Bilayer Composite Films Research Articles

Construction of broad-spectrum photocatalyst films through interface engineering: Orchestrating Bi nanoparticles in TiO2/BiVO4 Z-scheme heterojunctions

We successfully synthesized three-layered photocatalysts by modifying Bi nanoparticles on TiO2/BiVO4 bilayer composite films through a sol-gel process and sputtering. When exposed to ambient air, the surface of the prepared Bi nanoparticles oxidizes to form an amorphous ultra-thin Bi2O3 out layer. Under light exposure, this layer is reduced to metallic Bi, thanks to the band alignment between the Bi nanoparticles and TiO2/BiVO4 Z-scheme composite. The addition of Bi nanoparticles in the composite films improves visible-light absorption by the surface plasmon resonance (SPR), which contributes to the hot electron and enhances the photocatalytic characteristics. By constructing effective TiO2/BiVO4 Z-scheme heterostructures to facilitate photoinduced electron-hole pair separation and prevent recombination, Bi nanoparticles can efficiently capture photons and enhance the photocatalytic efficiency of semiconductors through the SPR effect. Optimizing the content of Bi nanoparticles decorated on the TiO2/BiVO4 Z-scheme composite film is a promising approach for designing a highly efficient photocatalyst, as evidenced by the performance of photoelectrochemical properties and RhB photodegradation ability.

Preparation of bi-layer composite films for controlled cefazolin delivery and enhanced antibacterial activity

In the present study, a wide-spectrum antibiotic drug, cefazolin was loaded into novel bi-layer composite films based on chitosan and alginate. The objective was to achieve sustained antibacterial activity at the application site, while enhancing the local efficacy of cefazolin. The physical properties of the composite films were characterized using techniques including FTIR, XRD, and SEM. Additionally, drug content uniformity, contact angle, weight variation, swelling index, drug release profiles, and kinetics were investigated. Antibacterial efficacy of the films was evaluated against Methicillin-resistant Staphylococcus aureus (MRSA), an important drug resistant pathogen. Multiple assays including time-kill, disk diffusion, and microbial penetration assays were employed to comprehensively assess various parameters of antibacterial action. The results demonstrated homogenous drug distribution and minimal weight variation in the films. Well-compatible film formations were shown by the SEM micrographs. Cefazolin release was sustained for 1440 min, and the release kinetics were fitted with the Korsmeyer-Peppas model. The fabricated films exhibited significant and sustained antibacterial activity against MRSA for a duration of 900 minutes, ultimately leading to complete eradication of viable bacterial populations. Taken together, novel films demonstrated good mechanical properties and hold great promise for biomedical applications, offering extended antibiotic release and sustained pathogen eradication.

Exploring electrochromic performance via layered deposition of tungsten oxide on niobium oxide composite electrode

Previous studies examined the incorporation of several transition metal oxides into niobium oxide (Nb2O5) to enhance the electrochromic (EC) performance. The objective was to improve the durability, color neutrality, coloring efficiency, and optical characteristics because individual metal oxides often exhibit limits that might affect overall functioning. Therefore, an innovative approach, integrating mixed metal oxides, emerges. This novel approach addresses these challenges and unlocks new possibilities to enhance EC efficiency. This paper introduces a new method for synthesizing niobium oxide/tungsten oxide (Nb2O5/WO3) bilayer composite materials using a combination of facile hydrothermal synthesis with electrodeposition. The electrochromic, structural, morphological, and optical characteristics of Nb2O5 thin films were enhanced by conducting thorough investigations into different electrodeposition cycles of WO3. X-ray diffraction confirmed the amorphous nature of WO3 in combination with the crystalline orthorhombic Nb2O5 structure. Raman spectroscopy examined the vibrational modes and structural attributes in the Nb2O5/WO3 bilayer composite thin films. X-ray photoelectron spectroscopy was conducted to examine the chemical composition, elemental state, and surface characteristics. Field emission scanning electron microscopy was used to examine the impact of different WO3 electrodeposition cycles on the morphology of Nb2O5 thin films, revealing the formation of porous, clumped, and dense nanogranules on the film surface. EC investigations highlight the superior performance of the NW-20 thin film, showing efficient Li+ accommodation. The optimized NW-20 sample exhibits excellent EC performance, including high optical modulation (81.48 %), good reversibility (98.11 %), and high coloration efficiency (115.09 cm2/C) with long-term cycling stability. The NW-20 electrode incorporated into a device form exhibited functionality on a real-world scale, delivering remarkable EC performance with substantial optical modulation (78.1 %) and excellent cycling stability. These findings expand the potential applications of Nb2O5/WO3 bilayer composite materials for EC performance.

A PVDF/MWCNTs/GO@MWCNTs/AgNWs bilayer structured composite film with ultra‐high EMI shielding and conductivity performance

AbstractElectromagnetic interference (EMI) shielding materials with easy processing, high electrical conductivity, and excellent absorption loss are urgently needed in aerospace, military stealth and portable electronic devices. In this study, a polyvinylidene fluoride/multi‐walled carbon nanotubes (PVDF/MWCNTs)‐3 wt% composite film prepared by simple solution mixing and polyethylene terephthalate (PET) nonwoven scraping method was used as the substrate, and the PVDF/MWCNTs/graphene oxide@multi‐walled carbon nanotubes (PVDF/MWCNTs/GO@MWCNTs) and PVDF/MWCNTs/GO@MWCNTs/silver nanowires (PVDF/MWCNTs/GO@MWCNTs/AgNWs) bilayer composite films were prepared by vacuum‐assisted filtration (VAF). When the amount of GO@MWCNTs was 20 mL, the conductivity of PVDF/MWCNTs/GO@MWCNTs film is 3.5 × 101 S m−1, the total EMI shielding effectiveness (EMI SET) was 15.5 dB and the EMI absorption efficiency (EMI SEA) was 10.7 dB, the specific EMI SE (SSE/T) was 539.5 dB/ dB/(cm−2 g). When the amount of AgNWs was 25 mL, the conductivity of PVDF/MWCNTs/GO@MWCNTs/AgNWs film with 0.47 mm thickness was 1.6 × 104 S m−1, the EMI SET was 69.1 dB, the EMI SEA was 61.1 dB, and the SSE/T was 2320.0 dB cm2 g−1. The results show that the absorption was played a dominant role in the EMI shielding mechanism of obtained films. The addition of GO@MWCNTs/AgNWs increases the electrical conductivity and EMI shielding performance of the film more than the addition of GO@MWCNTs. This is mainly because GO， MWCNTs and AgNWs formed a novel three‐dimensional conductive network structure inside the composite film due to their hydrogen bonding and van der Waals forces, which increases the carrier channels and promotes the interaction between the internal microcurrents and the electromagnetic waves, achieving the purpose of attenuating the electromagnetic waves. The obtained PVDF/MWCNTs/GO@MWCNTs/AgNWs film has good potential in EMI shielding in aerospace, military and electronic intelligence applications.Highlights Well‐dispersed and highly conductive GO@MWCNTs were prepared by hydrothermal synthesis. AgNWs with good conductivity and high aspect ratio were prepared. PVDF‐based bilayer composite films with novel 3D conductive network were prepared. The synergistic EMI shielding mechanism of the film is discussed.

Flaxseed Mucilage/Hydroxypropyl Methylcellulose and Sodium Alginate/Polyvinyl Alcohol Composite Bilayer Film as a Promising Drug Carrier for Periodontal Treatment.

The present study focused on the formulation of mucoadhesive bilayer composite films for the treatment of periodontitis and evaluation of their physicochemical properties. The solvent casting technique was used to prepare films. The primary layer (D) was prepared with flaxseed and hydroxypropyl methylcellulose composite to sustain the release of doxycycline hyclate. The second layer (S) comprised sodium alginate and polyvinyl alcohol composite for faster release of clove oil. Both layers were combined to generate the bilayer film (B). All formulations were characterized further to obtain an optimized formulation. Attenuated total reflection-Fourier transform infrared radiation results showed intactness of drug and clove oil in the presence of excipients. The pH of the films was compatible with the periodontal cavity and the thickness was suitable for inserting into the cavity. The immediate release layer showed faster disintegration and swelling. The content of clove oil was above 80%. The rate of swelling of the primary layer was slow and drug content complied with the United States Pharmacopoeia. Scanning electron microscope analysis revealed intact, non-porous and smooth films. Films exhibited better mechanical strength and bioadhesiveness. Clove oil was released from the immediate release layer within 10 min, and doxycycline hyclate release was retarded to a minimum of up to 8 h in the primary layer as well as the bilayer. Formulation also had a significant effect on both Escherichia coli and Staphylococcus aureus. In the current study, bilayers were successfully prepared and characterized. The optimized formulation can be effectively used for the treatment of periodontitis.

Nanoemulsion based edible coatings for quality retention of fruits and vegetables-decoding the basics and advancements in last decade

Fruits and vegetables (F&V) are highly perishable and have important contributions to nutritional and economic sustainability. Although the developing nations have shown an immense increase in the production of horticultural commodities, the post-harvest losses are significant and have an adverse impact on the resources, economy, and environment as well. Nanoemulsion-based carriers are recognized for their diversity, natural origin, and immense potential to restrict losses while boosting the functional attributes of produce. The recent findings attest to nanoemulsions potential for extending the shelf life, managing quality, and reducing the losses of the perishables for sustainable livelihood of the farmers. However, further studies are required to evaluate the biological fate, safety, or potential toxicity of the nanoemulsion-based edible coatings. This review precisely focuses on various matrices used in the production of nanoemulsions, fabrication methods, characterization techniques, and the use of natural emulsifiers instead of chemicals. The future research focus stresses on developing low-cost fabrication techniques for nanoemulsion, improvement of the transmission properties i. e gas transmission rate (GTR), water vapor transmission rate (WVTR), and enhancing the performance of monolayer, bilayer, and other composite nanoemulsion base films. This beyond reducing the postharvest losses shall also restrict burden of the food waste management and related environmental issues at the same time.

PVDF/MWCNTs/RGO@Fe3O4/AgNWs composite film with a bilayer structure for high EMI shielding and electrical conductivity

AbstractWith the renewal of electromagnetic shielding materials, conducting polymer electromagnetic shielding composites stand out. In the article, ferric tetraoxide‐modified reduced graphene oxide (RGO@Fe3O4), silver nanowires (AgNWs) and polyvinylpyrrolidone (PVP K30) were blended to form a solution colloid, and polyvinylidene fluoride/carbon nanotubes (PVDF/MWCNTs)‐3 wt% composite film was used as the substrate, then the PVDF‐based bilayer composite films were prepared by vacuum‐assisted filtration (VNF).When RGO@Fe3O4 was added in the amount of 10 mL, the electrical conductivity of PVDF/MWCNTs/RGO@Fe3O4‐10 bilayer composite film is 1.7 × 101 S·m−1, the total electromagnetic shielding effectiveness (EMI SET) was 20.4 dB, of which the absorption loss accounted for 82.4%, and the specific electromagnetic shielding effectiveness (SSE/t) was 590.9 dB/(cm2·g−1). After the addition of 25 mL AgNWs, the electrical conductivity of PVDF/MWCNTs/RGO@Fe3O4/AgNWs‐25 bilayer composite film up to 4.9 × 104 S·m−1, the EMI SET was 94.4 dB, of which the absorption loss accounted for 85.4%, and the specific electromagnetic shielding effectiveness (SSE/t) was 3629.3 dB/(cm2·g−1). It indicates that the electromagnetic shielding mechanism of both bilayer composite films is dominated by absorption loss. The addition of RGO@Fe3O4/AgNWs increases the electrical conductivity and electromagnetic shielding effectiveness of the bilayer composite films more than RGO@Fe3O4. The successful preparation of this bilayer composite film makes it possible to form lightweight superconducting nanoparticles from high‐density metal‐modified carbon‐based materials, which provides an easy method for the preparation of highly conductive electromagnetic shielding composites.Highlights In this article, well dispersed highly conductive‐doped nanomaterials Fe3O4@RGO were prepared and characterized by hydrothermal synthesis. In this article, silver nanowires with good conductivity and high aspect ratio were prepared and characterized by liquid phase polyol method. In this article, three‐dimensional mesh PVDF‐based bilayer composite films with more excellent electromagnetic shielding properties were prepared by solution blending and vacuum‐assisted filtration using PVDF/MWCNTs‐3 wt% composite films as substrates. In this article, the electromagnetic shielding mechanism of bilayer composite films is discussed from the knowledge of three‐dimensional aspects.

The simple synthesis of all‐organic polymer bilayer films: Achieving simultaneous enhancements in energy storage density and efficiency

AbstractAll‐organic dielectric polymers with excellent capacitive energy storage capabilities have great potential applications in the fields of modern electronics and power systems. However, it is still challenging to achieve simultaneous improvements in both energy density and efficiency in these all‐organic dielectric polymers. This work proposes the all‐organic bilayer composite films with ferroelectric polymer poly(vinylidene fluoride‐hexafluoropropylene) (P(VDF‐HFP)) and linear polymer fluorene polyester (FPE) as the energy storage dielectrics for film capacitors. Compared with pure FPE films, the bilayer composite films exhibit improved dielectric constant. What is more outstanding is that the bilayer composite films has higher energy storage density and energy storage efficiency under the same electric field compared with the pure P(VDF‐HFP) film. Particularly, an outstanding Ud of 7.00 J/cm3 accompanied with great η of 95.9% has been delivered in the resulting bilayer composite films via optimizing the P(VDF‐HFP) content (22.2 vol%) at 520 kV/mm. The compatibility of the two polymers was discussed by simulating the potential distribution of the two polymer molecular chains. This work opens up a new way to prepare compatible polymer flexible capacitor films on a large scale.

Temperature Dependence of AC Electrical Conduction in Plasma Polymerized Pyrrole-N,N,3,5 Tetramethylaniline Bilayer Composite Thin Films

The temperature dependence of alternating current (ac) electrical conduction in Plasma Polymerized Pyrrole-N,N,3,5 tetramethylaniline (PPPy-PPTMA) bilayer composite thin films have been discussed in this article. The thin films were deposited by using a parallel plate capacitively coupled glow discharge reactor. To study the temperature dependence of ac electrical conduction the variation of dielectric constant (<i>ε</i>′), the dielectric loss factor (<i>ε</i>"), and the ac conductivity (<i>σ_ac</i>) of the thin films were investigated in the frequency range 100 Hz to 10 MHz and in the temperature range 298K to 398K. The decrease of dielectric constant <i>ε</i>′ with increasing frequency was observed and was attributed to the dielectric relaxation process. The dielectric constant, however, is observed to be increased with temperature in all frequency regions which is due to greater freedom of movement of dipole molecular chain in polymer films at high temperature. The variation of dielectric loss factor <i>ε</i>" with frequency showed a loss minimum then rises to a sharp peak which was also attributed to the relaxation phenomena of polymer. It is, however, observed that the loss peaks have shifted towards the higher frequency side with the increase of temperature which is usually attributed to dipolar orientation. The dielectric loss factor is also observed to be increased with temperature in all frequency regions. At lower frequencies the increase of loss factor with temperature was attributed to the effective chain motion of polymer and at high frequencies this increase might indicate the orientational polarization due to chain motion in bilayer film. The linear behavior of the ac conductivity <i>σ_ac</i> with the frequency and the observed weak temperature dependence of <i>σ_ac</i> led to interpret the ac conduction mechanism as the hopping between localized states at the Fermi level.

Preparation and Properties of Blended Composite Film Manufactured Using Walnut-Peptide-Chitosan-Sodium Alginate.

In this study, layer-by-layer assembly was performed to prepare sodium alginate (SA) layer and walnut-peptide–chitosan (CS) bilayer composite films. Genipin was adopted to crosslink CS and walnut peptide. The properties of walnut peptide-CS-SA composite film were determined, and the influence of material ratio on the performance of composite film was explored. According to the results, the mechanical tensile property, oil absorption property, and water vapor barrier property of the composite film were improved with the presence of genipin. Moreover, the proportion of CS and walnut peptide had significant effects on color, transmittance, mechanical properties, barrier properties, and antioxidant properties of the composite films. Among them, the composite film containing 1% (w/v) CS, 1% (w/v) walnut peptide, and 0.01% (w/v) genipin showed the best performance, with a tensile strength of 3.65 MPa, elongation at break of 30.82%, water vapor permeability of 0.60 g·mm·m−2·h−1·kPa−1, oil absorption of 0.85%, and the three-phase electrochemistry of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging rate of 25.59%. Under this condition, the tensile property, barrier property, and oxidation resistance of the composite film are good, which can provide a good preservation effect for food, and has great application potential.

Enhanced energy storage performance of bilayer composite films with Na0.5Bi0.5TiO3 platelets

Polymer-based dielectric composites with enhanced energy storage performances occupy a pivotal position in the modern power electronics industry. Unfortunately, these dielectric composite materials still exist unsolvable problems, especially the deficient breakdown strength (Eb) and heat amassment caused by dielectric loss. Herein, the novel bilayer composite films comprised of pristine poly(vinylidene fluoride) (PVDF) as the top layer and Na0.5Bi0.5TiO3 (NBT)/PVDF composite doped with two-dimensional (2D) NBT platelets as the bottom layer were designed and prepared. Subsequently, the dielectric and energy storage properties of these bilayer structure composite films were analyzed. The results demonstrate that this bilayer structure with optimized NBT content increases the dielectric constant, enhances the Eb, and reduces the dielectric loss, thus notably improving discharged efficiency (η) and discharged energy density (Ue). Eventually, an ultrahigh η of 80.3% and a superior Ue of 22.6 J cm−3 are gained at 650 MV m−1 with the composite layer involving 5 vol% 2D NBT platelets. Therefore, this new strategy of simultaneously increasing the Ue and η of the composite film will provide new thoughts for the exploitation of high-performance capacitors.

Highly Thermally Conductive Graphene-Based Thermal Interface Materials with a Bilayer Structure for Central Processing Unit Cooling

Innovations of transistors toward miniaturization and integration aggravate heat accumulation of central processing units (CPUs). Thermal interface materials (TIMs) are critical to remove the generated heat and to guarantee the device reliability. Herein, maltose-assisted mechanochemical exfoliation was proposed to prepare maltose-g-graphene as a structural motif of TIMs. Then, maltose-g-graphene/gelatin composite films with a bilayer structure were prepared by two-step vacuum filtration to construct effective thermally conductive pathways consisting of the directionally arranged and tightly packed maltose-g-graphene. The bilayer composite film exhibited a remarkable in-plane thermal conductivity (30.8 W m-1 K-1) and strong anisotropic ratio (∼8325%) at 40 wt % maltose-g-graphene addition. More intriguingly, the cooling effect on CPUs was significantly better for the bilayer composite films than commercial thermal pads as TIMs. The outstanding thermally conductive stability in resistance to instantaneous and prolonged thermal shocks as well as fatigue stability was gathered. Our work offers a valuable reference to design and fabricate high-performance TIMs for CPU cooling to surmount harsh application scenarios.

Improved dielectric properties of La2O3–ZrO2 bilayer films for novel gate dielectrics

La2O3 film with large theoretical k value and ZrO2 film with large theoretical band gap are selected to fabricate bilayer composite dielectric films by magnetron sputtering. La2O3–ZrO2 bilayer films combine the advantages of both La2O3 and ZrO2 films. We demonstrate that Pt/La2O3–ZrO2/Si MOS capacitor is more favorable for transistors than Pt/ZrO2–La2O3/Si MOS capacitor, featuring for a larger dielectric constant (12.37) and a lower leakage current (3.5×10−4 A/cm2). Besides, our results indicate that optimal sublayer thicknesses of La2O3 and ZrO2 film are both 10 nm as well as the optimal temperature is 500 °C, which represents a significantly improved performance of larger dielectric constant (13.34) and lower leakage current density (8.19×10−5 A/cm2).

Effect of Ag layer thickness and scan line spacing during laser annealing of Ag/F-doped SnO2 bilayer composite thin films under ultrasonic vibration assistance

To further improve electrical performance of FTO single-layer films and obtain high-performance transparent electrodes, the effects of silver (Ag) layer thickness and scan line spacing on optical and electrical properties of Ag/F-doped SnO2 (FTO) bilayer composite thin films prepared by radio frequency (RF) magnetron sputtering and ultrasonic-vibration-assisted laser annealing were investigated. The results indicate that as compared to the untreated FTO single-layer film, the Ag/FTO composite film displays a dramatic decrease in sheet resistance with even an improvement in transparency when the Ag layer thickness reaches 5 nm under the combined effect of laser annealing and ultrasonic vibration. Furthermore, the XRD and SEM analyses reveal that only using the moderate scan line spacing during ultrasonic-vibration-assisted laser annealing can contribute to the grain growth of the films. The Ag/FTO film with an Ag layer thickness of 5 nm and a scan line spacing of 20 μm shows a remarkable overall performance with an increased figure of merit of 2.13 × 10−2 Ω−1 comparing to 1.13 × 10−2 Ω−1 for the untreated FTO film. This work confirms the opportunity of combining Ag layer deposition and ultrasonic-vibration-assisted laser annealing in significantly improving both optical and electrical properties of FTO single-layer films, providing a promising alternative to the conventional ITO transparent electrodes.

Effect of the thickness of Sr2Bi4Ti5O18 transition layer on the properties of BiFeO3/Sr2Bi4Ti5O18 bilayer composite thin films

BiFeO3(BFO)/Sr2Bi4Ti5O18(SBT) bilayer composite thin films were prepared using the sol-gel method. The influence of the SBT transition layer thickness on the properties of BFO/SBT bilayer composite thin films was studied. The results showed that an SBT transition layer with the proper thickness can improve the BFO/SBT bilayer composite film performance. X-ray diffraction (XRD) analysis revealed that a bismuth layered perovskite structure is formed in all of the thin films. The scanning electron microscopy (SEM) result showed that the BFO/80 nmSBT sample exhibits good crystallization, an improved density and a uniform minimum grain size compared with the other samples. The X-ray photoelectron spectroscopy (XPS) result showed that the Fe2+ content and oxygen vacancy concentration are lowest in the BFO/80 nm SBT sample. This sample has good ferroelectric properties: the leakage current density has the lowest value of J = 5.21 × 10-5 A/cm2 among the samples at 350 kV/cm, 2Ec = 900 kV/cm, and 2Pr = 151 μC/cm2. At a low electric field (E<100 kV/cm), the leakage mechanism of the thin film is ohmic conduction, and the Fowler-Nordheim (F–N) tunneling effect is observed at a high electric field (E>100 kV/cm). The relative dielectric constant (εr) is 121, the dielectric loss (tanδ) is 0.024 at 105 Hz.

Structure, electrical and magnetic properties of Co0.8Zn0.2Fe2O4/(K0.47Na0.47Li0.6) NbO3 bilayered thin films grown by pulsed laser deposition

Structural, ferroelectric, and magnetic properties of lead-free bilayer composite films with composition (K, Na, Li) NbO3-CoZnFe2O4 (P-S) and CoZnFe2O4-(K, Na, Li) NbO3 (S-P) layers deposited on Pt/Si substrates by a pulsed laser deposition technique have been studied. Structural analysis carried out by X-ray diffraction and Raman scattering confirmed the formation of individual phases of perovskite and spinel without any intermediate/secondary phase. To probe the stoichiometric elemental composition and cationic distribution at the interstitial sites, X-ray photoelectron spectroscopy measurement was carried out, which confirmed the mixed state of Fe-ions valence, while the Zn2+ state was retained. Ferroelectric and ferromagnetic behavior of the bilayered films was observed concurrently depending upon the growth sequence adopted. Magnetic properties of the film with spinel on the top layer exhibited higher saturation magnetization. Dielectric permittivity follows the Maxwell–Wagner polarization caused by thermally agitated carriers. Appreciable ferroelectric properties were achieved in S-P films while the P-S film exhibited a lossy ferroelectric hysteresis loop, which is attributed to a high leakage current value.

Surface Instability of Composite Thin Films on Compliant Substrates: Direct Simulation Approach

Surface instability via wrinkle formation is a common feature in thin films attached to a compliant substrate. Wrinkled thin-film structures have been increasingly exploited to enhance device performance. In this study a numerical technique utilizing embedded imperfections is employed for direct simulations of wrinkle formation, extending from a single-film structure to composite films involving two or more layers. The incorporation of material elements, bearing different elastic properties at the film-substrate interface, assists in triggering buckling instability when the compressive strain reaches a critical value. The wrinkle wavelength and amplitude obtained from the numerical modeling show excellent agreements with available theoretical solutions involving bi-layer composite films, over the entire span of volume ratios of the constituent layers. A valid range of imperfection distribution, resulting in uniform wrinkle formation, is identified. The current numerical approach is robust and easy to implement and yields great promises in generating reliable wrinkling patterns. It can be readily applied to cases where realistic features cannot be captured by theories, such as the generalized plane strain deformation, indirect compression, and multilayer composite films.

Laser-Induced Graphene Triboelectric Nanogenerators.

Triboelectric nanogenerators (TENGs) show exceptional promise for converting wasted mechanical energy into electrical energy. This study investigates the use of laser-induced graphene (LIG) composites as an exciting class of triboelectric materials in TENGs. Infrared laser irradiation is used to convert the surfaces of the two carbon sources, polyimide (PI) and cork, into LIG. This gives the bilayer composite films the high conductivity associated with LIG and the triboelectric properties of the carbon source. A LIG/PI composite is used to fabricate TENGs based on conductor-to-dielectric and metal-free dielectric-to-dielectric device geometries with open-circuit voltages >3.5 kV and peak power >8 mW. Additionally, a single sheet of PI is converted to a metal-free foldable TENG. The LIG is also embedded within a PDMS matrix to form a single-electrode LIG/PDMS composite TENG. This single-electrode TENG is highly flexible and stretchable and was used to generate power from mechanical contact with skin. The LIG composites present a class of triboelectric materials that can be made from naturally occurring and synthetic carbon sources.

Highly Stretchable Room-Temperature Self-Healing Conductors Based on Wrinkled Graphene Films for Flexible Electronics.

Flexible conductors are emerging soft materials for diverse electrical applications. However, it still remains a great challenge to fabricate high-performance soft conductors that are highly conductive, largely stretchable, and rapid room-temperature self-healable. Here, we design and fabricate flexible conductive bilayer composite films composed of healable elastomeric substrates and wrinkled graphenes. The elastomeric substrates, obtained by a facile bulk copolymerization of N-isopropylacrylamide and 2-methoxyethyl acrylate, show fast room-temperature self-healing efficiency of up to 96%, imparted by the reversible hydrogen bonds. Importantly, the substrates also display strong interfacial adhesion crucial to the formation of stable bilayer composite films based on a prestrain route. The synergy between self-healing of the substrates and wrinkled structures of graphene is endowed to the composite films for mechanical and electrical healing. By adjusting the prestrain ratio of the substrates, the composite films could display the tunable stretchability, conductivity, and self-healing. The optimal bilayer composite film exhibits a high conductivity of 126 S cm-1, a large stretchability of 300%, and rapid room-temperature self-healing. Moreover, it is demonstrated that the composite films are strain-sensitive and can be used as strain sensors to monitor stretching deformation and human motion. These prominent demonstrations suggest a great potential of the bilayer composite films in next-generation wearable electronics.

Mechanical and Electroconductive Properties of Mono- and Bilayer Graphene–Carbon Nanotube Films

This article presents the results of a computer study of electrical conductivity and deformation behavior of new graphene–carbon nanotube (CNT) composite films under bending and stretching. Mono- and bilayer hybrid structures with CNTs (10,0) and (12,0) and an inter-tube distance of 10 and 12 hexagons were considered. It is revealed that elastic deformation is characteristic for mono- and bilayer composite films both in bending and stretching. It is found that, in the case of bending in a direction perpendicular to CNTs, the composite film takes the form of an arc, and, in the case of bending in a direction along CNTs, the composite film exhibits behavior that is characteristic of a beam subjected to bending deformation as a result of exposure to vertical force at its free end. It is shown that mono- and bilayer composite films are more resistant to axial stretching in the direction perpendicular to CNTs. The bilayer composite films with an inter-tube distance of 12 hexagons demonstrate the greatest resistance to stretching in a direction perpendicular to CNTs. It is established that the CNT diameter and the inter-tube distance significantly affect the strength limits of composite films under axial stretching in a direction along CNTs. The composite films with CNT (10,0) and an inter-tube distance of 12 hexagons exhibit the highest resistance to stretching in a direction along CNTs. The calculated distribution of local stresses of the atomic network of deformed mono- and bilayer composite films showed that the maximum stresses fall on atoms forming covalent bonds between graphene and CNT, regardless of the CNT diameter and inter-tube distance. The destruction of covalent bonds occurs at the stress of ~1.8 GPa. It is revealed that the electrical resistance of mono- and bilayer composite films decreases with increasing bending. At the same time, the electrical resistance of a bilayer film is 1.5–2 times less than that of a monolayer film. The lowest electrical resistance is observed for composite films with a CNT (12,0) of metallic conductivity.