Anisotropic,Transparent Films with Aligned Cellulose Nanofibers

Transparent films or substrates are ubiquitously used in photonics and optoelectronics, with glass and plastics as traditional choice of materials. Transparent films made of cellulose nanofibers are reported recently. However, all these films are isotropic in nature. This work, for the first time, reports a remarkably facile and effective approach to fabricating anisotropic transparent films directly from wood. The resulting films exhibit an array of exceptional optical and mechanical properties. The well‐aligned cellulose nanofibers in natural wood are maintained during delignification, leading to an anisotropic film with high transparency (≈90% transmittance) and huge intensity ratio of transmitted light up to 350%. The anisotropic film with well‐aligned cellulose nanofibers has a mechanical tensile strength of up to 350 MPa, nearly three times of that of a film with randomly distributed cellulose nanofibers. Atomistic mechanics modeling further reveals the dependence of the film mechanical properties on the alignment of cellulose nanofibers through the film thickness direction. This study also demonstrates guided liquid transport in a mesoporous, anisotropic wood film and its possible application in enabling new nanoelectronic devices. These unique and highly desirable properties of the anisotropic transparent film can potentially open up a range of green electronics and nanofluidics.     

Self-Densification of Highly Mesoporous Wood Structure into a Strong and Transparent Film

In the native wood cell wall, cellulose microfibrils are highly aligned and organized in the secondary cell wall. A new preparation strategy is developed to achieve individualization of cellulose microfibrils within the wood cell wall structure without introducing mechanical disintegration. The resulting mesoporous wood structure has a high specific surface area of 197 m² g⁻¹ when prepared by freeze-drying using liquid nitrogen, and 249 m² g⁻¹ by supercritical drying. These values are 5 to 7 times higher than conventional delignified wood (36 m² g⁻¹) dried by supercritical drying. Such highly mesoporous structure with individualized cellulose microfibrils maintaining their natural alignment and organization can be processed into aerogels with high porosity and high compressive strength. In addition, a strong film with a tensile strength of 449.1 ± 21.8 MPa and a Young's modulus of 51.1 ± 5.2 GPa along the fiber direction is obtained simply by air drying owing to the self-densification of cellulose microfibrils driven by the elastocapillary forces upon water evaporation. The self-densified film also shows high optical transmittance (80%) and high optical haze (70%) with interesting biaxial light scattering behavior owing to the natural alignment of cellulose microfibrils.     

Muscle‐Inspired Highly Anisotropic,Strong, Ion‐Conductive Hydrogels

Biological tissues generally exhibit excellent anisotropic mechanical properties owing to their well‐developed microstructures. Inspired by the aligned structure in muscles, a highly anisotropic, strong, and conductive wood hydrogel is developed by fully utilizing the high–tensile strength of natural wood, and the flexibility and high‐water content of hydrogels. The wood hydrogel exhibits a high–tensile strength of 36 MPa along the longitudinal direction due to the strong bonding and cross‐linking between the aligned cellulose nanofibers (CNFs) in wood and the polyacrylamide (PAM) polymer. The wood hydrogel is 5 times and 500 times stronger than the bacterial cellulose hydrogels (7.2 MPa) and the unmodified PAM hydrogel (0.072 MPa), respectively, representing one of the strongest hydrogels ever reported. Due to the negatively charged aligned CNF, the wood hydrogel is also an excellent nanofluidic conduit with an ionic conductivity of up to 5 × 10^?4 S cm^–1 at low concentrations for highly selective ion transport, akin to biological muscle tissue. The work offers a promising strategy to fabricate a wide variety of strong, anisotropic, flexible, and ionically conductive wood‐based hydrogels for potential biomaterials and nanofluidic applications.     

A Highly Transparent Artificial Photonic Nociceptor

A nociceptor is an essential element in the human body, alerting us to potential damage from extremes in temperature, pressure, etc. Realizing nociceptive behavior in an electronics device remains a central issue for researchers, designing neuromorphic devices. This study proposes and demonstrates an all‐oxide‐based highly transparent ultraviolet‐triggered artificial nociceptor, which responds in a very similar way to the human eye. The device shows a high transmittance (>65%) and very low absorbance in the visible region. The current–voltage characteristics show loop opening, which is attributed to the charge trapping/detrapping. Further, the ultraviolet‐stimuli‐induced versatile criteria of a nociceptor such as a threshold, relaxation, allodynia, and hyperalgesia are demonstrated under self‐biased condition, providing an energy‐efficient approach for the neuromorphic device operation. The reported optically controlled features open a new avenue for the development of transparent optoelectronic nociceptors, artificial eyes, and memory storage applications.     

定向分布碳纤维复合材料介电性能研究

以碳纤维为填充物, 环氧树脂为基体, 制备了碳纤维/环氧树脂介电复合材料. 介绍了两种分布方式对复合材料介电性能的影响, 分别研究了两种分布方式的介电常数随碳纤维含量和长度的变化规律. 在2.6–8.2 GHz频率范围内, 轴向介电常数是径向介电常数的数倍; 实部和虚部都随着碳纤维含量的增加而增大; 碳纤维长度也对介电性能的各向异性影响显著. 双层微波传输带模型可以合理地解释这些规律.     

Extremely Vivid,Highly Transparent,and Ultrathin Quantum Dot Light‐Emitting Diodes

Displaying information on transparent screens offers new opportunities in next‐generation electronics, such as augmented reality devices, smart surgical glasses, and smart windows. Outstanding luminance and transparency are essential for such “see‐through” displays to show vivid images over clear background view. Here transparent quantum dot light‐emitting diodes (Tr‐QLEDs) are reported with high brightness (bottom: ≈43 000 cd m^?2, top: ≈30 000 cd m^?2, total: ≈73 000 cd m^?2 at 9 V), excellent transmittance (90% at 550 nm, 84% over visible range), and an ultrathin form factor (≈2.7 µm thickness). These superb characteristics are accomplished by novel electron transport layers (ETLs) and engineered quantum dots (QDs). The ETLs, ZnO nanoparticle assemblies with ultrathin alumina overlayers, dramatically enhance durability of active layers, and balance electron/hole injection into QDs, which prevents nonradiative recombination processes. In addition, the QD structure is further optimized to fully exploit the device architecture. The ultrathin nature of Tr‐QLEDs allows their conformal integration on various shaped objects. Finally, the high resolution patterning of red, green, and blue Tr‐QLEDs (513 pixels in.^?1) shows the potential of the full‐color transparent display.     

Highly Sensitive,Anisotropic, and Reversible Stress/Strain‐Sensors from Mechanochromic Nanofiber Composites

Mechanochromic polymeric systems are intensively investigated for real‐time stress detection applications. However, an effective stress‐sensing material must respond to low deformation with a detectable color change that should be quickly reversible upon force unloading. In this work, mechanochromic nanofibers made by electrospinning are used to produce mechanochromic nanofiber/poly(dimethylsiloxane) (PDMS) composites with isotropic and anisoptropic response. Due to chain alignment of spiropyran copolymer chains within the nanofibers, only very small strains are required to yield a mechanochromic response. Composites with aligned and isotropic nanofibers show anisotropic and isotropic mechanochromic behavior, respectively. Due to the special substitution pattern of spiropyran in the copolymer, the mechanochromic response of these nanofiber/PDMS composites shows fast reversibility upon force unloading. The outstanding benefit of using highly sensitive mechanochromic nanofibers as filler in composite materials allows the detection of directional stress and strain, and it is a step forward in the development of smart, mechanically responsive materials.     

Crystal Phase and Architecture Engineering of Lotus‐Thalamus‐Shaped Pt‐Ni Anisotropic Superstructures for Highly Efficient Electrochemical Hydrogen Evolution

The rational design and synthesis of anisotropic 3D nanostructures with specific composition, morphology, surface structure, and crystal phase is of significant importance for their diverse applications. Here, the synthesis of well‐crystalline lotus‐thalamus‐shaped Pt‐Ni anisotropic superstructures (ASs) via a facile one‐pot solvothermal method is reported. The Pt‐Ni ASs with Pt‐rich surface are composed of one Ni‐rich “core” with face‐centered cubic (fcc) phase, Ni‐rich “arms” with hexagonal close‐packed phase protruding from the core, and facet‐selectively grown Pt‐rich “lotus seeds” with fcc phase on the end surfaces of the “arms.” Impressively, these unique Pt‐Ni ASs exhibit superior electrocatalytic activity and stability toward the hydrogen evolution reaction under alkaline conditions compared to commercial Pt/C and previously reported electrocatalysts. The obtained overpotential is as low as 27.7 mV at current density of 10 mA cm^?2, and the turnover frequency reaches 18.63 H₂ s^?1 at the overpotential of 50 mV. This work provides a new strategy for the synthesis of highly anisotropic superstructures with a spatial heterogeneity to boost their promising application in catalytic reactions.     

Tetragonal Single‐Crystalline Boron Nanowires with Strong Anisotropic Light Scattering Behaviors and Photocurrent Response in Visible‐Light Regime

Boron is a narrow‐bandgap (1.56 eV) semiconductor with high melting‐point, low‐density, large Young's modulus and very high refractive index (3.03) close to silicon. Therefore, boron nanostructures is expected to possess strong visible‐light scattering properties. However, photonic and optoelectronic properties of the boron nanostructures are seldom studied until now. In this paper, we have successfully prepared single‐crystalline boron nanowire (BNW) arrays with high‐density on Si substrate. All the BNWs are found to possess strong light‐scattering behaviors in the visible regime. Most of all, the scattered light is found to polarize along the longitudinal direction of the nanowire. They also have excellent second‐harmonic generation (SHG) properties under ultrafast laser irradiation. Further optoelectronic measurements show that an individual BNW device exhibits notable photocurrent responses in the visible‐light range at ambient conditions, which can be attributed to the strong coupling effect between individual BNW and the visible light. The maximum photoresponsivity of an individual BNW can reach up to 12.12 A W^–1 at a voltage of 10 V, and the response time is only 18 ms. Therefore, it unveils that the BNWs have a promising future in visible‐light communications and detections.     

Highly Anisotropic Sb2Se3 Nanosheets: Gentle Exfoliation from the Bulk Precursors Possessing 1D Crystal Structure

2D materials, particularly those bearing in‐plane anisotropic optical and electrical properties such as black phosphorus and ReS₂, have spurred great research interest very recently as promising building blocks for future electronics. However, current progress is limited to layered compounds that feature atomic arrangement asymmetry within the covalently bonded planes. Herein, a series of highly anisotropic nanosheets (Sb₂Se₃, Sb₂S₃, Bi₂S₃, and Sb₂(S, Se)₃), which are composed of 1D covalently linked ribbons stacked together via van der Waals force, is introduced as a new member to the anisotropic 2D material family. These unique anisotropic nanosheets are successfully fabricated from their polymer‐like bulk counterparts through a gentle water freezing‐thawing approach. Angle‐resolved polarized Raman spectroscopy characterization confirms the strong in‐plane asymmetry of Sb₂Se₃ nanosheets, and photodetection study reveals their high responsivity and anisotropic in‐plane transport. This work can enlighten the synthesis and application of new anisotropic 2D nanosheets that can be potentially applied for future electronic and optoelectronic devices.     

Defect‐Free,Highly Uniform Washable Transparent Electrodes Induced by Selective Light Irradiation

A simple route to fabricate defect‐free Ag‐nanoparticle–carbon‐nanotube composite‐based high‐resolution mesh flexible transparent conducting electrodes (FTCEs) is explored. In the selective photonic sintering‐based patterning process, a highly soft rubber or thin plastic substrate is utilized to achieve close and uniform contact between the composite layer and photomask, with which uniform light irradiation can be obtained with diminished light diffraction. This well‐controlled process results in developing a fine and uniform mesh pattern (≈12 μm). The mesh patternability is confirmed to be dependent on heat distribution in the selectively light‐irradiated film and the pattern design for FTCE could be adopted for more precise patterns with desired performance. Moreover, using a very thin substrate could allow the mesh to be positioned closer to the strain‐free neutral mechanical plane. Due to strong interfacial adhesion between the mesh pattern and substrate, the mesh FTCE could tolerate severe mechanical deformation without performance degradation. It is demonstrated that a transparent heater with fine mesh patterns on thin substrate can maintain stability after 100 repeated washing test cycles in which a variety of stress situations occurring in combination. The presented highly durable FTCE and simple fabrication processes may be widely adoptable for various flexible, large‐area, and wearable optoelectronic devices.     

Novel Synthesis,Coating, and Networking of Curved Copper Nanowires for Flexible Transparent Conductive Electrodes

In this work, a whole manufacturing process of the curved copper nanowires (CCNs) based flexible transparent conductive electrode (FTCE) is reported with all solution processes, including synthesis, coating, and networking. The CCNs with high purity and good quality are designed and synthesized by a binary polyol coreduction method. In this reaction, volume ratio and reaction time are the significant factors for the successful synthesis. These nanowires have an average 50 nm in width and 25–40 μm range in length with curved structure and high softness. Furthermore, a meniscus‐dragging deposition (MDD) method is used to uniformly coat the well‐dispersed CCNs on the glass or polyethylene terephthalate substrate with a simple process. The optoelectrical property of the CCNs thin films is precisely controlled by applying the MDD method. The FTCE is fabricated by networking of CCNs using solvent‐dipped annealing method with vacuum‐free, transfer‐free, and low‐temperature conditions. To remove the natural oxide layer, the CCNs thin films are reduced by glycerol or NaBH₄ solution at low temperature. As a highly robust FTCE, the CCNs thin film exhibits excellent optoelectrical performance (T = 86.62%, R _s = 99.14 Ω ^?1), flexibility, and durability (R/R ₀ < 1.05 at 2000 bending, 5 mm of bending radius).