High-stress study of bioinspired multifunctional PEDOT:PSS/nanoclay nanocomposites using AFM, SEM and numerical simulation.
ABSTRACT: Bioinspired design has been central in the development of hierarchical nanocomposites. Particularly, the nacre-mimetic brick-and-mortar structure has shown excellent mechanical properties, as well as gas-barrier properties and optical transparency. Along with these intrinsic properties, the layered structure has also been utilized in sensing devices. Here we extend the multifunctionality of nacre-mimetics by designing an optically transparent and electron conductive coating based on PEDOT:PSS and nanoclays Laponite RD and Cloisite Na+. We carry out extensive characterization of the nanocomposite using transmittance spectra (transparency), conductive atomic force microscopy (conductivity), contact-resonance force microscopy (mechanical properties), and SEM combined with a variety of stress-strain AFM experiments and AFM numerical simulations (internal structure). We further study the nanoclay's response to the application of pressure with multifrequency AFM and conductive AFM, whereby increases and decreases in conductivity can occur for the Laponite RD composites. We offer a possible mechanism to explain the changes in conductivity by modeling the coating as a 1-dimensional multibarrier potential for electron transport, and show that conductivity can change when the separation between the barriers changes under the application of pressure, and that the direction of the change depends on the energy of the electrons. We did not observe changes in conductivity under the application of pressure with AFM for the Cloisite Na+ nanocomposite, which has a large platelet size compared with the AFM probe diameter. No pressure-induced changes in conductivity were observed in the clay-free polymer either.
Project description:A scalable electrophoretic deposition (EPD) approach is used to create novel thin, flexible, and lightweight carbon nanotube-based textile pressure sensors. The pressure sensors can be produced using an extensive variety of natural and synthetic fibers. These piezoresistive sensors are sensitive to pressures ranging from the tactile range (<10 kPa), the body weight range (?500 kPa), and very high pressures (?40 MPa). The EPD technique enables the creation of a uniform carbon nanotube-based nanocomposite coating, in the range of 250-750 nm thick, of polyethyleneimine (PEI) functionalized carbon nanotubes on nonconductive fibers. In this work, nonwoven aramid fibers are coated by EPD onto a backing electrode followed by film formation onto the fibers creating a conductive network. The electrically conductive nanocomposite coating is firmly bonded to the fiber surface and shows piezoresistive electrical/mechanical coupling. The pressure sensor displays a large in-plane change in electrical conductivity with applied out-of-plane pressure. In-plane conductivity change results from fiber/fiber contact as well as the formation of a sponge-like piezoresistive nanocomposite "interphase" between the fibers. The resilience of the nanocomposite interphase enables sensing of high pressures without permanent changes to the sensor response, showing high repeatability.
Project description:During their synthesis, multi-walled carbon nanotubes can be aligned and impregnated in a polymer matrix to form an electrically conductive and flexible nanocomposite with high backing density. The material exhibits the highest reported electrical conductivity of CNT-epoxy composites (350 S/m). Here, we show how conductive atomic force microscopy can be used to study the electrical transport mechanism in order to explain the enhanced electrical properties of the composite. The high spatial resolution and versatility of the technique allows us to further decouple the two main contributions to the electrical transport: (1) the intrinsic resistance of the tube and (2) the tunneling resistance due to nanoscale gaps occurring between the epoxy-coated tubes along the composite. The results show that the material behaves as a conductive polymer, and the electrical transport is governed by electron tunneling at interconnecting CNT-polymer junctions. We also point out the theoretical formulation of the nanoscale electrical transport between the AFM tip and the sample in order to derive both the composite conductivity and the CNT intrinsic properties. The enhanced electrical properties of the composite are attributed to high degree of alignment, the CNT purity, and the large tube diameter which lead to low junction resistance. By controlling the tube diameter and using other polymers, the nanocomposite electrical conductivity can be improved.
Project description:Optically transparent nanofiber paper containing silver nanowires showed high electrical conductivity and maintained the high transparency, and low weight of the original transparent nanofiber paper. We demonstrated some procedures of optically transparent and electrically conductive cellulose nanofiber paper for lightweight and portable electronic devices. The nanofiber paper enhanced high conductivity without any post treatments such as heating or mechanical pressing, when cellulose nanofiber dispersions were dropped on a silver nanowire thin layer. The transparent conductive nanofiber paper showed high electrical durability in repeated folding tests, due to dual advantages of the hydrophilic affinity between cellulose and silver nanowires, and the entanglement between cellulose nanofibers and silver nanowires. Their optical transparency and electrical conductivity were as high as those of ITO glass. Therefore, using this conductive transparent paper, organic solar cells were produced that achieved a power conversion of 3.2%, which was as high as that of ITO-based solar cells.
Project description:In this paper, we report the fabrication of highly conductive poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/cellulose nanofiber (CNF) nanocomposite paper with excellent flexibility through post-treatment with an organic solvent. The post-treated PEDOT:PSS/CNF porous nanocomposite papers showed a lower sulfur content, indicating the removal of residual PSS. The electrical conductivity of PEDOT:PSS/CNF porous nanocomposite paper was increased from 1.05 S/cm to 123.37 S/cm and 106.6 S/cm by post-treatment with dimethyl sulfoxide (DMSO) and ethylene glycol (EG), respectively. These values are outstanding in the development of electrically conductive CNF composites. Additionally, the highly conductive nanocomposite papers showed excellent bending stability during bending tests. Cyclic voltammetry (CV) showed a Faradaic redox reaction and non-Faradaic capacitance due to the redox activity of PEDOT:PSS and large surface area, respectively. Electrochemical energy storage ability was evaluated and results showed that capacitance improved after post-treatment. We believe that the highly conductive PEDOT:PSS/CNF porous nanocomposite papers with excellent flexibility described here are potential candidates for application in porous paper electrodes, flexible energy storage devices, and bioengineering sensors.
Project description:Mollusk nacre is a prototypical biological inorganic-organic composite that combines high toughness, stiffness, and strength by its brick-and-mortar microstructure, which has inspired several synthetic mimics. Its remarkable fracture toughness relies on inelastic deformations at the process zone at the crack tip that dissolve stress concentrations and stop cracks. The micrometer-scale structure allows resolving the size and shape of the process zone to understand the fracture processes. However, for better scalability, nacre-mimetic nanocomposites with aligned inorganic or graphene nanosheets are extensively pursued, to avoid the packing problems of mesoscale sheets like in nacre or slow in situ biomineralization. This calls for novel methods to explore the process zone of biomimetic nanocomposites. Here the fracture of nacre and nacre-inspired clay/polymer nanocomposite is explored using laser speckle imaging that reveals the process zone even in absence of changes in optical scattering. To demonstrate the diagnostic value, compared to nacre, the nacre-inspired nanocomposite develops a process zone more abruptly with macroscopic crack deflection shown by a flattened process zone. In situ scanning electron microscopy suggests similar toughening mechanisms in nanocomposite and nacre. These new insights guide the design of nacre-inspired nanocomposites toward better mechanical properties to reach the level of synergy of their biological model.
Project description:Metal oxide based polymer nanocomposites find diverse applications as functional materials, and in particular thiol-ene/TiO2 nanocomposites are promising candidates for dental restorative materials. The important mechanical and thermal properties of the nanocomposites, however, are still not well understood. In this study, the elastic modulus and thermal conductivity of thiol-ene/TiO2 nanocomposite thin films with varying weight fractions of TiO2 nanoparticles are investigated by using Brillouin light scattering spectroscopy and 3? measurements, respectively. As the TiO2 weight fraction increases from 0 to 90%, the effective elastic longitudinal modulus of the films increases from 6.2 to 37.5 GPa, and the effective thermal conductivity from 0.04 to 0.76 W/m K. The former increase could be attributed to the covalent cross-linking of the nanocomposite constituents. The latter one could be ascribed to the addition of high thermal conductivity TiO2 nanoparticles and the formation of possible conductive channels at high TiO2 weight fractions. The linear dependence of the thermal conductivity on the sound velocity, reported for amorphous polymers, is not observed in the present nanocomposite system.
Project description:We synthesized a hybrid nanocomposite comprised of selenium nanoparticles coated with a thin layer of a conductive polymer, poly(3,4-ethylenedioxythiophene), and studied its thermoelectric properties. The conductive polymer layer on the surface of nanoparticles in the composites formed a percolating network running between the stacked nanoparticles, exhibiting an electrical conductivity close to or higher than that of pure polymer. The thermoelectric power factor of the resulting composite was higher than that of individual polymer or selenium nanoparticles. We further increased the electrical conductivity of the composite by thermal annealing, thereby improving the power factor to 15 μW/cmK2 which is nine times higher than that of the polymer.
Project description:Novel hierarchical carbon nanohorns (CNHs) carried iron fluoride nanocomposites have been constructed by direct growth of FeF3·0.33H2O nanoparticles on CNHs. In the FeF3·0.33H2O@CNHs nanocomposite, the mesopore CNHs play the role as conductive matrix and robust carrier to support the FeF3·0.33H2O nanoparticles. The intimate conductive contact between the two components can build up an express way of electron transfer for rapid Li(+) insertion/extraction. The CNHs can not only suppress the growth and agglomeration of FeF3·0.33H2O during the crystallization process, but also sever as an "elastic confinement" to support FeF3·0.33H2O. As was to be expected, the hierarchical FeF3·0.33H2O@CNHs nanocomposite exhibits impressive rate capability and excellent cycle performance. Markedly, the nanocomposite proves stable, ultrahigh rate lithium ion storage properties of 81 mAh g(-1) at charge/discharge rate of 50 C (a discharge/charge process only takes 72 s). The integration of high electron conductivity, confined nano sized FeF3·0.33H2O (~5 nm), hierarchical mesopores CNHs and the "elastic confinement" support, the FeF3·0.33H2O@CNHs nanocomposite demonstrates excellent ultrahigh rate capability and good cycling properties.
Project description:A synthetic mimic of mussel adhesive protein, dopamine-modified four-armed poly(ethylene glycol) (PEG-D4), was combined with a synthetic nanosilicate, Laponite (Na(0.7+)(Mg5.5Li0.3Si8)O20(OH)4)(0.7-)), to form an injectable naoncomposite tissue adhesive hydrogel. Incorporation of up to 2 wt % Laponite significantly reduced the cure time while enhancing the bulk mechanical and adhesive properties of the adhesive due to strong interfacial binding between dopamine and Laponite. The addition of Laponite did not alter the degradation rate and cytocompatibility of PEG-D4 adhesive. On the basis of subcutaneous implantation in rat, PEG-D4 nanocomposite hydrogels elicited minimal inflammatory response and exhibited an enhanced level of cellular infiltration as compared to Laponite-free samples. The addition of Laponite is potentially a simple and effective method for promoting bioactivity in a bioinert, synthetic PEG-based adhesive while simultaneously enhancing its mechanical and adhesive properties.
Project description:Graphene-enhanced polymer matrix nanocomposites are attracting ever increasing attention in the electromagnetic (EM) interference (EMI) shielding field because of their improved electrical property. Normally, the graphene is introduced into the matrix by chemical functionalization strategy. Unfortunately, the electrical conductivity of the nanocomposite is weak because the graphene nanosheets are not interconnected. As a result, the electromagnetic interference shielding effectiveness of the nanocomposite is not as excellent as expected. Interconnected graphene network shows very good electrical conduction property, thus demonstrates excellent electromagnetic interference shielding effectiveness. However, its brittleness greatly limits its real application. Here, we propose to directly infiltrate flexible poly(dimethylsiloxane) (PDMS) into interconnected reduced graphene network and form nanocomposite. The nanocomposite is superflexible, light weight, enhanced mechanical and improved electrical conductive. The nanocomposite is so superflexible that it could be tied as spring-like sucker. Only 1.07 wt % graphene significantly increases the tensile strengths by 64% as compared to neat PDMS. When the graphene weight percent is 3.07 wt %, the nanocomposite has the more excellent electrical conductivity up to 103 S/m, thus more outstanding EMI shielding effectiveness of around 54 dB in the X-band are achieved, which means that 99.999% EM has been shielded by this nanocomposite. Bluetooth communication testing with and without our nanocomposite confirms that our flexible nanocomposite has very excellent shielding effect. This flexible nanocomposite is very promising in the application of wearable devices, as electromagnetic interference shielding shelter.