High Dielectric Performances of Flexible and Transparent Cellulose Hybrid Films Controlled by Multidimensional Metal Nanostructures

Various wearable electronic devices have been developed for extensive outdoor activities. The key metrics for these wearable devices are high touch sensitivity and good mechanical and thermal stability of the flexible touchscreen panels (TSPs). Their dielectric constants (k) are important for high touch sensitivities. Thus, studies on flexible and transparent cover layers that have high k with outstanding mechanical and thermal reliabilities are essential. Herein, an unconventional approach for forming flexible and transparent cellulose nanofiber (CNF) films is reported. These films are used to embed ultralong metal nanofibers that serve as nanofillers to increase k significantly (above 9.2 with high transmittance of 90%). Also, by controlling the dimensions and aspect ratios of these fillers, the effects of their nanostructures and contents on the optical and dielectric properties of the films have been studied. The length of the nanofibers can be controlled using a stretching method to break the highly aligned, ultralong nanofibers. These nanofiber‐embedded, high‐k films are mechanically and thermally stable, and they have better Young's modulus and tensile strength with lower thermal expansion than commercial transparent plastics. The demonstration of highly sensitive TSPs using high‐k CNF film for smartphones suggests that this film has significant potential for next‐generation, portable electronic devices.     

From Wood to Textiles: Top‐Down Assembly of Aligned Cellulose Nanofibers

Advanced textiles made of macroscopic fibers are usually prepared from synthetic fibers, which have changed lives over the past century. The shortage of petrochemical resources, however, greatly limits the development of the textile industry. Here, a facile top‐down approach for fabricating macroscopic wood fibers for textile applications (wood‐textile fibers) comprising aligned cellulose nanofibers directly from natural wood via delignification and subsequent twisting is demonstrated. Inherently aligned cellulose nanofibers are well retained, while the microchannels in the delignified wood are squeezed and totally removed by twisting, resulting in a dense structure with approximately two times higher mechanical strength (106.5 vs 54.9 MPa) and ≈20 times higher toughness (7.70 vs 0.36 MJ m^?3) than natural wood. Dramatically different from natural wood, which is brittle in nature, the resultant wood‐textile fibers are highly flexible and bendable, likely due to the twisted structures. The wood‐textile fibers also exhibit excellent knitting properties and dyeability, which are critical for textile applications. Furthermore, functional wood‐textile fibers can be achieved by preinfiltrating functional materials in the delignified wood film before twisting. This top‐down approach of fabricating aligned macrofibers is simple, scalable, and cost‐effective, representing a promising direction for the development of smart textiles and wearable electronics.     

Super‐Strong,Super‐Stiff Macrofibers with Aligned,Long Bacterial Cellulose Nanofibers

With their impressive properties such as remarkable unit tensile strength, modulus, and resistance to heat, flame, and chemical agents that normally degrade conventional macrofibers, high‐performance macrofibers are now widely used in various fields including aerospace, biomedical, civil engineering, construction, protective apparel, geotextile, and electronic areas. Those macrofibers with a diameter of tens to hundreds of micrometers are typically derived from polymers, gel spun fibers, modified carbon fibers, carbon‐nanotube fibers, ceramic fibers, and synthetic vitreous fibers. Cellulose nanofibers are promising building blocks for future high‐performance biomaterials and textiles due to their high ultimate strength and stiffness resulting from a highly ordered orientation along the fiber axis. For the first time, an effective fabrication method is successfully applied for high‐performance macrofibers involving a wet‐drawing and wet‐twisting process of ultralong bacterial cellulose nanofibers. The resulting bacterial cellulose macrofibers yield record high tensile strength (826 MPa) and Young's modulus (65.7 GPa) owing to the large length and the alignment of nanofibers along fiber axis. When normalized by weight, the specific tensile strength of the macrofiber is as high as 598 MPa g^?1 cm³, which is even substantially stronger than the novel lightweight steel (227 MPa g^?1 cm³).     

Printable Transparent Conductive Films for Flexible Electronics

Printed electronics are an important enabling technology for the development of low‐cost, large‐area, and flexible optoelectronic devices. Transparent conductive films (TCFs) made from solution‐processable transparent conductive materials, such as metal nanoparticles/nanowires, carbon nanotubes, graphene, and conductive polymers, can simultaneously exhibit high mechanical flexibility, low cost, and better photoelectric properties compared to the commonly used sputtered indium‐tin‐oxide‐based TCFs, and are thus receiving great attention. This Review summarizes recent advances of large‐area flexible TCFs enabled by several roll‐to‐roll‐compatible printed techniques including inkjet printing, screen printing, offset printing, and gravure printing using the emerging transparent conductive materials. The preparation of TCFs including ink formulation, substrate treatment, patterning, and postprocessing, and their potential applications in solar cells, organic light‐emitting diodes, and touch panels are discussed in detail. The rational combination of a variety of printed techniques with emerging transparent conductive materials is believed to extend the opportunities for the development of printed electronics within the realm of flexible electronics and beyond.     

纤维素纳米纤维在食品包装领域的研究进展

目的 对纤维素纳米纤维的制备及其在食品包装领域的研究进行综述,以期为食品包装材料的发展提供理论支持。方法 总结近几年纤维素纳米纤维的不同加工制造方法,关注食品包装材料的气体阻隔性能、抑菌性能、紫外线阻隔性能、疏水性能和新鲜度监测性能等,阐明纤维素纳米纤维在食品包装中的研究进展。结果 可以通过化学法、化学法结合机械法和酶法等方法制备纤维素纳米纤维,但均存在产率低、能耗高、尺寸分布不均匀等问题。纤维素纳米纤维可以应用于气体阻隔、抗菌、防紫外线、疏水及智能包装材料,现阶段的纳米纤维制品很难兼顾多功能性。结论 纤维素纳米纤维食品包装材料有望取代石油基塑料包装,在食品包装领域具有较大的应用前景。     

纳米纤维素/聚乳酸复合包装薄膜的制备及表征

目的添加适量的纳米纤维素改善聚乳酸的脆性,以适应产品的包装。方法将聚乳酸(PLA)与纳米纤维素(CNFs)共混制备复合包装材料,测试该复合材料的力学性能、透光率、红外谱图,并用扫描电子显微镜(SEM)观察了复合包装材料的表面形貌。结果纳米纤维素添加到聚乳酸中增加了其力学性能,当纳米纤维素质量分数为2%时,拉伸强度和冲击强度都达到最大;随着添加CNFS比例的增大,CNFs/PLA复合薄膜材料的透光率随之降低,雾度随之升高,但是该薄膜作为包装材料对商品的可视性影响不大。结论纳米纤维素(CNFs)是具有一定长径比的纳米级线状材料,对材料的拉伸强度具有增强作用。     

透明氧化物薄膜的制备及其发展趋势

对近几年透明氧化物薄膜的制备进行了综述，重点介绍了溶胶-凝胶法、电沉积法、水热电化学法和喷雾热解法等方法的制备特点、性能评价以及透明氧化物薄膜的应用领域，并对今后透明氧化物薄膜的制备发展趋势进行了预测。     

p型透明导电氧化物薄膜的研究进展

p型透明导电膜是近来发现的一种新型的材料,在透明有源器件、传感器、透明电极和电路等方面具有广泛的潜在应用.近来在这方面的研究取得了一些突出的进展.本文主要综述了关于p型透明导电膜在材料、沉积工艺以及相关器件方面的研究进展.     

纤维素氨基甲酸酯膜的制备及性能

采用碱/尿素/水体系对实验室自制的纤维素氨基甲酸酯(N%-1.8)在双螺杆中进行低温溶解,过滤、脱泡,得到清亮的纤维素氨基甲酸酯溶液。探讨制膜液浓度、凝固浴浓度、凝固浴温度,凝固时间对再生膜力学性能的影响,并结合FT-IR、XRD、SEM对膜的结构和形貌进行表征。结果表明,制膜液浓度为4.5wt%,凝固浴为H2SO4-8%、HOAc-16%和H2SO4/Na2SO4-7%/9%,凝固温度20~30℃,凝固时间为5min时所得的膜具有较好的力学性能,抗拉强度达到60~70MPa,断裂伸长率为6~10%。     

羧甲基纤维素增强膜的制备及性能

目的为了获得一种可用于食品包装的羧甲基纤维素增强膜。方法以羧甲基纤维素(CMC)为成膜基底,甘油为增塑剂,分别将质量分数为1%,3%,5%和10%的纳米纤维素(NCC)添加到CMC中,共混流延制备羧甲基纤维素增强膜(CMC-NCC)。结果 NCC的加入,提高了CMC的力学性能和对水蒸气的阻隔性能,还提高了CMC的热性能。FT-IR分析结果表明,CMC与NCC两者间形成了分子间氢键;XRD分析结果表明,NCC可以改变CMC的结晶排列。当添加质量分数为5%的NCC时,CMC-NCC的拉伸强度比纯CMC膜提高了25.6%,断裂伸长率降低了21.3%,透湿量降低了9%,热稳定性提高了2%,透光率维持在87%以上。结论 CMC增强膜具有力学性能高、阻湿性能好等优点,NCC提高了CMC的成膜品质。     

Flexible Transparent Films Based on Nanocomposite Networks of Polyaniline and Carbon Nanotubes for High‐Performance Gas Sensing

A flexible, transparent, chemical gas sensor is assembled from a transparent conducting film of carbon nanotube (CNT) networks that are coated with hierarchically nanostructured polyaniline (PANI) nanorods. The nanocomposite film is synthesized by in‐situ, chemical oxidative polymerization of aniline in a functional multiwalled CNT (FMWCNT) suspension and is simultaneously deposited onto a flexible polyethylene terephthalate (PET) substrate. An as‐prepared flexible transparent chemical gas sensor exhibits excellent transparency of 85.0% at 550 nm using the PANI/FMWCNT nanocomposite film prepared over a reaction time of 8 h. The sensor also shows good flexibility, without any obvious decrease in performance after 500 bending/extending cycles, demonstrating high‐performance, portable gas sensing at room temperature. This superior performance could be attributed to the improved electron transport and collection due to the CNTs, resulting in reliable and efficient sensing, as well as the high surface‐to‐volume ratio of the hierarchically nanostructured composites. The excellent transparency, improved sensing performance, and superior flexibility of the device, may enable the integration of this simple, low‐cost, gas sensor into handheld flexible transparent electronic circuitry and optoelectronic devices.     

Flexible Transparent Electronic Gas Sensors

Flexible and transparent electronic gas sensors capable of real‐time, sensitive, and selective analysis at room‐temperature, have gained immense popularity in recent years for their potential to be integrated into various smart wearable electronics and display devices. Here, recent advances in flexible transparent sensors constructed from semiconducting oxides, carbon materials, conducting polymers, and their nanocomposites are presented. The sensing material selection, sensor device construction, and sensing mechanism of flexible transparent sensors are discussed in detail. The critical challenges and future development associated with flexible and transparent electronic gas sensors are presented. Smart wearable gas sensors are believed to have great potential in environmental monitoring and noninvasive health monitoring based on disease biomarkers in exhaled gas.     

一种基于锡锑氧化物的透明PN结及整流特性

利用反应磁控溅射法制备了半导体锡锑氧化物薄膜 (TAO). 根据霍尔效应测试结果,当Sn/Sb 原子比处于0.22~0.33范围内时,TAO薄膜是p型导电的,在此范围之外,TAO薄膜是n型导电的. 光学带隙测量结果表明,不同Sn/Sb比的TAO薄膜的禁带宽度基本相同(~3.9eV).构造了一个全透明的PN结,其中n区为Sn/Sb原子比为0.5的TAO薄膜, p区为Sn/Sb原子比为0.33的TAO薄膜.n区TAO的电极用铟锡氧化物（ITO）,p区TAO的电极用Cu薄膜.实验结果表明,由于两种导电类型的TAO薄膜具有相同的禁带宽度,上述透明PN结构具有典型的准同质PN结的整流特性.     

Optically Transparent Multiscale Composite Films for Flexible and Wearable Electronics

One of the key breakthroughs enabling flexible electronics with novel form factors is the deployment of flexible polymer films in place of brittle glass, which is one of the major structural materials for conventional electronic devices. Flexible electronics requires polymer films with the core properties of glass (i.e., dimensional stability and transparency) while retaining the pliability of the polymer, which, however, is fundamentally intractable due to the mutually exclusive nature of these characteristics. An overview of a transparent fiber-reinforced polymer, which is suggested as a potentially viable structural material for emerging flexible/wearable electronics, is provided. This includes material concept and fabrication and a brief review of recent research progress on its applications over the past decade.     

AZO薄膜用于GaN基LED透明电极的性能研究

采用脉冲激光沉积法制备了Al掺杂ZnO(AZO)薄膜, 研究了不同沉积氧压下薄膜的光电性能。当沉积压强为0.1 Pa时, AZO薄膜光电性能最优。将该薄膜用于GaN基LED透明电极作为电流扩展层, 在20 mA正向电流下观察到了520 nm处很强的芯片发光峰, 但芯片工作电压较高, 约为10 V, 芯片亮度随正向电流的增大而增强。二次离子质谱测试表明, AZO薄膜与GaN层界面处两种材料导电性能的变化以及钝化层的形成是导致芯片工作电压偏高的原因。