Ordered Honeycomb Structure Surface Generated by Breath Figures for Liquid Reprography

In this paper, photoelectric cooperative induced patterned wetting is demonstrated on a hydrophobic ordered polymeric honeycomb structure surface, which is prepared by BF method, then photosensitizing with a dye and hydrophobizing with low‐surface‐energy materials; finally, photoelectric cooperative induced patterned wetting is achieved on such a hydrophobic honeycomb structure surface. These results indicate that this work is promising for broadening the applications of photoelectric cooperative liquid reprography, which break the limitations of only using inorganic materials and super‐hydrophobic materials. It should be of great scientific interest to extend the relevant research from inorganic nanorod, nanopore, and nanotube structures to polymeric honeycomb structures, because polymeric materials can overcome the inherent drawbacks of the inorganic materials owing to their advantages of low specific weight, flexibility, tunable material properties, and wide variety.     

Piezoelectric Nylon‐11 Nanowire Arrays Grown by Template Wetting for Vibrational Energy Harvesting Applications

Piezoelectric polymers, capable of converting mechanical vibrations into electrical energy, are attractive for use in vibrational energy harvesting due to their flexibility, robustness, ease, and low cost of fabrication. In particular, piezoelectric polymers nanostructures have been found to exhibit higher crystallinity, higher piezoelectric coefficients, and “self‐poling,” as compared to films or bulk. The research in this area has been mainly dominated by polyvinylidene fluoride and its copolymers, which while promising have a limited temperature range of operation due to their low Curie and/or melting temperatures. Here, the authors report the fabrication and properties of vertically aligned and “self‐poled” piezoelectric Nylon‐11 nanowires with a melting temperature of ≈200 °C, grown by a facile and scalable capillary wetting technique. It is shown that a simple nanogenerator comprising as‐grown Nylon‐11 nanowires, embedded in an anodized aluminium oxide (AAO) template, can produce an open‐circuit voltage of 1 V and short‐circuit current of 100 nA, when subjected to small‐amplitude, low‐frequency vibrations. Importantly, the resulting nanogenerator is shown to exhibit excellent fatigue performance and high temperature stability. The work thus offers the possibility of exploiting a previously unexplored low‐cost piezoelectric polymer for nanowire‐based energy harvesting, particularly at temperatures well above room temperature.     

Microstructured Nematic Liquid Crystalline Elastomer Surfaces with Switchable Wetting Properties

Inspired by the lotus leaf, scientists have developed many superhydrophobic surfaces, some of which show remarkable switching between hydrophobic and hydrophilic state under external stimuli. However, the switch usually relies on the change of chemical properties rather than on the modification of the topographic structure of the surface. In this paper, the roughness‐change‐related switchable wetting properties of microstructured responsive surfaces made of nematic liquid crystalline elastomers (LCEs) is reported. First, various carbonate LC monomers and side‐on LCEs are synthesized with low nematic‐to‐isotropic transition temperature, T_NI. Then, LCEs prepared from 3″‐vinylcarbonyloxypropyl 2,5‐di(4′‐octyloxybenzoyloxy)benzoate monomer, with T_NI of 76 °C and contraction of 34% are used to construct a surface covered with micropillar arrays by using a replica molding technique. The contraction of the micropillars induces a reversible roughness change of the microstructured surface. Water contact angle of this microstructured surface changed with temperature, indicating a successful approach at building a surface with switchable wetting properties.     

DNA Sensing Using Nanocrystalline Surface‐Enhanced Al2O3 Nanopore Sensors

A new solid‐state, Al₂O₃ nanopore sensor with enhanced surface properties for the real‐time detection and analysis of individual DNA molecules is reported. Nanopore formation using electron‐beam‐based decomposition transforms the local nanostructure and morphology of the pore from an amorphous, stoichiometric structure (O to Al ratio of 1.5) to a heterophase crystalline network, deficient in O (O to Al ratio of ≈0.6). Direct metallization of the pore region is observed during irradiation, thereby permitting the potential fabrication of nanoscale metallic contacts in the pore region with application to nanopore‐based DNA sequencing. Dose‐dependent phase transformations to purely γ and/or α‐phase nanocrystallites are also observed during pore formation, allowing for surface‐charge engineering at the nanopore/fluid interface. DNA transport studies reveal an order‐of‐magnitude reduction in translocation velocities relative to alternate solid‐state architectures, accredited to high surface‐charge density and the nucleation of charged nanocrystalline domains. The unique surface properties of Al₂O₃ nanopore sensors make them ideal for the detection and analysis of single‐stranded DNA, double‐stranded DNA, RNA secondary structures, and small proteins. These nanoscale sensors may also serve as useful tools in studying the mechanisms driving biological processes including DNA–protein interactions and enzyme activity at the single‐molecule level.     

Smart Anisotropic Wetting Surfaces with Reversed pH‐Responsive Wetting Directions

Smart pH‐responsive surfaces that could autonomously induce unidirectional wetting of acid and base with reversed directions are fabricated. The smart surfaces, consisting of chemistry‐asymmetric “Janus” silicon cylinder arrays (Si‐CAs), are prepared by precise modification of functional groups on each cylinder unit. Herein, amino and carboxyl groups are chosen as typical pH‐responsive groups, owing to their protonation/deprotonation effect in response to pH of the contacted aqueous solution. One side of the Si‐CAs is modified by poly(2‐(dimethylamino)ethyl methacrylate), while the other side is modified by mixed self‐assembled monolayers of 1‐dodecanethiol and 11‐mercaptoundecanoic acid. On such surfaces, it is observed that acid and base wet in a unidirectional manner toward corresponding directions that are modified by amino or carboxyl groups, which is caused by asynchronous change of wetting property on two sides of the asymmetric structures. The as‐prepared Janus surfaces could regulate the wetting behavior of acid and base and could direct unidirectional wetting of water with reversed directions when the surfaces are treated by strong acid or base. Due to the excellent response capability, the smart surfaces are potential candidates to be applied in sensors, microfluidics, oil/water separation, and smart interfacial design.     

Simultaneous Detection and Repair of Wetting Defects in Superhydrophobic Coatings via Cassie–Wenzel Transitions of Liquid Marbles

Superhydrophobic materials that prevent unwanted liquid adhesion can easily lose this property because of limited mechanical durability despite topological/chemical control and/or robust material selection. Here, long‐lasting superhydrophobic coatings with a system to effectively detect and repair damaged areas with “liquid marble,” a droplet covered with hydrophobic nanoparticles, are reported. The particles prevent direct contact between the droplet and the substrate (Cassie state). However, they can adhere to the non‐superhydrophobic damaged area in response to the substrate wettability via an external force or an increase in liquid volume via penetration of the outer nanoparticle layer (Wenzel state). This Cassie–Wenzel transition thus induces self‐assembly of the nanoparticles onto the non‐superhydrophobic area in response to the wettability, restoring superhydrophobicity.     

Electric‐Field‐Controlled Alignment of Rod‐Shaped Fluorescent Nanocrystals in Smectic Liquid Crystal Defect Arrays

Periodic micro‐arrays of straight linear defects containing nanoparticles can be created over large surface areas at the transition from the nematic to smectic‐A phase in a nanoparticle–liquid crystal (LC) composite material confined under the effect of conflicting anchoring conditions (unidirectional planar vs normal) and electric fields. Anisomeric dichroic dye molecules and rod‐shaped fluorescent semiconductor nanocrystals (dot‐in‐rods) with large permanent electric dipole and high linearly polarized photoluminescence quantum yield align parallel to the local LC molecular director and follow its reorientation under application of the electric field. In the nano‐sized core regions of linear defects, where the director is undefined, anisotropic particles align parallel to the defect whereas spherical quantum dots do not show any particular interaction with the defect. Under application of an electric field, ferroelectric semiconductor nanoparticles in the core region align along the field, perpendicular to the defect direction, whereas dichroic dyes remain parallel to the defect. This study provides useful insights into the complex interaction of anisotropic nanoparticles and anisotropic soft materials such as LCs in the presence of external fields, which may help the development of field‐responsive nanoparticle‐based functional materials.     

Photoresponsive Sponge‐Like Coating for On‐Demand Liquid Release

Many publications report on stimuli responsive coatings, but only a few on the controlled release of species in order to change the coating surface properties. A sponge‐like coating that is able to release and absorb a liquid upon exposure to light has been developed. The morphology of the porous coating is controlled by the smectic liquid crystal properties of the monomer mixture prior to its polymerization, and homeotropic order is found to give the largest contraction. The fast release of the liquid can be induced by a macroscopic contraction of the coating caused by a trans to cis conversion of a copolymerized azobenzene moiety. The liquid secretion can be localized by local light exposure or by creating a surface relief. The uptake of liquid proceeds by stimulating the back reaction of the azo compound by exposure at higher wavelength or by thermal relaxation. The surface forces of the sponge‐like coating in contact with an opposing surface can be controlled by light‐induced capillary bridging revealing that the controlled release of liquid gives access to tunable adhesion.     

用于液滴分析的光电液滴传感器的设计研究

介绍一种用于液体特性研究的光电液滴传感器(PLDS),其原理是基于插入液滴内部的光纤,及由滴头和环形极板构成的电容传感器。传感器中集成了二极管及部分处理电路,并对滴头及相关零件作了特殊的机械结构设计,从而能够有效地解决光信号强度损失严重、输出信号易受干扰、光纤位置不稳定、气泡影响液滴形状和滴头部件难以清洗等问题。同时,传感器中通过两路输入光纤引入了不同波长的光信号,通过可拆卸的环形极板便于进行CCD图像液滴分析。     

Automated,Ultra‐Fast Laser‐Drilling of Nanometer Scale Pores and Nanopore Arrays in Aqueous Solutions

The ability to quickly and reliably fabricate nanoscale pore arrays in ultra‐thin membranes such as silicon nitride (Si_xN) is extremely important for the growing field of nanopore biosensing. Laser‐based etching of thin Si_xN membranes immersed in aqueous solutions has recently been demonstrated as a method to produce stable functional pores. Herein, the principal mechanism governing material etching and pore formation using light is investigated. It is found that the process is extremely sensitive to the relative content of Si over N atoms in the amorphous membrane, produced by chemical vapor deposition. Commonly, Si_xN membranes are made to be Si‐rich to increase their mechanical stability, which substantially reduces the material's bandgap and increases the density of Si‐dangling bonds. Hence, even minimal batch‐to‐batch variation may lead to remarkably different etch rates. It is shown that higher Si content results in orders of magnitude faster etching rates. This rate is further accelerated in an alkaline environment allowing on‐demand controlled nanopore formation in about 10 s time even at low laser radiation intensities. These results highlight that photoactivation of the Si_xN by the incident beam is critical to the chemical etching process and can be used to readily produce nanopore arrays at any specific location.     

Organic/Inorganic Hybrid Nanochannels Based on Polypyrrole‐Embedded Alumina Nanopore Arrays: pH‐ and Light‐Modulated Ion Transport

Inspired by the asymmetric structure and responsive ion transport in biological ion channels, organic/inorganic hybrid artificial nanochannels exhibiting pH‐modulated ion rectification and light‐regulated ion flux have been constructed by introducing conductive polymer into porous nanochannels. The hybrid nanochannels are achieved by partially modifying alumina (Al₂O₃) nanopore arrays with polypyrrole (PPy) layer using electrochemical polymerization, which results in an asymmetric component distribution. The protonation and deprotonation of Al₂O₃ and PPy upon pH variation break the surface charge continuity, which contributes to the pH‐tunable ion rectification. The ionic current rectification ratio is affected substantially by the pH value of electrolyte and the pore size of nanochannels. Furthermore, the holes (positive charges) in PPy layer induced by the cooperative effect of light and protons are used to regulate the ionic flux through the nanochannels, which results in a light‐responsive ion current. The magnitude of responsive ionic current could be amplified by optimizing this cooperation. This new type of stimuli‐responsive PPy/Al₂O₃ hybrid nanochannels features advantages of unique optical and electric properties from conducting PPy and high mechanical performance from porous Al₂O₃ membrane, which provide a platform for creating smart nanochannels system.     

Stretchable‐Fiber‐Confined Wetting Conductive Liquids as Wearable Human Health Monitors

Wetting behaviors on stretchable supports are very common in our daily lives, however, received limited attention even they show promising potentials in flexible electronics and other fields. In this study, stretchable wetting behaviors of conductive liquids deposited onto two horizontal rubber fibers are investigated. A firm liquid/solid interaction during the stretching process can contribute to a stable liquid bridge between the fibers even under extremely stretching, showing their proof‐to‐principle ability to monitor human movement toward early diagnosis of Parkinson's disease or sports injury prevention.     

Polyhedral Liquid Marbles

A new type of armored droplet, a so‐called polyhedral liquid marble, is introduced in this work. These armored liquid marbles consist of liquid droplets stabilized by hydrophobic hexagonal plates made of poly(ethylene terephthalate), which adsorb to the liquid–air interface. Depending on the specific combination of plate size and droplet diameter, the plates self‐assemble into highly ordered hexagonally arranged domains. Even tetrahedral‐, pentahedral‐, and cube‐shaped liquid marbles composed of only 4 to 6 plates are demonstrated. During evaporation of the internal liquid, due to the high adsorption energy of the plates at the liquid–air interface, the overall surface area stays constant, resulting in strongly deformed polyhedral liquid marbles. In line with this, highly asymmetric polyhedral liquid marbles and letters are obtained due to the strong interfacial jamming exerted by the rigid hexagonal plates. This is particularly pronounced for larger plate sizes, leading to liquid marbles with unusually sharp edges (for example, rectangular edges). The polyhedral liquid marbles exhibit various stimuli‐responsive behaviors simultaneously being exposed to water, ammonia, or tetrahydrofuran vapors. Air‐driven polyhedral liquid marbles floating on water can reach velocities of several centimeters per second.     

Engineering Sensor Arrays Using Aggregation‐Induced Emission Luminogens for Pathogen Identification

Lacking rapid and reliable pathogen diagnostic platforms, inadequate or delayed antimicrobial therapy could be made, which greatly threatens human life and accelerates the emergence of antibiotic‐resistant pathogens. In this contribution, a series of simple and reliable sensor arrays based on tetraphenylethylene (TPE) derivatives are successfully developed for detection and discrimination of pathogens. Each sensor array consists of three TPE‐based aggregation‐induced emission luminogens (AIEgens) that bear cationic ammonium group and different hydrophobic substitutions, providing tunable logP (n‐octanol/water partition coefficient) values to enable the different multivalent interactions with pathogens. On the basis of the distinctive fluorescence response produced by the diverse interaction of AIEgens with pathogens, these sensor arrays can identify different kinds of pathogens, even normal and drug‐resistant bacteria, with nearly 100% accuracy. Furthermore, blends of pathogens can also be identified accurately. The sensor arrays exhibit rapid response (about 0.5 h), high‐throughput, and easy‐to‐operate without washing steps.     

Anti‐liquid‐Interfering and Bacterially Antiadhesive Strategy for Highly Stretchable and Ultrasensitive Strain Sensors Based on Cassie‐Baxter Wetting State

As a large number of strain sensors are put into practical use, their stability should be considered, especially in harsh environments containing water or microorganisms, which could affect strain sensing. Herein, a novel strategy to overcome liquid interference is proposed. The strain sensor is constructed with a sandwich architecture through layer‐by‐layer (LBL) spray‐coating of a 3‐(aminopropyl)triethoxysilane (APTES) bonding layer and multi‐walled carbon nanotubes/graphene (MWCNT/G) conductive layers on an elastomeric polydimethysiloxane (PDMS) substrate, and is further decorated with silver (Ag) nanoparticles and the (heptadecafluoro‐1,1,2,2‐tetradecyl) trimethoxysilane (FAS, F in short) to obtain a F/Ag/MWCNG/G‐PDMS (FAMG) strain sensor. The superhydrophobicity and underwater oleophobicity of the outer cover layer causes this FAMG strain sensor surface to exhibit stable strain sensing resistant to liquid interference upon stretching in the Cassie?Baxter wetting state, and resistance to bacterial adhesion (Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli)). The sensor attains ultrasensitivity (with a maximum gauge factor of 1989 in the condition of liquid interference), broad strain range (0.1–170%), fast response time (150 ms), and stable response after 1000 stretching–releasing cycles. The ultrasensitivity is provided by propagation of cracks in MWCNT/G conductive layers and terminal fracture of the intermediate separating layers (APTES/MWCNT/G). The microbridge effect of MWCNTs and slippage of APTES/MWCNT/G provide a large strain range. The FAMG strain sensor is successfully used to monitor a series of human activities and an electronic bird under artificial rain and bacterial droplets, indicating the potential use of this sensor in complex environments.     

Oil‐Impregnated Nanoporous Oxide Layer for Corrosion Protection with Self‐Healing

The major drawback of current passivation techniques for preventing corrosion is the lack of ability to withstand any external damages or local defects. In this study, oil‐impregnated nanoporous anodic aluminum oxide (AAO) layers are investigated to overcome such limitations and thus advance corrosion protection. By completely filling hydrophobized nanopores with oil via a solvent exchange method, a highly water‐repellent surface that prevents the penetration of corrosive media into the AAO layer and hence the corrosion of aluminum is achieved. The impregnation of oil into the hydrophobic nanoporous AAO layer enhances the corrosion resistance of an AAO layer by two and four orders of magnitude compared to that of a hydrophobic (i.e., air‐entrained) and a bare (hydrophilic) AAO, respectively. In the presence of local defects, the oil impregnated within the hydrophobic nanoporous AAO layer naturally permeates into the defects and ultimately inhibits the exposure of the aluminum surface to corrosive media. Whereas the corrosion current density of the air‐entrained hydrophobic AAO layer increases by more than 30 times after cracks, that of the oil‐impregnated AAO layer increases by no more than 4 times, showing superior anticorrosion property even after there are cracks, owing to the effective self‐healing capability.