Elaborately Aligning Bead‐Shaped Nanowire Arrays Generated by a Superhydrophobic Micropillar Guiding Strategy

Bead‐shaped 1D structures are of great interest due to their unique applications in mesoscopic optics/electronics and their specific ability to collect tiny droplets. Here, a novel method to fabricate aligning bead‐shaped nanowire arrays assisted by highly adhesive superhydrophobic surfaces based on a micropillar guiding strategy is presented. Different from previous fabrication techniques, bead‐shaped nanowires generated in this method are strictly oriented in a large scale. Rayleigh instability, which occurs at ultralow polymer concentration, can introduce bead‐shaped nanowires at the cost of structural strength. Thus, PS spheres are more suitable to serve as bead building blocks to generate firm bead‐shaped nanowire arrays. The bead number is tunable by tailoring the polystyrene‐sphere/polyvinyl‐formal ratio. Furthermore, as‐prepared bead‐shaped nanowires have the unique ability to directionally drive tiny drops and collect coalesced microdroplets when placed in mist. With an increase in humidity, the nanowires show a segmented swelling behavior in the “bead” parts whereas the “joint nanowire” parts remain the same. Because such bead‐shaped nanowires are formed regularly, collected microdroplets upon the beads would not interact with each other. The findings offer new insight into the alignment of bead‐shaped nanostructures and might provide promising opportunities in fundamental research and for industrial applications.     

Silver‐Nanoparticle‐Colored Cotton Fabrics with Tunable Colors and Durable Antibacterial and Self‐Healing Superhydrophobic Properties

Colored cotton fabrics with satisfactory color fastness as well as durable antibacterial and self‐healing superhydrophobic properties are fabricated via a convenient solution‐dipping method that involves the sequential deposition of branched poly(ethylenimine) (PEI), silver nanoparticles (AgNPs), and fluorinated decyl polyhedral oligomeric silsesquioxane (F‐POSS) on cotton fabrics. The deposited AgNPs with tunable surface plasmon resonance endow the cotton fabrics with abundant color and and antibacterial ability. However, in general, water‐soluble AgNPs cannot be firmly deposited onto cotton fabrics to endure the laundering process. The integration of self‐healing superhydrophobicity into the cotton fabrics by depositing F‐POSS/AgNP/PEI films significantly enhances the color fastness of the AgNPs against laundry and mechanical abrasion, while retaining the antibacterial property of the AgNPs. The F‐POSS/AgNP/PEI‐coated cotton fabric accommodates an abundance of F‐POSS, which autonomically migrates to the cotton surface to repetitively restore its damaged superhydrophobicity. The self‐healing superhydrophobicity of the F‐POSS/AgNPs/PEI‐coated cotton fabric guarantees long‐term protection of the underlying AgNPs against laundry and abrasion and allows the cotton fabric to be cleaned by simple rinsing with water.     

Electrophoretically‐Deposited Metal‐Decorated CNT Nanoforests with High Thermal/Electric Conductivity and Wettability Tunable from Hydrophilic to Superhydrophobic

A single‐step, room‐temperature, and scalable electrophoretic deposition process is reported to form nanocomposites on any electrically conductive surface with metal nanoparticle decorated carbon nanotubes (CNTs). The contact angles (CAs) can be easily tuned from ≈60° to 168° by varying the deposition voltage, while hydrophobicity and superhydrophobicity surprisingly arise from the hydrophilic CNTs being deposited. The relatively high voltage tends to vertically align CNTs during deposition, leading to architectural micro/nanoscale roughness on the surface. The combination of the multiscale roughness along with the low surface energy of hydrocarbon functional groups on the CNT surface has enabled facile wettability control, including the Petal and Lotus effects. Further, the relatively vertical orientation of the CNTs, without any coating, allows for current and heat transfer along their axis with superior conductivity. Similar behavior in terms of CA control is seen for all three divalent metal ions in the deposition solution (i.e., Cu²⁺, Ni²⁺, and Zn²⁺) that are used to charge the CNTs while eventually getting co‐deposited. This implies that this method could possibly be extended to other metals by selecting appropriate charging salt. A patterning technique is also demonstrated for facile fabrication of superhydrophobic CNT‐metal islands surrounded by hydrophilic CNT coating.     

Tunable Superhydrophobicity from 3D Hierarchically Nano-Wrinkled Micro-Pyramidal Architectures

Interfacial surfaces with hierarchical structures have triggered intense research interest and been used in a broad range of applications ranging from anti-icing, anti-fogging, surface-enhanced Raman spectroscopy to catalytic reaction. However, the high-cost manufacturing processes and the limited durability remain as great challenges that need to be addressed, especially for superhydrophobicity. In this work, a novel hybrid approach for stretchable, transparent, and robust superhydrophobic surfaces is proposed, constructing micro-pyramid architectures with tunable hierarchical wrinkles efficiently and in an environmentally friendly manner. Due to the multiscale structures, excellent superhydrophobicity is obtained with contact angle of ≈172° and sliding angle ≈5° in a steady “Lotus” state. Further, the wear resistance and stability tests also suggest a superior performance under simulated severe real-world applications. Utilizing such multiscale synergistic co-operation effects can be an excellent manufacturing strategy and be extended to other surface engineering where hierarchical architectures are needed.     

Bioinspired,Stimuli‐Responsive,Multifunctional Superhydrophobic Surface with Directional Wetting,Adhesion, and Transport of Water

A novel smart stimuli responsive surface can be fabricated by the subsequent self‐assembly of the graphene monolayer and the TiO₂ nanofilm on various substrates, that is, fabrics, Si wafers, and polymer thin films. Multiscale application property can be achieved from the interfacial interaction between the hierarchical graphene/TiO₂ surface structure and the underlying substrate. The smart surface possesses superhydrophobic property as a result of its hierarchical micro‐ to nanoscale structural roughness. Upon manipulating the UV induced hydrophilic conversion of TiO₂ on graphene/TiO₂ surface, smart surface features, such as tunable adhesiveness, wettability, and directional water transport, can be easily obtained. The existence of graphene indeed enhances the electron–hole pair separation efficiency of the photo‐active TiO₂, as the time required for the TiO₂ superhydrophilic conversion is largely reduced. Multifunctional characteristics, such as gas sensing, droplet manipulation, and self‐cleaning, are achieved on the smart surface as a result of its robust superhydrophobicity, tunable wettability, and high photo‐catalytic activity. It is also revealed that the superhydrophilic conversion of TiO₂ is possibly caused by the atomic rearrangement of TiO₂ under UV radiation, as a structural transformation from {101} to {001} is observed after the UV treatment.     

Standing‐Wave‐Assisted Creation of Nanopillar Arrays with Vertically Integrated Nanogaps for SERS‐Active Substrates

An optical method is used to create multi‐dimensional metal structures with three distinct periodicities for surface‐enhanced Raman scattering (SERS). Periodic arrays of nanopillars are formed by phase‐shift interference lithography on sub‐micrometer length scales. With the help of a standing wave, each nanopillar is made to be a disk‐stacking structure consisting of a series of 20‐nm‐thick metal nanogaps; the nanopillars consequently resemble a pagoda. The vertically integrated metal nanogaps of the metal‐deposited pagoda‐like nanopillars enable strong localization of an electromagnetic field and effective enhancement of Raman signals for molecules adsorbed on the metal surface. Moreover, the nanopillars are arranged in a regular lattice, which results in a low spatial variation of the SERS intensity and provides high reproducibility in measurements. Arrays of the nanopillars can be further micropatterned to have a periodicity ranging from tens of micrometers to a millimeter by subsequently employing photo‐lithography. The nanopillar arrays promote the wetting of sample fluids, which enables the selective confinement of fluids on the array regions of the micropatterns without spreading. Consequently, numerous fluid samples can be separately deposited, enabling SERS‐based analysis of multiple samples using a single substrate.     

Regular Metal Sulfide Microstructure Arrays Contributed by Ambient‐Connected Gas Matrix Trapped on Superhydrophobic Surface

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.     

Tunable Anisotropic Wettability of Rice Leaf‐Like Wavy Surfaces

Rice leaves can directionally shed water droplets along the longitudinal direction of the leaf. Inspired by the hierarchical structures of rice leaf surfaces, synthetic rice leaf‐like wavy surfaces are fabricated that display a tunable anisotropic wettability by using electrostatic layer‐by‐layer assembly on anisotropic microwrinkled substrates. The nanoscale roughness of the rice leaf‐like surfaces is controlled to yield tunable anisotropic wettability and hydrophobic properties that transitioned between the anisotropic/pinned, anisotropic/rollable, and isotropic/rollable water droplet behavior states. These remarkable changes result from discontinuities in the three‐phase (solid–liquid–gas) contact line due to the presence of air trapped beneath the liquid, which is controlled by the surface roughness of the hierarchical nanostructures. The mechanism underlying the directional water‐rolling properties of the rice leaf‐like surfaces provides insight into the development of a range of innovative applications that require control over directional flow.     

A Versatile Approach towards Multifunctional Robust Microcapsules with Tunable,Restorable, and Solvent‐Proof Superhydrophobicity for Self‐Healing and Self‐Cleaning Coatings

Numerous microencapsulation techniques have been developed to encase various chemicals, for which specific processing parameters are required to address the widely differing features of the encapsulated materials. Microencapsulation of reactive agents is a powerful technique that has been extensively applied to self‐healing materials. However, the poor solvent compatibility and insufficient thermal stability of microcapsules continue to pose challenges for long‐term storage, processing, and service in practical applications. Here, an easily modifiable and highly versatile method is reported for preparing various chemicals filled poly(urea‐formaldehyde) microcapsules that exhibit superior tightness against solvents and heat and that possess widely tunable, repetitiously self‐restorable, and solvent‐proof superhydrophobicity. In addition, the low‐cost fabrication of biomimetic multifunctional smart coatings is demonstrated for self‐healing anticorrosion and self‐cleaning antifouling applications by directly dispersing the superhydrophobic microcapsules into and onto a polymer matrix. The methodology presented in this study should inspire the development of multifunctional intelligent materials for applications in related fields.     

Fabrication of a Superhydrophobic Surface from a Smectic Liquid‐Crystal Defect Array

A novel fabrication method is developed for the preparation of superhydrophobic surfaces. The procedure uses focal conic structures of semi‐fluorinated smectic liquid crystals (LCs) whose periodic toric focal conic domains (TFCDs) are prepared on a surface modified substrate. Reactive ion etching (RIE) on the periodic TFCD surface leads to a superhydrophobic surface with a water contact angle of ～160° and a sliding angle of ～2° for a 10 µL water droplet. The results show that this phenomenon is due to the development of a dual‐scale surface roughness arising from the nanoscale protuberance caused by applying the RIE process to the top of the microscale TFCD arrays. The unique surface behavior is further verified by demonstrating that RIE on a flat lamellar liquid crystal film, in which the director is aligned parallel with surface, results in a relatively low hydrophobicity as compared to when periodic TFCDs are subjected to REI. The observations made in this publication suggest that a new approach exists for selecting potential candidates of superhydrophic surface formation based on spontaneous self‐assembly in smectic liquid‐crystalline materials.     

Superhydrophobic Shape Memory Polymer Arrays with Switchable Isotropic/Anisotropic Wetting

Smart surfaces with tunable wettability have aroused much attention in the past few years. However, to obtain a surface that can reversibly transit between the lotus‐leaf‐like superhydrophobic isotropic and rice‐leaf‐like superhydrophobic anisotropic wettings is still a challenge. This paper, by mimicking microstructures on both lotus and rice leaves, reports such a surface that is prepared by creating micro/nanostructured arrays on the shape memory polymer. On the surface, the microstructure shapes can be reversibly changed between the lotus‐leaf‐like random state and the rice‐leaf‐like 1D ordered state. Accordingly, repeated switch between the superhydrophobic isotropic and anisotropic wettings can be displayed. Research results indicate that the smart controllability is ascribed to the excellent shape memory effect of the polymer, which endows the surface with special ability in memorizing different microstructure shapes and wetting properties. Meanwhile, based on the smart wetting performances, the surface is further used as a rewritable functional platform, on which various droplet transportation programmes are designed and demonstrated. This work reports a superhydrophobic surface with switchable isotropic/anisotropic wettings, which not only provides a novel functional material but also opens a new avenue for application in controlled droplet transportation.     

Fabrication of Ordered Nanostructured Arrays Using Poly(dimethylsiloxane) Replica Molds Based on Three‐Dimensional Colloidal Crystals

Hexagonally arrayed structures of colloidal crystals with uniform surface are a good candidate for master molds to be used in soft lithography. Here, the fabrication of periodically arrayed nanostructures using poly(dimethylsiloxane) (PDMS) molds based on three‐dimensionally (3D) ordered colloidal crystals is reported. A robust, high‐quality 3D colloidal‐crystal master molds is prepared using the colloidal suspension containing a water‐soluble polymer. The surface patterns of the 3D colloidal crystals can then be transferred onto a polymer film via soft lithography, by means of the replication of the surface pattern with PDMS. Various hexagonally arrayed nanostructure patterns can be fabricated, including close‐packed and non‐close‐packed 2D arrays and honeycomb structures by the structural modification of the 3D colloidal‐crystal templates. The replicated hexagonally arrayed structures can also be used as templates for producing colloidal crystals with 2D superlattices.     

Large‐Scale Nano Piezo Force Position Arrays as Ultrahigh‐Resolution Micro‐ and Nanoparticle Tracker

Defining the position of an object on a planar substrate by force sensors is a common technology nowadays. Many products are commercialized worldwide, which make use of force sensors, especially, for instance, touchpads. Here advanced lithography processes together with piezoelectric materials are demonstrated to fabricate an extremely high resolution force sensor. The approach combines a large array of nanoscale piezoelectric lines fabricated on Si wafer by phase‐shift lithography and atomic‐layer‐deposition‐based spacer lithography techniques. These key lithography methods are utilized to fabricate ultralong (cm range) nanolines on the wafer scale. ZnO and P(VDF‐TrFE) are selected here as materials for piezoelectric signal generators. The detection mechanisms are explained and simulations combined with experimental data are demonstrated to prove the concept. The signal generated when an object approaches one single line is in the nanoampere range. The result enables a new and simple path for a device fabrication, which defines the position with micro‐ and nanometer resolution and can be used, for example, as micro‐ and nanoparticle trackers.     

Hierarchical Superhydrophobic Surfaces Fabricated by Dual‐Scale Electron‐Beam‐Lithography with Well‐Ordered Secondary Nanostructures

Recent studies on superhydrophobic surfaces have revealed the important roles of structural hierarchy in the overall properties of these surfaces. Here, a novel, versatile, and efficient technique is introduced for fabricating macroscopic hierarchical superhydrophobic surfaces with both well‐defined primary microstructures and well‐ordered secondary nanostructures using electron‐beam lithography. With this technique, the engineering capability of controlling the size, shape, and distribution of the secondary‐features is demonstrated, which allows a systematic and quantitative study of the individual effects of these parameters. Superhydrophobic surfaces produced by this new technique exhibit two distinctive wetting behaviors, high and low adhesion. The structural characteristics and structure‐property relations of each of those two regimes are discussed.     

A Hierarchically Structured Ni(OH)2 Monolayer Hollow‐Sphere Array and Its Tunable Optical Properties over a Large Region

The fabrication of a hierarchically structured Ni(OH)₂ monolayer hollow‐sphere array with the shell composed of building blocks of nanoflakelets is demonstrated based on a colloidal monolayer and electrochemical deposition. The morphology can be easily controlled by the colloidal monolayer and deposition parameters. Importantly, such monolayer hollow‐sphere array shows a morphology‐ and size‐dependent tunable optical transmission stop band. This stop band can be easily tuned from 455–1855 nm by changing the size of the hollow spheres between 1000 and 4500 nm, and also fine‐adjusted by changing the deposition time. The array exhibits a nearly incident‐angle‐independent position of the stop band that 3D photonic crystals do not possess. This structure may have potential applications in optical devices, photonic crystals, and sensors for gas detection.     

Efficiently Releasing the Trapped Energy Flow in White Organic Light‐Emitting Diodes with Multifunctional Nanofunnel Arrays

White organic light‐emitting diodes (OLEDs) hold great promise for applications in displays and lighting due to high efficiency and superior white color balance. However, further improvement in efficiency remains a continuous and urgent demand due to limited energy flow extraction. A powerful method for drastically releasing the trapped energy flow in conventional white OLEDs is demonstrated by implementing unique quasi‐periodic subwavelength nanofunnel arrays (NFAs) via soft nanoimprinting lithography, which is ideal for enhancing light extraction without any spectral distortion or angular dependence. The resulting efficiency is over 2 times that of a conventional OLED used as a comparison. The external quantum efficiency and power efficiency are raised to 32.4% and 56.9 lm W^?1, respectively. Besides, the substantial increase in efficiency over a broad bandwidth with angular color stability, the experimental proofs show that the NFA‐based extraction structure affords the enticing capacity against scrubbing and the self‐cleaning feature, which are critical to the commercial viability in practical applications.     

Size‐Scalable and High‐Density Liquid‐Metal‐Based Soft Electronic Passive Components and Circuits Using Soft Lithography

The use of conducting liquids with high electrical conductivity, such as eutectic gallium–indium (EGaIn), has great potential in electronics applications requiring stretchability and deformability beyond conventional flexible electronics relying on solid conductors. An advanced liquid metal thin‐line patterning process based on soft lithography and a compatible vertical integration technique are presented that enable size‐scalable and high‐density EGaIn‐based, soft microelectronic components and circuits. The advanced liquid metal thin‐line patterning process based on poly(dimethylsiloxane) (PDMS) substrates and soft lithography techniques allows for simultaneous patterning of uniform and residue‐free EGaIn lines with line width from single micrometers to several millimeters at room temperature and under ambient pressure. Using this fabrication technique, passive electronic components and circuits are investigated under elastic deformations using numerical and experimental approaches. In addition, soft through‐PDMS vias with high aspect ratio are demonstrated for multilayer interconnections in 2.5D and 3D integration approaches. To highlight the system‐level potential of the patterning technique, a chemical sensor based on an integrated LC resonance circuit with a microfluidic‐tunable interdigitated capacitor and a planar spiral inductor is fabricated and characterized. Finally, to show the flexibility and stretchability of the resulting electronics, circuits with embedded light emitting diodes (LEDs) are investigated under bending, twisting, and stretching deformations.     

Kirigami/Origami‐Based Soft Deployable Reflector for Optical Beam Steering

The beam steering mechanism has been a key element for various applications ranging from sensing and imaging to solar tracking systems. However, conventional beam steering systems are bulky and complex and present significant challenges for scaling up. This work introduces the use of soft deployable reflectors combining a soft deployable structure with simple kirigami/origami reflective films. This structure can be used as a macroscale beam steering mechanism that is both simple and compact. This work first develops a soft deployable structure that is easily scalable by patterning of soft linear actuators. This soft deployable structure is capable of increasing its height several folds by expanding in a continuous and controllable manner, which can be used as a frame to deform the linearly stretchable kirigami/origami structures integrated into the structure. Experiments on the reflective capability of the reflectors are conducted and show a good fit to the modeling results. The proposed principles for deployment and for beam steering can be used to realize novel active beam steering devices, highlighting the use of soft robotic principles to produce scalable morphing structures.