A Stretchable Expanded Polytetrafluorethylene-Silicone Elastomer Composite Electret for Wearable Sensor

Soaring developments in wearable electronics raise an urgent need for stretchable electrets. However, achieving soft electrets simultaneously possessing excellent stretchability, longevity, and high charge density is still challenging. Herein, a facile approach is proposed to prepare an all-polymer hybrid composite electret based on the coupling of elastomer and ePTFE membrane. The composite electrets are fabricated via a facile casting and thermal curing process. The obtained soft composite electrets exhibit constantly high surface potential (-0.38 kV) over a long time (30 days), large strain (450%), low hysteresis, and excellent durability (15,000 cycles). To demonstrate the applications, the stretchable electret is utilized to assemble a self-powered flexible sensor based on the electrostatic induction effect for the monitoring of human activities. Additionally, output signals in the pressure mode almost two orders of magnitude larger than those in the strain mode are observed and the sensing mechanism in each mode is investigated.

Highly Stretchable Composite Foams via Sustainable Utilization of Waste Tire Rubbers for Temperature-Dependent Electromagnetic Wave Absorption

Recently, the sustainable utilization of waste resources has become a low-cost and effective strategy to design high-performance functional materials to solve the increasingly serious environmental pollution problem. Herein, the flexible and highly stretchable polyurethane (PU) composite foams assisted by one-dimensional carbon nanotubes (CNTs) and zero-dimensional Fe3O4 were fabricated using waste tire rubbers (WTRs) as reinforcements during a simple self-foaming process. The collaborative introduction of conductive CNTs, magnetic Fe3O4, and WTRs with three-dimensional cross-linked structures enabled the construction of an efficient electronic transmission path and heterointerfaces inside the composite foam. The resulting composite foam possessed a desired minimum reflection loss (RLmin) of −47.43 dB, and also exhibited superior mechanical properties with a tensile strength of >3 MPa and multiple tensile deformation recovery abilities. In addition, increasing the temperature could significantly improve the electromagnetic wave absorption performance of the composite foam. This comprehensive composite foam derived from WTRs has shown a promising development potential for using waste materials to relieve electromagnetic pollution.

Flower-like bimetal-organic framework derived composites with tunable structures for high-efficiency electromagnetic wave absorption

Recently, high-performance functional composites for electromagnetic wave absorption (EWA) with tunable nano/micro-structures have attracted extensive attention. Herein, the flower-like electrically conductive and magnetic cobalt-nickel@carbon (CoNi@C) composites derived from bimetallic metal-organic frameworks (MOFs) were fabricated via solvothermal method and pyrolysis. By adjusting the ratios of different precursors, different morphological features of composites were formed. When the molar ratio of Co and Ni was 1:2, the CoNi@C composites exhibited the optimal minimum reflection loss (RL_min) of -56.89 dB at 6.7 GHz with an effective absorption bandwidth of 4.7 GHz, due to the coordinated dielectric and magnetic loss caused by the electromagnetic properties of each component as well as the interactions between the unique three-dimensional (3D) interfaces of flower-like structures that promoted the absorption and dissipation of composites for microwaves. The composites are expected to become promising candidates as high-efficiency absorbers in the electromagnetic protection field.

Understanding the linear and nonlinear optical responses of few-layer exfoliated MoS2and WS2nanoflakes: experimental and simulation studies

Understanding the linear and nonlinear optical (NLO) responses of two-dimensional nanomaterials is essential to effectively utilize them in various optoelectronic applications. Here, few-layer MoS₂and WS₂nanoflakes with lateral size less than 200 nm were prepared by liquid-phase exfoliation, and their linear and NLO responses were studied simultaneously using experimental measurements and theoretical simulations. Finite-difference time-domain (FDTD) simulations confirmed the redshift in the excitonic transitions when the thickness was increased above 10 nm indicating the layer-number dependent bandgap of nanoflakes. WS₂nanoflakes exhibited around 5 times higher absorption to scattering cross-section ratio than MoS₂nanoflakes at various wavelengths. Open aperture Z scan analysis of both the MoS₂and WS₂nanoflakes using 532 nm nanosecond laser pulses reveals strong nonlinear absorption activity with effective nonlinear absorption coefficient (β_eff) of 120 cm GW^-1and 180 cm GW^-1, respectively, which was attributed to the combined contributions of ground, singlet excited and triplet excited state absorption. FDTD simulation results also showed the signature of strong absorption density of few layer nanoflakes which may be account for their excellent NLO characteristics. Optical limiting threshold values of MoS₂and WS₂nanoflakes were obtained as ∼1.96 J cm^-2and 0.88 J cm^-2, respectively, which are better than many of the reported values. Intensity dependent switching from saturable absorption (SA) to reverse SA was also observed for MoS₂nanoflakes when the laser intensity increased from 0.14 to 0.27 GW cm^-2. The present study provides valuable information to improve the selection of two-dimensional nanomaterials for the design of highly efficient linear and nonlinear optoelectronic devices.

High-Performance Dielectric Elastomer Nanogenerator for Efficient Energy Harvesting and Sensing via Alternative Current Method

Soft, low-cost, high-performance generators are highly desirable for harvesting ambient low frequency mechanical energy. Here, a dielectric elastomer nanogenerator (DENG) is reported, which consists of a dielectric elastomer capacitor, an electret electrostatic voltage source, and a charge pump circuit. Under biaxial stretching, DENG can convert tensile mechanical energy into electrical power without any external power supply. Different from traditional DEG with the charge outward transfer in direct current (DC), the DENG works based on shuttle movement of internal charges in an alternating current (AC). Through alternating current (AC) method, the charge density of the DENG can reach 26 mC m^-2 per mechanical cycle, as well as energy density of up to 140 mJ g^-1 . Due to the all-solid-state structure without air gap, the DENG is capable of working stably under different ambient humidity (20 RH%-100 RH%). To demonstrate the applications, a water wave harvester based on the DENG is constructed. The integrated device powers a sensing communication module for self-powered remote weather monitoring, showing the potential application in ocean wave energy harvesting.

Anisotropic cellulose nanofibril composite sponges for electromagnetic interference shielding with low reflection loss

With the development of the electronic industry bringing convenience to people, a series of caused electromagnetic pollution problems (e.g., electromagnetic interference (EMI)) have recently also become urgent tasks. In this work, an anisotropic composite sponge consisting of cellulose nanofibrils (CNFs) and chemical co-precipitated silver nanowire (AgNW)@Fe₃O₄ composites was successfully prepared. Due to the introduction of anisotropic structures and the synergistic effect among CNFs, AgNWs, and Fe₃O₄, this composite sponge exhibited low density (16.76 mg/cm³), good saturation magnetization (4.21 emu/g) and electrical conductivity (0.02 S/cm), and anisotropic EMI shielding ability. By adjusting the proportion (1:0.3) between AgNWs and Fe₃O₄ and their loading (0.15 vol%) inside the sponge, the reflection loss of the sponge with the improved interface impedance mismatch was only 2.3 dB, accounting for 7.2% of the total loss. It is expected to become a promising EMI shielding material, especially for effectively alleviating the secondary reflection EM pollution.

Liquid Transport and Real-Time Dye Purification via Lotus Petiole-Inspired Long-Range-Ordered Anisotropic Cellulose Nanofibril Aerogels

Nowadays, large-scale oriented functional porous materials have been sought after by researchers. However, regulation of the long-range uniform and oriented structures of the material remains a challenge. Herein, ultralong anisotropic cellulose nanofibril (CNF) aerogels with uniformly ordered structures of pore walls inspired by lotus petioles were constructed by applying external speeds to counterbalance the growth driving forces of ice crystals. Based on the growth law of ice crystals, the ice crystals grew at a stable rate when the applied external speed was 0.04 mm/s, ensuring the consistent orientation of the large-scale CNF aerogel. The aerogel exhibited a rapid long-range directional transport ability to different liquid solvents, delivering ethanol up to 40 mm from bottom to top within 50 s. Moreover, by introducing rectorites with good cation-exchange properties, the resulting long-range composite possessed an enhanced adsorption capacity for methylene blue. Furthermore, aerogel successfully achieved real-time dye purification at a long distance, such as fast dye adsorption or selective adsorption. This flexible and straightforward strategy of fabricating ultralong oriented CNF aerogel materials is expected to promote the development of functional aerogels in directional liquid transport and sewage treatment.

Enhanced nonlinear absorption and efficient power limiting action of Au/Ag@ graphite core-shell nanostructure synthesized by laser ablation

Here we report a drastic enhancement of nonlinear absorption behaviour and exceptional optical limiting action of two core-shell systems (Au@graphite and Ag@graphite) prepared by adopting a fairly easy way in which we did not use any graphitic substrate. We carried out pulsed laser ablation of Au and Ag targets in toluene, monosubstituted benzene from which graphite layers of nanometer thickness has emerged as a result of photochemical reactions. The prepared samples were characterized and analyzed by UV/Vis spectroscopy, Raman spectroscopy, and TEM. Theoretical simulations of the core-shell nanostructures were done by the finite-difference time-domain method underlined the quenching of SPR in the case of both Au and Ag NPs by the graphitic layers evolved from toluene. Au and/or Ag@graphite core-shell structure exhibited a huge improvement in the nonlinear absorption behaviour and the optical limiting efficiency of these systems is found to be better than that of many benchmark optical limiters. The enhancement in nonlinear absorption property and the limiting actions of these systems were attributed to the enhanced excited-state absorption as well as free-carrier absorption arose as a result of the modification in the electronic structure of graphite on core-shell formation. Moreover, the metallic NPs also enhances nonlinear absorption through free-carrier absorption free-carrier absorption. So we believe these results are quite useful for guiding the characterization, monitoring the synthesis of similar nanostructures and for, the development of nanohybrids with desired properties for nonlinear optical, optoelectronic and photocatalytic applications.

Structure–property correlations of the nonlinear optical properties of a few bipodal D–π–A molecules – an experimental and theoretical approach

The nonlinear optical (NLO) properties of a series of pyran based bipodal D–π–A molecules have been studied experimentally and theoretically.

Quick Heat Dissipation in Absorption-Dominated Microwave Shielding Properties of Flexible Poly(vinylidene fluoride)/Carbon Nanotube/Co Composite Films with Anisotropy-Shaped Co (Flowers or Chains)

The facile fabrication of thin flexible electromagnetic interference (EMI) shielding materials with fast heat dissipation for adaptable tuning in both civil and military applications is in urgent demand. In our work, the flexible poly(vinylidene fluoride) (PVDF)/carbon nanotube (CNT) composite films decorated with anisotropy-shaped Co in flowers or chains were prepared and studied. The results showed that by increasing the Co filler contents, the EC (electrical conductivity), TC (thermal conductivity), and EMI shielding properties of such PVDF/CNT/Co (flowers or chains) flexible films were significantly improved. In contrast, the PVDF/CNT/Co-chain flexible films exhibit higher performance with respect to the EC, TC, and EMI shielding properties. Total shielding of 35.3 and 32.2 dB were, respectively, obtained by the PVDF/CNT/6 wt % Co-chain with an EC of 2.28 S/cm and the PVDF/CNT/6 wt % Co-flower with an EC of 1.94 S/cm at a film thickness of 0.3 mm. Possibly owing to the conductive dissipation, interfacial polarization, magnetic loss, multiple reflections, and scattering of EM waves, such flexible composite films possessed a remarkable absorption-dominated EMI shielding behavior. These new composite films with enhanced TC are easily able to transform microwave energy into Joule heating systems, making themselves greatly potential for effective EMI shielding as well as rapid heat dissipation.

Optoelectrical, morphological and mechanical features of nitrophenyl supported poly(1,3,4-oxadiazole)s and their nanocomposites with TiO2

Charge transfer phenomenon and redox behaviour, of PPNO/PNPPO nanocomposites, triggered by TiO₂ nanoparticles.