Cellulose‐Based Nanomaterials for Energy Applications

Cellulose is the most abundant natural polymer on earth, providing a sustainable green resource that is renewable, degradable, biocompatible, and cost effective. Recently, nanocellulose‐based mesoporous structures, flexible thin films, fibers, and networks are increasingly developed and used in photovoltaic devices, energy storage systems, mechanical energy harvesters, and catalysts components, showing tremendous materials science value and application potential in many energy‐related fields. In this Review, the most recent advancements of processing, integration, and application of cellulose nanomaterials in the areas of solar energy harvesting, energy storage, and mechanical energy harvesting are reviewed. For solar energy harvesting, promising applications of cellulose‐based nanostructures for both solar cells and photoelectrochemical electrodes development are reviewed, and their morphology‐related merits are discussed. For energy storage, the discussion is primarily focused on the applications of cellulose‐based nanomaterials in lithium‐ion batteries, including electrodes (e.g., active materials, binders, and structural support), electrolytes, and separators. Applications of cellulose nanomaterials in supercapacitors are also reviewed briefly. For mechanical energy harvesting, the most recent technology evolution in cellulose‐based triboelectric nanogenerators is reviewed, from fundamental property tuning to practical implementations. At last, the future research potential and opportunities of cellulose nanomaterials as a new energy material are discussed.     

Structuring of Functional Spider Silk Wires,Coatings, and Sheets by Self‐Assembly on Superhydrophobic Pillar Surfaces

Spider silk has recently become a material of high interest for a large number of biomedical applications. Previous work on structuring of silk has resulted in particles (0D), fibers (1D), films (2D), and foams, gels, capsules, or microspheres (3D). However, the manufacturing process of these structures is complex and involves posttreatment of chemicals unsuitable for biological applications. In this work, the self‐assembly of recombinant spider silk on micropatterned superhydrophobic surfaces is studied. For the first time, structuring of recombinant spider silk is achieved using superhydrophobic surfaces under conditions that retain the bioactivity of the functionalized silk. By tuning the superhydrophobic surface geometry and the silk solution handling parameters, this approach allows controlled generation of silk coatings, nanowires, and sheets. The underlying mechanisms and governing parameters are discussed. It is believed that the results of this work pave the way for fabrication of silk formations for applications including vehicles for drug delivery, optical sensing, antimicrobial coatings, and cell culture scaffolds.     

Anti‐Icing Superhydrophobic Surfaces Based on Core‐Shell Fossil Particles

A novel approach for the design of functional coatings using fossil diatomaceous earth particles decorated by a thin layer of grafted polymer chains is reported. The polymer‐modified diatomaceous earth particles are able to form liquid marbles, superhydrophobic surfaces, and are highly promising for the design of anti‐icing coatings.     

疏水二氧化硅/聚苯乙烯超疏水复合涂层的简易制备及其防沾污性研究

采用喷枪及家用简易喷雾器在含有聚乙烯(PE)膜的纸张表面制备了含疏水二氧化硅纳米颗粒和聚苯乙烯的超疏水复合涂层。随着疏水二氧化硅纳米颗粒含量的增加,表面逐渐被二氧化硅颗粒覆盖,并且形成微纳米孔洞结构,达到超疏水性,并具有良好的耐粘附稳定性,水、牛奶和橙汁等液滴可从这些超疏水表面滚落而不残留,具有良好的防沾污能力。     

Facile Fabrication of Eco‐Friendly Durable Superhydrophobic Material from Eggshell with Oil/Water Separation Property

Most superhydrophobic surfaces are fragile and even lose their functions under harsh conditions especially in outdoor applications. In this study, we have demonstrated a facile strategy for fabricating eco‐friendly and mechanical durable superhydrophobic material from eggshell. The as‐prepared superhydrophobic materials possess not only excellent self‐cleaning property and under oil superhydrophobicity, but also high‐efficient oil/water separation capability. More importantly, the obtained materials show outstanding and mechanical durable water repellency, which can maintain superhydrophobicity after 360 cm abrasion length of sandpaper. In addition, the materials also show durable superhydrophobic toward strong acidic/alkali solutions, UV irradiation, and water droplet impact, which demonstrates the outstanding chemical and environmental stability. This facile fabrication of the mechanical durable superhydrophobic materials and the utilization of daily garbage will provide the new ideas for engineering materials and accelerate the real application of the super‐repellent materials.

     

超疏水材料制备及其在油水分离中的应用研究进展

仿生界面油水分离材料的研究主要集中在超疏水超亲油材料,其具有高吸油能力和油品回收方便快捷等特性。本文评述了近几年超疏水材料制备及其在油水分离中应用的研究进展。     

Mineral Oil Barrier Testing of Cellulose‐Based and Polypropylene‐Based Films

Recycled cardboard has been identified as a major source of mineral oil hydrocarbon (MOH) contamination of foods. Identifying and using appropriate functional barriers is a mechanism through which this problem can be addressed. A number of cellulose‐based and biaxially oriented polypropylene (BOPP) films were evaluated as potential functional MOH barriers. The films were tested using a donor material, a paper containing MOH placed on one side of the film barrier and a paper which acted as the receptor on the other. Testing was performed at accelerated conditions of 60°C, the receptor analysed periodically for MOH. The results demonstrated that the cellulose‐based film types provided an MOH barrier of >3.5 years. This contrasted with the BOPP selected films, for which only the proprietary acrylic‐coated BOPP film provided an effective barrier to MOH migration. Further investigation of the MOH barrier properties of the proprietary acrylic‐coated BOPP film was undertaken. Various coating strategies were employed including increasing the coating application weight, increasing the number of coating lay downs and coating one or both surfaces of the film. It was found that an MOH barrier of 1.5 years when tested at 40°C could be achieved for the proprietary acrylic‐coated BOPP film; however, barrier effectiveness was dependent on the coating integrity of the film. Further work with a vertical form filler packaging machine and the use of a staining technique with transmission microscopy proved effective at highlighting and assessing the coating integrity of packets during a typical packaging operation. Copyright © 2014 John Wiley & Sons, Ltd.     

Cellulose‐Based Microparticles for Magnetically Controlled Optical Modulation and Sensing

Responsive materials with birefringent optical properties have been exploited for the manipulation of light in several modern electronic devices. While electrical fields are often utilized to achieve optical modulation, magnetic stimuli may offer an enticing complementary approach for controlling and manipulating light remotely. Here, the synthesis and characterization of magnetically responsive birefringent microparticles with unusual magneto‐optical properties are reported. These functional microparticles are prepared via a microfluidic emulsification process, in which water‐based droplets are generated in a flow‐focusing device and stretched into anisotropic shapes before conversion into particles via photopolymerization. Birefringence properties are achieved by aligning cellulose nanocrystals within the microparticles during droplet stretching, whereas magnetic responsiveness results from the addition of superparamagnetic nanoparticles to the initial droplet template. When suspended in a fluid, the microparticles can be controllably manipulated via an external magnetic field to result in unique magneto‐optical coupling effects. Using a remotely actuated magnetic field coupled to a polarized optical microscope, these microparticles can be employed to convert magnetic into optical signals or to estimate the viscosity of the suspending fluid through magnetically driven microrheology.     

新型陶瓷基复合超疏水涂层的制备及其性能

为了研究开发新型超疏水涂层的制备方法,改善涂层的结构与性能,以Al₂O₃-40%TiO₂(AT40)、PFA(全氟烷氧基乙烯基醚共聚物)粉末为原始材料,采用大气等离子喷涂(APS)技术,并调整电流、氩气流量等喷涂参数,在铝合金基体表面制备了两种不同的AT40/PFA复合超疏水涂层。利用相对应的测试仪器及分析手段对喷涂态涂层的相组成、显微结构、摩擦系数及基本性能等进行了表征分析。结果表明,两种涂层的相组成均为C₂₀F₄₂、Al₂TiO₅及少量的γ-Al₂O₃、α-Al₂O₃相;涂层表面均为圆形和椭圆形的粒状突起结构,其中突起结构的表面均存在类似荷叶表面结构的二元微纳米乳突结构,其表面粗糙度为9.3 μm和12.41 μm;所得涂层具有良好的综合性能,与水的静态接触角均达到了150°以上,滚动角为4~5°;在其他参数不变的情况下,随着电流的增大及氩气流量的减小,涂层中的陶瓷相含量增加,涂层的粗糙度、摩擦系数、显微硬度及结合强度均增大。     

Highly Stretchable Superhydrophobic Composite Coating Based on Self‐Adaptive Deformation of Hierarchical Structures

With the rapid development of stretchable electronics, functional textiles, and flexible sensors, water‐proof protection materials are required to be built on various highly flexible substrates. However, maintaining the antiwetting of superhydrophobic surface under stretching is still a big challenge since the hierarchical structures at hybridized micro‐nanoscales are easily damaged following large deformation of the substrates. This study reports a highly stretchable and mechanically stable superhydrophobic surface prepared by a facile spray coating of carbon black/polybutadiene elastomeric composite on a rubber substrate followed by thermal curing. The resulting composite coating can maintain its superhydrophobic property (water contact angle ≈170° and sliding angle <4°) at an extremely large stretching strain of up to 1000% and can withstand 1000 stretching–releasing cycles without losing its superhydrophobic property. Furthermore, the experimental observation and modeling analysis reveal that the stable superhydrophobic properties of the composite coating are attributed to the unique self‐adaptive deformation ability of 3D hierarchical roughness of the composite coating, which delays the Cassie–Wenzel transition of surface wetting. In addition, it is first observed that the damaged coating can automatically recover its superhydrophobicity via a simple stretching treatment without incorporating additional hydrophobic materials.     

仿生超疏水表面的发展及其应用研究进展

受自然界荷叶 “出淤泥而不染”的启发, 超疏水现象引起了研究者广泛的关注, 并成功制备了人工超疏水表面。本文对典型的仿生超疏水材料进行梳理, 并针对近期研究成果进行了综述, 对超疏水涂层的诸多制备方法作了优缺点总结和评述, 概述了超疏水涂层在自清洁、防覆冰、耐腐蚀和油水分离领域的应用研究现状, 尤其对超疏水防覆冰的机理及实现方式作了总结分析, 剖析了现阶段超疏水研究过程中面临的挑战, 展望了未来的发展趋势, 希望为超疏水涂层在工程领域的应用研究提供参考。     

Laser‐Induced Graphene in Controlled Atmospheres: From Superhydrophilic to Superhydrophobic Surfaces

The modification of graphene‐based materials is an important topic in the field of materials research. This study aims to expand the range of properties for laser‐induced graphene (LIG), specifically to tune the hydrophobicity and hydrophilicity of the LIG surfaces. While LIG is normally prepared in the air, here, using selected gas atmospheres, a large change in the water contact angle on the as‐prepared LIG surfaces has been observed, from 0° (superhydrophilic) when using O₂ or air, to >150° (superhydrophobic) when using Ar or H₂. Characterization of the newly derived surfaces shows that the different wetting properties are due to the surface morphology and chemical composition of the LIG. Applications of the superhydrophobic LIG are shown in oil/water separation as well as anti‐icing surfaces, while the versatility of the controlled atmosphere chamber fabrication method is demonstrated through the improved microsupercapacitor performance generated from LIG films prepared in an O₂ atmosphere.     

Thermoreversible Self‐Assembly of Perfluorinated Core‐Coronas Cellulose‐Nanoparticles in Dry State

Self‐assembly of nanoparticles (NPs) forming unique structures has been investigated extensively over the past few years. However, many self‐assembled structures by NPs are irreversible, because they are generally constructed using their suspensions. It is still challenging for NPs to reversibly self‐assemble in dry state, let alone of polymeric NPs with general sizes of hundreds of nm. Herein, this study reports a new reversible self‐assembly phenomenon of NPs in dry state, forming thermoreversible strip‐like supermolecular structures. These novel NPs of around 150 nm are perfluorinated surface‐undecenoated cellulose nanoparticles (FSU‐CNPs) with a core‐coronas structure. The thermoreversible self‐assembled structure is formed after drying in the air at the interface between FSU‐CNP films and Teflon substrates. Remarkably, the formation and dissociation of this assembled structure are accompanied by a reversible conversion of the surface hydrophobicity, film transparency, and anisotropic properties. These findings show novel feasibility of reversible self‐assembly of NPs in dry state, and thereby expand our knowledge of self‐assembly phenomenon.     

仿生超疏水棉织物的制备与表面分析

以荷叶表面微/纳米结构为参考模型,先用硅溶胶处理天然棉织物,再用N-β-氨乙基-γ-氨丙基聚二甲基硅氧烷(ASO-1)对其进行修饰,获得了微/纳米二元粗糙的超疏水织物,水滴在该织物表面接触角可达160.5°。场发射扫描电子显微镜(FE-SEM)观察发现超疏水纤维表面存在大量均匀分布的纳米微凸体。接触角分析表明织物织造过程中形成的微米级粗糙度和ASO-1膜的存在是织物疏水的主要原因,纳米微凸体能减少纤维与水的接触面积,提高水在纤维表面的接触角,使织物由疏水转变为超疏水。最后用X射线光电子能谱仪(XPS)证实了纤维表面SiO2粒子和ASO-1膜的存在。