Fine Optimization of Colloidal Photonic Crystal Structural Color for Physically Unclonable Multiplex Encryption and Anti-Counterfeiting.

Robust anti-counterfeiting techniques aim for easy identification while remaining difficult to forge, especially for high-value items such as currency and passports. However, many existing anti-counterfeiting techniques rely on deterministic processes, resulting in loopholes for duplication and counterfeiting. Therefore, achieving high-level encryption and easy authentication through conventional anti-counterfeiting techniques has remained a significant challenge. To address this, this work proposes a solution that combined fluorescence and structural colors, creating a physically unclonable multiplex encryption system (PUMES). In this study, the physicochemical properties of colloidal photonic inks are systematically adjusted to construct a comprehensive printing phase diagram, revealing the printable region. Furthermore, the brightness and color saturation of inkjet-printed colloidal photonic crystal structural colors are optimized by controlling the substrate's hydrophobicity, printed droplet volume, and the addition of noble metals. Finally, fluorescence is incorporated to build PUMES, including macroscopic fluorescence and structural color patterns, as well as microscopic physically unclonable fluorescence patterns. The PUMES with intrinsic randomness and high encoding capacity are authenticated by a deep learning algorithm, which proved to be reliable and efficient under various observation conditions. This approach can provide easy identification and formidable resistance against counterfeiting, making it highly promising for the next-generation anti-counterfeiting of currency and passports.

Rapid Construction of Caffeic Acid/p-Phenylenediamine Antifouling Hydrophilic Coating on a PVDF Membrane for Emulsion Separation.

The current methods of constructing modification strategies for hydrophilic membranes are time-consuming, complex in operation, and poor in universality, which limit their application on membranes. In this work, inspired by the adhesion properties and versatility of caffeic acid (CA) and p-phenylenediamine (PPDA), a simple, rapid, and universal method was designed for the separation of oil-in-water emulsion by preparing a stable hydrophilic coating separation membrane. The preparation time of the membrane was shortened to 40 min. The developed PVDF-PCA/PPDA membrane showed superhydrophilic and underwater superoleophobic properties. When applied to petroleum ether-in-water emulsion, isooctane-in-water emulsion, and dodecane-in-water emulsion separation, the oil rejection was more than 99.0%. In the circulating separation of 10 g/L soybean oil-in-water emulsion, the oil rejection was more than 99.3%, and the highest flux was 1036 L·m-2·h-1. The prepared PVDF-PCA/PPDA membrane performed well in the separation test of oily wastewater. The proposed strategy is simple and rapid; it may become a universal method for preparing membranes with super strong antifouling properties against viscous oil and accelerate the research progress of membrane separation of oil-in-water emulsions.

Ultrasonic-Excited Ultrafast Seamless Integration of Heterostructured Liquid Crystalline Elastomers for Multi-responsive Soft Actuators.

Multicomponent/heterostructured liquid crystalline elastomers (LCEs) have recently garnered extensive attention for the design of soft robots with high dexterity and flexibility. However, the reported integration strategies of LCEs seriously suffer from high welding temperature, long processing time, and poor joint quality. Herein, the high-efficiency seamless ultrasonic welding (UW) of reprogrammable silver nanowire-LCE composites (AgNW-LCEs) have been realized without any auxiliary reagents based on the dynamic silver-disulfide coordination interactions. The elaborate combination of silver-disulfide coordination interactions and UW technology establishes an effective double-network welding mechanism of AgNWs and dynamic LC networks due to the high-frequency vibration at the welding interface. During the UW process, monolithic AgNW-LCEs can be integrated into heterostructured actuators at room temperature for 0.68 s. Furthermore, the welded AgNW-LCEs demonstrate an exceptional strain healing efficiency of ∼100%, a stress healing efficiency of ∼85%, and a maintained orientation of the LC alignment. Taking advantage of the high-efficiency UW technology, the heterostructured AgNW-LCE actuators with different LC alignments or LC monomers have been successfully implemented for a multi-degree-of-freedom soft robotic arm and a time-modulated flower-mimic actuator. This work provides an efficient approach toward the development of multi-responsive entirely soft actuators based on smart polymers.

Ultralight and Highly Conductive Silver Nanowire Aerogels for High-Performance Electromagnetic Interference Shielding.

Metal-based materials possess superior electromagnetic interference (EMI) shielding performance because of their extraordinary electrical conductivity. Nevertheless, the high density and structural rigidity of metals seriously limit their applicability in portable and wearable electronic equipment. A common method for reducing the density of metal-based materials is to prepare metal nanowire aerogels by freeze-drying, but the weak connection among the nanowires results in poor mechanical and electrical properties. Herein, a facile approach is developed for the one-step synthesis of silver nanowire (AgNW) aerogels with ultralow density, good flexibility, high electrical conductivity, and a robust structure. The gel is directly formed by in situ assembly of AgNWs. The end-to-end nanojoining of AgNWs contributes to constructing an interconnected three-dimensional (3D) network, resulting in improved mechanical and electrical properties. The AgNW aerogel with an ultralow density of 4.87 mg cm-3 demonstrates a high electrical conductivity of 4584 S m-1. Moreover, the porous structure of the AgNW aerogel provides numerous interfaces for multiple reflections and scattering of EM waves, allowing them to be continuously absorbed and dissipated within the aerogel. Thus, the AgNW aerogel exhibits a superb EMI shielding effectiveness (SE) of 109.3 dB and a normalized surface specific SE (SSE/t, calculated as the SE divided by the density and thickness) of 353 183 dB cm2 g-1, significantly above that of previously known shielding materials. This work provides a new route for preparing high-performance metal nanowire aerogels and their great potential in EMI shielding.

Additively Manufactured Flexible Electronics with Ultrabroad Range and High Sensitivity for Multiple Physiological Signals' Detection.

Flexible electronics can be seamlessly attached to human skin and used for various purposes, such as pulse monitoring, pressure measurement, tensile sensing, and motion detection. Despite their broad applications, most flexible electronics do not possess both high sensitivity and wide detection range simultaneously; their sensitivity drops rapidly when they are subjected to even just medium pressure. In this study, ultrabroad-range, high-sensitivity flexible electronics are fabricated through additive manufacturing to address this issue. The key to possess high sensitivity and a wide detection range simultaneously is to fabricate flexible electronics with large depth-width ratio circuit channels using the additive manufacturing inner-rinsing template method. These electronics exhibit an unprecedented high sensitivity of 320 kPa-1 over the whole detection range, which ranges from 0.3 to 30,000 Pa (five orders of magnitude). Their minimum detectable weight is 0.02 g (the weight of a fly), which is comparable with human skin. They can stretch to over 500% strain without breaking and show no tensile fatigue after 1000 repetitions of stretching to 100% strain. A highly sensitive and flexible electronic epidermal pulse monitor is fabricated to detect multiple physiological signals, such as pulse signal, breathing rhythm, and real-time beat-to-beat cuffless blood pressure. All of these signals can be obtained simultaneously for detailed health detection and monitoring. The fabrication method does not involve complex expensive equipment or complicated operational processes, so it is especially suitable for the fabrication of large-area, complex flexible electronics. We believe this approach will pave the way for the application of flexible electronics in biomedical detection and health monitoring.

Facile Gold-Nanoparticle Boosted Graphene Sensor Fabrication Enhanced Biochemical Signal Detection.

Graphene has been considered as an excellent biochemical sensors' substrate material because of its excellent physical and chemical properties. Most of these sensors have employed enzymes, antibodies, antigens, and other biomolecules with corresponding recognition ability as recognition elements, to convert chemical signals into electrical signals. However, oxidoreductase enzymes that grow on graphene surfaces are affected significantly by the environment and are easily inactivated, which hinders the further improvement of detection sensitivity and robusticity. A gold-boosted graphene sensor was fabricated by the in situ electrochemical deposition of inorganic gold nanoparticles on vertical graphene nanosheets. This approach solves the instability of biological enzymes and improves the detection performance of graphene-based sensors. The uric acid sensitivity of the gold-boosted electrode was 6230 µA mM-1 cm-2, which is 6 times higher than the original graphene electrode. A 7 h GNSs/CC electrode showed an impressive detection performance for ascorbic acid, dopamine, and uric acid, simultaneously. Moreover, it exhibited a reliable detection performance in human serum in terms of uric acid. The possible reason could be that the vertical aliened graphene nanosheet acts as a reaction active spot. This 3D graphene-nanosheet-based doping approach can be applied to a wide variety of inorganic catalytic materials to enhance their performance and improve their durability in aspects such as single-atom catalysis and integration of multiple catalytic properties.

A facile fabrication of conjugated fluorescent nanoparticles and micro-scale patterned encryption via high resolution inkjet printing.

Conjugated fluorescent materials are getting more and more attention in the biomedical arena due to their high fluorescence intensity, non-bleaching and good biocompatibility. However, conjugated fluorescent materials are still not widely used in the field of anti-counterfeiting and pattern encryption due to their extremely low solubility and enormous difficulties in processing. Here, we use a facile approach to fabricate conjugated polymer fluorescent nanoparticles through a classic micro-emulsion method to address these issues. The particle size, loading materials and fluorescence intensity can be tuned as demanded. Later, these particles are transformed into invisible inks for inkjet printers to achieve micro-scale pattern encryption. These patterns show an ultra-high accuracy of around 30 micrometres. They can be used as QR codes for information encryption with 3 times more information encryption and great anti-counterfeiting ability. Finally, we establish an identification recognition system to check their validity. The scenario is the patient identification system of a hospital. The results show that these tags can be read in less than 3 seconds and they can last for 12 months at least. This facile approach holds great potential and bright prospects in the field of privacy protection, information encryption and anti-counterfeiting.

Effects of ozonation on disinfection by-product formation potentials and biostability in a pilot-scale drinking water treatment plant with micro-polluted water.

The accelerated urbanization in China has caused intensified micro-pollution problems for drinking water sources, severely challenging drinking water treatment efficiencies and its biostability. This study mainly investigated the effects of ozonation on disinfection by-product formation potentials (DBPFPs) and biological dissolved organic carbon (BDOC) in a pilot-scale ozonation-biological activated carbon advanced drinking water treatment plant with micro-polluted raw water. The results indicated that the micro-polluted water would be effectively treated in the advanced treatment processes with DBPFPs significantly eliminated. The total removal rates of trihalomethane formation potentials (THMFPs) and haloacetic acid formation potentials (HAAFPs) increased with the elevated ozone dosage to finally a relatively stable stage, and the maximum removal rates of 77.3% and 57.0%, respectively, were achieved at the ozone dosage of 2 mg/L. The bromine incorporation in total THMFPs (TTHMFPs) was dramatically suppressed after integrated advanced treatment processes, while that in total HAAFPs (THAAFPs) was promoted with the corresponding increment of up to 25.3% for bromine incorporation factor, which caused relatively high brominated HAAFP proportions in the treated water than in the raw water. In addition, the BDOC generation rate and THAAFP removal rate during the post-ozonation treatment displayed apparent positive correlation, and a similar relationship was observed for the BDOC degradation rate and TTHMFP removal rate during the BAC treatment in the studied ozone dosage (1 ∼ 5 mg/L). The findings strongly implied a promising alternative to measure DBPFP removal rate instead of BDOC level for more sensitive and convenient monitoring of the biostability in the reclaimed water.

Wearable Circuits Sintered at Room Temperature Directly on the Skin Surface for Health Monitoring.

A soft body area sensor network presents a promising direction in wearable devices to integrate on-body sensors for physiological signal monitoring and flexible printed circuit boards (FPCBs) for signal conditioning/readout and wireless transmission. However, its realization currently relies on various sophisticated fabrication approaches such as lithography or direct printing on a carrier substrate before attaching to the body. Here, we report a universal fabrication scheme to enable printing and room-temperature sintering of the metal nanoparticle on paper/fabric for FPCBs and directly on the human skin for on-body sensors with a novel sintering aid layer. Consisting of polyvinyl alcohol (PVA) paste and nanoadditives in the water, the sintering aid layer reduces the sintering temperature. Together with the significantly decreased surface roughness, it allows for the integration of a submicron-thick conductive pattern with enhanced electromechanical performance. Various on-body sensors integrated with an FPCB to detect health conditions illustrate a system-level example.

Ultrasonic-accelerated metallurgical reaction of Sn/Ni composite solder: Principle, kinetics, microstructure, and joint properties.

The high-melting-point joints by transient-liquid-phase are increasingly playing a crucial role in the die bonding for the high temperature electronic components. In this study, three kinds of Sn/Ni composite solder pastes composed of different sizes of Ni particles were synthesized to accelerate metallurgical reaction among Sn/Ni interfaces under the ultrasonic-assisted transient liquid phase (U-TLP) soldering. The temperature evolution, microstructure and mechanical property in joints composed by these composite solder pastes with or without ultrasonic energy were systemically investigated. The intermetallic joint consisted of high-melting-point sole Ni3Sn4 intermetallic compound with a little residual Ni was obtained under the conditions of no pressure and lower power (200 W) in a high-temperature duration of only 10 s, its shear strength was up to 45.3 MPa. Ultrasonic effects significantly accelerated the reaction among the interfaces of liquid Sn and solid Ni, which attributed to the temperature rise caused by acoustic cavitation because of large number of liquid/solid interfaces during U-TLP, resulting in accelerated solid/liquid interfacial diffusion and growth of intermetallic compounds. This intermetallic joint formed by U-TLP soldering has a promising potential for applications in high-power device packaging.

Ultrafast control of vortex microlasers.

The development of classical and quantum information-processing technology calls for on-chip integrated sources of structured light. Although integrated vortex microlasers have been previously demonstrated, they remain static and possess relatively high lasing thresholds, making them unsuitable for high-speed optical communication and computing. We introduce perovskite-based vortex microlasers and demonstrate their application to ultrafast all-optical switching at room temperature. By exploiting both mode symmetry and far-field properties, we reveal that the vortex beam lasing can be switched to linearly polarized beam lasing, or vice versa, with switching times of 1 to 1.5 picoseconds and energy consumption that is orders of magnitude lower than in previously demonstrated all-optical switching. Our results provide an approach that breaks the long-standing trade-off between low energy consumption and high-speed nanophotonics, introducing vortex microlasers that are switchable at terahertz frequencies.

Multi-layer silver nanowire/polyethylene terephthalate mesh structure for highly efficient transparent electromagnetic interference shielding.

Electromagnetic interference protection in optoelectronic devices is challenging because of the dual requirements of optical transmittance and high shielding effectiveness (SE). Herein, we propose a novel silver nanowire (AgNW)/polyethylene terephthalate (PET) multi-layer mesh pattern structure for transparent electromagnetic shielding obtained via laser marking and transfer printing. A three-layer composite shielding film with an optical transmittance of 67.8% exhibits a SE of 44 dB at 10 GHz, which is superior to most of the reported transparent shielding films composed of AgNWs to date. The newly designed multi-layer composite structure can enhance the transparent shielding properties of the shielding film via optimization of the AgNW distribution and the shielding film structure. It is expected that this multi-layer mesh composite structure will have splendid application prospects in electromagnetic shielding films, which require both light transmittance and high SE.

Nano oxide intermediate layer assisted room temperature sintering of ink-jet printed silver nanoparticles pattern.

Sintering of metallic nanoparticles (NPs) at low temperature is highly wanted in the manufacturing of flexible electronics. And for ink-jet printing, the metallic NPs after printing usually need thermal or chemical post-treatment to remove stabilizing agents and achieve conductivity. Here, we reported a facile method to realize one-step printed sintering of silver nanoparticle (AgNP) ink at room temperature by using intermediate coated layers composed of oxide NPs and polyvinyl alcohol (PVA) mixture. We found that the detachment of the stabilizer (citrate) from the AgNPs was caused by hydroxyl groups on the surface of the oxide NPs, which enabled the coalescence and sintering of the AgNPs. With the aid of SiO2 NPs based intermediate layer, the patterns showed resistivity as low as 3.45 µΩ cm after sintering. Moreover, the mixed PVA could ensure the forming quality of patterns owing to its adsorption of ink and the high adhesiveness of PVA with substrates. So, we envision that this approach could serve as an adaptive method for sintering of AgNPs based conductive patterns on various substrates at room temperature and promote the manufacture of printed electronics.

A flexible and conductive metallic paper-based current collector with energy storage capability in supercapacitor electrodes.

The development of flexible current collectors as an indispensable component in energy storage devices has been in strong demand for the ever-growing market of flexible and wearable electronics. Herein, flexible and conductive paper-based current collectors are fabricated by directly depositing a metallic Ni layer composed of spiny Ni nanospheres of 400 nm diameter on the surface of filter paper via electroless deposition. The metallic paper shows excellent electric and mechanical properties: the sheet resistance is 2.7 Ω cm-2 (R0 = 0.8 Ω cm-2) after 5000 bending cycles and the mass density is only 0.35 g cm-3. MnO2 is selected as an electrode active material to explore the role of flexible and conductive paper-based current collectors in supercapacitors. Electrochemical results reveal that the largest areal specific capacitance is 1095 mF cm-2 at 1 mA cm-2 and the excellent electrochemical performance can be attributed to the hierarchical porous fibre structure of paper and the lower contact resistance between the active material and the current collector. Note that the approach can be applied to an enlarged size of metallic conductive paper or textile, presenting a simple and feasible method to fabricate flexible current collectors in a large scale.

Droplet-based microfluidics systems in biomedical applications.

Microfluidics has made a very impressive progress in the past decades due to its unique and instinctive advantages. Droplet-based microfluidic systems show excellent compatibility with many chemical and biological reagents and are capable of performing variety of operations that can implement microreactor, complex multiple core-shell structure, and many applications in biomedical research such as drug encapsulation, targeted drug delivery systems, and multifunctionalization on carriers. Droplet-based systems have been directly used to synthesize particles and encapsulate many biological entities for biomedicine applications due to their powerful encapsulation capability and facile versatility. In this paper, we review its origin, deviation, and evolution to draw a clear future, especially for droplet-based biomedical applications. This paper will focus on droplet generation, variations and complication as starter, and logistically lead to the numerous typical applications in biomedical research. Finally, we will summarize both its challenge and future prospects relevant to its droplet-based biomedical applications.

Highly Sensitive and Transparent Strain Sensors with an Ordered Array Structure of AgNWs for Wearable Motion and Health Monitoring.

Sensitivity and transparency are critical properties for flexible and wearable electronic devices, and how to engineer both these properties simultaneously is dramatically essential. Here, for the first time, we report the assembly of ordered array structures of silver nanowires (AgNWs) via a simple water-bath pulling method to align the AgNWs embedded on polydimethylsiloxane (PDMS). Compared with sensors prepared by direct drop-casting or transfer-printing methods, our developed sensor represents a considerable breakthrough in both sensitivity and transparency. The maximum transmittance was 86.3% at a wavelength of 550 nm, and the maximum gauge factor was as high as 84.6 at a strain of 30%. This remarkably sensitive and transparent flexible sensor has strictly stable and reliable responses to motion capture and human body signals; it is also expected to be able to help monitor disabled physical conditions or assist medical therapy while ensuring privacy protection.

Highly stretchable patternable conductive circuits and wearable strain sensors based on polydimethylsiloxane and silver nanoparticles.

Patterned circuits on highly stretchable conductive films are critical in the practical application of next-generation flexible and wearable devices. Currently, most patterned circuits do not exhibit highly stretchable properties, and a lithography process in vacuum is required. In this study, silver nanoparticles (AgNPs) and liquid polydimethylsiloxane (PDMS) are mixed together to form liquid conductive adhesives (CAs). Various stretchable patterned circuits are prepared using this CA to achieve all required functions. Six basic patterns, including rhombus, straight lines, serpentine, triangle, ellipses, and fold line, are studied for their stretchable and electrical properties. The film is found to maintain excellent conductivity after withstanding tensile strain of up to 320% and more than 10 000 stretching-releasing cycles of 0%-150%. More than 86% of visible lights can be penetrated through the film due to the transparent substrates. Functional and wearable devices are manufactured, and devices fabricated from rhombus-pattern circuits are found to exhibit stable electrical conductivity when subjected to very high tensile strains. According to the sensitivity of the straight-line patterned circuit to strain, a repeatable use sensitive strain sensor is studied. Also, two types of artificial electrical skin are demonstrated.

Size-Dependent Phase Transformation during Gas Atomization Process of Cu⁻Sn Alloy Powders.

For binary element atomization, it is essential to investigate the phase transformation from liquid to solid as a functions of the droplet sizes, as well as the reaction competitiveness, during gas atomizing solidification of their nuclei. In the present work, a series of phase transformations of undercooled Cu (60.9 wt.%)/Sn droplets were analyzed when atomized by pressure gas. The results indicated that the microstructures of the obtained powders and their morphologies were highly relevant to the droplet size. According to the phase characteristics analyzed by the microstructural observations in combination with the transient nucleation theory, powders with sizes from 10 to 100 µm were divided into three categories, exhibiting lotus-leaf, island, and stripe morphologies. The competitive formation of Cu6Sn5 or Cu3Sn was also controlled by the droplet sizes, and a diameter of approximately 45 µm was identified as the threshold size. After heat treatment at 300 °C for 4 h, the powders consisted of a single η' Cu6Sn5 phase. The obtained Cu6Sn5 phase powders can be used in the field of high-temperature applications as intermetallic balls for integrated chip interconnects.

An invisible private 2D barcode design and implementation with tunable fluorescent nanoparticles.

The popularity of 2D barcodes is playing a key role in simplifying people's daily life activities, such as identification, quick payment, checking in and checking out, etc. However, relevant issues have emerged as their popularity has soared. The most urgent and representative problem is decryption, which may lead to serious information leakage and substantial damage to organizations, such as governments and international enterprises. This issue is mainly due to the visibility of 2D barcodes. In order to prevent potential privacy violation and sensitive information leakage through easy access of those visible 2D barcodes, we have designed and fabricated invisible 2D barcodes that will only be visible under UV illumination. This approach provides a promising solution to address the previous problem by transferring 2D barcodes into an invisible state. We have employed a typical micro-emulsion method to fabricate polystyrene (PS) fluorescent nanoparticles due to its simplicity. The invisible patterns can and will only be accessed and recognized under UV light illumination to protect personal private information. These invisible 2D barcodes provide a feasible solution for personal information protection and fit with a patient's privacy protection scenario very well, as we have demonstrated.

Conductivity enhancement of silver nanowire networks via simple electrolyte solution treatment and solvent washing.

As a promising replacement material for indium tin oxide in flexible electronics, silver nanowires (AgNWs) usually need complicated post-treatment to reduce the high contact resistance across the intersections when used as transparent conductive films. In this work, a widely applicable nano-joining method for improving the overall conductivity of AgNW networks with different kinds of electrolyte solutions is presented. By treatment with an electrolyte solution with appropriate ionic strengths, the insulating surfactant layer (polyvinylpyrrolidone, PVP) on the AgNWs could be desorbed, and the AgNW network could be densified. The sheet resistance of the AgNW film on a glass slide is reduced by 60.9% (from 67.5 to 26.4 Ohm sq-1) with a transmittance of 92.5%. High-resolution transmission electron microscopy analysis indicates that atomic diffusion occurs at the intersection of two AgNWs. Thus, metallurgical bonding on the nanometer scale is achieved across the junctions of the AgNWs, leading to a significant enhancement in the conductivity of the AgNW network.