Noncontact Charge Shielding Knife for Liquid Microfluidics.

Multibehavioral droplet manipulation in a precise and programmed manner is crucial for stoichiometry, biological virus detection, and intelligent lab-on-a-chip. Apart from fundamental navigation, merging, splitting, and dispensing of the droplets are required for being combined in a microfluidic chip as well. Yet, existing active manipulations including strategies from light to magnetism are arduous to use to split liquids on superwetting surfaces without mass loss and contamination, because of the high cohesion and Coanda effect. Here, we demonstrate a charge shielding mechanism (CSM) for platforms to integrate with a series of functions. In response to attachment of shielding layers from the bottom, the instantaneous and repeatable change of local potential on our platform achieves the desired loss-free manipulation of droplets, with a wide-ranging surface tension from 25.7 mN m-1 to 87.6 mN m-1, functioning as a noncontact air knife to cleave, guide, rotate, and collect reactive monomers on demand. With further refinement of the surface circuit, the droplets, just as the electron, can be programmed to be transported directionally at extremely high speeds of 100 mm s-1. This new generation of microfluidics is expected to be applied in the field of bioanalysis, chemical synthesis, and diagnostic kit.

Photothermal Solid Slippery Surfaces with Rapid Self-Healing, Improved Anti/De-Icing and Excellent Stability.

Icing phenomenon that occurs universally in nature and industry gets a great impact on human life. Over the past decades, extensive efforts have been made for a wide range of anti-icing/deicing surfaces, but the preparation of anti-icing/deicing interfaces that combine stability, rapid self-healing and excellent anti-icing/deicing performance remains a challenge. In this study, a photothermal solid slippery surface with excellent comprehensive performance is prepared by integrating cellulose acetate film, carbon nanotubes with paraffin wax (CCP). Apart from the excellent anti-icing and deicing properties at -17 ± 1.0 °C under 1 sun illumination, the surface can further achieve deicing at temperatures as low as -22 ± 1.0 °C under infrared light. The fabricated surface also exhibits great stability when placed in harsh conditions such as underwater or ultra-low temperature environments for over 30 days. Even when suffering from physical damage, the prepared surface can rapidly self-repair under 1 sun illumination or near-infrared (NIR) illumination within 16.0 ± 1.5 s. Due to the rapid and repeatable self-healing performance, the lubricating properties of the interface material do not deteriorate even after 50 repeated abrasing-repairing cycles. The photothermal solid slippery surface possesses wide-ranging applications and commercial value at high latitude and altitude regions.

Preparation of Polyurethane/Graphite Composite Films with Stable Mechanical Property and Wear Resistance Underwater.

The wear resistance and stable mechanical properties affect the service life of the underwater functional materials to a certain extent. Unfortunately, the current study of underwater functional materials is rarely related to these aspects. Herein, we successfully designed and prepared polyurethane/graphite nanosheet (PU/GN) composite materials, which exhibited excellent wear resistance and stable mechanical properties underwater. The PU/GN composite films were prepared by evaporating a mixed solution of PU and GN on concave hexagonal honeycomb silicon templates. The mechanical properties of the composite films were determined by tensile test, and the wear resistance was evaluated by comparing the surface morphology before and after grind. By adjusting the content of graphite in the composite films, we found that the composite films containing 23 wt% GN had higher tensile strength and superior wear resistance. Moreover, this composite film showed an outstanding stability when expose to water. The impressive results along with simple preparation process made PU/GN composite films had potential applications in robust underwater functional materials.

Wettability with Aggregation-Induced Emission Luminogens.

Aggregation-induced emission luminogens (AIEgens) have become an emerging field since the concept of AIE was proposed in 2001. Recently, AIEgens have attracted considerable attention due to their abnormal non-emissive fluorescent behavior in solution but strongly emissive behavior in the aggregate state. By utilizing the inherent hydrophobicity, AIEgens can be used to monitor the crystal formation and dewetting behavior in the self-assembly process. More importantly, some stimuli-responsive AIE-active surfaces have been successfully fabricated. In this perspective review, we outline the advances of surface wettability of AIEgens and its applications.

Special adhesion of natural honeycomb walls and their application.

In this paper, we investigated the wettability and adhesive behavior of the natural honeycomb wall for water and honey droplets. The cell walls have hydrophobic and highly adhesive properties for both water and honey in air. This highly adhesive cell wall was used as a "mechanical hand" to transfer micro-droplets. These findings will help us to comprehensively understand the surface properties of honeycomb walls, and will provide a novel strategy for achieving functional biomimetics based on honeycombs.

A visual and organic vapor sensitive photonic crystal sensor consisting of polymer-infiltrated SiO2 inverse opal.

A photonic crystal (PC) sensor that can selectively detect organic vapors through visual color changes has been proposed. The sensor was fabricated by infiltrating a tetraphenylethene polymer (TPEP) into the voids of SiO2 inverse opal photonic crystal. When the sensor was exposed to tetrahydrofuran or acetone vapor, a red shift of the stopband of more than 50 nm could be clearly observed; meanwhile, the film's color changed from violet to cyan. Subsequently, when exposed to air, the stopband underwent a blue shift and the color returned to violet. The reason for the observed change is that a reversible adsorption-desorption process occurs on alternate exposure of the sensor to organic vapor and air, due to the high specific surface area of the inverse opal macroporous structure and the high affinity of TPEP to tetrahydrofuran and acetone. The adsorption of vapor analyte can increase the PC's effective refractive index, which will induce the stopband red shift and the resulting color change according to Bragg's Law. The reversible adsorption-desorption of organic vapors varied the effective refractive index of the sensor repeatedly, causing the reversible stopband shift and color change, and providing a general method for the design of visual vapor sensors.

Silole-infiltrated photonic crystal films as effective fluorescence sensor for Fe3+ and Hg2+.

We develop a highly effective silole-infiltrated photonic crystal (PC) film fluorescence sensor with high sensitivity, good selectivity and excellent reproducibility for Fe(3+) and Hg(2+) ions. Hexaphenylsilole (HPS) infiltrated PCs show amplified fluorescence due to the slow photon effect of PC because the emission wavelength of HPS is at the blue band edge of the selected PC's stopband. The fluorescence can be quenched significantly by Fe(3+)/Hg(2+) ions owing to electron transfer between HPS and metal ions. The amplified fluorescence enhances the sensitivity of detection, with a detection limit of 5 nM for Fe(3+)/Hg(2+) ions. The sensor is negligibly responsive to other metal ions and can easily be reproduced by rinsing with pure water due to the special surface wettability of PC. As a result, a highly effective Fe(3+)/Hg(2+) ions sensor based on HPS-infiltrated PC film has been achieved, which will be important for effective and practical detection of heavy metal ions.

Flexible solid-liquid bi-continuous electrically and thermally conductive nanocomposite for electromagnetic interference shielding and heat dissipation.

In the era of 5 G, the rise in power density in miniaturized, flexible electronic devices has created an urgent need for thin, flexible, polymer-based electrically and thermally conductive nanocomposites to address challenges related to electromagnetic interference (EMI) and heat accumulation. However, the difficulties in establishing enduring and continuous transfer pathways for electrons and phonons using solid-rigid conductive fillers within insulative polymer matrices limit the development of such nanocomposites. Herein, we incorporate MXene-bridging-liquid metal (MBLM) solid-liquid bi-continuous electrical-thermal conductive networks within aramid nanofiber/polyvinyl alcohol (AP) matrices, resulting in the AP/MBLM nanocomposite with ultra-high electrical conductivity (3984 S/cm) and distinguished thermal conductivity of 13.17 W m-1 K-1. This nanocomposite exhibits excellent EMI shielding efficiency (SE) of 74.6 dB at a minimal thickness of 22 µm, and maintains high EMI shielding stability after enduring various harsh conditions. Meanwhile, the AP/MBLM nanocomposite also demonstrates promising heat dissipation behavior. This work expands the concept of creating thin films with high electrical and thermal conductivity.

Noncontact Microfluidics of Highly Viscous Liquids for Accurate Self-Splitting and Pipetting.

Accurate dosing for various liquids, especially for highly viscous liquids, is fundamental in wide-ranging from molecular crosslinking to material processing. Despite droppers or pipettes being widely used as pipetting devices, they are powerless for quantificationally splitting and dosing highly viscous liquids (>100 mPa s) like polymer liquids due to the intertwined macromolecular chains and strong cohesion energy. Here, a highly transparent photopyroelectric slippery (PS) platform is provided to achieve noncontact self-splitting for liquids with viscosity as high as 15 000 mPa s, just with the assistance of sunlight and a cooling source to provide a local temperature difference (ΔT). Moreover, to guarantee the accuracy for pipetting liquids (>80%), the ultrathin MXene film (within a thickness of 20 nm) is self-assembled as the photo-thermal layers, overcoming the trade-off between transparency and photothermal property. Compared with traditional pipetting strategies (≈1.3% accuracy for pipetting polymer liquids), this accurate microfluidic chip shows great potential in adhesive systems (bonding strength, twice than using the droppers or pipettes).

Light-Induced Dynamic Manipulation of Liquid Metal Droplets in the Ambient Atmosphere.

Dynamic manipulation of liquid metal (LM) droplets, a material combining metallicity and fluidity, has recently revealed tremendous potential in developing unconstrained microrobots. LM manipulating techniques based on magnetic fields, electric fields, chemical reactions, and ion concentration gradients in liquid environments have advanced considerably, but dynamic manipulation in air remains a challenge. Herein, a photoresponsive pyroelectric superhydrophobic (PPS) platform is proposed for noncontact, flexible, and controllable manipulation in the ambient atmosphere. The PPS can generate additional free charges when illuminated by light, thus generating the driving force to manipulate liquid metal droplets. By using the synergistic effect of dielectrophoretic and electrostatic forces generated under light navigation, liquid metal droplets can achieve a series of complex motion behaviors, such as climbing slopes, going over steps, avoiding obstacles, crossing mazes, etc. We further extend the light control of liquid metal droplets to robots applied in electronic circuits, including circuit switching robots and circuit welding robots. This light strategy for manipulating liquid metal droplets provides insights into the development of intelligent, responsive interfaces and simultaneously provides possibilities for the application of liquid metals.

Infinite Self-Propulsion of Circularly On/Discharged Droplets.

Self-propulsion of droplets in a controlled and long path at a high-speed is crucial for organic synthesis, pathological diagnosis and programable lab-on-a-chip. To date, extensive efforts have been made to achieve droplet self-propulsion by asymmetric gradient, yet, existing structural, chemical, or charge density gradients can only last for a while (<50 mm). Here, this work designs a symmetrical waved alternating potential (WAP) on a superhydrophobic surface to charge or discharge the droplets during the transport process. By deeply studying the motion mechanisms for neutral droplets and charged droplets, the circularly on/discharged droplets achieve the infinite self-propulsion (>1000 mm) with an ultrahigh velocity of meters per second. In addition, after permutation and combination of two motion styles of the droplets, it can be competent for more interesting work, such as liquid diode and liquid logic gate. Being assembled into a microfluidic chip, the strategy would be applied in chemical synthesis, cell culture, and diagnostic kits.

Bioinspired design of honeycomb structure interfaces with controllable water adhesion.

Inspired by biological attachment systems, we fabricated the honeycomb structural films with different diameters by breath figure (BF) method, which were similar to the patterned octopus suckers. The experimental results showed, besides different van der Waals forces between the polystyrene (PS) surfaces and water, another important factor; that is, different negative pressures produced by different volumes of sealed air could be a crucial factor for the different adhesions. So the water adhesive forces of the as-prepared films can be effectively controlled from relative high to relative low adhesion by varying the pore diameters, which effectively adjusted the negative pressures produced by the pores. This unique adhesive phenomenon of honeycomb structure will be very useful for manipulating water droplet behaviors, as well as controlling liquid collection and transportation. These findings are interesting and helpful for us to further understand the biological attachment systems and to optimize the design of artificial analogues.

Ordered honeycomb structural interfaces for anticancer cells growth.

The patterned honeycomb structure film with the aggregation-induced emission property was prepared successfully by the breath figure method and photopolymerization method. Characterization of the HeLa and HepG2 cell culture on this surface indicates the porous honeycomb structures show anticancer cells growth function. So this kind of honeycomb structure will be promising for the control of cancer cell growth behaviors and achieving the application of anticancer.

Highly sensitive, selective and reusable mercury(II) ion sensor based on a ssDNA-functionalized photonic crystal film.

We have developed a highly sensitive, selective and reusable fluorescence sensor with photonic crystal (PC) films for mercury(II) ion detection, based on the Bragg reflection of PCs and formation of thymine-Hg(2+)-thymine (T-Hg(2+)-T) complexes. The T-rich single stranded DNA (ssDNA) labeled by a fluorophore was self-assembled on the surface of Au-sputtered PCs through Au-thiol binding, in which the DNA exists in a single stranded chain. The obtained ssDNA-functionalized PC films show a strong fluorescence emission derived from the Bragg reflection of PCs, because the fluorescence wavelength of ssDNA is in the range of the selected PC stopband. After reaction with Hg(2+) ions, the conformation of ssDNA changes from the original single stranded chain to a folded hairpin structure due to the formation of T-Hg(2+)-T complexes. This leads to a fluorescence resonance energy transfer process between the fluorophore and the thin gold film, which results in significant fluorescence quenching. The sensitivity of the fluorescence detection, with a detection limit of 4 nM, can be obviously enhanced by the Bragg reflection of PCs compared to the control sample without PC structures. The prepared sensor is negligibly responsive to other metal ions. In addition, the sensor can also be easily regenerated and reused by decoupling the T-Hg(2+)-T base pairs using cysteine. As a result, a highly sensitive, selective and reusable Hg(2+) ion sensor based on a ssDNA-functionalized PC film has been achieved, which will be of importance for the effective and practical detection of heavy metal ions.

Thermoresponsive wettability of photonic crystals fabricated by core-shell poly(styrene-acrylamide) nano/microspheres.

The photonic crystals (PCs) films with tunable wettability were fabricated from self-assembly of an amphiphilic latex nano/microspheres poly(styrene-acrylamide) at different temperatures. The results demonstrate that the surface wettability of the PCs film can be tuned from high hydrophilic (CA, 17 degrees) to high hydrophobic (CA, 127.8 degrees) by controlling the assembly temperature from 30 degrees C to 90 degrees C, while the position of the photonic stopbands of the PCs films unchanged virtually. The obvious wettability transition is due to the change of the surface chemical component of the latex spheres, which mainly derives from the phase separation of polymer segments driven toward minimum interfacial energy. The facile method could open new application fields of PCs in diverse environments.

Photoelectric synergistic anisotropic slippery interface for directional droplets manipulation.

Stimuli-responsive anisotropic slippery surfaces have displayed remarkable performance in directionally manipulating droplet transport behavior. However, most current reported anisotropic slippery materials have been limited to a single response mode, which often fails to satisfy the practical conditions of double or synergetic stimulation in complex environments. Here, an anisotropic photoelectric synergistic responsive paraffin-injected directional oxidized copper foam slippery interface (P/DOC3-S) with a low response threshold is reported. Owing to the fast photoelectric response of P/DOC3-S, the reversible control of the anisotropic sliding behavior of droplets is realized by remotely switching on and off the photoelectric field. Additionally, through optimizing the structure, the response voltage for P/DOC3-S can be reduced to 0.3 V under one sunlight. This work will provide insights into creating new types of smart slippery surfaces, which are potentially useful in microfluidics, directional liquid transportation, the semiconductor industry, and other related fields.

Slippery Graphene-Bridging Liquid Metal Layered Heterostructure Nanocomposite for Stable High-Performance Electromagnetic Interference Shielding.

Gallium-based liquid metal (LM) with intriguing high electrical conductivity and room-temperature fluidity has attracted substantial attention for its potential application in flexible electromagnetic interference (EMI) shielding. However, the EMI shielding performance of the existing LM-based composites is unsatisfying due to the irreconcilable contradiction between high EMI shielding efficiency (SE) and low thickness. In addition, the research on environmentally stable EMI shielding material has become an urgent need due to the increasingly sophisticated application scenarios. Herein, we prepared a reduced graphene oxide (rGO) bridging LM layered heterostructure nanocomposite with the liquid-infused slippery surface (S-rGO/LM), which exhibits an ultrahigh X-band EMI SE of 80 dB at a mere internal thickness of 33 µm, and an extremely high value of 100 dB at an internal thickness of 67 µm. More significantly, protected by the ultrathin (2 µm) yet effective slippery surface, the S-rGO/LM film exhibits exceptional EMI shielding stability (EMI SE stays above 70 dB) after enduring various harsh conditions (harsh chemical environments, extreme operating temperatures, and severe mechanical wearing). Moreover, the S-rGO/LM film also demonstrates satisfying photothermal behavior and excellent Joule heating performance (surface temperature of 179 °C at 1.75 V, thermal response <10 s), which endows it with the capability of anti-icing/de-icing. This work proposes a way to construct an LM-based nanocomposite with reliable high-performance EMI shielding capability, which shows great potential for applications in wearable devices, defense, and aeronautics and astronautics.

Morphology controllable self-assembly of hierarchical hexaphenylsilole structures and their properties.

Morphology controllable hexaphenylsilole hierarchical homo-aggregations have been prepared by the self-assembly method in this paper. Tuning the solvent parameters can significantly affect the morphologies of the resulting HPS aggregations. The solvent properties play an important role in the shape-controlled synthesis of nanostructures. The possible self-assembly mechanism was also discussed. All of the different hierarchical structures aggregated from different solvents show different florescence and different absorption spectra properties, which could be of importance and have potential applications in the fields of optoelectronic functional materials.

Sensing mechanism of nanofibrous membranes for fluorescent detection of metal ion.

We have reported a hexaphenylsilole/polymethyl methacrylate (HPS/PMMA) composite film with a lotus-leaf-like structure shows highly stability and excellent sensitivities for metal ions (Fe3+ and Hg2+) a few years ago. In the above paper, it was considered that the special surface morphology is the important aspects which enhance the stability of the sensor. But it is still a lack of research on the sensing mechanism. In this paper, the sensing mechanism of fiber membrane is continuing to study in detail. The experimental results show that the electron-transfer mechanism is a crucial factor for the fluorescent quenching.

Dual high adhesion surface for water in air and for oil underwater.

A new type of dual high surface adhesion both in an oil/water/solid system and in a water/air/solid system is reported. A walnutlike cuprous iodide (CuI) microcrystal surface, which is composed of numerous CuI nanocrystals, shows an amphiphobic, highly adhesive surface for water in air and for oil underwater. The maximum adhesive force is about 120.3 ± 1.6 µN in the air for a water droplet and about 23.8 ± 2.1 µN underwater for an oil droplet. These findings will help us to design novel high adhesive materials in two-phase or multiphase mediums.