Reversibly Light‐Switchable Wettability of Hybrid Organic/Inorganic Surfaces With Dual Micro‐/Nanoscale Roughness

Here, an approach to realize “smart” solid substrates that can convert their wetting behavior between extreme states under selective light irradiation conditions is described. Hybrid organic/inorganic surfaces are engineered by exploiting photolithographically tailored SU‐8 polymer patterns as templates for accommodating closely packed arrays of colloidal anatase TiO₂ nanorods, which are able to respond to UV light by reversibly changing their surface chemistry. The TiO₂‐covered SU‐8 substrates are characterized by a dual micro‐/nanoscale roughness, arising from the overlapping of surfactant‐capped inorganic nanorods onto micrometer‐sized polymer pillars. Such combined architectural and chemical surface design enables the achievement of UV‐driven reversible transitions from a highly hydrophobic to a highly hydrophilic condition, with excursions in water contact angle values larger than 100°. The influence of the geometric and compositional parameters of the hybrid surfaces on their wettability behavior is examined and discussed within the frame of the available theoretical models.     

Open Air Plasma Deposition of Superhydrophilic Titania Coatings

A method for the deposition and functionalization of a nanostructured organotitanate thin film, which imparts superhydrophilicity to a surface with a one‐step, open‐air process, is described. Extreme wetting (Θ < 5°) is achieved through synergistic contributions from both nanoscale roughness, visible light absorption caused by nonmetal dopants, and oxygen vacancies and surface activation by reactive plasma species. To test the efficacy of this material as an antifog coating, glass is coated and subjected to aggressive changes in humidity. Under both fogging and defrosting conditions, the superhydrophilic coating achieves a high degree of transparency, showing nearly two orders of magnitude improvement over the bare glass. The measured adhesion of the superhydrophilic coating is 5.9 J m^?2, nearly double that of the solution‐processed control. The reliability of the coating is further validated by demonstrating scratch‐resistance. Additionally, the incorporation of organic matter into the molecular structure of the coating disrupts long‐range crystallinity from developing. This structural and subsequent chemical analysis of the coating reveals that inorganic and organic species are intimately connected at the nanoscale via alkyl and alkoxy bridges. The amorphous organotitanate material is distinct from conventional TiO₂, which requires high temperature crystallization and extensive UV irradiation to display similar superhydrophilic qualities.     

Ionic Liquid-Mediated Scanning Probe Electro-Oxidative Lithography as a Novel Tool for Engineering Functional Oxide Micro- and Nano-Architectures

Functional oxides have extensively been investigated as a promising class of materials in a broad range of innovative applications. Harnessing the novel properties of functional oxides in micro- to nano-scale applications hinges on establishing advanced fabrication and manufacturing techniques able to synthesize these materials in an accurate and reliable manner. Oxidative scanning probe lithography (o-SPL), an atomic force microscopy (AFM) technique based on anodic oxidation at the water meniscus formed at the tip/substrate contact, not only combines the advantages of both “top-down” and “bottom-up” fabrication approaches, but also offers the possibility of fabricating oxide nanomaterials with high patterning accuracy. While the use of self-assembled monolayers (SAMs) broadened the application of o-SPL, significant challenges have emerged owing to the relatively limited number of SAM/solid surface combinations that can be employed for o-SPL, which constrains the ability to control the chemistry and structure of oxides formed by o-SPL. In this work, a new o-SPL technique that utilizes room-temperature ionic liquids (RTILs) as the functionalizing material to mediate the electrochemistry at AFM tip/substrate contacts is reported. The results show that the new IL-mediated o-SPL (IL-o-SPL) approach allows sub-100 nm oxide features to be patterned on a model solid surface, namely steel, with an initiation voltage as low as −2 V. Moreover, this approach enables high tunability of both the chemical state and morphology of the patterned iron oxide structures. Owing to the high chemical compatibility of ILs, which derives from the possibility of synthesizing ILs able to adsorb on a wide variety of solid surfaces, IL-o-SPL can be extended to other material surfaces and provide the opportunity to accurately tailor the chemistry, morphology, and electronic properties within nanoscale domains, thus opening new pathways to the development of novel micro- and nano-architectures for advanced integrated devices.     

Tunable Structural Color Surfaces with Visually Self‐Reporting Wettability

Functional materials with wettability of specific surfaces are important for many areas. Here, a new lubricant‐infused elastic inverse opal is presented with tunable and visually “self‐reporting” surface wettability. The elastic inverse opal films are used to lock in the infused lubricating fluid and construct slippery surfaces to repel droplets of various liquids. The films are stretchable, and the lubricating fluid can penetrate the pores under stretching, leaving the surface layer free of lubrication; the resultant undulating morphology of the inverse opal scaffold topography can reversibly pin droplets on the fluidic film rather than the solid substrate. This mechanical stimulation process provides an effective means of dynamically tuning the surface wettability and the optical transparency of the inverse opal films. In particular, as the adjustments are accompanied by simultaneous deformation of the periodic macroporous structure, the inverse opal films can self‐report on their surface status through visible structural color changes. These features make such slippery structural color materials highly versatile for use in diverse applications.     

Optical Nanoscale Pool‐on‐Surface Design for Control Sensing Recognition of Multiple Cations

General design of optical chemical nanosensors is needed to develop efficient sensing systems with high flexibility, and low capital cost for control recognition of toxic analytes. Here, we designed optical chemical nanosensors for simple, high‐speed detection of multiple toxic metal ions. The systematic design of the nanosensors was based on densely patterned chromophores with intrinsic mobility, namely, “building‐blocks” onto three‐dimensional (3D) nanoscale structures. The ability to precisely modify the nanoscale pore surfaces by using a broad range of chromophores that have different molecular sizes and characteristics enables detection of multiple toxic ions. A key feature of this building‐blocks design strategy is that the surface functionality and good adsorption characteristics of the fabricated nanosensor arrays enabled the development of “pool‐on‐surface” sensing systems in which high flux of the metal analytes across the probe molecules was achieved without significant kinetic hindrance. Such a sensing design enabled sensitive recognition of metal ions up to sub‐picomolar detection limits (～10^?11 mol dm^?3), for first time, with rapid response time within few seconds. Moreover, because these sensing pools exhibited long‐term stability, reversibility and selectivity in detecting most pollutant cations, for example, Cr(VI), Pb(II), Co(II), and Pd(II) ions, they are practical and inexpensive. The key result in our study is that the pool‐on‐surface design for optical nanosensors exhibited significant ion‐selective ability of these target ions from environmental samples and waste disposals.     

A Simple Poly(Vinyl Sulfonate) Coating for All-Purpose,Self-Cleaning Applications: Molecular Packing Density–Defined Surface Superhydrophilicity

In this study, poly(vinyl sulfonate) (PVS)–capped surfaces are constructed on the polyelectrolyte multilayers (PEMs) of poly(diallyldimethylammonium chloride) and poly(styrene sulfonate) via electrostatic assembly. The water wetting behavior on the resulting PVS-capped PEMs is meticulously correlated with the number of surface sulfonate groups with the aid of sum frequency generation spectroscopy and quartz crystal microbalance. It is found that when the molecular packing density of surface sulfonate groups is adjusted to be comparable to the maximal packing density of spheres in two dimensions (≈0.9), the PVS capping is able to effectively adsorb water molecules from the surrounding to form hydrogen-bonded networks, which not only promote complete surface wetting by water in air but also diminish surface affinity to adhesion of ice, oil and wax deposited atop. As a result, the PVS-capped PEMs are able to fulfil all the self-cleaning functions proposed for superhydrophilic surfaces including anti-fogging, anti-icing, anti-grease, anti-smudge, anti-graffiti, and anti-wax. After being coated with the self-cleaning PVS-capped PEMs, conventional stainless steel meshes are able to perform oil-water separation without prior water wetting.     

Fine‐Tuning of Superhydrophobicity Based on Monolayers of Well‐defined Raspberry Nanoparticles with Variable Dual‐roughness Size and Ratio

Superhydrophobic surfaces have been extensively investigated for self‐cleaning, low‐adhesion, anti‐corrosion or reduced‐drag applications. Roughness and its characteristics, i.e., morphology, overall roughness and individual feature size, is an essential factor for superhydrophobicity. Several experimental methods and theoretical models strived to predict how the surface wettability is affected by the surface roughness. However, due to the difficulty of making practical surfaces with well‐defined roughness profiles, only limited and arbitrary experimental studies focused on practical superhydrophobic films. Here, the roughness factors which determine the wetting properties of films are reported, based on monolayers of well‐defined raspberry silica‐silica nanoparticles, exhibiting a wide‐range and systematic variation of individual features sizes and ratios (large over small features). The advancing water contact angle does not depend on the feature size or ratio, while the contact angle hysteresis (CAH) is strongly dependent on both. The minimum size and size ratio to reach superhydrophobicity were determined. These new insights into the wetting of rough surfaces can be used to direct the design of practical superhydrophobic materials for advanced applications such as solar panels, microelectronics or microfluidic devices.     

Synthetic Surfaces with Robust and Tunable Underwater Superoleophobicity

Surfaces with extreme wetting properties are useful for the collection, manipulation, transport, and avoidance of aqueous and organic fluids of commercial and strategic importance. Two major obstacles to the deployment of synthetic non‐wetting materials in practical scenarios are their lack of mechanical durability and their susceptibility to fouling in contaminated or chemically complex media. Here, crosslinked and nanoporous polymer multilayers are reported that overcome these limitations and exhibit robust and tunable “underwater superoleophobicity”, or the ability to almost completely prevent contact with oils and other organic fluids when submerged in water. These entirely organic coatings mimic key chemical and structural features found on the scales of fish and other natural anti‐oil‐fouling surfaces, and are remarkably tolerant to physical, chemical, and environmental insults commonly encountered in natural and synthetic aqueous environments. This approach also permits facile manipulation and patterning of surface chemistry and, thus, tunable spatial control over other important aspects of interfacial behavior, such as underwater oil adhesiveness, that extend and expand the potential utility of synthetic anti‐oil‐fouling surfaces in aqueous, aquatic, and marine environments.     

Bioinspired Directional Surfaces for Adhesion,Wetting, and Transport

In Nature, directional surfaces on insect cuticle, animal fur, bird feathers, and plant leaves are composed of dual micro‐nanoscale features that tune roughness and surface energy. Here, experimental and theoretical approaches for the design, synthesis, and characterization of new bioinspired surfaces demonstrating unidirectional surface properties are summarized. The experimental approaches focus on bottom‐up and top‐down synthesis methods of unidirectional micro‐ and nanoscale films to explore and characterize their anomalous features. The theoretical component focuses on computational tools to predict the physicochemical properties of unidirectional surfaces.     

熔石英抛光表面结构的蚀刻和热处理表征

利用HF蚀刻和热处理,结合原子力显微(AFM)分析,对传统抛光和磁流变抛光的表面结构进行了表征。为了分析热处理凸起的形成源,抛光表面在热处理前分别采用超声清洗、化学沥滤和HF蚀刻三种不同的表面处理技术进行处理,去除了不同表面材料。蚀刻形貌和热处理形貌及其关联性表明,传统抛光表面存在着大量纳米级缺陷,这些缺陷由易于诱导激光损伤的纳米级微裂纹和颗粒状分布的抛光杂质组成。结合抛光机制的分析,建立了传统抛光表面的微裂纹-颗粒杂质结构模型。     

Special features of photoluminescence in silicon-on-insulator structures implanted with hydrogen ions

The special features of photoluminescence spectra of silicon-on-insulator structures implanted with hydrogen ions are studied. An increase in the photoluminescence intensity with increasing hydrostatic pressure P during annealing and the formation of narrow periodic photoluminescence peaks in the spectral range from ～500 to 700 nm are revealed for the structures annealed at P > 6 kbar. It is shown that the fine structure of the photoluminescence spectra correlates with the slowing-down of hydrogen effusion from the implanted samples and with the suppression of the formation of hydrogen microbubbles in the surface layer. These processes promote the formation of an optical resonator, with the mirrors formed by the “silicon-on-insulator-air” and “silicon-on-insulator-SiO₂” interfaces and with the optically active layer formed by hydrogen ion implantation and subsequent annealing.     

A Rubberlike Stretchable Fibrous Membrane with Anti‐Wettability and Gas Breathability

The fabrication of a stable, anti‐wetting surface is a very challenging issue in surface chemistry. In general, superhydrophobicity highly depends on the surface structure. Moreover, mechanical deformation of the surface structure can produce dramatic changes in the surface wetting state, and in some cases, may even result in a complete loss of the surface's unique wettability. However, the study of stable surfaces under mechanical deformation conditions has been limited to flexible surfaces or small strain. Here, a mechanically stable superhydrophobic membrane is presented, which possesses high stretchability and gas breathability. The membrane, which consists of an elastic polyurethane fibrous matrix coated with polyaniline hairy nanostructures and polytetrafluoroethylene, exhibites excellent superhydrophobic properties under ≥300% strain. The breathability and wettability of the membrane is examined by examining various static and dynamic wetting parameters. The robust membrane maintaines its anti‐wettability (water contact angle ≈160°, hysteresis ≈10°) for 1000 stretching cycles. It is also determined that the stretchable and superhydrophobic surface suppresses the fragmentation and rebound of impact droplets, compared with rigid superhydrophobic surfaces. Finally, underwater gas sensing is demonstrated as a novel application.     

Bioinspired Surfaces with Superamphiphobic Properties: Concepts,Synthesis, and Applications

Among diverse wetting phenomena in surface science, superamphiphobicity is regarded as one of the most special super‐antiwetting states. In this paper, a systematic summary is presented to cover the characterization of surface wettability, the construction techniques, and selected functional applications. With respect to fabrication techniques, the following three types of technology routes, viz., “pre‐texturing + post‐modifying,” “pre‐modifying + post‐texturing,” and in situ one‐step construction will be discussed. The merits and demerits of each technology route are discussed. It is vital to rationally design or adopt appropriate construction strategies in diverse conditions. Appropriately constructed superamphiphobic multifunctional surfaces can be applied in many fields, however, most have not been scaled‐up and utilized for practical applications due to some specific difficulties required to be resolved in the future. These challenges and further outlook for super‐antiwetting surfaces are discussed in this review.     

Solute Incorporation at Oxide–Oxide Interfaces Explains How Ternary Mixed‐Metal Oxide Nanocrystals Support Element‐Specific Anisotropic Growth

Fundamental understanding of anisotropic growth in oxide nanocrystals is crucial to establish new synthesis strategies and to tailor the nanoscale electronic, magnetic, optical, and electrocatalytic properties of these particles. While several growth investigations of metal alloy nanoparticles have been reported, mechanistic studies on the growth of ternary oxide materials are still missing. This work constitutes the first study on the evolution of anisotropic growth of manganese–cobalt oxide nanoparticles by monitoring the elemental distribution and morphology during the particle evolution via scanning transmission electron microscopy–X‐ray spectroscopy. A new growth mechanism based on a “solution‐solid‐solid” pathway for mixed manganese cobalt oxides is revealed. In this mechanism, the MnO seed formation occurs in the first step, followed by the surface Co enrichment, which catalyzes the growth along the <100> directions in all the subsequent growth stages, creating rod, cross‐, and T‐shaped mixed metal oxides, which preferentially expose {100} facets. It is shown that the interrelation of both Mn and Co ions initializes the anisotropic growth and presents the range of validity of the proposed mechanism as well as the shape‐determining effect based on the metal‐to‐metal ratio.     

Interface Engineering and Direct Bonding of Lithium Tantalate Crystals

A method for modifying the surface free energy of lithium tantalate (LT) ferroelectric crystals is reported. Ultraviolet illumination and low-energy electron irradiation have been used for tuning the surface free energy (wettability) resulting in a wide range of contact angles (6 deg to 87 deg). The ultraviolet (UV) illumination makes the LT crystal surface superhydrophilic while the low-energy electron irradiation decreases the surface wetting. Fabrication of various wetting configurations allows demonstration of high-quality direct bonding of LT plates with hydrophilic polar faces.     

Core–Shell Nanoparticle Interface and Wetting Properties

Latex colloids are among the most promising materials for broad thin film applications due to their facile surface functionalization. Yet, the effect of these colloids on chemical film and wetting properties cannot be easily evaluated. At the nanoscale, core–shell particles can deform and coalesce during thermal annealing, yielding fine‐tuned physical properties. Two different core–shell systems (soft and rigid) with identical shells but with chemically different core polymers and core sizes are investigated. The core–shell nanoparticles (NPs) are probed during thermal annealing in order to investigate their behavior as a function of nanostructure size and rigidity. X‐ray scattering allows to follow the re‐arrangement of the NPs and the structural evolution in situ during annealing. Evaluation by real‐space imaging techniques reveals a disappearance of the structural integrity and a loss of NP boundaries. The possibility to fine‐tune the wettability by tuning the core–shell NPs morphology in thin films provides a facile template methodology for repellent surfaces.     

Immunoregulation of Macrophages by Controlling Winding and Unwinding of Nanohelical Ligands

Developing materials with the capability of changing their innate features can help to unravel direct interactions between cells and ligand-displaying features. This study demonstrates the grafting of magnetic nanohelices displaying cell-adhesive Arg-Gly-Asp (RGD) ligand partly to a material surface. These enable nanoscale control of rapid winding (“W”) and unwinding (“UW”) of their nongrafted portion, such as directional changes in nanohelix unwinding (lower, middle, and upper directions) by changing the position of a permanent magnet while keeping the ligand-conjugated nanohelix surface area constant. The unwinding (“UW”) setting cytocompatibility facilitates direct integrin recruitment onto the ligand-conjugated nanohelix to mediate the development of paxillin adhesion assemblies of macrophages that stimulate M2 polarization using glass and silicon substrates for in vitro and in vivo settings, respectively, at a single cell level. Real time and in vivo imaging are demonstrated that nanohelices exhibit reversible unwinding, winding, and unwinding settings, which modulate time-resolved adhesion and polarization of macrophages. It is envisaged that this remote, reversible, and cytocompatible control can help to elucidate molecular-level cell–material interactions that modulate regenerative/anti-inflammatory immune responses to implants.     

Microtribology of Aqueous Carbon Nanotube Dispersions

The tribological behavior of carbon nanotubes (CNTs) in aqueous humic acid (HA) solutions was studied using a surface forces apparatus (SFA) and shows promising lubricant additive properties. Adding CNTs to the solution changes the friction forces between two mica surfaces from “adhesion controlled” to “load controlled” friction. The coefficient of friction with either single‐walled (SW) or multi‐walled (MW) CNT dispersions is in the range 0.30–0.55 and is independent of the load and sliding velocity. More importantly, lateral sliding promotes a redistribution or accumulation, rather than squeezing out, of nanotubes between the surfaces. This accumulation reduced the adhesion between the surfaces (which generally causes wear/damage of the surfaces), and no wear or damage was observed during continuous shearing experiments that lasted several hours even under high loads (pressures ～10 MPa). The frictional properties can be understood in terms of the Cobblestone Model where the friction force is related to the fraction of the adhesion energy dissipated during impacts of the nanoparticles. We also develop a simple generic model based on the van der Waals interactions between particles and surfaces to determine the relation between the dimensions of nanoparticles and their tribological properties when used as additives in oil‐ or water‐based lubricants.     

Dynamically Gas‐Phase Switchable Super(de)wetting States by Reversible Amphiphilic Functionalization: A Powerful Approach for Smart Fluid Gating Membranes

In nature, cellular membranes perform critical functions such as endocytosis and exocytosis through smart fluid gating processes mediated by nonspecific amphiphilic interactions. Despite considerable progress, artificial fluid gating membranes still rely on laborious stimuli‐responsive mechanisms and triggering systems. In this study, a room temperature gas‐phase approach is presented for dynamically switching a porous material from a superhydrophobic to a superhydrophilic wetting state and back. This is realized by the reversible attachment of bipolar amphiphiles, which promote surface wetting. Application of this reversible amphiphilic functionalization to an impermeable nanofibrous membrane induces a temporary state of superhydrophilicity resulting in its pressure‐less permeation. This mechanism allows for rapid smart fluid gating processes that can be triggered at room temperature by variations in the environment of the membrane. Owing to the universal adsorption of volatile amphiphiles on surfaces, this approach is applicable to a broad range of materials and geometries enabling facile fabrication of valve‐less flow systems, fluid‐erasable microfluidic arrays, and sophisticated microfluidic designs.     

Deformable,Programmable, and Shape‐Memorizing Micro‐Optics

The use of shape memory polymers is demonstrated for deformable, programmable, and shape‐memorizing micro‐optical devices. A semi‐crystalline shape memory elastomer, crosslinked poly(ethylene‐co‐vinyl acetate), is used to prepare various micro‐optic components, ranging from microlens and microprism arrays to diffraction gratings and holograms. The precise replication of surface features at the micro‐ and nanoscale and the formation of crosslinked shape memory polymer networks can be achieved in a single step via compression molding. Further deformation via hot pressing or stretching of micro‐optics formed in this manner allows manipulation of the microscopic surface features, and thus the corresponding optical properties. Due to the shape memory effect, the original surface structures and the optical properties can be recovered and the devices be reprogrammed, with excellent reversibility in the optical properties. Furthermore, arrays of transparent resistive microheaters can be integrated with deformed micro‐optical devices to selectively trigger the recovery of surface features in a spatially programmable manner, thereby providing additional capabilities in user‐definable optics.