Flexible Nanocomposites Research Articles

One‐Step Synthesis of Conductive BNC/PPy·CuCl2 Hybrid Flexible Nanocomposites by In Situ Polymerization

This work reports the one‐step synthesis of bacterial nanocellulose (BNC) incorporated with polypyrrole (PPy) by chemical in situ polymerization of pyrrole (Py) using CuCl2·2H2O as both oxidant agent and functional component, varying the concentration and molar ratio. Electrical, morphological, and physical‐chemical properties of these nanocomposites were investigated. The results revealed that with the increase of Py concentration and molar ratio, the nanocomposites presented traces of copper chloride and copper oxide as shown by Raman and XRD analysis. The quality of bacterial cellulose nanofibers coating by the polymer and the electrical conductivity of the nanocomposites was directly affected by those variables. The combination of the conducting polymer with the oxidant agent offers possibilities for different applications such as electronic devices and sensors.

Enhancing electrical energy storage capability of dielectric polymer nanocomposites via the room temperature Coulomb blockade effect of ultra-small platinum nanoparticles.

Introducing a high dielectric constant (high-k) nanofiller into a dielectric polymer is the most common way to achieve flexible nanocomposites for electrostatic energy storage devices. However, the significant decrease of breakdown strength and large increase of dielectric loss has long been known as the bottleneck restricting the enhancement of practical energy storage capability of the nanocomposites. In this study, by introducing ultra-small platinum (<2 nm) nanoparticles, high-k polymer nanocomposites with high breakdown strength and low dielectric loss were prepared successfully. Core-shell structured polydopamine@BaTiO3 (PDA@BT) and core-satellite ultra-small platinum decorated PDA@BT (Pt@PDA@BT) were used as nanofillers. Compared with PDA@BT nanocomposites, the maximum discharged energy density of the Pt@PDA@BT nanocomposites is increased by nearly 70% because of the improved energy storage efficiency. This research provides a simple, promising and unique way to enhance energy storage capability of high-k polymer nanocomposites.

Highly conductive nanocomposites based on cellulose nanofiber networks via NaOH treatments

Developing functional nanocomposites with the utilization of the sustainable natural resources (e.g. cellulose) is one most importance strategy. In this study, a novel method was developed and used to fabricate flexible conductive nanocomposite. The key innovation of this method is that carbon nanotubes (CNTs) was incorporated into cellulose nanofiber (CNF) gel which processed by alkali treatment. We found that the gelation process caused the shrinking of CNF/CNT gel-film, which result in forming a robust 3D network structure. While the shrinking attributed to constructing high density CNTs electron transport pathways and achieve improved electrical conductivity. Results clearly show that CNFs, a dispersing agent, were used to well-dispersed the CNTs in the nanocomposite. After the alkali treatments, the as-prepared CNF/CNT gel-film had a conductivity of 5.02 S/cm, which is almost 3-fold higher than the CNF/CNT film (without alkai treatment), at 20 wt% CNTs. Conductivity of the CNF/CNT gel-film was further improved to as high as 17.04 S/cm, when adding 50 wt% CNTs. Morphology investigation exhibited that CNFs and CNTs formed into a high density 3D network affording adequate electron transport pathways, and giving the gel-film remarkable electrical conductive properties. Additionally, in lights of its excellent electrical performance, low cost, and environmental friendliness, the CNF/CNT gel-film may have a promising application in the flexible electrodes and conductive papers.

Surface modification-based three-phase nanocomposites with low percolation threshold for optimized dielectric constant and loss

Integration of the excellent attributes of high dielectric constant and low dielectric loss in flexible polymer-based nanocomposites has attracted increased research attention because of their extensive applications in modern electronic and electric industry. In this study, to obtain the optimized dielectric constant and loss, the fabrication and properties of a three-phase nanocomposites, including poly(vinylidene fluoride) (PVDF) and two nanofillers, namely, surface-modified multi-wall carbon nanotubes (mCNTs) and barium titanate nanoparticles (mBTs), are investigated in detail. The mCNTs and mBTs were obtained via the hydrolysis of 3-aminopropyltriethoxysilane (AMEO) and condensation reactions between the AMEO and nanofillers. The three-phase nanocomposites are fabricated by a phase-separation and hot-pressing process. The mCNTs and mBTs can be uniformly dispersed within the PVDF polymer matrix because of the enhanced hydrogen bonding interaction and compatibility with the polymer matrix. The percolation threshold (as low as 0.50vol%) of the two-phase mCNTs/PVDF nanocomposites is adopted to optimize the dielectric properties of the three-phase mCNTs/mBTs/PVDF nanocomposites. At the frequency of 102Hz, a high dielectric constant of 109 and low loss of 0.06 are obtained for the three-phase nanocomposites with only 0.41vol% mCNTs and 2.8vol% mBTs, respectively. Meanwhile, owing to the low percolation threshold and enhanced surface compatibility between the nanofillers and PVDF, the tensile strength of the three-phase nanocomposites is greater than that of PVDF by a factor of greater than 1.5. Owing to their high dielectric constant, low dielectric loss and good mechanical properties, these PVDF-based ternary nanocomposites show potential for applications in electronic devices and energy storage systems.

Nanocomposite Capacitors with Significantly Enhanced Energy Density and Breakdown Strength Utilizing a Small Loading of Monolayer Titania

AbstractThe dielectric capacitor with high electric energy density is demanded for modern electronic and electrical power systems. However, their energy density is considerably limited by a low dielectric constant and low breakdown strength. Here, thin flexible polymer nanocomposites with high energy density are obtained by only adding a small loading of 2D monolayer titania along with concurrent improvements of dielectric constant and breakdown strength. This work not only first reveals that monolayer titania is an excellent filler that can be comparable to existing fillers in nanocomposite capacitors but also provides a facile approach to thin flexible compact dielectric films with ultrahigh energy density and breakdown strength for energy storage applications.

Development of a flexible and conductive elastomeric composite based on chloroprene rubber

Flexible and conductive nanocomposites with enhanced mechanical and dielectric properties have been fabricated from reduced graphene oxide (RGO) reinforced polychloroprene rubber (CR). Composites were prepared on a two-roll mixing mill and the morphological analysis using SEM and TEM showed good dispersibility and exfoliation of RGO layers in the matrix. It imparted a critical role in the enhancement of mechanical and electrical properties of the composites. Composites with 0.9 phr of RGO showed an enhancement in tensile strength, tensile modulus and electrical conductivity as 92%, 75%, and 103% respectively more than the pristine polychloroprene. RGO formed a good conducting percolating network in the polychloroprene matrix and it led to the formation of a dielectric composite material with enhanced electrical properties.

A flexible mesoporous Li4Ti5O12-rGO nanocomposite film as free-standing anode for high rate lithium ion batteries

Advanced flexible electrode is crucial in the development of flexible energy storage devices for emerging wearable and portable electronics. Herein, a free-standing flexible mesoporous Li4Ti5O12-rGO (LTO-rGO) nanocomposite film is rationally designed and fabricated for lithium ion batteries (LIBs). This efficient synthesis involves the growth of lithium titanate hydrate (LTH) precursors on the graphene oxide (GO) by a hydrothermal reaction, assembly into LTH-GO film by vacuum filtration with some extra GO added, and subsequent conversion into LTO-rGO nanocomposite film through calcination. When rGO content in the LTO-rGO film is set, the addition sequence of GO is found to affect its textural and mechanical properties. The resultant free-standing LTO-rGO electrode, taking advantages of high Li4Ti5O12 loading of 73.9%, mesoporous layer-stacked channels with good electron/ion conductivity, good mechanical strength, and enlarged electrode/electrolyte contact area, delivers excellent electrochemical performance (e.g., specific capacity of 135.4 mAh g−1 at 40 C) over the electrode of conventional configuration. Moreover, no organic but all inorganic reagents are used in the synthesis, offering an eco-friendly, cost-efficient, and easily scalable way to fabricate binder-free flexible electrode for LIBs.

Multiple Interfacial Fe3O4@BaTiO3/P(VDF-HFP) Core-Shell-Matrix Films with Internal Barrier Layer Capacitor (IBLC) Effects and High Energy Storage Density.

Flexible nanocomposites composed of high dielectric constant fillers and polymer matrix have shown great potential for electrostatic capacitors and energy storage applications. To obtain the composited material with high dielectric constant and high breakdown strength, multi-interfacial composited particles, which composed of conductive cores and insulating shells and possessed the internal barrier layer capacitor (IBLC) effect, were adopted as fillers. Thus, Fe3O4@BaTiO3 core-shell particles were prepared and loaded into the poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) polymer matrix. As the mass fraction of core-shell fillers increased from 2.5 wt % to 30 wt %, the dielectric constant of the films increased, while the loss tangent remained at a low level (<0.05 at 1 kHz). Both high electric displacement and high electric breakdown strength were achieved in the films with 10 wt % core-shell fillers loaded. The maximum energy storage density of 7.018 J/cm3 was measured at 2350 kV/cm, which shows significant enhancement than those of the pure P(VDF-HFP) films and analogous composited films with converse insulating-conductive core-shell fillers. A Maxwell-Wagner capacitor model was also adopted to interpret the efficiency of IBLC effects on the suppressed loss tangent and the superior breakdown strength. This work explored an effective approach to prepare dielectric nanocomposites for energy storage applications experimentally and theoretically.

Mussel byssus-inspired engineering of synergistic nanointerfacial interactions as sacrificial bonds into carbon nanotube-reinforced soy protein/nanofibrillated cellulose nanocomposites: Versatile mechanical enhancement

Achieving flexible and stretchable biobased nanocomposites combining high strength and toughness is still a very challenging endeavor. Herein, we described a novel and versatile biomimetic design for tough and high-performance TEMPO-oxidized nanofibrillated cellulose (TONFC)/soy protein isolate (SPI) nanocomposites, which are triggered by catechol-mimetic carbon nanotubes (PCT) and iron ions (Fe(III)) to yield a strong yet sacrificial metal-ligand motifs into a chemically cross-linked architecture network. Taking advantage of self-polymerization of catechol-inspired natural tannic acid, PCT nanohybrid was prepared through adhering reactive poly-(tannic acid) (PTA) layer onto surfaces of carbon nanotubes via a simple dip-coating process. The high-functionality PCT induced the formation of the metal-ligand bonds through the ionic coordinates between the catechol groups in PCT and –COOH groups of TONFC skeleton with Fe(III) mediation that mimicked mussel byssus. Upon stretching, this tailored TONFC-Fe(III)-catechol coordination bonds served as sacrificial bonds that preferentially detach prior to the covalent network, which gave rise to efficient energy dissipation that the nanocomposites integrity was survived. As a result of these kind of synergistic interfacial interactions (sacrificial and covalent bonding), the optimal nanocomposite films processed high tensile strength (ca. 11.5MPa), large elongation (ca. 79.3%), remarkable toughness (ca. 6.9MJm−3), and favorable water resistance as well as electrical conductivity. The proposed bioinspired strategy for designing plant protein-based materials enables control over their mechanical performance through the synergistic engineering of sacrificial bonds into the composite interface.

Size-dependent nanoparticle dynamics in semiflexible ring polymer nanocomposites

By employing molecular dynamics simulations, we explored different size-dependent dynamics of NPs in semiflexible linear and ring polymer nanocomposites. Large NPs diffuse faster slightly in flexible ring polymer nanocomposites than in flexible linear polymer ones. However, the motions of large NPs in semiflexible ring polymer nanocomposites with large bending energies are very slow and NPs exhibit the glassy state in which the NPs are all caged by the neighbouring semiflexible ring polymers, while large NPs in semiflexible linear polymer nanocomposites transport much faster than those in semiflexible ring polymer ones because rod-like structures of semiflexible linear polymers can favour the motions of NPs. Meanwhile, the diffusion coefficients Dpolymer of semiflexible ring polymers decrease monotonously with increasing bending energy Kb, while the minimum diffusion coefficient for semiflexible linear polymers occurs at the moderate bending energy such as Kb = 6, in which the semiflexible linear polymers hold the maximum entanglement density. NP size, polymer topological constraint as well as chain stiffness affect the dynamics of NPs in polymer nanocomposites seriously, and this investigation can help us understand the complicated dynamical behaviours for NPs in polymer nanocomposites.

Preparation of Novel Magnetic Polyurethane Flexible Foam Nanocomposites

Novel magnetic polyurethane flexible foam nanocomposites were synthesized by incorporation of modified magnetic iron oxide nanoparticles into polyurethane flexible foam. Core shell magnetic nanoparticles (MNPs) Fe3O4@SiO2 were synthesized via co‐precipitation and sol‐gel methods and incorporated in the structure of the composites by in‐situ polymerization of monomers in the presence of MNPs. The magnetic core‐shell NPs were used up to 3.0% in the foam formulation and the optimum percentage was defined. The prepared nanocomposites were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT‐IR), vibrating sample magnetometery (VSM), thermo‐mechanical analysis (TMA), and thermogravimetric analysis (TGA). The thermogravimetric analysis results showed an increased thermal stability of the polyurethane flexible foam nanocomposites by incorporation of magnetic core shell nanoparticles.

Highly conductive and flexible nano-structured carbon-based polymer nanocomposites with improved electromagnetic-interference-shielding performance

Widespread usage and development of electrical/electronic devices can create severe problems for various other devices and in our everyday lives due to harmful exposure to electromagnetic (EM) radiation. Herein, we report on the electromagnetic interference (EMI)-shielding performance of highly flexible and conductive chlorinated polyethylene (CPE)/carbon nanofiber (CNF) nanocomposites fabricated by a probe-sonication-assisted simple solution-mixing process. The dispersion of CNF nanofillers inside the CPE matrix has been studied by electron micrographs. This dispersion is reflected in the formation of continuous conductive networks at a low percolation-threshold value of 2.87 wt% and promising EMI-shielding performance of 41.5 dB for 25 wt% CNF in the X-band frequency (8.2–12.4 GHz). Such an intriguing performance mainly depends on the unique filler–filler or filler–polymer networks in CPE nanocomposites. In addition, the composite material displays a superior EMI efficiency of 47.5 dB for 2.0 mm thickness at 8.2 GHz. However, we have been encouraged by the promotion of highly flexible and lightweight CPE/CNF nanocomposite as a superior EMI shield, which can protect electronic devices against harm caused by EM radiation and offers an adaptable solution in advanced EMI-shield applications.

Graphene‐polymer nanocomposites for biomedical applications

Despite the significant efforts in the synthesis of new polymers, the mechanical properties of polymer matrices can be considered modest in most cases, which limits their application in demanding areas. The isolation of graphene and evaluation of its outstanding properties, such as high thermal conductivity, superior mechanical properties, and high electronic transport, have attracted academic and industrial interest, and opened good perspectives for the integration of graphene as a filler in polymer matrices to form advanced multifunctional composites. Graphene‐based nanomaterials have prompted the development of flexible nanocomposites for emerging applications that require superior mechanical, thermal, electrical, optical, and chemical performance. These multifunctional nanocomposites may be tailored to synergistically combine the characteristics of both components if proper structural and interfacial organization is achieved. The investigations carried out in this aim have combined graphene with different polymers, leading to a variety of graphene‐based nanocomposites. The extensive research on graphene and its functionalization, as well as polymer graphene composites, aiming at applications in the biomedical field, are reviewed in this paper. An overview of the polymer matrices adequate for the biomedical area and the production techniques of graphene composites is presented. Finally, the applications of such nanocomposites in the biomedical field, particularly in drug delivery, wound healing, and biosensing, are discussed.

Fabrication and characterization of ZnO/MnO2 and ZnO/TiO2 flexible nanocomposites for energy storage applications

ZnO based nanostructure composites are attractive for high-tech applications of energy conversion and energy storage due to wide range in operating potential window. This study presents about fabrication of ZnO/MnO2 and ZnO/TiO2 composites via hydrothermal method in two consecutive steps. Furthermore lignocelluloses fiber directly collected form self-growing plant Monochoria Vagina, were incorporated in fabricated ZnO/MnO2 and ZnO/TiO2 composites for development of flexible and bulk paper composite electrode. The structural and morphological analysis were carried out using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), respectively. XRD analysis confirm the crystalline structures for ZnO/MnO2 and ZnO/TiO2 samples with crystallite size ∼62 nm and ∼63 nm, respectively. SEM images shows the sheet-like and nanorods morphology for ZnO and MnO2 nanostructures, respectively. Fourier Transform Infrared (FTIR) Spectroscopy absorbance spectrum reveal the composite formation of ZnO/MnO2/LC and ZnO/TiO2/LC as bulk paper electrodes whereas cyclic Voltammetry measurement showed the capacitive behavior of composite paper electrodes for the suitable applications in supercapacitors and batteries.

Highly durable piezo-electric energy harvester by a super toughened and flexible nanocomposite: effect of laponite nano-clay in poly(vinylidene fluoride)

A highly durable piezoelectric energy harvester is introduced by integrating the toughness and flexibility of a non-electrically poled, laponite nano-clay mineral-induced γ-phase (up to 98%) in a poly(vinylidene-fluoride) (PVDF) matrix by a simple solvent evaporation technique. Owing to a superior electromechanical coupling effect, PVDF/laponite nanocomposites retain excellent biomechanical energy harvesting capabilities under external vibration (as high as 6 V output voltage and 70 nA output current under a compressive force of 300 N) and charge storage properties under an external high electric field (maximum of discharged energy density at a breakdown strength of 302 MV m−1). As a proof of concept, the fabricated nanogenerator (NG) possesses a high output power density (~6.3 mW m−2) that directly drives several consumer electronics without using any storage system or batteries. It paves the way for potential applicability in next generation electronics, particularly as a self-powered device and to configure sustainable internet of things (IoT) sensor networks.

Resistive Hysteresis of Carbon Nanofiber Doped Elastomeric Nanocomposite Polymer

Micropatternable flexible elastomeric nanocomposites find application in sensing biomechanical strains and biopotential signals [1-5]. While many polymers have been used to fabricate flexible MEMS polydimethylsiloxane (PDMS), a silicone based elastomer, has been widely used because of its biocompatibility, low cost, low toxicity, high oxidative and thermal stability, optical transparent, low permeability to water, low electrical conductivity, and ease of micropatterning [6-15]. Previously, we had demonstrated fabrication of various PDMS based micropatternable nanocomposite polymers which are either electrically conductive and magnetic in nature [16-17]. We have developed improved electrically and thermally conducuctive micropatternable PDMS based nanocomposite polymer containg milled carbon fibers, prepared by ultrasonically assisted processing technology. The prepared nanocomposite microstructures show interesting resistance hysteresis loop. This paper also discusses the underlying mechanisims that are responsible for resistance hysteresis loop. Acknowledgements: Authors would like to thank Nippon Graphite Fiber Co., Ltd, Japan; for proving milled carbon fiber and technical support for this project.

Vertically Aligned and Interconnected Boron Nitride Nanosheets for Advanced Flexible Nanocomposite Thermal Interface Materials.

The continuous evolution toward semiconductor technology in the "more-than-Moore" era and rapidly increasing power density of modern electronic devices call for advanced thermal interface materials (TIMs). Here, we report a novel strategy to construct flexible polymer nanocomposite TIMs for advanced thermal management applications. First, aligned polyvinyl alcohol (PVA) supported and interconnected 2D boron nitride nanosheets (BNNSs) composite fiber membranes were fabricated by electrospinning. Then, the nanocomposite TIMs were constructed by rolling the PVA/BNNS composite fiber membranes to form cylinders and subsequently vacuum-assisted impregnation of polydimethylsiloxane (PDMS) into the porous cylinders. The nanocomposite TIMs not only exhibit a superhigh through-plane thermal conductivity enhancement of about 10 times at a low BNNS loading of 15.6 vol % in comparison with the pristine PDMS but also show excellent electrical insulating property (i.e., high volume electrical resistivity). The outstanding thermal management capability of the nanocomposite TIMs was practically confirmed by capturing the surface temperature variations of a working LED chip integrated with the nanocomposite TIMs.

Electrical and multiferroic characteristics of PVDF-MnFe2O4 nanocomposites

Thin films of PVDF-MnFe2O4 nano-multiferroic composites (in 0–3 connectivity) of varying compositions have been prepared through a solution-casting route. X-ray diffraction and scanning electron microscopy techniques have been used to study basic crystal structure and micrograph respectively of the composites. Structural investigation confirms the presence of polymeric electro-active β-phase in PVDF matrix and PVDF-MnFe2O4 nano-composites. Flexible nano-composites of PVDF and MnFe2O4 exhibit high dielectric constant and low tangent loss. The impedance spectroscopy technique has provided some interesting results on the contributions of grain and grain boundary in the total resistive properties of the composites. The nature of frequency dependence of alternating conductivity obeys Jonscher's power law. Some multiferroic properties (electric and magnetic polarization and magneto-electric coupling coefficient) have provided important experimental data of composites useful for multifunctional devices. The improved conductivity and dielectric properties suggest some promising applications in the embedded capacitors.

Highly Thermally Stable, Transparent, and Flexible Polybenzoxazine Nanocomposites by Combination of Double-Decker-Shaped Polyhedral Silsesquioxanes and Polydimethylsiloxane

In this study a new type of bifunctional phenolic compound based on a double-decker silsesquioxane (DDSQ-BP) was synthesized from phenyltrimethylsilane and then reacted (Mannich condensation) with allylamine and CH2O to form a bis-allyl benzoxazine DDSQ derivative (DDSQ-BZ). The structures of these DDSQ derivatives were confirmed using Fourier transform infrared and nuclear magnetic resonance spectroscopy and MALDI-TOF mass spectrometry. Highly thermally stable, transparent, and flexible polybenzoxazine prepolymers were obtained after hydrosilylation of DDSQ-BZ with polydimethylsiloxane (PDMS) as the flexible segment; these materials were characterized using differential scanning calorimetry, thermogravimetric analysis, microtensile testing, and UV–vis spectroscopy. The char yield of DDSQ-BZ-PDMS was 73 wt %, significantly higher than that of a typical polybenzoxazine; in addition, DDSQ-BZ-PDMS displayed high flexibility and transparency after thermal curing.

Flexible cellulose and ZnO hybrid nanocomposite and its UV sensing characteristics

This paper reports the synthesis and UV sensing characteristics of a cellulose and ZnO hybrid nanocomposite (CEZOHN) prepared by exploiting the synergetic effects of ZnO functionality and the renewability of cellulose. Vertically aligned ZnO nanorods were grown well on a flexible cellulose film by direct ZnO seeding and hydrothermal growing processes. The ZnO nanorods have the wurtzite structure and an aspect ratio of 9 ~ 11. Photoresponse of the prepared CEZOHN was evaluated by measuring photocurrent under UV illumination. CEZOHN shows bi-directional, linear and fast photoresponse as a function of UV intensity. Electrode materials, light sources, repeatability, durability and flexibility of the prepared CEZOHN were tested and the photocurrent generation mechanism is discussed. The silver nanowire coating used for electrodes on CEZOHN is compatible with a transparent UV sensor. The prepared CEZOHN is flexible, transparent and biocompatible, and hence can be used for flexible and wearable UV sensors.