosynthetic pigments in two of the most abundant urban trees in Mexico City: Liquidambar styraciflua L. and Fraxinus uhdei (Wenz.) Lingelsh. We first described the leaf anatomy of both species. Then, we used one-year-old trees sprayed with sulfuric acid solutions at pH 2.5 and 3.8, and evaluated visible leaf damage, anatomical alterations, and chlorophyll contents. In both species, the pH 2.5 caused cuticle alterations and areas of total tissue destruction. L. styraciflua showed greater sensitivity, but we discuss some of the tolerance mechanisms. Finally, acid rain also reduced the chlorophyll contents. These results contribute toward a catalogue of urban tree species to describe pollution-induced damages, and the identification of tolerant species useful for short- and mid-term detection of environmental crisis, in cities with similar environmental conditions and urban tree composition.

The leaf miner Phyllocnistis populiella negatively impacts water relations in aspen

Within the North American boreal forest, a widespread outbreak of the epidermal leaf miner Phyllocnistis populiella Cham. has damaged quaking aspen (Populus tremuloides Michx.) for nearly 20 years. In a series of experiments, we tested the effects of feeding damage by P. populiella on leaf water relations and gas exchange. Relative to insecticide-treated trees, the leaves of naturally mined trees had lower photosynthesis, stomatal conductance to water vapor, transpiration, water-use efficiency, predawn water potential and water content, as well as more enriched foliar δ13C. The magnitude of the difference between naturally mined and insecticide-treated trees did not change significantly throughout the growing season, suggesting that the effect is not caused by accumulation of incidental damage to mined portions of the epidermis over time. The contributions of mining-related stomatal malfunction and cuticular transpiration to these overall effects were investigated by restricting mining damage to stomatous abaxial and astomatous adaxial leaf surfaces. Mining of the abaxial epidermis decreased photosynthesis and enriched leaf δ13C, while increasing leaf water potential and water content relative to unmined leaves, effects consistent with stomatal closure due to disfunction of mined guard cells. Mining of the adaxial epidermis also reduced photosynthesis but had different effects on water relations, reducing midday leaf water potential and water content relative to unmined leaves, and did not affect δ13C. In the laboratory, extent of mining damage to the adaxial surface was positively related to the rate of water loss by leaves treated to prevent water loss through stomata. We conclude that overall, despite water savings due to closure of mined stomata, natural levels of damage by P. populiella negatively impact water relations due to increased cuticular permeability to water vapor across the mined portions of the epidermis. Leaf mining by P. populiella could exacerbate the negative effects of climate warming and water deficit in interior Alaska.

Practical Applications of Superhydrophobic Materials and Coatings: Problems and Perspectives

Synthetic superhydrophobic (SH) surfaces were developed after 1990s, and the number of publications in this field is around 13 500 at present. However, the industrial production of SH coatings is very unsatisfying after the intensive research activity in the last two decades. The main reason is the loss of the water repellence properties when SH surfaces are exposed to outdoor conditions due to their weak mechanical properties and contamination from the medium which removes the initial SH properties. In this Feature Article, we focus on the scientific and technical reasons which prevent the application of the SH surfaces in our daily lives by highlighting some well-known but mostly overlooked problems in this area. (The synthesis methods of SH surfaces are not the subject of this article since they were reviewed previously in very good articles.) The basic contact angle science and the issue of the cancellation of the Wenzel and Cassie-Baxter equations are reviewed in the first part. The issues of the expensive and small-scale SH surface preparation problems, the difficulties in obtaining a transparent SH surface, the troubles arising from the water vapor condensation on an SH surface, the lack of robustness and abrasion resistance of most of the SH surfaces, the drawbacks of the fabricated self-healing SH surfaces, the short useful service life of self-cleaning SH surfaces due to surface contamination, and the ineffective anti-icing SH coatings are reviewed in the following text. Some important problems affecting the unsuccessful industrial applications of the SH surfaces are discussed critically in the Conclusions and Outlook section. Finally, some proposals are presented for future directions on the synthesis and applications of SH surfaces.

Rotator phases in alkane systems: In bulk, surface layers and micro/nano-confinements

Medium- and long-chain alkanes and their mixtures possess a remarkable physical property - they form intermediate structured phases between their isotropic liquid phase and their fully ordered crystal phase. These intermediate phases are called "rotator phases" or "plastic phases" (soft solids) because the incorporated alkane molecules possess a long-range positional order while preserving certain mobility to rotate, which results in complex visco-plastic rheological behaviour. The current article presents a brief overview of our current understanding of the main phenomena involved in the formation of rotator phases from single alkanes and their mixtures. In bulk, five rotator phases with different structures were identified and studied in detail. Along with the thermodynamically stable rotator phases, metastable and transient (short living) rotator phases were observed. Bulk rotator phases provided important information about several interfacial phenomena of high scientific interest, such as the energy of crystal nucleation, entropy and enthalpy of alkane freezing, interfacial energy between a crystal and its melt, etc. In alkane mixtures, the region of existence of rotator phases increases significantly, reflecting the disturbed packing of different molecules. All these phenomena are very important in the context of alkane applications as lubricants, in cosmetics, as phase-change materials for energy storage, etc. Significant expansion of the domain of rotator phases was observed also in confinements - in the pores of solid materials impregnated with alkanes, in polymeric microcapsules containing alkanes, and in micrometer sized emulsion droplets. The rotator phases were invoked to explain the mechanisms of two recently discovered phenomena in cooled alkane-in-water emulsions - the spontaneous "self-shaping" and the spontaneous "self-bursting" (fragmentation) of emulsion drops. The so-called "α-phases" formed by fatty acids and alcohols, and the "gel phase" formed in phospholipid and soap systems exhibit structural characteristics similar to those in the alkane rotator phases. The subtle connections between all these diverse systems are outlined, providing a unified outlook of the main phenomena related to the formation of such soft solid materials. The occurrence of alkane rotator phases in natural materials and in several technological applications is also reviewed to illustrate the general importance of these unique materials and the related phenomena.

Lipids: Source of Static Electricity of Regenerative Natural Substances and Nondestructive Energy Harvesting

It is familiar to everyone that human skin and hair easily lose electrons and cause static electricity as they undergo friction with other materials. Such natural regenerative substances take a high ranking in the triboelectric series. Even though the static electricity of regenerative natural substances has been a long-term curiosity in human history, it is not yet clear which of their components causes the positive static charges. This study reveals that lipid layers on the surface of regenerative substances (skin, hair, leaves, cells) and even synthetic lipids are responsible for this positive static electricity and shows that it is possible to manufacture lipid-based triboelectric nanogenerators (TENGs). Using the characteristic that lipids on leaves regenerate within a few hours, lipids from living tree leaves are collected, and lipid-based nondestructive TENGs are fabricated. The concept of energy-harvesting vines is also presented, which can generate electricity when they are wrapped loosely on living tree branches. This study suggests how to harvest electricity while preserving nature as it is.

Healable and Foldable Carbon Nanotube/Wax Conductive Composite

In this study, a composite material with healable and foldable features is formulated to print conductive patterns on rough surfaces, such as paper, cloth, and three-dimensional (3D) printed objects. Carbon nanotubes (CNTs) are mixed with wax to formulate a solid composite for pen writing. The composite has a low percolation threshold of 2.5 wt % CNTs and can be written on various rough substrates, such as paper and cloth, to create conductive patterns for electronic conductors. Because of the strong infrared (IR) absorption of CNTs, the printed patterns can be selectively sintered by noncontact IR radiation efficiently to show great electrical conductivity. The electrical resistance of the written patterns on paper also show an insignificant increase after bending, folding, and crumpling. Furthermore, the conductive composite exhibits great healability after destructive damages. The conductivity of the damaged patterns after severe folding or knife cutting recovers to its original value with thermal or IR heating. Several examples, such as conductive tracks on paper, cloth, or 3D printed objects, are also demonstrated to show the potential of this healable conductive composite for electronic applications.

Molecular Adsorption Mechanism of Elemental Carbon Particles on Leaf Surface

Plant leaves can effectively capture and retain particulate matter (PM), improving air quality and human health. However, little is known about the adsorption mechanism of PM on leaf surface. Black carbon (BC) has great adverse impact on climate and environment. Four types of elemental carbon (EC) particles, carbon black as a simple model for BC, graphite, reduced graphene oxide, and graphene oxide, and C₃₆H₇₄/C₄₄H₈₈O₂ as model compounds for epicuticular wax were chosen to study their interaction and its impact at the molecular level using powder X-ray diffraction and vibrational spectroscopy (infrared and Raman). The results indicate that EC particles and wax can form C-H···π type hydrogen bonding with charge transfer from carbon to wax; therefore, strong attraction is expected between them due to the cooperativity of hydrogen bonding and London dispersion from instantaneous dipoles. In reality, once settled on the leaf surface, especially without wax ultrastructures, BC with extremely large surface-to-volume ratio will likely stick and stay. On the other hand, BC particles can lead to phase transition of epicuticular wax from crystalline to amorphous structures by creating packing disorder and end- gauche defects of wax molecular chain, potentially causing water loss and thereby damage of plants.

Super anticorrosion of aluminized steel by a controlled Mg supply

The current anticorrosion strategy makes use of coatings to passively protect the steel, which faces increasing challenge due to the tightened environmental regulations and high cost. This paper reports a new method for achieving a super anticorrosion function in Al-Si alloys through Mg nano-metallurgy, which was characterized by real-time synchrotron measurements. The unique function is based on the formation of an amorphous and self-charge-compensated MgAl₂O₄-SiO₂ phase between the grain boundaries to help prevent the penetration of oxygen species through the grain boundaries. Through this, the corrosion resistance of pristine aluminized steel could be improved almost 20 fold. An analysis of the phases, microstructures of the Mg-coated aluminized layer and corrosion products consistently supported the proposed mechanism. This charge-compensated corrosion resistance mechanism provides novel insight into corrosion resistance.

Structure and Biosynthesis of Branched Wax Compounds on Wild Type and Wax Biosynthesis Mutants of Arabidopsis thaliana

The cuticle is a waxy composite that protects the aerial organs of land plans from non-stomatal water loss. The chemical make-up of the cuticular wax mixture plays a central role in defining the water barrier, but structure-function relationships have not been established so far, in part due to gaps in our understanding of wax structures and biosynthesis. While wax compounds with saturated, linear hydrocarbon tails have been investigated in detail, very little is known about compounds with modified aliphatic tails, which comprise substantial portions of some plant wax mixtures. This study aimed to investigate the structures, abundances and biosynthesis of branched compounds on the species for which wax biosynthesis is best understood: Arabidopsis thaliana. Microscale derivatization, mass spectral interpretation and organic synthesis identified homologous series of iso-alkanes and iso-alcohols on flowers and leaves, respectively. These comprised approximately 10-15% of wild type wax mixtures. The abundances of both branched wax constituents and accompanying unbranched compounds were reduced on the cer6, cer3 and cer1 mutants but not cer4, indicating that branched compounds are in part synthesized by the same machinery as unbranched compounds. In contrast, the abundances of unbranched, but not branched, wax constituents were reduced on the cer2 and cer26 mutants, suggesting that the pathways to both types of compounds deviate in later steps of chain elongation. Finally, the abundances of branched, but not unbranched, wax compounds were reduced on the cer16 mutant, and the (uncharacterized) CER16 protein may therefore be controlling the relative abundances of iso-alkanes and iso-alcohols on Arabidopsis surfaces.

Cuticle Structure in Relation to Chemical Composition: Re-assessing the Prevailing Model

The surface of most aerial plant organs is covered with a cuticle that provides protection against multiple stress factors including dehydration. Interest on the nature of this external layer dates back to the beginning of the 19th century and since then, several studies facilitated a better understanding of cuticular chemical composition and structure. The prevailing undertanding of the cuticle as a lipidic, hydrophobic layer which is independent from the epidermal cell wall underneath stems from the concept developed by Brongniart and von Mohl during the first half of the 19th century. Such early investigations on plant cuticles attempted to link chemical composition and structure with the existing technologies, and have not been directly challenged for decades. Beginning with a historical overview about the development of cuticular studies, this review is aimed at critically assessing the information available on cuticle chemical composition and structure, considering studies performed with cuticles and isolated cuticular chemical components. The concept of the cuticle as a lipid layer independent from the cell wall is subsequently challenged, based on the existing literature, and on new findings pointing toward the cell wall nature of this layer, also providing examples of different leaf cuticle structures. Finally, the need for a re-assessment of the chemical and structural nature of the plant cuticle is highlighted, considering its cell wall nature and variability among organs, species, developmental stages, and biotic and abiotic factors during plant growth.

Bioinspired Omniphobic Coatings with a Thermal Self-Repair Function on Industrial Materials

Inspired by the wax regeneration ability of plant leaves and the slippery surfaces of the Nepenthes pitcher plants, we have developed a new form of cross-species bioinspired slippery liquid-infused porous surfaces (X-SLIPS) that can self-repair under thermal stimulation even under large-area physical and chemical damage. The performance and underlying mechanism of the thermal-healing property has been studied and characterized in detail. These thermally self-healing omniphobic coatings can be applied to a broad range of metals, plastics, glass, and ceramics of various shapes and show excellent repellency toward aqueous and organic liquids.

Fabrication of robust, damage-tolerant superhydrophobic coatings on naturally micro-grooved wood surfaces

Damage-tolerant superhydrophobic wood surfaces were fabricated by applying an epoxy-resin primer coating and subsequent construction of silica/epoxy-resin/fluorinated alkylsilane composite films.

Electrically conductive PEDOT coating with self-healing superhydrophobicity

A self-healing electrically conductive superhydrophobic poly(3,4-ethylenedioxythiophene) (PEDOT) coating has been prepared by chemical vapor deposition of a fluoroalkylsilane (POTS) onto a PEDOT film, which was obtained by electrochemical deposition. The coating not only maintained high conductivity with a low resistivity of 3.2 × 10(-4) Ω·m, but also displayed a water contact angle larger than 156° and a sliding angle smaller than 10°. After being etched with O2 plasma, the coating showed an excellent self-healing ability, spontaneously regaining its superhydrophobicity when left under ambient conditions for 20 h. This superhydrophobicity recovery process was found to be humidity-dependent, and could be accelerated and completed within 2 h under a high humidity of 84%. The coating also exhibited good superhydrophobicity recovering ability after being corroded by strong acid solution at pH 1 or strong base solution at pH 14 for 3 h.

Molecular organization of the nanoscale surface structures of the dragonfly Hemianax papuensis wing epicuticle

The molecular organization of the epicuticle (the outermost layer) of insect wings is vital in the formation of the nanoscale surface patterns that are responsible for bestowing remarkable functional properties. Using a combination of spectroscopic and chromatographic techniques, including Synchrotron-sourced Fourier-transform infrared microspectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) depth profiling and gas chromatography-mass spectrometry (GCMS), we have identified the chemical components that constitute the nanoscale structures on the surface of the wings of the dragonfly, Hemianax papuensis. The major components were identified to be fatty acids, predominantly hexadecanoic acid and octadecanoic acid, and n-alkanes with even numbered carbon chains ranging from C14 to C30. The data obtained from XPS depth profiling, in conjunction with that obtained from GCMS analyses, enabled the location of particular classes of compounds to different regions within the epicuticle. Hexadecanoic acid was found to be a major component of the outer region of the epicuticle, which forms the surface nanostructures, and was also detected in deeper layers along with octadecanoic acid. Aliphatic compounds were detected throughout the epicuticle, and these appeared to form a third discrete layer that was separate from both the inner and outer epicuticles, which has never previously been reported.

Recent Development in Clay Based Functional Coating for Corrosion Protection

There is a large variety of techniques available to protect metals from various types of corrosion. Till date chromate containing metal coatings is one of the most commonly used methods. Layered clays are basically of two types depending on the type of ion exchange capacity. In the recent years different researchers demonstrated the use of such cation/ anionic clays as potential nanocontainers for the inhibitors. These nanocontainers can be used in the coating to induce self-repairing capacity when the coating surface is damaged. Due to the disturbance in the pH and availability of chloride ions clay based nanocontainers can release the inhibitor to protect the surface. In the recent year use of anionic clay like hydrotalcites or layered double hydroxides are much studied in comparison to cationic clay like montmorillonite. This review critically analysed the potential of these clay in the future development of self-healing coating.

Durability and restoring of superhydrophobic properties in silica-based coatings

The durability and restorable properties of superhydrophobicity are a most important issue essential for utilization of superhydrophobic materials in industrial and domestic fields. In this work, we have focused on the sol-gel dip coating synthesis, durability, and restoring properties of a superhydrophobic surface composed of spherical silica particles with low energy free surface successfully achieved on the surface of glass substrates. The water contact angle (WCA) of the as-prepared superhydrophobic coatings reached as high as 170±1° (WCA=170±1°) and the sliding angle was 3±1° (WSA=3±1°). The behavior of wettability on superhydrophobic coating surface under various external disturbances including outdoor environments, heat, and mild acidic condition is investigated. It is shown in particular that degradation and repairing of surface methyl groups between two such surfaces leads to a fully restorable coating surface by the surface modification with trimethylchlorosilane (TMCS) at room temperature. The coating also holds good thermal stability; it holds superhydrophobicity up to 550 °C and gets degrade into superhydrophilicity above 600 °C without deforming surface morphology. The results confirm the durability of the silica coating under different external disturbances and sol-gel dip coating method and restoring property provide the best solution to fabricate superhydrophobic silica coating surface with extended durability at low cost.

Mechanically durable superhydrophobic surfaces

Development of durable non-wetting surfaces is hindered by the fragility of the microscopic roughness features that are necessary for superhydrophobicity. Mechanical wear on superhydrophobic surfaces usually shows as increased sticking of water, leading to loss of non-wettability. Increased wear resistance has been demonstrated by exploiting hierarchical roughness where nanoscale roughness is protected to some degree by large scale features, and avoiding the use of hydrophilic bulk materials is shown to help prevent the formation of hydrophilic defects as a result of wear. Additionally, self-healing hydrophobic layers and roughness patterns have been suggested and demonstrated. Nevertheless, mechanical contact not only causes damage to roughness patterns but also surface contamination, which shortens the lifetime of superhydrophobic surfaces in spite of the self-cleaning effect. The use of photocatalytic effect and reduced electric resistance have been suggested to prevent the accumulation of surface contaminants. Resistance to organic contaminants is more challenging, however, oleophobic surface patterns which are non-wetting to organic liquids have been demonstrated. While the fragility of superhydrophobic surfaces currently limits their applicability, development of mechanically durable surfaces will enable a wide range of new applications in the future.

Enhancement of active corrosion protection via combination of inhibitor-loaded nanocontainers

The present work reports the synthesis of layered double hydroxides (LDHs) nanocontainers loaded with different corrosion inhibitors (vanadate, phosphate, and 2-mercaptobenzothiazolate) and the characterization of the resulting pigments by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The anticorrosion activity of these nanocontainers with respect to aluminum alloy AA2024 was investigated by electrochemical impedance spectroscopy (EIS). The bare metallic substrates were immersed in dispersions of nanocontainers in sodium chloride solution and tested to understand the inhibition mechanisms and efficiency. The nanocontainers were also incorporated into commercial coatings used for aeronautical applications to study the active corrosion protection properties in systems of industrial relevance. The results show that an enhancement of the active protection effect can be reached when nanocontainers loaded with different inhibitors are combined in the same protective coating system.