Nacre-Inspired,Liquid Metal-Based Ultrasensitive Electronic Skin by Spatially Regulated Cracking Strategy

The realization of liquid metal-based wearable systems will be a milestone toward high-performance, integrated electronic skin. However, despite the revolutionary progress achieved in many other components of electronic skin, liquid metal-based flexible sensors still suffer from poor sensitivity due to the insufficient resistance change of liquid metal to deformation. Herein, a nacre-inspired architecture composed of a biphasic pattern (liquid metal with Cr/Cu underlayer) as “bricks” and strain-sensitive Ag film as “mortar” is developed, which breaks the long-standing sensitivity bottleneck of liquid metal-based electronic skin. With 2 orders of magnitude of sensitivity amplification while maintaining wide (>85%) working range, for the first time, liquid metal-based strain sensors rival the state-of-art counterparts. This liquid metal composite features spatially regulated cracking behavior. On the one hand, hard Cr cells locally modulate the strain distribution, which avoids premature cut-through cracks and prolongs the defect propagation in the adjacent Ag film. On the other hand, the separated liquid metal cells prevent unfavorable continuous liquid-metal paths and create crack-free regions during strain. Demonstrated in diverse scenarios, the proposed design concept may spark more applications of ultrasensitive liquid metal-based electronic skins, and reveals a pathway for sensor development via crack engineering.     

Photoresponse of composites of zinc oxide and poly(3-hexythiophene) under selective UV and white-light illumination

We investigate charge transport in UV sensing devices based on organic-inorganic semiconductor composites with the metal-semiconductor-metal (MSM) structure. Composite materials of zinc oxide (ZnO) nanoparticles and poly(3-hexylthiophene) (P3HT) were prepared by drop-casting their colloidal mixture in chloroform onto low-cost interdigitated copper electrodes. The current-voltage characteristics of the devices were investigated under both dark and illuminated conditions in the UV–visible range. The highest photoresponse was observed for an optimal P3HT:ZnO ratio of 1:8 w/w in the wavelength range between 310 and 380 nm. The dynamic response was investigated by pulsing a 365 nm UV light with a long period to reveal the response time of 4 s and the recovery time of less than 1 s. The photoresponse of the materials was also investigated for a shorter period of UV pulsing, using a rotating chopper. The response time and recovery time for the short UV pulse were found to be approximately 20 m and 25 m, respectively. The dual response times should stem from the presence of two types of semiconductor materials, namely ZnO with a high electron mobility and P3HT with a moderate hole mobility. To probe the charge generation and transport mechanisms, we further investigate the photoresponse using UV pulsing under background white light of different intensities, and vice versa. The background white light was found to deteriorate the UV photoresponse of the materials. On the other hand, the background UV illumination produced an anomalous photoresponse pattern with the white light pulsing. Understanding the charge transport mechanisms for composite materials is highly important for future applications in low-cost UV sensors and tunable optoelectronic devices.     

Synchronous Visual/Infrared Stealth Using an Intrinsically Flexible Self-Healing Phase Change Film

Phase change materials (PCMs) have been particularly concerned as infrared stealth functional materials due to their superior thermal management capability. However, traditional PCMs usually behave rigid solid or flowing liquid states with fixed transition temperature, greatly limiting their application especially in multi-band stealth and multiple scenes. Herein, an intrinsically flexible self-healing phase change film used for synchronous visual/infrared stealth for the first time is designed and constructed. The phase change film possesses a solid–solid phase transition behavior with adjustable transition temperature (from 38.8 to 51.1 °C) and enthalpy (from 79.7 to 116.7 J g⁻¹), long-term cycling stability (500 cycles), and outstanding flexible and self-healing performance. Remarkably, the phase change film can be customized with different colors and various configurations to exhibit attractive visual stealth functions in multiple scenes. Additionally, owing to phase transition property, this phase change film can possess a thermal management capability and behave infrared stealth performance for objectives at various temperatures. Combining the above unique functions, the intrinsically flexible self-healing phase change film developed in this work may show great potential for applications in the synchronous visual/infrared stealth across a wide range of scenarios and temperatures.     

Analysis of tunable photonic crystal devices comprising liquid crystal materials as defects

The tuning properties of two-dimensional dielectric and metallic photonic crystals, which contain nematic liquid crystal materials as defect elements or layers, are thoroughly analyzed using appropriate formulations of the finite difference time domain (FDTD) method. Our methodology correctly incorporates the anisotropy introduced by the liquid crystal materials together with the dispersive properties of the metallic elements; it is used for calculating both the dispersion diagrams of the defect-free photonic crystal as well as the device response in the presence of the defect elements. Numerical simulations reveal that defect states originating from the liquid crystal impurities can be effectively tuned by the application of a local static electric field. Indeed, tuning ranges up to almost 100 nm can be achieved requiring operating voltages lower than 4 V. It is also concluded that the placement of a defect mode relative to the bandgap edges greatly influences both its linewidth as well as its tuning range.     

Microwave characteristics of liquid-crystal tunable capacitors

This letter investigates the microwave characteristics of the liquid crystal tunable capacitors for the first time. With the dielectric anisotropy properties, the liquid crystal capacitors present very different characteristics compared to the semiconductor or MEMS tunable capacitors. A quality factor of 310 with a control voltage of 5 V was achieved at 4 GHz. A tuning range of 25.3% for the control voltages from 0 to 5 V was obtained at 5 GHz. The results demonstrate the potential applications of liquid crystals as dielectric materials for capacitors with high quality factors and wide tuning ranges at high frequencies, particularly suitable for the future flexible electronics with transparent substrates.     

Synthesis and characterization of CuO–SnO2 nanocomposite and its application as liquefied petroleum gas sensor

Present paper reports the synthesis of CuO–SnO₂ nanocomposite via sol–gel route as a sensing material for a liquefied petroleum gas (LPG). X-ray diffraction analysis confirmed the formation of CuO–SnO₂ nanocomposite. Crystallite size was found 5 nm. The optical band gap of the nanocomposite was found 4.1 eV. The thin/thick films were fabricated using spin coating and screen printing technology respectively and investigated with the exposition of LPG at room temperature (25 °C). Surface morphology of the thin film exhibits that it has a number of gas adsorption sites. The sensitivities of the thick and thin film sensors were found 4.1 and 42 respectively. The response and recovery times of the fabricated film sensor were 180 and 200 s respectively. Maximum sensor response of thin film sensor was found 4100. Better sensitivity and percentage sensor response, small response and recovery times, and good reproducibility and stability recognize the fabricated thin film of CuO–SnO₂ as a challenging material for the detection of LPG.     

Humidity-Initiated Gas Sensors for Volatile Organic Compounds Sensing

A new volatile organic compounds (VOCs) sensing concept called humidity-initiated gas (HIG) sensors is described and demonstrated. HIG sensors employ the impedance of water assembled at sensor interfaces when exposed to humidity to sense VOCs at low concentrations. Here, two HIG sensor variants are studied—Type I and Type II. Type I sensors benefit from simplicity, but are less attractive in terms of key performance metrics, including response time and detection limits. Type II sensors are more complex, but are more attractive in terms of key performance metrics. Notably, it is observed that the best-in-class Type II HIG sensors achieve <2 min response times and <10 ppb detection limit for geranyl acetone, a VOC linked to the asymptomatic form of Huanglongbing (HLB) citrus disease. Both Type I and Type II sensors are assembled from off-the-shelf materials and demonstrate remarkable stability at high humidity. HIG sensors are proposed as an attractive alternative to existing VOCs sensors for remote field detection tasks, including VOCs detection to diagnose HLB citrus disease.     

Nanoparticle-Based Strain Gauges: Anisotropic Response Characteristics,Multidirectional Strain Sensing,and Novel Approaches to Healthcare Applications

Directional strain sensing is essential for advanced sensor applications in the field of human-machine interfaces and healthcare. Here, the angle dependent anisotropic strain sensitivity caused by charge carriers percolating through cross-linked gold nanoparticle (GNP) networks is studied and these versatile materials are used for the fabrication of wearable triaxial pulse and gesture sensors. More specifically, the anisotropic response of 1,9-nonanedithiol cross-linked GNP films is separated into geometric and piezoresistive contributions by fitting the measured data with an analytic model. Hereby, piezoresistive coefficients of g₁₁ ∼ 32 and g₁₂ ∼ 21 are extracted, indicating a slightly anisotropic response behavior of the GNP-based material. To use the material for healthcare applications, arrangements of three GNP transducers are patterned lithographically and fully embedded into a highly flexible silicone polymer (Dragon Skin 30). The new encapsulation method ensures good and robust electrical contacts and enables facile handling and protection from external influences. A facile read-out with wireless data transmission using off-the-shelf electrical components underlines the great potential of these devices for applications as skin-wearable healthcare sensors.     

Optical absorptive response of platinum doped TiO2 transparent thin films with Au nanoparticles

In this paper different optical absorption bands associated to the surface plasmon of resonance of a nanoparticle containing sample were achieved by a sol–gel processing route. We study the linear and nonlinear optical absorptive properties of a titanium dioxide thin film with superficial Au nanoparticles. A chaotic behavior related with modification of the optical absorption by a multi-wave mixing interaction was investigated. A characteristic Mandelbrot group tendency was used to describe the possibility of a resulting absorptive response. The analysis of the observations showed that an excitation at 488 nm wavelength in the nanocomposite can originate a measurable change in the absorptive properties for the propagation of optical beams at 532 nm and at 650 nm. However, the inhibition of this condition exhibited by the film can be obtained by the shift of its plasmonic response. It is considered that the near resonance participation of the Au nanoparticles is mainly responsible for avoiding the photodarkening contribution to the optical absorptive response of the sol–gel TiO₂ film with embedded Au nanoparticles. Potential applications of the samples are proposed for development of optical sensors or transparent thin films for filtering functions.     

基于液晶材料的带宽可重构毫米波滤波器

根据液晶材料在毫米波段良好的介电特性和调谐能力,设计了一款基于液晶材料的毫米波带宽可重构宽带带通滤波器。滤波器使用一个高通滤波器和一个低通滤波器级联实现带通效果;在低通部分加载液晶材料,通过调谐液晶材料的等效介电常数改变低通滤波器的响应频率,实现带宽的可重构。仿真结果表明,当调谐液晶介电常数从2.4变化到3.8时,滤波器的高频截止频率从52 GHz下降至48 GHz,相对带宽从84.9%变为78.3%。     

3D-Printed Photoresponsive Liquid Crystal Elastomer Composites for Free-Form Actuation

Direct ink writing of liquid crystal elastomers (LCEs) offers a new opportunity to program geometries for a wide variety of shape transformation modes toward applications such as soft robotics. So far, most 3D-printed LCEs are thermally actuated. Herein, a 3D-printable photoresponsive gold nanorod (AuNR)/LCE composite ink is developed, allowing for photothermal actuation of the 3D-printed structures with AuNR as low as 0.1 wt.%. It is shown that the printed filament has a superior photothermal response with 27% actuation strain upon irradiation to near-infrared (NIR) light (808 nm) at 1.4 W cm⁻² (corresponding to 160 °C) under optimal printing conditions. The 3D-printed composite structures can be globally or locally actuated into different shapes by controlling the area exposed to the NIR laser. Taking advantage of the customized structures enabled by 3D printing and the ability to control locally exposed light, a light-responsive soft robot is demonstrated that can climb on a ratchet surface with a maximum speed of 0.284 mm s⁻¹ (on a flat surface) and 0.216 mm s⁻¹ (on a 30° titled surface), respectively, corresponding to 0.428 and 0.324 body length per min, respectively, with a large body mass (0.23 g) and thickness (1 mm).     

A Stiff yet Rapidly Self-Healable Elastomer in Harsh Aqueous Environments

Rapid underwater self-healing elastomers with high mechanical strength at ambient temperature are highly desirable for dangerous underwater operations. However, current room temperature self-healing materials have shortcomings, such as low healing strength (below megapascal), long healing time (hours), and decay of healing functions in harsh environments (salty, acidic, and basic solutions), limiting their practical applications. Herein, it is introduced water-stable Debye forces and high-density nano-sized physical crosslinking into one network to achieve a stiff yet rapid self-healing elastomer that can work in harsh aqueous environments. The obtained elastomer possesses a high Young's modulus of 48 MPa (24 times than that of natural elastomer), and it can achieve 90% of maximum mechanical strength healing for 10 s at ambient temperature in all types of harsh aqueous conditions, outperforming three orders of magnitudes in healing speed of reported room-temperature self-healing elastomers with Young's modulus over 10 MPa. The new stiff yet rapidly healable elastomers have great potential in emergent repair in urgent and dangerous cases.     

Light-Responsive Programmable Shape-Memory Soft Actuator Based on Liquid Crystalline Polymer/Polyurethane Network

Liquid crystalline polymers (LCPs), especially liquid crystalline elastomers (LCEs) can generate ultrahigh shape change amplitude but has lower mechanical strength. Although some attempts have been tried to improve the mechanical performance of LCE, there are still limitations including complicated fabrication and high actuation temperature. Here, a versatile method is reported to fabricate light-driven actuator by covalently cross-linking polyurethane (PU) into LCP networks (PULCN). This new scheme is distinct from the previous interpenetrating network strategy, the hydrogen bonds and covalent bonds are used in this study to improve the miscibility of non-liquid-crystalline PU and LCP materials and enhance the stability of the composite system. This material not only possesses the shape memory properties of PU but shows shape-changing behavior of LCPs. With a shrinkage ratio of 20% at the phase transition temperature, the prepared materials reached a maximum mechanical strength of 20 MPa, higher than conventional LCP. Meanwhile, the resulting film shows diverse and programmable initial shapes by constructing crosslinking density gradient across the thickness of the film. By integration of PULCN with near-infrared light-responsive polydopamine, local and sequential light control is achieved. This study may provide a new route for the fabrication of programmable and mechanically robust light-driven soft actuator.     

应变液晶研究进展

近年来在聚合物分散液晶与聚合物网络液晶研究中发现的应变液晶（stressed liquid crystal,SLC）引起国外研究者的极大兴趣。鉴于国内还缺乏相关研究的报导,本文综述了应变液晶之剪切液晶、拉伸液晶及压缩液晶的概念、基本理论和独特电光特性;并分别介绍了其在快速转换装置、大相位调制材料、空间光调制器、大孔径液晶透镜及棱镜、以及可调光栅等方面应用的研究进展以及可能在微显示、光学衍射元件和分光器件上的应用。     

Tunable and Robust Mid-Infrared Saturable Absorber Employing Tungsten Doping Cadmium Oxide

Mid-infrared (MIR) pulsed lasers operating at 2–5 µm have important applications in communication, sensing, and medicine. However, the lack of robust MIR saturable absorbers (SAs) remains a major obstacle. Here, a semiconductor material cadmium oxide (CdO) film with high laser-induced damage threshold (800 nm, 134 mJ cm⁻²) and broadband saturable absorption (2.0–3.9 µm) is investigated. The effective tuning of the nonlinear optical response of CdO is demonstrated by adjusting the carrier concentration via a tungsten (W)-doping scheme. The saturable absorption is improved and carrier relaxation process is accelerated after increasing the W-dopant level. Based on these findings, the robust CdO-SAs with customizable parameters are realized and Q-switched lasers with decreasing pulse width from 372 to 254.3 ns are obtained at 2 µm. The design flexibility provided by CdO opens up a large parameter space that enables the continuous improvement of compact and high-performance MIR ultrafast lasers.     

Microflotronics: A Flexible,Transparent, Pressure‐Sensitive Microfluidic Film

There is an increasing demand for sensitive, flexible, and low‐cost pressure sensing solutions for health monitoring, wearable sensing, robotic and prosthetic applications. Here, the first flexible and pressure‐sensitive microfluidic film is reported, referred to as a microflotronic, with high transparency and seamless integratability with the state‐of‐the‐art microelectronics. The microflotronic film represents the initial effort to utilize a continuous microfluidic layer as the sensing elements for large‐area dynamic pressure mapping applications, and meanwhile an ultrahigh sensitivity of 0.45 kPa^?1 has been achieved in a compact, flexible, and transparent packaging. The response time of the device is in the millisecond range, which is at least an order of magnitude faster than that of its conventional flexible solid‐state counterparts. In addition, the fabrication process of the device is fully compatible with the industrial‐scale manufacturing of capacitive touchscreen devices and liquid‐crystal displays. The overall device packaging can be as thin as 200 μm with an optical transparency greater than 80%. Several practical applications were successfully demonstrated, including surface topology mapping and dynamic blood pressure monitoring. The microflotronic devices offer an alternative approach to the solid‐state pressure sensors, by offering an unprecedented sensitivity and ultrafast response time in a completely transparent, flexible and adaptive platform.     

Multiscale Structural Nanocellulosic Triboelectric Aerogels Induced by Hofmeister Effect

The advent of self-powered wearable electronics will revolutionize the fields of smart healthcare and sports monitoring. This technological advancement necessitates more stringent design requirements for triboelectric materials. The triboelectric aerogels must enhance their mechanical properties to address the issue of structural collapse in real-world applications. This study fabricates stiff nanocellulosic triboelectric aerogels with multiscale structures induced by the Hofmeister effect. The aggregation and crystallization of polymer molecular chains are enhanced by the Hofmeister effect, while ice crystal growth imparts a porous structure to the aerogel at the micron scale. Therefore, the triboelectric aerogel exhibits exceptional stiffness, boasting a Young's modulus of up to 142.9 MPa and a specific modulus of up to 340.6 kN m kg^–1, while remaining undeformed even after supporting 6600 times its weight. Even after withstanding an impact of 343 kPa, highly robust wearable self-powered sensors fabricated with triboelectric aerogels remain operational. Additionally, the self-powered sensor is capable of accurately detecting human movements, particularly in abnormal fall postures detection. This study provides considerable research and practical value for promoting material design and broadening application scenarios for self-powered wearable electronics.     

Micro-mechanical testing of SiLK by nanoindentation and substrate curvature techniques

Advanced micro-mechanical characterization methods provide material properties of thin films for modeling thermo-mechanical behavior of thin films for micro-electronic applications. Here, we focus on the local measurement method of nanoindentation for finding visco-elastic properties, and a global method of substrate curvature testing that provides linear elastic properties. Our specimen SiLK, Dow chemicals, is a low-k dielectric thin polymer film with a thickness of 400 nm, 6 and 8 μm, deposited on Si substrate. Our results show temperature dependent linear elastic and linear visco-elastic material properties for thin film materials.     

Thermoreversible Siloxane Networks: Soft Biomaterials with Widely Tunable Viscoelasticity

Polysiloxane elastomers represent a widely utilized soft material with excellent rubber‐like elasticity, biocompatibility, and biodurability; however, there is a lack of an effective and straightforward approach to manipulate the material's viscoelastic response. A facile hydrosilylation reaction is employed to integrate ureidopyrimidinone hydrogen‐bonding side‐groups into linear and crosslinked siloxane polymers to achieve biocompatible soft materials with a highly tunable viscoelastic relaxation timescale. Stacking of H‐bonded moieties is avoided in the designed macromolecular architectures with tight, side‐groups substituents. The obtained siloxane network features the presence of both covalent crosslinks and truly thermoreversible crosslinks, and can be formulated across a broad material design space including elastic solids, recoverable viscoelastic solids, and viscous liquids. The elastomers exhibit unique temperature‐dependent shape‐memory capability and show good cytocompatibility. Importantly, a deformed material's shape‐recovery occurs regardless of external triggering, and through manipulation of network formulations, the shape‐recovery timescale can be easily tuned from seconds to days, opening new possibilities for biomedical, healthcare, and soft material applications.