Understanding the behavior of gas bubbles in aqueous media and realizing their spontaneous and directional manipulation are of vital importance in both scientific research and industrial applications, owing to their significant influences on many processes, such as waste water treatment, gas evolution reactions, and the recovery of valuable minerals. However, the behaviors of gas bubbles in aqueous media are mainly dominated by the buoyant force, which greatly impedes gas bubble transportation to any other direction except upward. Consequently, the spontaneous and directional transportation of gas bubbles in aqueous media is still identified as a big issue. Here, superhydrophobic copper cones have been successfully fabricated by integrating low-surface-tension chemical coatings with conical morphology. The generated superhydrophobic copper cones are capable of transporting gas bubbles from their tip to the base spontaneously and directionally underwater, even when they are vertically fixed with tips pointing up. The present study will inspire people to develop novel strategies to achieve efficient manipulation of gas bubbles in practical applications.

The separation of oil–water mixtures in highly acidic, alkaline, and salty environment remains a great challenge. Simple, low-cost, efficient, eco-friendly, and easily scale-up processes for the fabrication of novel materials to effective oil–water separation in highly acidic, alkaline, and salty environment, are urgently desired. Here, a facile approach is reported for the fabrication of stable hydrogel-coated filter paper which not only can separate oil–water mixture in highly acidic, alkaline, and salty environment, but also separate surfactant-stabilized emulsion. The hydrogel-coated filter paper is fabricated by smartly crosslinking filter paper with hydrophilic polyvinyl alcohol through a simple aldol condensation reaction with glutaraldehyde as a crosslinker. The resultant multiple crosslinked networks enable the hydrogel-coated filter paper to tolerate high acid, alkali, and salt up to 8 m H₂SO₄, 10 m NaOH, and saturated NaCl. It is shown that the hydrogel-coated filter paper can separate oil–water mixtures in highly acidic, alkaline, and salty environment and oil-in-water emulsion environment, with high separation efficiency (>99%).

Synthetic stimuli-gated nanodevices displaying intelligent ion transport properties similar to those observed in biological ion channels have attracted increasing interests for their wide potential applications in biosensors, nanofluidics, and energy conversions. Here, bioinspired asymmetric shaped nanodevices are reported that can exhibit symmetric and linear pH-gating ion transport features based on polyelectrolyte-asymmetric-functionalized asymmetric hourglass-shaped nanochannels. The pH-responsive polymer brushes grafted on the inner channel surface are acted as a gate that open and close in response to external pH changing to linearly and symmetrically regulate transmembrane ionic currents of the channel. A complete experimental characterization of the pH-dependent ion transport behaviors of the nanodevice and a comprehensive discussion of the experimental results in terms of theoretical simulation are also presented. Both experimental and theoretical data shown in this work demonstrate the feasibility of using the asymmetric chemical modification method to achieve symmetric pH gating behaviors inside the asymmetric nanochannels, and lay the foundation to build diverse stimuli-gated artificial asymmetric shaped ion channels with symmetric gating ion transport features.

Bio-inspired nanochannels have emerged as an interface to mimic the functionalities of biological nanochannels. One remaining challenge is to develop double-gated nanochannels with dual response, which can regulate the ion transport direction by alternately opening and closing the two gates. In this work, a bio-inspired potassium and pH responsive double-gated nanosystem is presented, constructed through immobilizing C-quadruplex and G-quadruplex DNA molecules onto the top and bottom tip side of a cigar-shaped nanochannel, respectively. It is demonstrated that the two gates of the nanochannel can be opened and closed alternately/simultaneously. This phenomenon results from the attached DNA conformational transition caused by adjusting the concentrations of potassium ion and proton. This design is believed to be the first example of dual-responsive double-gated nanosystem, and paves a new way to investigate more intelligent bio-inspired nanofluidic system.

Das Maßschneidern von Benetzbarkeit ist in den Oberflächenwissenschaften zwar wohlbekannt, aber dennoch ein hochinteressantes Thema, das bei der Lösung von größeren praktischen Problemen von enormem Interesse ist. In letzter Zeit wurden sowohl in der Natur als auch in Experimenten verschiedene superbenetzbare Systeme entdeckt. In diesem Aufsatz stellen wir drei Arten von Superbenetzbarkeit vor: dreidimensionale, zweidimensionale und eindimensionale Materialoberflächen. Durch das Kombinieren verschiedener Superbenetzbarkeiten lassen sich neue funktionale Grenzflächensysteme generieren und in Bauteile integrieren, die anschließend zur Lösung von aktuellen und zukünftigen Problemen im Zusammenhang mit Ressourcen, Energie, Umwelt und Gesundheit verwendet werden können.

Engineered wettability is a traditional, yet key issue in surface science and attracts tremendous interest in solving large-scale practical problems. Recently, different super-wettability systems have been discovered in both nature and experiments. In this Review we present three types of super-wettability, including the three-dimensional, two-dimensional, and one-dimensional material surfaces. By combining different super-wettabilities, novel interfacial functional systems could be generated and integrated into devices for use in tackling current and the future problems including resources, energy, environment, and health.

Engineering the wettability of solid materials is a traditional, yet key issue in surface science and attracts tremendous interest by researchers in diverse fields. Recently, different superwetting phenomena have been discovered in both nature and experimental results. Therefore, in this review, various superwetting states, leading to a “superwettability” system, are summarized and predicted. Fundamental rules for understanding superwettability are discussed, mainly taking superhydrophobicity in air as an example. Then, some recent application progress of individual members of this “superwettability” system are introduced. Notably, several novel application fields, mainly gas, water, oil and/or other liquid environments, are presented in the following section. By combining different members of this “superwettability” system, new interfacial functions can be generated, allowing unexpected applications, such as in environmental protection, energy, green industry, and many other important domains. Finally, the future development of this interesting “superwettability” system is discussed.

With the increasing world population and the rapid development of the global industry, clean water is becoming scarcer and scarcer. Means of translating latent water in fog to dominant available water, i.e., fog collection, therefore becomes highly desirable. Previously, it was demonstrated that the cactus O. Microdasys has an integrated fog collection system arising from the evenly distributed clusters of spines and trichomes on the cactus stem. Here, it is reported that the intersite of the clusters on the cactus stem is densely covered with cones, which are also capable of collecting water from fog efficiently. Inspired by these cones, using a simple method combining mechanical perforating and template replica technology, polydimethylsiloxane (PDMS) cone arrays are fabricated with different arrangements and the one in hexagonal arrangement proves to be more efficient due to the more turbulent flow filed around the staggered cones and the rapid directional movement of water drops along each cone. This investigation opens up new avenue to collect water efficiently and may also provide clues to research about dust filtering and smog removal, which is attracting increasing attention worldwide.

Controlling the position of metal sulfide architectures is prerequisite and facilitates their device applications in solar cells, light-emitting diodes, and many other optoelectronic fields. Thanks to ambient-connected gas network trapped upon superhydrophobic surfaces, H₂S gas can be continuously transported and reacted with metal ions along solid/liquid/gas triphase contact interface. Therefore, precisely positioning metal sulfide microstructure arrays are generated accordingly. The growth mechanisms as well as influencing factors are investigated to tailor the morphology, structure, and chemical composition of these metal sulfide materials. This interface-mediated strategy can be widely applied to many other metal sulfides, such as PbS, MnS, Ag₂S, and CuS. In particular, heterostructured metal sulfide architectures, such as PbS/CdS concentric microflower arrays, can be generated by stepwise replacement of metal ions inside liquid, exhibiting the advanced applications of this interface-mediated growth strategy.

Surfaces with anisotropic wettability, widely found in nature, have inspired the development of one-dimensional water control on surfaces relying on the well-arranged surface features. Controlling the wetting behavior of organic liquids, especially the motion of oil fluid on surfaces, is of great importance for a broad range of applications including oil transportation, oil-repellent coatings, and water/oil separation. However, anisotropic oil-wetting surfaces remain unexplored. Here, the unique skin of a filefish Navodon septentrionalis shows anisotropic oleophobicity under water. On the rough skin of N. septentrionalis, oil droplets tend to roll off in a head-to-tail direction, but pin in the opposite direction. This pronounced wetting anisotropy results from the oriented hook-like spines arrayed on the fish skin. It inspires further exploration of the artificial anisotropic underwater oleophobic surfaces: By mimicking the oriented hook-like microstructure on a polydimethylsiloxane layer via soft lithography and subsequent oxygen-plasma treatment to make the PDMS hydrophilic, artificial fish skin is fabricated which has similar anisotropic underwater oleophobicity. Drawn from the processing of artificial fish skin, a simple principle is proposed to achieve anisotropic underwater oleophobicity by adjusting the hydrophilicity of surface composition and the anisotropic microtextures. This principle can guide the simple mass manufacturing of various inexpensive high surface-energy materials, and the principle is demonstrated on commercial cloth corduroy. This study will profit broad applications involving low-energy, low-expense oil transportation, underwater oil collection, and oil-repellant coatings on ship hulls and oil pipelines.

Inspired by living systems that have the inherent skill to convert solar energy into bioelectric signals with their light-driven cross-membrane proton pump, a photoelectric conversion system that can work in alkaline conditions based on photoinduced reversible pH changes by malachite green carbinol base and a smart gating hydroxide ion-driven nanofluidic channel is demonstrated. In this system, solar energy can be considered as the only source of cross-membrane proton motive force that induces diffusion potential and photocurrent flowing through the external circuit. The conversion performances are 0.00825% and 36%, which are calculated from the photoelectric conversion and Gibbs free energy diffusion, respectively. The results suggest that electric power generation and performance could be further optimized by selecting appropriate photosensitized molecules and enhancing the surface-charge density as well as adopting the appropriate channel size. This facile, cost-efficient, and environmentally friendly photoelectric conversion system has potential applications for future energy demands such as production of power for in vivo medical devices.

Over millions of years, complex processes of intelligent control have evolved in nature. Learning from nature is a continuing theme in the development of smart materials and intelligent systems. For example, biological nanochannels, which are typically ion channels, play a very important role in basic biochemical processes in cells. Inspired by ion channels, in which the components are asymmetrically distributed between the membrane surfaces, the generation of biomimetic smart nanochannels is a broad and varied scientific research field. The design and development of new biomimetic channels includes the use of different shapes of channels, different stimuli-responsive molecules, and different symmetric/asymmetric modification methods. In this Minireview, we summarize recent developments in building functional nanochannels by applying various symmetric and asymmetric modifications.

Biological ion channels are able to control ion-transport processes precisely because of their intriguing properties, such as selectivity, rectification, and gating. Learning from nature, scientists have developed a promising system—solid-state single nanochannels—to mimic biological ion-transport properties. These nanochannels have many impressive properties, such as excess surface charge, making them selective; the ability to be produced or modified asymmetrically, endowing them with rectification; and chemical reactivity of the inner surface, imparting them with desired gating properties. Based on these unique characteristics, solid-state single nanochannels have been explored in various applications, such as sensing. In this context, we summarize recent developments of bioinspired solid-state single nanochannels with ion-transport properties that resemble their biological counterparts, including selectivity, rectification, and gating; their applications in sensing are also introduced briefly.

Die Natur hat über die Jahrmillionen komplexe Prozesse hervorgebracht, die über ausgeklügelte Kontrollmechanismen verfügen. Das Prinzip, von der Natur zu lernen, spielt bei der Entwicklung “intelligenter” Materialien und Systeme seit langem eine tragende Rolle. Biologische Nanokanäle, typischerweise Ionenkanäle, spielen zum Beispiel eine gewichtige Rolle bei den grundlegenden biochemischen Prozessen in der Zelle. Die Entwicklung biomimetischer Nanokanäle wurde durch Ionenkanäle angeregt, deren Komponenten unsymmetrisch über die Membran verteilt sind, und präsentiert sich gegenwärtig als ein vielseitiges Forschungsgebiet. Die Gestaltung neuer biomimetischer Kanäle umfasst den Einsatz von unterschiedlich geformten Kanälen, von Molekülen, die auf unterschiedliche Stimuli reagieren, und von unterschiedlichen Methoden zur symmetrischen oder unsymmetrischen Modifikation.

The construction and application of superoleophobic surfaces have aroused worldwide interest during the past few years. These surfaces are of great significance not only for fundamental research but also for various practical applications in self-cleaning, oil-repellent coatings, and antibioadhesion. The unique properties of polymers have made them one of the most important materials for constructing superoleophobic materials. This article reviews recent developments in the design, fabrication, and application of polymeric superoleophobic surfaces. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

The rapidly increasing research interest in nanodevices, including nanoelectronics, nano-optoelectronics, and sensing, requires the development of surface-patterning techniques to obtain large-scale arrays of nanounits (mostly nanocrystals and/or nanoparticles) on a silicon substrate. Herein, we demonstrate a “clinging-microdroplet” method to fabricate patterning crystal arrays based on the employment of high-adhesion, superhydrophobic, pillar-structured silicon substrates. Different from the previous hydrophilic/hydrophobic patterned self-assembly monolayer technique, this method provides a novel strategy to fabricate patterning crystal arrays upon pillar-structured silicon substrates of homogenous superhydrophobicity and high adhesion, which greatly simplifies the modification process of the supporting substrates. Ordered crystal arrays with a tunable size and distribution density were successfully generated, and individual crystals grew on the top of each micropillar. Besides soluble inorganic materials, protein microspheres and suspending Ag-nanoparticle or polystyrene-microsphere aggregations could also be patterned in regular arrays, showing the wide adaptation of such an adhesive patterning technique. This novel and low-cost technique for patterning crystal arrays upon silicon substrates could yield breakthroughs in areas ranging from nanodevices to nanoelectronics.

Surface wettability as a response to the cooperation of different stimuli has been intensively studied and provides more advantages than as a response to a single stimulus. Recently, we demonstrated the patterned wettability transition from the Cassie to the Wenzel state on a superhydrophobic aligned-ZnO-nanorod array surface via a photoelectric cooperative wetting process. However, the specific aligned-nanorod array structure of such devices is easily damaged due to their low mechanical strength and cannot sustain multiple transfer printing. Meanwhile, the patterned wetting process is not easily controlled due to the air-permeable structure of adjacent nanorods. As a result, in practice, it is difficult to apply liquid reprography on such a nanostructure. Here, we demonstrate photoelectric cooperative induced patterned wetting on the superhydrophobic aligned-nanopore array surface of TiO₂-coated nanoporous AAO film, which has a high mechanical strength and excellent controllability. Liquid reprography is achieved through the patterned wetting process on the superhydrophobic aligned-nanopore array surface, which is a new progression in liquid reprography, and is promising for gearing up the application of photoelectric cooperative liquid reprography.

Controlling liquid adhesion is a fundamental issue in many applications for special wettable surfaces. Compared to superhydrophobic surfaces of different water adhesion, superoleophobic surfaces of controllable oil adhesion are much more practical, as it leads to non-wetting for both water and oil. However, previously the investigation for oil adhesion ability on superoleophobic surfaces in oil/air/solid system has been extremely rare. In this work, we describe a convenient approach to fabricate superoleophobic surfaces through perfluorothiolate reaction on Cu(OH)₂ nanostructure surfaces and investigate their possible application in oil droplet transportation. The prepared surfaces exhibit controllable oil adhesive force depending on surface nanostructures or external preloads on the oil droplet. A model of the penetrating Cassie state is used to help analyze the unique phenomena on oil adhesion. Moreover, we provide a proof of demonstrate of oil transportation for application in oil-based microreactors via our surfaces. Our results give a useful attempt in understanding the fabrication principle of preparing superoleophobic surfaces with controllable oil adhesion.

Construction and application of surfaces with switchable liquid–solid adhesion have generated worldwide interest during the past a few years. These surfaces are of great importance not only for fundamental research but for various practical applications in smart and fluid-controllable devices. This Feature Article reviews several techniques that have been developed to switch the adhesion on liquid/solid interfaces, including tuning the surface chemical composition, tailoring the surface morphology, and applying external stimuli. Particular attention is paid to superhydrophobic surfaces with reversible switching between low- and high-adhesion to water droplets in response to external stimuli. The dynamic behavior of water droplets on such surfaces can be controlled ranging from rolling to pinning state, while maintaining superhydrophobic states. In addition, smart adhesion in oil/water/solid system and platelet/water/solid system are also discussed, which is of importants for application in designing novel anti-bioadhesion materials.

A dual-functional nanofluidic device is demonstrated that integrates the ionic gate and the ionic rectifier within one solid-state nanopore. The functionalities are realized by fabricating temperature- and pH-responsive poly(N-isopropyl acrylamide-co-acrylic acid) brushes onto the wall of a cone-shaped nanopore. At ca. 25 °C, the nanopore works on a low ion conducting state. When the temperature is raised to ca. 40 °C, the nanopore switches to a high ion conducting state. The closing/opening of the nanopore results from the temperature-triggered conformational transition of the attached copolymer brushes. Independently, in neutral and basic solutions, the conical nanopore rectifies the ionic current. While in acid solutions, no ion rectifying properties can be found. The charge properties of the copolymer brushes, combined with the asymmetrical pore geometry, render the nanopore a pH-tunable ionic rectifier. The chemical modification strategy could be applied to incorporate other stimuli-responsive materials for designing smart multi-functional nanofluidic systems resembling the “live” creatures in nature.

Superhydrophobic surfaces of dynamic stability are crucial for applications in water-repellent materials. In this work, a hierarchical structure composed of a dendritic microporous surface with nanostructured porosity is demonstrated that shows robust superhydrophobicity with dynamic stability. The hierarchical structures are obtained on both copper foils and wires by a dynamic gas-bubble template-assisted electrochemical deposition method. The substrates can then be modified with alkyl thiols to obtain the surface superhydrophobicity. A new kind of testing, mechanical monitor-assisted continuous water surface strokes, is developed to reveal the dynamic stability of the as-prepared superhydrophobic copper wires. The as-prepared superhydrophobic copper wires can exert a high propulsive force, and particularly, show little adhesive force in the process of continuous strokes on the water surface, exhibiting robust superhydrophobicity with dynamic stability. The approach allows a strategy for the fabrication of superhydrophobic surfaces with dynamic stability, and suggests a new method to evaluate the dynamic stability of superhydrophobic surfaces.

Inspired by the light-driven, cross-membrane proton pump of biological systems, a photoelectric conversion system based on a smart-gating, proton-driven nanochannel is constructed. In this system, solar energy is the only source of cross-membrane proton motive force that induces a diffusion potential and photocurrent flowing through the external circuit. Although the obtained photoelectric conversion performance is lower than that of conventional solid photovoltaic devices, it is believed that higher efficiencies can be generated by enhancing the protonation capacity of the photo-acid molecules, optimizing the membrane, and synthesizing high-performance photosensitive molecules. This type of facile and environmentally friendly photoelectric conversion has potential applications for future energy demands such as the production of power for in vivo medical devices.

Inspired by biological systems that have the inherent skill to generate considerable bioelectricity from the salt content in fluids with highly selective ion channels and pumps on cell membranes, herein, a fully abiotic single-pore nanofluidic energy-harvesting system that efficiently converts Gibbs free energy in the form of a salinity gradient into electricity is demonstrated. The maximum power output with the individual nanopore approaches ∼26 pW. By exploiting parallelization, the estimated power density can be enhanced by one to three orders over previous ion-exchange membranes. A theoretical description is proposed to explain the power generation with the salinity-gradient-driven nanofluidic system. Calculation results suggest that the electric-power generation and its efficiency can be further optimized by enhancing the surface-charge density (up to 100 mC m⁻²) and adopting the appropriate nanopore size (between 10 and 50 nm). This facile and cost-efficient energy-harvesting system has the potential to power biomedical tiny devices or construct future clean-energy recovery plants.

The robustness of superhydrophobicity is a fundamental issue for the applications of water-repellent materials. Inspired by the hierarchical structures of water-strider legs, this work describes a new water-repellent material decorated with ribbed, conical nanoneedles, successfully achieved on the surface of copper and consisting of copper hydroxide nanoneedle arrays sculptured with nanogrooves. The behavior of water drops on an as-prepared surface under various external disturbances is investigated. It is shown in particular that squeezing and relaxing drops between two such surfaces leads to a fully reversible exploration of the solid surface by the liquid, which is distinct from other superhydrophobic surfaces. This unique character is attributed to the penetrating Cassie state that occurs at the ribbed, conical nanoneedles. The proprietary lateral nanogrooves can, not only vigorously support the enwrapped liquid-air interface when a force is applied to the drop, but also provide reliable contact lines for the easy de-pinning of the deformed interface when the force is released from the drop. The results confirm the exceptional ability of strider legs to repel water, and should help to further the design of robust water-repellent materials and miniaturized aquatic devices.

Herein we demonstrate a fully abiotic smart single-nanopore device that rectifies ionic current in response to the temperature. The temperature-responsive nanopore ionic rectifier can be switched between a rectifying state below 34 °C and a non-rectifying state above 38 °C actuated by the phase transition of the poly(N-isopropylacrylamide) [PNIPAM] brushes. On the rectifying state, the rectifying efficiency can be enhanced by the dehydration of the attached PNIPAM brushes below the LCST. When the PNIPAM brushes have sufficiently collapsed, the nanopore switches to the non-rectifying state. The concept of the temperature-responsive current rectification in chemically-modified nanopores paves a new way for controlling the preferential direction of the ion transport in nanofluidics by modulating the temperature, which has the potential to build novel nanomachines with smart fluidic communication functions for future lab-on-chip devices.

In this Review, recent achievements in the multilevel interior-structured hollow 0D and 1D micro/nanomaterials are presented and categorized. The 0D multilevel interior-structured micro/nanomaterials are classified into four main interior structural categories that include a macroporous structure, a core-in-hollow-shell structure, a multishell structure, and a multichamber structure. Correspondingly, 1D tubular micro/nanomaterials are of four analogous structures, which are a segmented structure, a wire-in-tube structure, a multiwalled structure, and a multichannel structure. Because of the small sizes and complex interior structures, some special synthetic strategies that are different from routine hollowing methods, are proposed to produce these interior structures. Compared with the same-sized solid or common hollow counterparts, these fantastic multilevel hollow-structured micro/nanomaterials show a good wealth of outstanding properties that enable them broad applications in catalysis, sensors, Li-ion batteries, microreactors, biomedicines, and many others.

In this review a strategy for the design of bioinspired, smart, multiscale interfacial (BSMI) materials is presented and put into context with recent progress in the field of BSMI materials spanning natural to artificial to reversibly stimuli-sensitive interfaces. BSMI materials that respond to single/dual/multiple external stimuli, e.g., light, pH, electrical fields, and so on, can switch reversibly between two entirely opposite properties. This article utilizes hydrophobicity and hydrophilicity as an example to demonstrate the feasibility of the design strategy, which may also be extended to other properties, for example, conductor/insulator, p-type/n-type semiconductor, or ferromagnetism/anti-ferromagnetism, for the design of other BSMI materials in the future.

Inspired by the gecko's ability to reversibly stick and unstick to a variety of solid surfaces during locomotion, a new superhydrophobic iron surface that has a tunable adhesive force with the superparamagnetic microdroplet as a function of the magnetic field was fabricated by a simple and inexpensive method. The as-prepared surface is low adhesive, and a superparamagnetic microdroplet can roll easily on the surface. After the surface is magnetized, it becomes highly adhesive, which can pin a superparamagnetic microdroplet. Further demagnetizing the surface that has been magnetized, a superparamagnetic microdroplet can roll on the surface again, indicating that the surface returns to its initial low adhesive state. Reversible transition between the high adhesive pinning state and low adhesive rolling state can be achieved by simply magnetizing and demagnetizing the surface alternately. The tunable effect maybe attribute to the cooperation of the soft ferromagnetic property of iron plate and the microstructure on the surface. Such intelligent surface could potentially be used in a wide range of applications such as biochemical separation, no-loss transport of microdroplet, and in situ detection.