Programmable 3D Shape Changes in Liquid Crystal Polymer Networks of Uniaxial Orientation

3D programmable materials are highly interesting and have a great potential to enable smart robotic devices. Stimuli‐responsive liquid crystal polymer networks (LCNs) offer an attractive platform for the design and fabrication of 3D programmable materials. To date, extensive efforts have been devoted to the design of 3D programmable LCNs by spatially modulating the orientation of liquid crystals. However, the practical application of LCN actuators has been elusive, partly due to tedious orientation technology and monotonous geometry. To resolve this issue, programmable 3D shape changes achieved in LCNs with uniaxial orientation and homogenous composition using a mechanical programming process inspired by the “programming process” of shape‐memory polymers are reported. The mechanical programming process is suitable for LCNs with distinct geometries, for example, the film and fiber, suggesting a promising way for the design of 3D programmable LCN actuators with complex geometries, and deformation profiles (buckle, helix, horn).     

Low temperature bonded Cu/LCP materials for FPCs and their characteristics

A new cladding process has been developed using the surface activated bonding (SAB) method. In this process, the surfaces of materials to be bonded are cleaned, activated by Ar ion sputter etching, and immediately rolled together with low distortion at room temperature in a vacuum chamber . This process is applicable not only to cladding metals but also to laminating polymer film on metal without adhesives. We focused on laminating liquid crystal polymer (LCP) on copper (Cu) foil using the SAB method , which is different from other conventional methods . We also investigated the chemical state at the interface between the Cu foil and LCP film before and after heat treatment (up to 300/spl deg/C), by comparing with that on raw LCP film. All laminated materials were etched and cropped out, and the LCP surfaces were analyzed with X-ray photoelectron spectrometer (XPS). After the heat treatment, the ratio of C=O increased with increasing heat treatment temperature. It indicated that, under the high temperature of the heat treatment, the oxidation occurs not only at the Cu foil/sputtered Cu but also the LCP surfaces. We reported previously that the peel strength of laminated material made by the SAB method was improved by using Cu sputtering on the LCP film , . But after a heat-resistance test, the peel strength significantly decreased. This decrease resulted from the oxidation around the interface between the Cu foil/sputtered Cu and the LCP film due to gas permeation through the LCP film, and the softening of the Cu foil by its recrystallization due to high temperature. To prevent this loss of peel strength, we used Cu-0.02%Zr alloy foil with a higher recrystallization temperature and sputter Cu-Ni alloy or Ni-Cr alloy on the LCP film instead of Cu. It is also shown that the Cu/LCP materials produced by the SAB method have excellent electrical properties and etching ability.     

液晶聚合物薄膜的介电性能

研究了两种液晶聚合物薄膜的介电性能。结果表明,液晶聚合物的介电常数随频率的增加而缓慢变小,高温下的介电常数较大。介电损耗在一定的温度范围内（室温至３５０℃）出现峰值,峰值位置随频率的增加向高温方向移动。     

Specific Functionalization of Carbon Nanotubes for Advanced Polymer Nanocomposites

A novel approach to chemically functionalize multiwalled carbon nanotubes (MWCNTs) for making advanced polymeric nanocomposites with liquid crystalline polymers (LCPs) is presented. In this approach, two types of chemical moieties (i.e., carboxylic and hydroxyl benzoic acid groups) are selectively introduced onto the sidewalls of the MWCNTs. Fourier transform IR and Raman spectroscopy are used to examine the interaction between the functionalized MWCNTs and the LCP. The strong interaction between the functionalized MWCNTs and the LCP greatly improved the dispersion of MWCNTs in the polymer matrix as well as the interfacial adhesion. The dispersion of the MWCNTs in the LCP matrix is observed by optical microscopy and field‐emission scanning electron microscopy. As a result, the addition of 1 wt% MWCNTs in the LCP resulted in the significant improvement (41 and 55%) in the tensile strength and modulus of the LCP.     

Biomimetic Materials with Multiple Protective Functionalities

Natural tissues possess superior material properties such as self‐healing, mechanical robustness, and mechanical gradients that allow organisms to adapt and survive in dangerous environments. Although highly desired, imparting synthetic materials with these biomimetic protective features remains a challenge. Here, the versatile dimethylglyoxime–urethane (DOU) moiety is used to create a multifunctional polyurethane (DOU‐PU). The reactivities of DOU including reversible dissociation, metal coordination, photolysis enabled self‐healing, high strength and toughness, mechanical gradient formation, and spatially controlled functionalization. By incorporating DOU, a multifunctional protective film is produced with superior resistance to mechanical damage, rapid room temperature self‐healing, and anti‐counterfeiting features. This super biomimetic film is expected to be very useful for the protection of various types of valuable objects such as electronics, diplomas, currency, and automobiles.     

Humidity-Responsive Liquid Crystalline Network Actuator Showing Synergistic Fluorescence Color Change Enabled by Aggregation Induced Emission Luminogen

Imitating the structures and behaviors of natural creatures is of great significance to scientists to explore novel materials for practical applications. However, the design and fabrication of biomimetic devices with complex and outstanding performances is still on the way. A bilayer film composed of liquid crystalline networks (LCN) film and hydrochromic aggregation-induced-emission molecule-doped hydrophilic layer is prepared. Under different relative humidity, the composite film can deform and change fluorescence color simultaneously. The influence of the content of the hydrophilic matrix on the fluorescent property and humidity-responsive behaviors of the bilayer film is investigated. Thanks to the mechanical anisotropy provided by uniform-aligned LCN film, different modes of deformation of the bilayer film are achievable, like bending, curling, and twisting. More importantly, due to the independence of the LCN film and the non-mesogenic molecules brought by this bimorph strategy, complex alignment of the LCN film and modification by immiscible molecules are realized in a single LCN actuator. Based on the functional composite film, artificial flowers showing synergistic blooming and shape-changing is prepared. By regulating the molecular alignment of the LC mesogens of the LCN film, the artificial flowers can imitate various blooming behaviors of natural flowers like confederate jasmine and jade lotus.     

LCP基板在微波/毫米波系统封装的应用

液晶聚合物(LCP)在微波/毫米波频段内介电常数低,损耗小,并且其热稳定性高、机械强度大、吸湿率低,是一种适合于微波/毫米波电路应用、综合性能优异的聚合物材料。LCP基板可实现无源、有源器件的埋置和集成,且具有一定的气密特性,是一种具备实现系统级封装(SOP)能力的基板技术。文章系统地介绍了基于LCP材料基板的性能,并分析了相对于传统聚四氟乙烯(PTFE)基板的优势。还综述了近年来LCP基板作为微波/毫米波系统封装的研究进展,并指出LCP基板是一种具有良好发展前景的微波/毫米波系统级封装技术路线。     

Numerical Simulation of the Thermomechanical Behavior of Extruded Bismuth Telluride Alloy Module

Our research group developed over the past years a method to produce n- and p-type bismuth telluride alloys by mechanical alloying and powder extrusion. The resulting extruded rods possess a particular crystalline texture, which is advantageous for module fabrication processes but may have an impact on the stress distribution in modules under operating conditions. The reported mechanical strength of the extruded polycrystalline thermoelectric (TE) materials is larger than those of materials produced by directional solidification, allowing the fabrication of thinner TE modules in order to increase power densities. The stress arising from the resulting higher thermal gradients in thinner legs can eventually become greater than the TE material strength, which would limit further module thickness reduction. We present results of numerical simulations of TE modules behavior undertaken to evaluate the effect of leg lengths (1 mm, 500 μm, and 250 μm) on the stress level imposed by a given temperature difference that could cause their fracture. Different boundary conditions were imposed on the outer ceramic surfaces delimiting the module (e.g., both free or one anchored on a flat rigid surface). The boundary conditions and the mechanical strength of the soldering alloys are significant factors influencing the stress distribution in the TE alloy elements. We have also examined the effect of the crystalline texture of the extruded TE materials on the distribution and levels of stress, and found it to be marginal.     

LCP柔性基板的薄膜电阻制作技术

针对液晶聚合物(LCP)柔性基板高频电子封装应用需求,采用一种薄膜溅射工艺直接在LCP柔性基板上制作TaN薄膜电阻,研究不同等离子体预处理方式对LCP表面形貌和LCP表面薄膜金属膜层附着强度的影响,进一步研究溅射气压和氮气体积分数等参数对电阻性能的影响,考察LCP柔性基板上的TaN薄膜电阻精度及电阻温度系数(TCR),并制备出50Ω的薄膜电阻。结果表明:当射频功率为300 W的氧等离子体预处理600 s时,LCP表面的面粗糙度低,LCP基板表面薄膜金属膜层附着强度高,其值>5.0 N/mm²;当溅射功率为400 W、氮气体积分数为3%、溅射气压为0.2 Pa时,制备的TaN薄膜电阻的阻值精度高,阻值精度≤±4%,TCR电阻稳定性能好。     

Accordion‐like Actuators of Multiple 3D Patterned Liquid Crystal Polymer Films

This work describes the fabrication, characterization, and modelling of liquid crystalline polymer network films with a multiple patterned 3D nematic director profile, a stimuli‐responsive material that exhibits complex mechanical actuation under change of temperature or pH. These films have a discrete alternating striped or checkerboard director profile in the plane, and a 90‐degree twist through the depth of the film. When actuated via heating, the striped films deform into accordion‐like folds, while the film patterned with a checkerboard microstructure buckles out‐of‐plane. Furthermore, striped films are fabricated so that they also deform into an accordion shaped fold, by a change of pH in an aqueous environment. Three‐dimensional finite element simulations and elasticity analysis provide insight into the dependence of shape evolution on director microstructure and the sample's aspect ratio.     

4D Chiral Photonic Actuators with Switchable Hyper-Reflectivity

Cholesteric liquid crystals (CLCs) are chiral photonic materials reflecting only circularly polarized light with the same handedness as the helical polymer structure. Concurrent shape and color changes can be achieved using CLCs, but the fabrication of CLCs with switchable 3D shape, structural color, and hyper-reflectivity, that is, reflecting both left- and right-handed circularly polarized light simultaneously, has not yet been achieved. Here, CLC elastomer (CLCE) actuators are reported to reflect equal amounts of left- and right-handed circularly polarized light. Hyper-reflectivity is achieved by uniaxially stretching the partially crosslinked film to induce helix deformation which is then fully crosslinked to fix the deformed helical structure. The shape, structural color, and hyper-reflectivity of the polymer film are switchable with temperature. At high temperatures, only right-handed circularly polarized light is reflected and the color is redshifted. The film can be shaped in three dimensions: a structural colored 3D shaped beetle is fabricated using molding, which reflects both left- and right-handed circularly polarized light and shows reversible, temperature responsive structural color and 3D shape changes. Hence, 4D engineered bioinspired multifunctional materials are fabricated, which are interesting for applications ranging from sensing actuators to switchable hyper-reflective films and objects.     

Design of 50–70 GHz Planar Wideband Bandpass Filter on Liquid Crystal Polymer Substrate

In this paper, the authors propose a novel and compact 50-70 GHz planar microstrip bandpass filter, possessing sharp-rejection, low insertion-loss and wide-band characteristics, based on Liquid Crystal Polymer (LCP) substrates. The filter is fabricated on LCP substrates by using standard processing technologies. The proposed filter exhibits a return loss level better than 10 dB, an insertion loss of 5 dB and a 3-dB bandwidth of 30%.The measured and simulated results show good agreement, proving that LCPs are potential and very promising materials for flexible millimeter-wave substrate applications.     

退火温度对二氧化钒薄膜红外

针对提高用溶胶–凝胶法制备的VO 薄膜的红外透过率的问题,提出了制备时的最佳退火温度。简 要介绍了用无机溶胶凝胶法制备VO 薄膜的过程,对制备的VO 薄膜进行了差示扫描量热(DSC)、X射线电子能谱仪 (XPS)测试,分析了VO 薄膜的成分及相变温度。根据瑞利–高斯散射公式,通过散射截面与粒子密度计算和不同退火 温度下薄膜透过率的测试,重点讨论了退火温度、晶粒尺寸和红外透射率三者的关系。     

Elastically and Plastically Foldable Electrothermal Micro‐Origami for Controllable and Rapid Shape Morphing

Integrating origami principles within traditional microfabrication methods can produce shape morphing microscale metamaterials and 3D systems with complex geometries and programmable mechanical properties. However, available micro‐origami systems usually have slow folding speeds, provide few active degrees of freedom, rely on environmental stimuli for actuation, and allow for either elastic or plastic folding but not both. This work introduces an integrated fabrication–design–actuation methodology of an electrothermal micro‐origami system that addresses the above‐mentioned challenges. Controllable and localized Joule heating from electrothermal actuator arrays enables rapid, large‐angle, and reversible elastic folding, while overheating can achieve plastic folding to reprogram the static 3D geometry. Because the proposed micro‐origami do not rely on an environmental stimulus for actuation, they can function in different atmospheric environments and perform controllable multi‐degrees‐of‐freedom shape morphing, allowing them to achieve complex motions and advanced functions. Combining the elastic and plastic folding enables these micro‐origami to first fold plastically into a desired geometry and then fold elastically to perform a function or for enhanced shape morphing. The proposed origami systems are suitable for creating medical devices, metamaterials, and microrobots, where rapid folding and enhanced control are desired.     

Paper‐Like,Thin, Foldable,and Self‐Healable Electronics Based on PVA/CNC Nanocomposite Film

The facile fabrication of thin and foldable self‐healing electronics on a poly(vinyl alcohol)/cellulose nanocrystal (PVA/CNC) composite film is reported. The self‐healing property of the PVA/CNC nanocomposite film can be activated by spraying water on the film surface, via dynamic formation of hydrogen bonding. The self‐healing efficiency of PVA/CNC is influenced by the content of CNC in the film, pH of the spraying solution, and the temperature. Via vacuum filtration and pattern transfer techniques, both a supercapacitor and a temperature sensor are fabricated on the same PVA/CNC film using gold nanosheet (AuNS) and polyaniline/multiwalled nanotube (PANI/MWCNT) electrodes. The fabricated supercapacitor with a gel‐type electrolyte exhibits a high electrochemical performance, and the thermoresistive temperature sensor shows a linear sensitivity with a fast response. Both devices exhibit superior mechanical stability and self‐healing property over 100 repetitive folding and five repetitive healing cycles, respectively, retaining the device performance owing to the percolated network of the conductive materials. This work demonstrates that our paper‐like thin PVA/CNC film‐based self‐healable devices can serve as highly durable and deformable electronics with longevity.     

Molecular Stacking Induced by Intermolecular C–H···N Hydrogen Bonds Leading to High Carrier Mobility in Vacuum‐Deposited Organic Films

Simple bottom‐up fabrication processes for molecular self‐assembly have been developed for the construction of higher‐order structures using organic materials, and have contributed to maximization of the potential of organic materials in chemical and bioengineering. However, their application to organic thin‐film devices such as organic light‐emitting diodes have not been widely considered because simple fabrication of a solid film containing an internal self‐assembly structure has been regarded as difficult. Here it is shown that the intermolecular C–H···N hydrogen bonds can be simply formed even in vacuum‐deposited organic films having flat interfaces. By designing the molecules containing pyridine rings properly for the intermolecular interaction, one can control the molecular stacking induced by the intermolecular hydrogen bonds. It is also demonstrated that the molecular stacking contributes to the high carrier mobility of the film. These findings provide new guidelines to improve the performance of organic optoelectronic devices and open up the possibilities for further development of organic devices with higher‐order structures.     

Ultralarge Contraction Directed by Light‐Driven Unlocking of Prestored Strain Energy in Linear Liquid Crystal Polymer Fibers

Anisotropic 1D contraction motion of polymeric actuating materials has drawn growing interests in fields ranging from soft robotics to biomimetic muscles. Although light‐driven liquid crystal polymers (LCPs) represent promising candidates to realize contraction (<20%) triggered remotely and spatially, there remain multitudes of challenges to develop an LCP system possessing ultralarge contraction rate. Here, a novel strategy combining shape memory effect and photochemical phase transition is presented to realize light‐driven contraction as large as 81% in a newly designed linear liquid crystal copolymer, where the eutectic mesogens of azobenzene and phenyl benzoate self‐organize into the smectic B phase. Importantly, this highly ordered structure as the switching segment firmly locks the stress‐induced strain energy, which is rapidly released by reversible trans–cis photoisomerization that destroys the lamellar liquid crystal phase, therefore leading to such ultralarge contraction. Fibers serve as light‐driven building blocks to achieve precise origami, to mimic the recovery of a “broken” spider web and to screen objects in different sizes, laying new ground for advanced applications of light‐driven LCPs from biomimetic robots to human assists.     

Transparent Light-Driven Hydrogel Actuator Based on Photothermal Marangoni Effect and Buoyancy Flow for Three-Dimensional Motion

Marangoni-effect-driven actuators (MDAs) have the advantages of direct light-to-work conversion and convenient operation, which makes it widely researched in the cutting-edge fields including robots, micromachines, and intelligent systems. However, the MDA relies on the surface tension difference and it only works on the 2D liquid–air interface. Besides, the MDAs are normally pure black due to the light-absorption material limitation. Herein, a transparent light-driven 3D movable actuator (LTMA) and a 3D manipulation strategy are proposed. The LTMA is composed of photothermal nanoparticles-doped temperature-responsive hydrogel, whose surface energy changes as the nanoparticles absorb light energy. The 3D manipulation strategy combines Marangoni effect with photothermal buoyancy flow for realizing complex self-propellant and floating/sinking motions. The LTMA can perform more advanced tasks such as 3D obstacle avoidance and 3D sampling. Benefiting from the porous structure of hydrogel, LTMA can naturally absorb the chemical molecules for remote sampling and automated drug delivery. The light-driven, transparent, three-dimensionally movable, and programmable actuator has promising prospects in the field of micromachines and intelligent systems.     

Multiple H-Bonding Chain Extender-Based Ultrastiff Thermoplastic Polyurethanes with Autonomous Self-Healability,Solvent-Free Adhesiveness,and AIE Fluorescence

Developing an autonomous room temperature self-healing supramolecular polyurethane (PU) with toughness and stiffness remains a great challenge. Herein, a novel concept that utilizes a T-shaped chain extender with double amide hydrogen bonds in a side chain to extend PU prepolymers to construct highly stiff and tough supramolecular PU with integrated functions is reported. Mobile side-chain H-bonds afford a large flexibility to modulate the stiffness of the PUs ranging from highly stiff and tough elastomer (105.87 MPa Young's modulus, 27 kJ m⁻² tearing energy), to solvent-free hot-melt adhesive, and coating. The dynamic side-chain multiple H-bonds afford an autonomous self-healability at room temperature (25  ° C). Due to the rapid reconstruction of hydrogen bonds, this PU adhesive demonstrates a high adhesion strength, fast curing, reusability, long-term adhesion, and excellent low-temperature resistance. Intriguingly, the PU emits intrinsic blue fluorescence presumably owing to the aggregation-induced emission of tertiary amine domains induced by side-chain H-bonds. The PU is explored as a counterfeit ink coated on the predesigned pattern, which is visible-light invisible and UV-light visible. This work represents a universal and facile approach to fabricate supertough supramolecular PU with tailorable functions by chain extension of PU prepolymers with multiple H-bonding chain extenders.     

退火对CNx薄膜光学性质的影响

报道了退火对电子回旋共振(ECR)辅助脉)中激光溅射方法制备的CNx薄膜样品光学性质的影响，X射线衍射(XRD)结果显示CNx薄膜基本为无定形结构，但存在微量的多晶结构，拉曼散射谱显示所制备的CNx薄膜样品主要由C≡N、少量的C—C和微量的C≡N组成，随着退火温度的升高，拉曼散射谱不但在1357cm^-1附近出现了一个新峰(新峰对应无序的CN键)，而且C≡N和CN的相对含量比随着退火温度的提高大致呈先减小后增大再减小的趋势，从而证实在退火过程中部分N原子发生了迁移，椭偏仪所测量的CNx薄膜的光学常数表明退火温度对ε1、ε2、n、κ的大小和谱线的形状均产生了显著影响，结合拉曼散射谱可断定其原因为退火改变了CNx薄膜样品的内部结构和键结构，实验中得到的ε1、ε2、n、κ随光子能量的变化关系可用洛伦兹色散理论得到很好解释。