Highly Robust Lithium Ion Battery Anodes from Lignin: An Abundant,Renewable, and Low‐Cost Material

The synthesis, processing, and performance of a low‐cost monolithic battery electrode, produced entirely of natural and renewable resources, are reported. This anode material exhibits tunable electrochemical performance suitable for both high power and high energy applications. A synthesis method that directly results in electrically interconnected three‐dimensional architectures is presented, where the carbon framework functions as current collector and lithium insertion material, eliminating the extra mass and expense of inactive materials in conventional designs. Fibrous carbon electrode materials are produced from solvent extracted lignin using scalable melt processing technology and thermal conversion methods. The resulting free‐standing electrodes exhibit comparable electrochemical performance to commercial carbon‐based anodes at a fraction of the materials and processing costs. Compositional and electrochemical characterization shows that carbonized lignin has a disordered nano‐crystalline microstructure. The carbonized mats cycle reversibly in conventional aprotic organic electrolytes with Coulombic efficiencies over 99.9%. Moreover, lignin carbon fibers carbonized at 2000 °C can cycle reversibly in 1 m LiPF₆ in propylene carbonate.     

Dielectric Properties of Sustainable Nanocomposites Based on Zein Protein and Lignin for Biodegradable Insulators

Two types of lignin, alkali lignin and lignosulfonic acid sodium salt, are blended into thermoplastic zein through melt mixing in order to develop biodegradable insulator materials for multifunctional applications in electronics. The effects of lignin type and content on the dielectric properties of the resulting bio‐nanocomposites are investigated. The results indicate that, by modifying the structural arrangement of the zein with the use of lignin, it is possible to obtain bio‐nanocomposites characterized by tunable dielectric properties. The bio‐nanocomposites containing low amounts of lignin derivatives exhibit extensive protein structural changes together with a modification of the dielectric properties compared to the pristine thermoplastic zein. Changes in the dielectric properties of these systems are also observed to change over time, indicating a loss of plasticizer, as is evident by a decrease in the glass‐transition temperature. At high frequencies, the resulting values of the dielectric permittivity and of the loss tangent demonstrate that the bio‐nanocomposite can be used as biodegradable dielectric material for transient (temporary) electronics.     

Self‐Powered Optical Switch Based on Triboelectrification‐Triggered Liquid Crystal Alignment for Wireless Sensing

Here, a self‐powered optical switch (OS) composed of a surface‐etched single‐electrode triboelectric nanogenerator (TENG) and a polymer‐dispersed liquid crystal (PDLC) film is reported. The working principle of the developed OS is that the liquid crystal alignment can be driven by triboelectrification‐generated voltage, inducing the PDLC film to rapidly switch its initial translucent state to an instantaneous transparent state. An output voltage of 360 V is generated upon the PDLC film when a nitrile rubber film contacts with the TENG at an area of 25 cm² and a velocity of 0.4 m s^?1. As such, a wide dimming range with the relative transmitted light intensity from 0.05 to 0.85 can be achieved for the OS. Enabled by the unique mechano‐electro‐optical reaction, the effects of a series of structural parameters on the performance of the OS are methodically studied. Particularly, through integrating the OS with a visible‐light‐operated signal‐processing circuit, a complete wireless sensing system with a fully power‐free sensing node is developed. The paradigms of hand touching and foot stepping triggered wireless alarms are demonstrated, explicitly showing great potential for the system in many possible interactive human–machine interface applications, such as surveillance, security systems, remote operation, and automatic control.     

Wood‐Derived Lightweight and Elastic Carbon Aerogel for Pressure Sensing and Energy Storage

Lightweight and elastic carbon materials have attracted great interest in pressure sensing and energy storage for wearable devices and electronic skins. Wood is the most abundant renewable resource and offers green and sustainable raw materials for fabricating lightweight carbon materials. Herein, a facile and sustainable strategy is proposed to fabricate a wood‐derived elastic carbon aerogel with tracheid‐like texture from cellulose nanofibers (CNFs) and lignin. The flexible CNFs entangle and assemble into an interconnected framework, while lignin with high thermal stability and favorable stiffness prevents the framework from severe structural shrinkage during annealing. This strategy leads to an ordered tracheid‐like structure and significantly reduces the thermal deformation of the CNFs network, producing a lightweight and elastic carbon aerogel. The wood‐derived carbon aerogel exhibits excellent mechanical performance, including high compressibility (up to 95% strain) and fatigue resistance. It also reveals high sensitivity at a wide working pressure range of 0–16.89 kPa and can detect human biosignals accurately. Moreover, the carbon aerogel can be assembled into a flexible and free‐standing all‐solid‐state symmetric supercapacitor that reveals satisfactory electrochemical performance and mechanical flexibility. These features make the wood‐derived carbon aerogel highly attractive for pressure sensor and flexible electrode applications.     

Lignin as a Wood‐Inspired Binder Enabled Strong,Water Stable,and Biodegradable Paper for Plastic Replacement

Plastic waste has been increasingly transferred from land into the ocean and has accumulated within the food chain, causing a great threat to the environment and human health, indicating that fabricating an eco‐friendly and biodegradable replacement is urgent. Paper made of cellulose is attractive in terms of its favorable biodegradability, resource abundance, large manufacturing scale, and low material cost, but is usually hindered by its inferior stability against water and poor mechanical strength for plastic replacement. Here, inspired by the reinforcement principle of cellulose and lignin in natural wood, a strong and hydrostable cellulosic material is developed by integrating lignin into the cellulose. Lignin as a reinforced matrix is incorporated to the cellulose fiber scaffold by successive infiltration and mechanical hot‐pressing treatments. The resulting lignin‐cellulose composite exhibits an outstanding isotropic tensile strength of 200 MPa, which is significantly higher than that of conventional cellulose paper (40 MPa) and some commercial petroleum‐based plastics. Additionally, the composite demonstrates a superior wet strength of 50 MPa. Adding lignin also improves the thermostability and UV‐blocking performance of cellulose paper. The demonstrated lignin‐cellulose composite is biodegradable and eco‐friendly with both components from natural wood, which represents a promising alternative that can potentially replace the nonbiodegradable plastics.     

Synthesis and Fabrication of Multifunctional Nanocomposites: Stable Dispersions of Nanoparticles Tethered with Short,Dense and Polydisperse Polymer Brushes in Poly(methyl methacrylate)

This paper presents a melt‐processable multifunctional nanocomposite material that shows highly controlled tunability in refractive index, glass transition temperature (T_g) and energy bandgap. ZnO quantum dots tethered with polymer brushes are melt‐blended into the matrix polymer, giving rise to multiple functionalities in the nanocomposites. Brush–matrix polymer interactions are important in determining the ability of polymer‐grafted nanoparticles to disperse in a polymer melt, of which graft density (σ), brush (N) and matrix (P) polymer lengths are the critical parameters. It is generally assumed that long polymer brushes (N > P) and an optimum graft density are necessary to achieve a good dispersion. Here it is demonstrated that nanoparticles tethered with short, dense and polydisperse polymer brushes via radical copolymerization can exhibit a stable, fine dispersion in the polymer melt. The quality of the dispersion of the nanoparticles is characterized by measuring physical properties that are sensitive to the state of the dispersion. This synthesis method presents a general approach for the inexpensive and high‐throughput fabrication of high quality, melt‐blendable nanocomposites that incorporate functional nanoparticles, paving the way for wider application of high performance nanocomposites.     

Flexible,Highly Graphitized Carbon Aerogels Based on Bacterial Cellulose/Lignin: Catalyst‐Free Synthesis and its Application in Energy Storage Devices

Currently, most carbon aerogels are based on carbon nanotubes (CNTs) or graphene, which are produced through a catalyst‐assisted chemical vapor deposition method. Biomass based organic aerogels and carbon aerogels, featuring low cost, high scalability, and small environmental footprint, represent an important new research direction in (carbon) aerogel development. Cellulose and lignin are the two most abundant natural polymers in the world, and the aerogels based on them are very promising. Classic silicon aerogels and available organic resorcinol–formaldehyde (RF) or lignin–resorcinol–formaldehyde (LRF) aerogels are brittle and fragile; toughening of the aerogels is highly desired to expand their applications. This study reports the first attempt to toughen the intrinsically brittle LRF aerogel and carbon aerogel using bacterial cellulose. The facile process is catalyst‐free and cost‐effective. The toughened carbon aerogels, consisting of blackberry‐like, core–shell structured, and highly graphitized carbon nanofibers, are able to undergo at least 20% reversible compressive deformation. Due to their unique nanostructure and large mesopore population, the carbon materials exhibit an areal capacitance higher than most of the reported values in the literature. This property makes them suitable candidates for flexible solid‐state energy storage devices. Besides energy storage, the conductive interconnected nanoporous structure can also find applications in oil/water separation, catalyst supports, sensors, and so forth.     

Secondary Bonds Modifying Conjugate‐Blocked Linkages of Biomass‐Derived Lignin to Form Electron Transfer 3D Networks for Efficiency Exceeding 16% Nonfullerene Organic Solar Cells

Fabricating high‐efficient electron transporting interfacial layers (ETLs) with isotropic features is highly desired for all‐directional electron transfer/collection from an anisotropic active layer, achieving excellent power conversion efficiency (PCEs) on nonfullerene acceptor (NFA) organic solar cells (OSCs). The complicated synthesis and cost‐consumption in exploring versatile materials arouse great interest in the development of binary‐doping interlayers without phase separation and flexible manipulation. Herein, for the first time, a novel cathode interfacial layer based on biomass‐derived demethylated kraft lignin (D_MeKL) is proposed. Features of multiple phenolic‐hydroxyl (PhOH) and uniform‐distributed render D_MeKL to exhibit an excellent bonding capacity with amino terminal substituted perylene diiminde (PDIN), and successfully form a high‐efficient isotropic electron transfer 3D network. Synchronously, secondary bonds completely modify conjugate‐blocked linkages of D_MeKL, significantly enhance the electron transporting performance on cross‐section and vertical‐sections, and repair the contact of PDIN with active layer. The D_MeKL/PDIN‐based 3D‐network exhibits well‐matched work function (WF) (–4.34 eV) with cathode (–4.30 eV) and energy level of electron acceptor (–4.11 eV). D_MeKL/PDIN‐based NFAs‐OSC shows excellent short‐circuit current density (26.61 mA cm^–2) and PCE (16.02%) beyond the classic PDIN‐based NFA‐OSC (25.64 mA cm^–2, 15.41%), which is the highest PCEs among biomaterials interlayers. The results supply a novel method to achieve high‐efficient cathode interlayer for NFAs‐OSCs.     

Controlled Encapsulation of Hydrophobic Liquids in Hydrophilic Polymer Nanofibers by Co‐electrospinning

There are many technical situations, such as various biological or medical applications, in which a hydrophobic fluid must be encapsulated inside a hydrophilic polymer shell in the form of tiny microscopic pieces. A novel approach is presented, based on the co‐electrospinning of the hydrophilic polymer melt (outside) and the hydrophobic fluid (inside), which results in beaded micro‐ and nanofibers, such that the hydrophobic fluid is efficiently encapsulated inside the beads. For the selected fluid couple, the low liquid–liquid surface tension and the high viscosity of the melt prevent the varicose break‐up of inner fluid in the coaxial electrified jet until the very end of the co‐electrospinning process. The resulting fibers present beads filled with the hydrophobic fluid, separated by a rather uniform distance whose length depends partially on the melt flow rate. The bead diameter grows with the inner flow rate, going from a monosized to a bisized distribution. In the case under study, the maximum relative (inner‐to‐outer) flow rate is one. The diameter of the solid fibers between beads scales well with existing theories for simple electrospinning.     

Polyarylene Networks via Bergman Cyclopolymerization of Bis‐ortho‐diynyl Arenes

Bis‐ortho‐diynylarene (BODA) monomers, prepared from common bisphenols in three high yielding steps, undergo free‐radical‐mediated thermal polymerization via an initial Bergman cyclo‐rearrangement. Polymerization is carried out at 210 °C in solution or neat with large pre‐vitrification melt windows (4–5 h) to form branched oligomers containing reactive pendant and terminal aryldiynes. Melt‐ and solution‐processable oligomers with weight‐average molecular weight M_w = 3000–24 000 g mol^–1 can be coated as a thin film or molded using soft lithography techniques. Subsequent curing to 450 °C affords network polymers with no detectable glass transition temperatures below 400 °C and thermal stability ranging from 0.5–1.5 % h^–1 isothermal weight loss measured at 450 °C under nitrogen. Heating to 900–1000 °C gives semiconductive glassy carbon in high yield. BODA monomer synthesis, network characterization and kinetics, processability, thin‐film photoluminescence, and thermal properties are described.     

A Bi‐Sheath Fiber Sensor for Giant Tensile and Torsional Displacements

Current research about resistive sensors is rarely focusing on improving the strain range and linearity of resistance–strain dependence. In this paper, a bi‐sheath buckled structure is designed containing buckled carbon nanotube sheets and buckled rubber on rubber fiber. Strain decrease results in increasing buckle contact by the rubber interlayer and a large decrease in resistance. The resulting strain sensor can be reversibly stretched to 600%, undergoing a linear resistance increase as large as 102% for 0–200% strain and 160% for 200–600% strain. This strain sensor shows high linearity, fast response time, high resolution, excellent stability, and almost no hysteresis.     

Cover Picture: Controlled Encapsulation of Hydrophobic Liquids in Hydrophilic Polymer Nanofibers by Co‐electrospinning (Adv. Funct. Mater. 16/2006)

The cover shows an optical image of co‐electrospun nanofibers of poly(vinyl pyrrolidone) (outside) and hydrophobic oil (inside), irradiated by UV light. The resulting non‐woven mats present monosized beads regularly distributed along the nanofibers in work reported by Loscarteles and co‐workers on p. 2110. Only the beads fluoresce, due to special markers added to the oil, indicating that the oil is indeed wholly encapsulated inside the beads. There are many technical situations, such as various biological or medical applications, in which a hydrophobic fluid must be encapsulated inside a hydrophilic polymer shell in the form of tiny microscopic pieces. A novel approach is presented, based on the co‐electrospinning of the hydrophilic polymer melt (outside) and the hydrophobic fluid (inside), which results in beaded micro‐ and nanofibers, such that the hydrophobic fluid is efficiently encapsulated inside the beads. For the selected fluid couple, the low liquid–liquid surface tension and the high viscosity of the melt prevent the varicose break‐up of inner fluid in the coaxial electrified jet until the very end of the co‐electrospinning process. The resulting fibers present beads filled with the hydrophobic fluid, separated by a rather uniform distance whose length depends partially on the melt flow rate. The bead diameter grows with the inner flow rate, going from a monosized to a bisized distribution. In the case under study, the maximum relative (inner‐to‐outer) flow rate is one. The diameter of the solid fibers between beads scales well with existing theories for simple electrospinning.     

A Simple and Versatile Pathway for the Synthesis of Visible Light Photoreactive Nanoparticles

This work pioneers the design of visible (415 nm) and UV‐B light (300 nm) reactive nanoparticles via radical polymerization in aqueous heterogeneous media based on methyl methacrylate (MMA) and unique acrylates bearing tetrazole functionalities in a simple and straightforward two step reaction. Stable colloidal nanoparticles with an average diameter of 150 nm and inherent tetrazole functionality (varying from 2.5 to 10 wt% relative to MMA) are prepared via one‐pot miniemulsion polymerization. In a subsequent step, fluorescent pyrazoline moieties serving as linkage points are generated on the nanoparticles by either photoinduced nitrile imine‐mediated tetrazole‐ene cycloaddition (NITEC) or nitrile imine carboxylic acid ligation (NICAL) in water, thus enabling the particles as fluorescent tracers. Through in‐depth molecular surface analysis, it is demonstrated that the photoreactive nanoparticles undergo ligation to a variety of substrates bearing functionalities including maleimides, acrylates, or carboxylic acids, illustrating the versatility of the particle modification process. Critically, the unique ability of the photoreactive nanoparticles to be activated with visible light allows for their decoration with UV light–sensitive molecules. Herein, the ligation of folic acid—a vitamin prone to degradation under UV light—to the photoreactive nanoparticles using visible light is exemplified, demonstrating the synthetic power of our photoreactive fluorescent nanoparticle platform technology.     

Self‐Repairable,High Permittivity Dielectric Elastomers with Large Actuation Strains at Low Electric Fields

A one‐step process for the synthesis of elastomers with high permittivity, excellent mechanical properties and increased electromechanical sensitivity is presented. It starts from a high molecular weight polymethylvinylsiloxane, P1 , whose vinyl groups serve two functions: the introduction of polar nitrile moieties by reacting P1 with 3‐mercaptopropionitrile ( 1 ) and the introduction of cross‐links to fine tune mechanical properties by reacting P1 with 2,2′‐(ethylenedioxy)diethanethiol ( 2 ). This twofold chemical modification furnished a material, C2 , with a powerful combination of properties: permittivity of up to 10.1 at 10⁴ Hz, elastic modulus Y_10% = 154 kPa, and strain at break of 260%. Actuators made of C2 show lateral actuation strains of 20.5% at an electric field as low as 10.8 V μm^–1. Additionally, such actuators can self‐repair after a breakdown, which is essential for an improved device lifetime and an attractive reliability. The actuators can be operated repeatedly and reversibly at voltages below the first breakdown. Due to the low actuation voltage and the large actuation strain applications of this material in commercial products might become reality.     

Nature of Charge Carriers in a High Electron Mobility Naphthalenediimide Based Semiconducting Copolymer

The nature of charge carriers in recently developed high mobility semiconducting donor‐acceptor polymers is debated. Here, localization due to charge relaxation is investigated in a prototypal system, a good electron transporting naphthalenediimide based copolymer, by means of current‐voltage I‐V electrical characteristics and charge modulation spectroscopy (CMS) in top‐gate field‐effect transistors (FETs), combined with density functional theory (DFT) and time dependent DFT (TDDFT) calculations. In particular, pristine copolymer films are compared with films that underwent a melt‐annealing process, the latter leading to a drastic change of the microstructure. Despite the packing modification, which involves also the channel region, both the electron mobility and the energy of polaronic transitions are substantially unchanged upon melt‐annealing. The polaron absorption features can be rationalized and reproduced by TDDFT calculations for isolated charged oligomers. Therefore, it is concluded that in such a high electron mobility copolymer the charge transport process involves polaronic species which are intramolecular in nature and, from a more general point of view, that interchain delocalization of the polaron is not necessary to sustain charge mobilities in the 0.1 to 1 cm² V^{– 1} s^–1 range. These findings contribute to the rationalization of the charge transport process in the recently developed class of donor‐acceptor π‐conjugated copolymers featuring high charge mobilities and complex morphologies.     

Theoretical and experimental investigation of aluminum‐boron codoping of silicon

We present a detailed study on aluminum‐boron codoping of silicon by alloying from screen‐printed aluminum pastes containing boron additives (Al–B pastes). We derive an analytical model for the formation of the Al–B acceptor profiles by quantitatively describing (i) the composition of the Al–B–Si melt and (ii) the incorporation of Al and B acceptor atoms into the recrystallizing Si lattice. We show that measured Al–B dopant profiles can be excellently described by this model, which therefore offers a straightforward method for the comprehensive investigation of alloying from Al–B pastes. The formation of a characteristic kink in the Al–B dopant profile curve can thus be ascribed to the exhaustion of the B additive dissolution during alloying. By intentionally adding elemental B powder to an Al paste, we demonstrate that only a low percentage of the B powder actually dissolves into the melt. We show that this incomplete dissolution of the B additive strongly affects the recombination characteristics of Al–B–p⁺ regions and, thus, is an important element of alloying from Al–B pastes. This study therefore provides improved understanding of aluminum‐boron codoping of silicon. Copyright © 2015 John Wiley & Sons, Ltd.     

Temperature‐Induced Switchable Adhesion using Nickel–Titanium–Polydimethylsiloxane Hybrid Surfaces

A switchable dry adhesive based on a nickel–titanium (NiTi) shape‐memory alloy with an adhesive silicone rubber surface has been developed. Although several studies investigate micropatterned, bioinspired adhesive surfaces, very few focus on reversible adhesion. The system here is based on the indentation‐induced two‐way shape‐memory effect in NiTi alloys. NiTi is trained by mechanical deformation through indentation and grinding to elicit a temperature‐induced switchable topography with protrusions at high temperature and a flat surface at low temperature. The trained surfaces are coated with either a smooth or a patterned adhesive polydimethylsiloxane (PDMS) layer, resulting in a temperature‐induced switchable surface, used for dry adhesion. Adhesion tests show that the temperature‐induced topographical change of the NiTi influences the adhesive performance of the hybrid system. For samples with a smooth PDMS layer the transition from flat to structured state reduces adhesion by 56%, and for samples with a micropatterned PDMS layer adhesion is switchable by nearly 100%. Both hybrid systems reveal strong reversibility related to the NiTi martensitic phase transformation, allowing repeated switching between an adhesive and a nonadhesive state. These effects have been discussed in terms of reversible changes in contact area and varying tilt angles of the pillars with respect to the substrate surface.     

Piezoresistive Behavior Study on Finger‐Sensing Silicone Rubber/Graphite Nanosheet Nanocomposites

A novel finger‐sensing nanocomposite with remarkable and reversible piezoresistivity is successfully fabricated by dispersing homogeneously conductive graphite nanosheets (GNs) in a silicone rubber (SR) matrix. Because of the high aspect ratio of the graphite nanosheets, the nanocomposite displays a very low percolation threshold. The SR/GN nanocomposite with a volume fraction of conductive nanosheets closest to that for the percolation threshold presents a sharp positive‐pressure coefficient effect of the resistivity under very low pressure, namely, in the finger‐pressure range (0.3–0.7 MPa), whereby the abrupt transition could be attributed to compressive‐stress‐induced deformation of the conducting network. The super‐sensitive piezoresistive behavior of the nanocomposite is accounted for by an extension of the tunneling conduction theory which provides a good approximation to the piezoresistive effect.     

Purification of metallurgical‐grade silicon up to solar grade

An estimate has been made of the feasibility of a metallurgical purification process, the NEDO (New Energy and Industrial Technology Development Organization) melt‐purification process, for manufacturing solar‐grade silicon from metallurgical‐grade silicon. Equipment has been developed to pilot manufacturing plant scale. The system comprises an electron‐beam furnace for phosphorus removal and a plasma furnace for boron removal. Each furnace has a mold for directional solidification to remove metallic impurities. The concentration of each impurity in the silicon ingot purified through the whole process satisfied the solar‐grade level. The Solar‐grade silicon produced showed p‐type polarity and resistivity within the range 0·5–1·5 Ω cm. Copyright © 2001 John Wiley & Sons, Ltd.     

Liquid‐Crystalline Phase Behavior in a Zwitterionic Tetraazapentacene

A 5,7‐dioctadecylquinoxalinophenazine zwitterion 1 has been investigated to determine its thermal phase behavior. A combination of differential scanning calorimetry (DSC), variable temperature low‐ and high‐angle X‐ray diffraction (XRD), and deuterium solid‐state NMR spectroscopy were used to characterize the different phases of the tetraazapentacene 1 . This molecule is found to exist in a variety of crystalline solid phases between room temperature and 167 °C, with different room‐temperature phases resulting from crystallization from solution compared with cooling from the melt. Interestingly, the molecule exhibits liquid‐crystalline behavior at high temperatures, between 167 °C and 186 °C, above which it becomes an isotropic fluid. The presence of liquid‐crystalline behavior in a zwitterionic system opens up the potential for the use of these or related molecules in optoelectronic switching.