Super‐Fast Switching of Twisted Nematic Liquid Crystals on 2D Single Wall Carbon Nanotube Networks

We have developed a high performance liquid crystal (LC) alignment layer of ultra‐thin single wall carbon nanotubes (SWNTs) and a conjugated block copolymer nanocomposite that is solution‐processible for conventional twisted nematic (TN) LC cells. The alignment layer is based on the non‐destructive solution dispersion of nanotubes with a poly(styrene‐b‐ paraphenylene) (PS‐b‐PPP) copolymer and subsequent spin coating, followed by conventional rubbing without a post‐annealing process. Topographically grooved nanocomposite films with two dimensionally (2D) networked SWNTs embedded in a block copolymer matrix were created using a rubbing process in which bundles of SWNTs on the composite surface were effectively removed. The LCs were well aligned with a stable pre‐tilt angle of approximately 2° on our extremely transparent nanocomposite, which gave rise to superfast switching of the TN LC molecules that was approximately 3.8 ms, or four times faster than that on a commercial polyimide layer. Furthermore, the TN LCD cells containing our SWNT nanocomposite alignment layers exhibited low power operation at an effective switching voltage amplitude of approximately 1.3 V without capacitance hysteresis.     

Highly Stretchable Conducting SIBS‐P3HT Fibers

Poly(styrene‐β‐isobutylene‐β‐styrene)‐poly(3‐hexylthiophene) (SIBS‐P3HT) conducting composite fibers are successfully produced using a continuous flow approach. Composite fibers are stiffer than SIBS fibers and able to withstand strains of up 975% before breaking. These composite fibers exhibit interesting reversible mechanical and electrical characteristics, which are applied to demonstrate their strain gauging capabilities. This will facilitate their potential applications in strain sensing or elastic electrodes. Here, the fabrication and characterization of highly stretchable electrically conducting SIBS‐P3HT fibers using a solvent/non‐solvent wet‐spinning technique is reported. This fabrication method combines the processability of conducting SIBS‐P3HT blends with wet‐spinning, resulting in fibers that could be easily spun up to several meters long. The resulting composite fiber materials exhibit an increased stiffness (higher Young’s modulus) but lower ductility compared to SIBS fibers. The fibers’ reversible mechanical and electrical characteristics are applied to demonstrate their strain gauging capabilities.     

氰酸酯树脂的改性及其反应机理的研究

本文介绍了目前氰酸酯（CE）树脂的几种改性途径及其反应机理．包括热同性树脂、热塑性树脂、橡胶弹性体、晶须及含不饱和双键的化合物等改性方法．其中主要阐述了环氧（EP）树脂和双马来酰亚胺（BMI）树脂改性CE的机理及共聚体系的性能。     

Polarization mode dispersion in spun fibers with different linearbirefringence and spinning parameters

This paper shows how the initial linear birefringence determines the necessary spinning parameters to produce spun fiber with optimum differential group delay (DGD) and polarization mode dispersion (PMD) properties. DGD measurements are reported on two pairs of fibers, each pair having been fabricated from a particular fiber preform. The fiber pairs each consist of a sample of spun and unspun fiber. These measurements are then compared with theoretical simulations for each fiber to determine the required range of spinning parameters for a given initial linear birefringence. These results should help in optimizing the spinning parameters for producing high-performance spun fibers     

Functional Polysaccharide Sutures Prepared by Wet Fusion of Interfacial Polyelectrolyte Complexation Fibers

This study reports polysaccharide‐based fibers that can be utilized as biocompatible functional sutures. Fibers are spontaneously formed by spinning at the interface between two oppositely charged polysaccharide solutions. Unlike the common belief that polysaccharide fibers prepared by electrostatic interactions would exhibit weak mechanical strength, it is demonstrated that fibers spun at the interface between two droplets of positively charged chitosan and negatively charged heparin can exhibit high mechanical strength through spontaneous wet‐state fusion of interfiber strands at a spinning wheel. Dry solidification results in multistranded fibers that were ≈100 µm in diameter with a tensile strength of ≈220 MPa. Post fibrous manipulation yields various morphology with straight or twisted fibers, fabrics, or springs. To demonstrate application of the fiber, it is applied as a medical suture. As heparin has a unique ability to bind adeno‐associated virus (AAV), a therapeutic, biocompatible suture exhibiting localized AAV‐mediated gene delivery function can be prepared. This study shows that multistrand fusion of fibers, formed by weak, electrostatic interactions and followed by drying solidification counterintuitively results in mechanically strong, functional fibers with various potential applications.     

High Mechanical Performance Composite Conductor: Multi‐Walled Carbon Nanotube Sheet/Bismaleimide Nanocomposites

Multi‐walled carbon nanotube (MWNT)‐sheet‐reinforced bismaleimide (BMI) resin nanocomposites with high concentrations (～60 wt%) of aligned MWNTs are successfully fabricated. Applying simple mechanical stretching and prepregging (pre‐resin impregnation) processes on initially randomly dispersed, commercially available sheets of millimeter‐long MWNTs leads to substantial alignment enhancement, good dispersion, and high packing density of nanotubes in the resultant nanocomposites. The tensile strength and Young's modulus of the nanocomposites reaches 2 088 MPa and 169 GPa, respectively, which are very high experimental results and comparable to the state‐of‐the‐art unidirectional IM7 carbon‐fiber‐reinforced composites for high‐performance structural applications. The nanocomposites demonstrate unprecedentedly high electrical conductivity of 5 500 S cm^?1 along the alignment direction. Such unique integration of high mechanical properties and electrical conductance opens the door for developing polymeric composite conductors and eventually structural composites with multifunctionalities. New fracture morphology and failure modes due to self‐assembly and spreading of MWNT bundles are also observed.     

Liquid‐Crystal Composites Composed of Photopolymerized Self‐Assembled Fibers and Aligned Smectic Molecules

A new liquid‐crystal composite, composed of photopolymerizable self‐assembled fibers and a smectic liquid crystal, and its photopolymerized composite have been prepared. The fibers oriented along the smectic layers are obtained by self‐assembly of an amino acid derivative with terminal methacryloyl groups in the smectic liquid crystal. The oriented fibrous structures are fixed by photopolymerization, resulting in the formation of microgrooves on the substrate surfaces. The aligned direction of the liquid‐crystalline molecules is changed to the direction along the fibers after thermal annealing. The patterning of liquid‐crystal alignment is achieved for these liquid‐crystal composites by patterned photopolymerization.     

ZnO/PVA Macroscopic Fibers Bearing Anisotropic Photonic Properties

Composite PVA/ZnO‐nanorods fibers, synthesized through co‐axial flux extrusion exhibit higher anisotropic photonic properties, both in absorption and emission, as a result of the collective alignment of the ZnO nanorods along the main axis of the PVA fiber. This photonic anisotropy is triggered by a synergistic interaction between the PVA matrix, stretched above the glass transition temperature (Tg), and cooled down under strain. Compared with non‐elongated fibers that present an isotropic emission, composite fibers previously submitted to a tensile stress absorb selectively UV emission when the polarized laser beam is parallel to the main axis of the fiber. In addition, their photolumincescence is also anisotropic, with a waveguide behavior along the main axis of the fiber. Mechanical properties of these composite fibers are also drastically improved, compared with pure PVA fibers: the longitudinal Young modulus of these fibers is increased from 2 to 6 GPa upon ZnO addition, a value similar to those already observed for composite fibers, prepared either with carbon nanotubes, or V₂O₅ macroscopic fibers.     

A Versatile,Molecular Engineering Approach to Simultaneously Enhanced,Multifunctional Carbon‐Nanotube– Polymer Composites

Single‐walled carbon nanotubes (SWNTs) are recognized as the ultimate carbon fibers for high‐performance, multifunctional composites. The remarkable multifunctional properties of pristine SWNTs have proven, however, difficult to harness simultaneously in polymer composites, a problem that arises largely because of the smooth surface of the carbon nanotubes (i.e., sidewalls), which is incompatible with most solvents and polymers, and leads to a poor dispersion of SWNTs in polymer matrices, and weak SWNT–polymer adhesion. Although covalently functionalized carbon nanotubes are excellent reinforcements for mechanically strong composites, they are usually less attractive fillers for multifunctional composites, because the covalent functionalization of nanotube sidewalls can considerably alter, or even destroy, the nanotubes' desirable intrinsic properties. We report for the first time that the molecular engineering of the interface between non‐covalently functionalized SWNTs and the surrounding polymer matrix is crucial for achieving the dramatic and simultaneous enhancement in mechanical and electrical properties of SWNT–polymer composites. We demonstrate that the molecularly designed interface of SWNT–matrix polymer leads to multifunctional SWNT–polymer composite films stronger than pure aluminum, but with only half the density of aluminum, while concurrently providing electroconductivity and room‐temperature solution processability.     

Carbon Nanotube Wires Sheathed by Aramid Nanofibers

Coaxial fibers are the key elements in many optical, electrical, and biomedical applications. Recent success in materials synthesis has provided versatile choices for the core part, but the search of high‐performance sheath materials remains much less productive. These surface coatings are however as important as the core for their role as protection layers and interaction medium with the externals, thereby critically affecting the real performance of coaxial fibers. Here it is shown that aramid nanofibers (ANFs) with exceptional environmental stability and mechanical properties can be advanced coating materials for both wet‐ and dry‐spun carbon nanotube (CNT) wires. Co‐wet‐spinning ANFs with CNT aqueous dispersion can produce coaxial fibers with a compact sheath comprised of aligned ANFs, showing much enhanced mechanical properties by transferring stress to the sheath without sacrificing the conductivity. On the other hand, an immersion‐precipitation process is used to prepare a porous sheath made from randomly distributed nanofibers on dry‐spun CNT wires, which can be combined with ionic conductive gel electrolyte as a strong packaging layer for flexible solid‐state supercapacitors. The excellent intrinsic characteristics as well as variable ways of structural organizations make ANF‐based coatings an attractive tool for the design of multifunctional high‐performance hybrid materials.     

Quantitative In Situ Mechanical Characterization of the Effects of Chemical Functionalization on Individual Carbon Nanofibers

Carbon nanofibers (CNFs) have been used for applications in composite material for decades because of their unique mechanical, thermal, and electrical properties. Consequently, an in‐depth understanding of mechanical properties of individual CNFs, particularly after chemical functionalization, would provide important insight into its effective integration into composite materials. Fluorination and amination of CNFs is achieved and systematic chemical characterizations of functionalized CNFs are performed. An in situ tensile testing method, which combines a simple microfabricated device with a quantitative nanoindenter inside a scanning electron microscope (SEM) chamber, is used to measure mechanical properties of individual pristine, fluorinated, and amino‐functionalized CNFs. The nominal CNFs strengths follow the Weibull distribution and the fluorinated CNFs are found to possess higher nominal strength but similar strain when compared with the pristine and amino‐functionalized CNFs. SEM fracture surfaces analysis shows that all nanofibers failed in a similar cup‐and‐cone fashion. Microscopy image sof fluorinated CNFs reveal an unexpected change in the hollow core before and after fiber fracture, which is attributed to the possible effects of fluorination‐induced compression on nanofiber surfaces. The results demonstrate the potential of fluorination for improving both the mechanical properties of CNFs and their successful integration into composites.     

Strain‐Responsive Polyurethane/PEDOT:PSS Elastomeric Composite Fibers with High Electrical Conductivity

It is a challenge to retain the high stretchability of an elastomer when used in polymer composites. Likewise, the high conductivity of organic conductors is typically compromised when used as filler in composite systems. Here, it is possible to achieve elastomeric fiber composites with high electrical conductivity at relatively low loading of the conductor and, more importantly, to attain mechanical properties that are useful in strain‐sensing applications. The preparation of homogenous composite formulations from poly­urethane (PU) and poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) that are also processable by fiber wet‐spinning techniques are systematically evaluated. With increasing PEDOT:PSS loading in the fiber composites, the Young's modulus increases exponentially and the yield stress increases linearly. A model describing the effects of the reversible and irreversible deformations as a result of the re‐arrangement of PEDOT:PSS filler networks within PU and how this relates to the electromechanical properties of the fibers during the tensile and cyclic stretching is presented.     

Interactions Between Amino Acid‐Tagged Naphthalenediimide and Single Walled Carbon Nanotubes for the Design and Construction of New Bioimaging Probes

A new synthetic route to functionalized single walled carbon nanotubes (SWNTs) via supramolecular interactions using a specifically designed naphthalenediimide (NDI) nanoreceptor is demonstrated. The tendency of the NDI to spontaneously form composites with carbon nanomaterials leads to fluorescent amino acid tagged SWNTs, which are dispersible in widely accessible organic solvents (CHCl₃, DMSO) as well as in biocompatible cell medium (EMEM, Eagle's modified essential medium). The X‐ray crystal structure of the first iodine‐tagged and amino acid‐functionalized NDI molecule, designed especially to facilitate the high resolution transmission electron microscopy (HR TEM) imaging whilst retaining its ability to self‐assemble into a nanodimensional receptor in weakly polar solvents, is also described. A new hybrid material, NDI@SWNT, was prepared and characterized as dispersed in organic solvents and aqueous media and in the solid state by HR TEM, tapping mode atomic force microscopy (TM AFM), scanning electron microscopy (SEM), circular dichroism, Raman and fluorescence spectroscopies (steady‐state single and two‐photon techniques). Combined microscopy techniques, density functional theory (DFT) calculations using the Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) program and spectroscopic measurements in solution indicate that amino acid‐functionalized NDI interacts strongly with SWNTs and forms a donor‐acceptor complex. Density functional theory (DFT) calculations predicted the geometry and the binding energies of an NDI molecule loaded onto a SWNT strand and the possibility of charge transfer interactions within the hybrid. The NDI@SWNT composite translocates into cells (e.g. FEK‐4, HeLa, MCF‐7) as an intact object and localizes in the cells' cytoplasm and partially in the nucleus. The NDI coating enhances the biocompatibility of SWNTs and mediates its intracellular localization as shown by confocal fluorescence imaging and fluorescence lifetime imaging (FLIM) techniques. The excited state fluorescence lifetime of the probes in cells versus solution phase indicates that the probes remain unaffected by the change in their chemical environment within the experimental timescale (2 h).     

Reinforcing Epoxy Polymer Composites Through Covalent Integration of Functionalized Nanotubes

Strong interfacial bonding and homogenous dispersion have been found to be necessary conditions to take full advantage of the extraordinary properties of nanotubes for reinforcement of composites. We have developed a fully integrated nanotube composite material through the use of functionalized single‐walled carbon nanotubes (SWNTs). The functionalization was performed via the reaction of terminal diamines with alkylcarboxyl groups attached to the SWNTs in the course of a dicarboxylic acid acyl peroxide treatment. Nanotube‐reinforced epoxy polymer composites were prepared by dissolving the functionalized SWNTs in organic solvent followed by mixing with epoxy resin and curing agent. In this hybrid material system, nanotubes are covalently integrated into the epoxy matrix and become part of the crosslinked structure rather than just a separate component. Results demonstrated dramatic enhancement in the mechanical properties of an epoxy polymer material, for example, 30–70 % increase in ultimate strength and modulus with the addition of only small quantities (1–4 wt.‐%) of functionalized SWNTs. The nanotube‐reinforced epoxy composites also exhibited an increased strain to failure, which suggests higher toughness.     

Local Birefringence in Unidirectionally Spun Fibers

The application of a spinning step in the drawing process is known to improve optical-fiber polarization mode dispersion. For a more comprehensive understanding of the mechanism through which spinning modifies fiber performances, in this paper, the authors investigate the effect of unidirectional spinning on local fiber birefringence in terms of the effectiveness of spin-function transfer and reduction of the local intrinsic birefringence under different drawing conditions. The actual frozen-in spin is experimentally recovered by means of a cut-back procedure. Different from the case of a periodic spinning, a unidirectional spinning correctly reproduces the nominally imparted spin rate in agreement with theoretical modelizations of the transfer effectiveness of the spinning process. A theoretical explanation for the experimental evidence, recently proved by tomographic stress measurements, of spinning affecting fiber linear intrinsic birefringence is provided. In particular, the interaction of drawing parameters and spinning process in defining stress development into fibers is considered. To validate the proposed model, further tomographic reconstructions of stress profiles in fiber spun at different rates and drawing speed were carried out. Besides, corresponding stress-induced birefringence values were estimated and compared with those recovered by the cut-back technique. Variations of spun fiber beatlength values with respect to the unspun case, as obtained from both measurement techniques, are in good agreement, providing a further reliable confirmation that an improvement of the beatlength may proceed as a consequence of the applied spin     

Carbon Fiber–Bismaleimide Composites Filled with Nickel‐Coated Single‐Walled Carbon Nanotubes for Lightning‐Strike Protection

Multifunctional carbon fiber composites are imperative for next‐generation lightweight aircraft structures. However, lightning‐strike protection is a feature that is lacking in many modern carbon fiber high‐temperature polymer systems, due to their high electrical resistivity. This work presents a study on processing, materials optimization, and property development of high‐temperature bismaleimide (BMI)–carbon fiber composites filled with nickel‐coated single‐walled carbon nanotubes (Ni‐SWNTs) based on three key factors: i) dispersion of Ni‐SWNTs, ii) their surface coverage on the carbon plies and, iii) the composite surface resistivity. Atomic force microscopy analysis revealed that coating purified SWNTs with nickel enabled improved dispersion which resulted in uniform surface coverage on the carbon plies. The electrical resistivity of the baseline composite system was reduced by ten orders of magnitude by the addition of 4 wt% Ni‐SWNTs (calculated with respect to the weight of a single carbon ply). Ni‐SWNT–filled composites showed a reduced amount of damage to simulated lightning strike compared to their unfilled counterparts, as indicated by the minimal carbon fiber pull‐out.     

Polarization properties of randomly-birefringent spun fibers

The spinning of single-mode telecommunication fibers is a technique currently and widely used to reduce polarization mode dispersion. Yet, this technique was originally envisaged as a way to produce fibers with arbitrarily low birefringence, to be used in sensor applications. In spite of their applicative significance, spun fibers are still not completely understood. In this paper, we report an extensive analysis of the polarization properties of spun fiber. Both unidirectional and periodic spin profiles are considered. It is shown that very high polarization maintaining capabilities may be achieved by properly tuning the spin parameters.     

First- and second-order PMD statistical properties of constantly spun randomly birefringent fibers

Polarization-mode dispersion (PMD) causes significant impairment for high bit-rate optical telecommunications systems. It is known that PMD can be strongly reduced by spinning the fiber as it is drawn. In this paper, we focus on the case of randomly birefringent fibers spun at a constant rate, providing analytical expressions for the asymptotic statistical properties of PMD. In particular, we investigate the behavior of the first- and second-order PMD, demonstrating that a constantly spun fiber behaves asymptotically as an unspun fiber. Conversely, we show that the distance at which the PMD reaches its asymptotic trend increases with the spin rate up to lengths of several kilometers.     

Ag Nanowire Reinforced Highly Stretchable Conductive Fibers for Wearable Electronics

Stretchable conductive fibers have received significant attention due to their possibility of being utilized in wearable and foldable electronics. Here, highly stretchable conductive fiber composed of silver nanowires (AgNWs) and silver nanoparticles (AgNPs) embedded in a styrene–butadiene–styrene (SBS) elastomeric matrix is fabricated. An AgNW‐embedded SBS fiber is fabricated by a simple wet spinning method. Then, the AgNPs are formed on both the surface and inner region of the AgNW‐embedded fiber via repeated cycles of silver precursor absorption and reduction processes. The AgNW‐embedded conductive fiber exhibits superior initial electrical conductivity (σ₀ = 2450 S cm^?1) and elongation at break (900% strain) due to the high weight percentage of the conductive fillers and the use of a highly stretchable SBS elastomer matrix. During the stretching, the embedded AgNWs act as conducting bridges between AgNPs, resulting in the preservation of electrical conductivity under high strain (the rate of conductivity degradation, σ/σ₀ = 4.4% at 100% strain). The AgNW‐embedded conductive fibers show the strain‐sensing behavior with a broad range of applied tensile strain. The AgNW reinforced highly stretchable conductive fibers can be embedded into a smart glove for detecting sign language by integrating five composite fibers in the glove, which can successfully perceive human motions.     

Arbitrarily Shaped Fiber Assemblies from Spun Carbon Nanotube Gel Fibers

Experimental methods, apparatus, and practically useful theoretical analysis are provided for the coagulation‐based spinning of effectively unlimited lengths of carbon nanotube fibers having exceptional toughness and reasonably high strength. This spinning process fundamentally depends on the mechanical properties of intermediate gel state fibers, which we find are surprising elastic up to about 20 % strain and sufficiently strong for diverse processing methods. More specifically, we show that assemblies of these gel fibers can be used as intermediates for making nanotube sheets, large diameter fibers, and conformal coatings. When suitably processed, these composites (comprising many parallel solution‐spun nanotube fibers) have useful strength and extraordinary toughness.