Nanocellulose-Based Functional Materials: From Chiral Photonics to Soft Actuator and Energy Storage

Nanocellulose is currently in the limelight of extensive research from fundamental science to technological applications owing to its renewable and carbon-neutral nature, superior biocompatibility, tailorable surface chemistry, and unprecedented optical and mechanical properties. Herein, an up-to-date account of the recent advancements in nanocellulose-derived functional materials and their emerging applications in areas of chiral photonics, soft actuators, energy storage, and biomedical science is provided. The fundamental design and synthesis strategies for nanocellulose-based functional materials are discussed. Their unique properties, underlying mechanisms, and potential applications are highlighted. Finally, this review provides a brief conclusion and elucidates both the challenges and opportunities of the intriguing nanocellulose-based technologies rooted in materials and chemistry science. This review is expected to provide new insights for nanocellulose-based chiral photonics, soft robotics, advanced energy, and novel biomedical technologies, and promote the rapid development of these highly interdisciplinary fields, including nanotechnology, nanoscience, biology, physics, synthetic chemistry, materials science, and device engineering.     

Polymer‐Based Magnetoelectric Materials

Polymer‐based magnetoelectric (ME) materials are an interesting, challenging and innovative research field, that will bridge the gap between fundamental research and applications in the near future. Here, the current state of the art on the different materials, the used configurations for the development of sensors and actuators, as well as the main values of the ME coupling obtained for the different polymer‐based systems are summarized. Further, some of the specific applications that are being developed for those polymer‐based ME materials are addressed as well as the main advantages and remaining challenges in this research field.     

Electric Field-Driven Dielectrophoretic Elastomer Actuators

Dielectrophoresis is the electro-mechanical phenomenon where a force is generated on a dielectric material when exposed to a non-uniform electric field. It has potential to be exploited in smart materials for robotic manipulation and locomotion, but to date it has been sparsely studied in this area. Herein, a new type of dielectrophoretic actuator exploiting a novel electroactive polymer is described, termed as dielectrophoretic elastomer (DPE), which undergoes electric field-driven actuation through dielectrophoresis. Unique deflection and morphing behavior of the elastomer induced by controlling the dielectrophoretic phenomenon, such as out-of-plane deformation and independence of electric field polarity, are illustrated. The dielectric and mechanical properties of the DPE are studied to gain insight into the influence of materials composition on deformation. Actuation performance using different electrode parameters is experimentally investigated with supplementary analysis through finite element simulation, revealing the relationship between electric field inhomogeneity and deflection. The applications of DPE actuators in a range of robotic devices is demonstrated, including a pump, an adjustable optical lens, and a walking robot. This diverse range of applications illustrates the wide potential of these new soft-and-smart electric field-driven materials for use in soft robotics and soft compliant devices.     

Bioinspired Self-healing Soft Electronics

Inspired by nature, various self-healing materials that can recover their physical properties after external damage have been developed. Recently, self-healing materials have been widely used in electronic devices for improving durability and protecting the devices from failure during operation. Moreover, self-healing materials can integrate many other intriguing properties of biological systems, such as stretchability, mechanical toughness, adhesion, and structural coloration, providing additional fascinating experiences. All of these inspirations have attracted extensive research on bioinspired self-healing soft electronics. This review presents a detailed discussion on bioinspired self-healing soft electronics. Firstly, two main healing mechanisms are introduced. Then, four categories of self-healing materials in soft electronics, including insulators, semiconductors, electronic conductors, and ionic conductors, are reviewed, and their functions, working principles, and applications are summarized. Finally, human-inspired self-healing materials and animal-inspired self-healing materials as well as their applications, such as organic field-effect transistors (OFETs), pressure sensors, strain sensors, chemical sensors, triboelectric nanogenerators (TENGs), and soft actuators, are introduced. This cutting-edge and promising field is believed to stimulate more excellent cross-discipline works in material science, flexible electronics, and novel sensors, accelerating the development of applications in human motion monitoring, environmental sensing, information transmission, etc.     

Development of Film Sensors Based on Conjugated Polymers for Copper (II) Ion Detection

A fluorescent film sensor was prepared by chemical modification of a polyfluorene derivative on a glass‐plate surface. X‐ray photoelectron spectroscopy and ellipsometry measurements demonstrate the covalent attachment of the polyfluorene derivative to the glass‐plate surface. The sensor was used to detect Cu²⁺ ions in aqueous solution by a mechanism exploiting fluorescence quenching of conjugated polymers. Among the tested metal ions, the film sensor presents good selectivity towards Cu²⁺ ions. Further experiments show that the sensing process is reversible. Moreover, sensory microarrays based on conjugated polymers targeting Cu²⁺ ions are constructed, which display similar sensing performance to that of the film sensor. The structural motif in which conjugated polymers are covalently confined to a solid substrate surface offers several attractive advantages for sensing applications. First, in comparison with film sensors in which small fluorescent molecules are employed as sensing elements, the sensitivity of our new film sensor is enhanced due to the signal‐amplifying effect of the conjugated polymers. Second, the film sensors or microarrays can be used in aqueous environments, which is crucial for their potential use in a wide range of real‐world systems. Since the sensing process is reversible, the sensing materials can be reused. Third, unlike physically coated polymer chains, the covalent attachment of the grafted chains onto a material surface precludes desorption and imparts long‐term stability of the polymer chains.     

Multifunctional Visible‐Light Powered Micromotors Based on Semiconducting Sulfur‐ and Nitrogen‐Containing Donor–Acceptor Polymer

Photosensitive micromotors that can be remotely controlled by visible light irradiation demonstrate great potential in biomedical and environmental applications. To date, a vast number of light‐driven micromotors are mainly composed from costly heavy and precious metal‐containing multicomponent systems, that limit the modularity of chemical and physical properties of these materials. Herein, a highly efficient photocatalytic micromotors based exclusively on a purely organic polymer framework—semiconducting sulfur‐ and nitrogen‐containing donor–acceptor polymer, is presented. Thanks to precisely tuned molecular architecture, this material has the ability to absorb visible light due to a conveniently situated energy gap. In addition, the donor‐acceptor dyads within the polymer backbone ensure efficient photoexcited charge separation. Hence, these polymer‐based micromotors can move in aqueous solutions under visible light illumination via a self‐diffusiophoresis mechanism. Moreover, these micromachines can degrade toxic organic pollutants and respond to an increase in acidity of aqueous environments by instantaneous colour change. The combination of autonomous motility and intrinsic fluorescence enables these organic micromotors to be used as colorimetric and optical sensors for monitoring of the environmental aqueous acidity. The current findings open new pathways toward the design of organic polymer‐based micromotors with tuneable band gap architecture for fabrication of self‐propelled microsensors for environmental control and remediation applications.     

Connecting at the speed of light

Light has a clear advantage over electronics as the medium of ultrafast information transmission. Optical fibers are used extensively in long-distance telecommunications applications and are making a strong showing in local-area networks. Board-to-board interconnects for terrabit data rates are just over the horizon. These technologies will see their full potential only when active, all-optical switches and logic can be coupled to present-day passive technologies. The key ingredient of the new systems will be the availability of nonlinear optical materials that meet active device needs. In this paper, material performance is shown to depend intimately on quantum mechanics, which sets fundamental limits on the nonlinear-optical response. While today's materials are already good enough to make devices, an understanding of the underlying quantum mechanics of how a material interacts with light can lead to even better materials.     

Wireless Technology in Industrial Networks

With the success of wireless technologies in consumer electronics, standard wireless technologies are envisioned for the deployment in industrial environments as well. Industrial applications involving mobile subsystems or just the desire to save cabling make wireless technologies attractive. Nevertheless, these applications often have stringent requirements on reliability and timing. In wired environments, timing and reliability are well catered for by fieldbus systems (which are a mature technology designed to enable communication between digital controllers and the sensors and actuators interfacing to a physical process). When wireless links are included, reliability and timing requirements are significantly more difficult to meet, due to the adverse properties of the radio channels. In this paper, we thus discuss some key issues coming up in wireless fieldbus and wireless industrial communication systems: 1) fundamental problems like achieving timely and reliable transmission despite channel errors; 2) the usage of existing wireless technologies for this specific field of applications; and 3) the creation of hybrid systems in which wireless stations are incorporated into existing wired systems.     

Messenger Materials Moving Forward: The Role of Functional Polymer Architectures as Enablers for Dynamic Nano-to-Macro Messaging

Identifying changes in the nanoscopic domain is a key challenge in the physicochemical sciences, where great interest is on sensing complex processes that involve cellular biochemical reactions, chemical heterogeneities, contact forces, and other interfacial phenomena. This has stimulated the development of diverse materials that allow subtle nanoscopic environments to be "seen". The challenge in the nano-domain has always been the ability to sense changes on the minute scale and rapidly transduce the information out for macroscopical observation. Ideally, materials should inform when processes are occurring. Recently, new systems that leverage established concepts with fluorescence- and plasmonic-based sensing have been devised, which has reinvigorated the domain, where functional polymers coupled in specific architectures to transducing motifs allow for a new basis of messenger materials to be realized. The key aspect in this regard is that the polymers allow for sensing to be achieved only when they are carefully coupled to the amplification system. In this perspective, the role of specific functional polymer architectures for the realization of nano-to-macro sensing of subtle nano-messengers is discussed and where the exciting field of messenger materials is seen moving forward is pointed out.     

Molecularly Imprinted Polymers and Electrospinning: Manufacturing Convergence for Next‐Level Applications

Micro‐ and especially nanofiber‐type of materials are extremely attractive for a number of applications, ranging from separation and analysis to drug delivery and tissue engineering, and the majority of them are currently produced worldwide via the extremely popular and effective electrospinning technique. The addition of specific tailored molecular recognition capability to these electrospun materials via the established molecular imprinting technology can be extremely beneficial for a number of applications, as indicated by the number of examples in the literature over the past 15 years. However, the integration of these two technologies has proven to be quite challenging, mainly due to the different processing methodologies which characterize the two approaches. In this progress report, the practical difficulties related to the combination of electrospinning and molecular imprinting and to the production of molecularly imprinted electrospun fibers are addressed, discussing the main aspects to take into consideration when designing and optimizing the experimental protocols, as well as highlighting the most prolific research applications that have been explored thus far, to conclude with a commercial/industrial and economic perspective on the envisaged market for these hybrid products.     

太赫兹复合材料无损检测技术及其应用

随着材料科学的迅速发展,复合材料、高分子材料在航空航天领域得到了广泛应用。由于这些材料的特殊性质,现有的较为成熟的探伤手段都不能有效对其进行检测。但对于太赫兹波来说,许多非极性、非金属材料都是半透明,可以有效探测到这些材料的内部缺陷。本文简要介绍了太赫兹的性质及太赫兹无损探伤原理,并以航天领域应用较广的几种复合材料为例对太赫兹无损检测应用做了简介。     

Production and Patterning of Liquid Phase–Exfoliated 2D Sheets for Applications in Optoelectronics

2D materials (2DMs), which can be produced by exfoliating bulk crystals of layered materials, display unique optical and electrical properties, making them attractive components for a wide range of technological applications. This review describes the most recent developments in the production of high‐quality 2DMs based inks using liquid‐phase exfoliation (LPE), combined with the patterning approaches, highlighting convenient and effective methods for generating materials and films with controlled thicknesses down to the atomic scale. Different processing strategies that can be employed to deposit the produced inks as patterns and functional thin‐films are introduced, by focusing on those that can be easily translated to the industrial scale such as coating, spraying, and various printing technologies. By providing insight into the multiscale analyses of numerous physical and chemical properties of these functional films and patterns, with a specific focus on their extraordinary electronic characteristics, this review offers the readers crucial information for a profound understanding of the fundamental properties of these patterned surfaces as the millstone toward the generation of novel multifunctional devices. Finally, the challenges and opportunities associated to the 2DMs' integration into working opto‐electronic (nano)devices is discussed.     

现代电子材料

系统地介绍了现代电子材料,对其中的几种新型材料,如纳米材料、智能材料、梯度材料等作了重点论述。为了从理论上说明新型电子材料的特性,特别着重分析其微观结构。并依此为根据,说明其宏观性能。从材料的微观结构出发,来分类新型材料,并标示出有代表性的材料。此外,还指出了电子材料的一些发展方向。     

Conductive “Smart” Hybrid Hydrogels with PNIPAM and Nanostructured Conductive Polymers

Stimuli‐responsive hydrogels with decent electrical properties are a promising class of polymeric materials for a range of technological applications, such as electrical, electrochemical, and biomedical devices. In this paper, thermally responsive and conductive hybrid hydrogels are synthesized by in situ formation of continuous network of conductive polymer hydrogels crosslinked by phytic acid in poly(N‐isopropylacrylamide) matrix. The interpenetrating binary network structure provides the hybrid hydrogels with continuous transporting path for electrons, highly porous microstructure, strong interactions between two hydrogel networks, thus endowing the hybrid hydrogels with a unique combination of high electrical conductivity (up to 0.8 S m^?1), high thermoresponsive sensitivity (significant volume change within several seconds), and greatly enhanced mechanical properties. This work demonstrates that the architecture of the filling phase in the hydrogel matrix and design of hybrid hydrogel structure play an important role in determining the performance of the resulting hybrid material. The attractive performance of these hybrid hydrogels is further demonstrated by the developed switcher device which suggests potential applications in stimuli‐responsive electronic devices.     

Conjugated Polymers of Intrinsic Microporosity (C‐PIMs)

Conjugated microporous polymers (CMPs) have shown great potential for energy and environmental issues, however, poor solubility and processability of most of these materials limit their applications. Herein, a range of linear conjugated polymers of intrinsic microporosity (C‐PIMs) is reported, combining for the first time the properties of conjugated microporous polymers, such as tunable electronic properties and compositional variation, with those of linear polymers of intrinsic microporosity (PIMs) allowing for solution processability and film formation. These soluble materials have a number of potential applications, for example as components in devices where large, porous interfaces are combined with extended electronic conjugation.     

Three‐Dimensionally Ordered Macroporous Polymeric Materials by Colloidal Crystal Templating for Reversible CO2 Capture

The design and preparation of porous materials with controlled structures and functionalities is crucial to a variety of absorption‐ or separation‐relevant applications, including CO₂ capture. Here, novel functional polymeric materials with three‐dimensionally ordered macroporous (3DOM) structures are prepared by using colloidal crystals as templates using relatively simple, rapid, and inexpensive approaches. These ordered structures are used for the reversible CO₂ capture from ambient air by humidity swing. Typically, the colloidal crystal template is synthesized from polymer latex particles of poly(methyl methacrylate) (PMMA) or polystyrene (PS). To maintain the functionality of the material, it is important to prevent the porous structure collapsing, which can occur by the hydrolysis of the ester bonds in conventional crosslinkers under basic conditions. This hydrolysis can be prevented by using a water‐soluble crosslinker containing two quaternary ammonium moieties, which can be used to prepare stable porous crosslinked polymers with the monomer (vinylbenzyl)trimethylammonium chloride (VBTMACl) and using a PMMA‐based colloidal crystal template. The hydroxide‐containing monomer and dicationic crosslinker are synthesized from their chloride precursors, avoiding the ion‐exchange step which causes shrinkage of the pores. An analysis of different methods for infiltrating the monomer solution into the colloidal crystal template shows that infiltration using capillary forces leads to fewer defects than infiltration under a partial vacuum. In addition, functional macroporous films with micrometer thickness are prepared from a template of PS‐based colloidal crystals in a thin film. In general, the colloidal crystal templated materials showed improved CO₂ absorption/desorption rates and swing sizes compared to a commercially available material with similar functional groups. This work could easily be extended to create a new generation of ordered macroporous polymeric materials with tunable functionalities for other applications.     

Deep Eutectic Solvents for Boosting Electrochemical Energy Storage and Conversion: A Review and Perspective

The pursuit of sustainable energy utilization arouses increasing interest in efficiently producing durable battery materials and catalysts with minimum environmental impact. As green, safe, and cheap eutectic mixtures, deep eutectic solvents (DESs) provide tremendous opportunities and open up attractive perspectives as charge transfer and reaction media for electrochemical energy storage and conversion (EESC). In this review, the fundamental properties of DESs are first summarized. Then, the important roles that DESs play in various EESC technologies including advanced electrolytes for batteries/supercapacitors, media for the preparation of electrode materials and catalysts, and extracting agents for battery recycling are systematically reviewed. A particular focus is placed on the fundamental understanding of structure–composition–property–performance relationships. Finally, the challenges for the controllable design of DESs for EESC applications and future developments are presented. This review is expected to shed light on developing advanced DESs for next-generation EESC systems.     

Mechanical Properties Tailoring of 3D Printed Photoresponsive Nanocellulose Composites

3D printing technologies allow control over the alignment of building blocks in synthetic materials, but compositional changes often require complex multimaterial printing steps. Here, 3D printable materials showing locally tunable mechanical properties are produced in a single printing step of Direct Ink Writing. These new inks consist of a polymer matrix bearing biocompatible photoreactive cinnamate derivatives and up to 30 wt% of anisotropic cellulose nanocrystals. The printed materials are mechanically versatile and can undergo further crosslinking upon illumination. When illuminating the material and controlling the irradiation doses, the Young's moduli can be adjusted between 15 and 75 MPa. Moreover, spatially controlled illumination allows patterning stiff geometries, resulting in 3D printed structures with segments of different mechanical properties tailoring the mechanical behavior under compression. The high design freedom implemented by 3D printing and photopatternability opens the venue to rapid manufacturing of devices for applications such as prosthetics or soft robotics where the 3D shapes and mechanical properties must be tailored for personalized load cases.     

Thermal Transport in Conductive Polymer–Based Materials

The demand for flexible conductive materials has motivated many recent studies on conductive polymer–based materials. However, the thermal conductivity of conductive polymers is relatively low, which may lead to serious heat dissipation problems for device applications. This review provides a summary of the fundamental principles for thermal transport in conductive polymers and their composites, and recent advancements in regulating their thermal conductivity. The thermal transport mechanisms in conductive polymer–based materials and up‐to‐date experimental approaches for measuring thermal conductivity are first summarized. Effective approaches for the regulation of thermal conductivity are then discussed. Finally, thermal‐related applications and future perspectives are given for conductive polymers and their composites.     

A Unique Processable Green Polymer with a Transmissive Oxidized State for Realization of Potential RGB‐Based Electrochromic Device Applications

Realization of commercial RGB‐based polymer electrochromic‐device applications can only be achieved by processable materials that possess three complementary colors in the reduced state and are transparent in the oxidized state. This report highlights the synthesis of the first processable green polymer with a transmissive oxidized state. The polymer revealed superior optical contrast in the visible region with fast switching times and robust stability. Hence, this material is the outstanding candidate for completion of RGB color space through commercial polymeric electrochromics.