Search

Two trimellitic anhydride-functionalized, thermally reduced graphenes with different aspect ratios, Af, and the same C/O ratio (8:1) were prepared and melt-mixed into poly(ethylene terephthalate) (PET), and the mechanical properties of the resulting nanocomposites were studied with a focus on plastic deformation behavior. A slight increase in the G′ of the melt was observed for the surface-modified low-Af graphene composites (Af = 20) below the percolation threshold, whereas a significant enhancement in G′ was observed for higher-Af graphene composites (Af = 80) at all graphene loadings, both below and above the percolation concentration. Furthermore, the use of modified low-Af graphene caused an improvement both in Young’s modulus and elongation at break of the resulting PET nanocomposites because of enhancement of interfacial adhesion between filler and matrix which resulted in the formation of a coupled network via covalent bonding and the suppression both of strain-induced orientation and strain-induced crystallization. By contrast, the use of modified higher-Af surface graphene in nanocomposites caused a drastic improvement in Young’s modulus but lower elongation-at-break than with the unmodified counterpart; the former effect is due to the formation of denser coupled networks and stronger interfacial adhesion as a result of graphene surface modification and the latter is due to the added geometrical restriction in unentangling chains from the PET matrix in the presence of higher-Af graphene. The preceding observations demonstrate the potential impacts of tuning both surface chemistry and aspect ratio of graphene in the fabrication of PET/graphene composites.

Graphene of two different aspect ratios, Af, was melt mixed with poly(ethylene terephthalate) (PET) to form amorphous PET/graphene composites with less than 5% crystallinity. The higher-order structure and mechanical properties of poly(ethylene terephthalate) (PET) in these composites were investigated using techniques such as differential scanning calorimetry and dynamic mechanical analysis, whereas transmission electron microscopy, melt rheology, and electrical conductivity were used to study the graphene dispersion. A decrease in heat capacity changes, ΔCp, of PET in nanocomposites at the glass transition temperature, Tg, without Tg change suggests that a rigid amorphous fraction (RAF) of PET was formed at the PET/graphene interface. The stiffening effect of graphene below 1 wt % loading is quite small in the glassy state region and independent of the Af of graphene. Above 2 wt %, graphene forms a mechanical percolation network with the RAF of PET and the PET chains are geometrically restricted by the incorporation of graphene with a high Af, resulting in an unexpectedly higher modulus of nanocomposites both below and above Tg.

Graphene was modified with trimellitic anhydride groups, and its polyethylene-terephthalate-based (PET-based) nanocomposites were prepared by melt-mixing. Percolation thresholds observed from chang...

Triboelectric nanogenerators (TENGs) are considered promising next-generation mechanical energy harvesters owing to their desirable attributes such as light weight, portability, eco-friendliness, and low cost. However, cost-effective, scalable, and facile manufacturing methods are still required for the commercialization of TENGs, especially for textile-type TENGs compatible with a variety of textile products. In this work, we report for the first time the layer-by-layer (LbL) assembly of graphene multilayers for low-cost, durable, scalable, and wearable TENGs. The LbL-based graphene multilayers are fabricated on polymer substrates with flat, undulated, and textile surfaces, where graphene multilayers play dual roles as a positive tribo-material and as an electrode. The polymer substrate here is utilized as a negative tribo-material. We identify the optimal number of layers for graphene composites and analyze this outcome using their morphological and electrical properties. Due to the hydrogen bonding-based LbL wet processes, graphene composite multilayers could be well deposited on undulated surfaces as well as on large-scale fabric textiles. These LbL-deposited graphene multilayers yield graphene based-TENGs (G-TENGs) with high durability and high performance. Finally, a graphene multilayer on a textile sample is demonstrated as a scalable and wearable textile-based G-TENG (TG-TENG) operated in a single electrode mode, thereby enabling low-cost manufacturing and high compatibility with textile products such as cloths, curtains, bags and so on. The simple, cost-effective, scalable, and versatile LbL assembly can therefore enable the fabrication of wearable energy harvesting sources for many portable personal microelectronic devices (e.g., self-powered wireless sensors).

Next-generation electronics require mechanical flexibility and durability as well as electrical conductivity. In this report, few-layer graphene and polyelectrolytes were assembled into ultrathin films on flexible plastic substrates by a simple and cost-effective layer-by-layer technique. This technique integrated high electrical conductivity and excellent oxygen barrier property into a single film. These characteristics have been rarely reported for other types of thin films prepared by solution processing. The optical properties, film thickness, and mass of the films were precisely controlled by the number of bilayers. After a brief exposure to nitric acid (HNO3) vapor, the films exhibited much improved electrical conductivity while preserving their other properties. Raman, x-ray photoelectron, and FT-IR spectroscopy proved that the effects of the HNO3 treatment were due to the removal of polymeric components and restricted to the film surface, and not due to the chemical doping of graphene.

Background/Aims: Tenofovir disoproxil fumarate (TDF) exhibits similar antiviral efficacy against treatment-naïve and lamivudine (LAM)-resistant chronic hepatitis B (CHB). However, there are few clinical reports on the antiviral effects of TDF–LAM combination therapy compared to TDF monotherapy in patients with LAM-resistant CHB. Methods: We investigated the antiviral efficacy of TDF monotherapy vs. TDF–LAM combination therapy in 103 patients with LAM-resistant CHB. Results: The study subjects were treated with TDF alone (n=40) or TDF–LAM combination therapy (n=63) for ≥6 months. The patients had previously been treated with TDF-based rescue therapy for a median of 30.0 months (range, 8–36 months). A virologic response (VR) was achieved in 99 patients (96.1%): 95.0% (38/40) of patients in the TDF monotherapy group and 96.8% (61/63) of patients in the TDF–LAM combination therapy group. The VR rates were not significantly different between the TDF monotherapy and TDF–LAM combination therapy groups (88.9 vs. 87.3% at month 12, and 94.4 vs. 93.7% at month 24, log-rank p=0.652). Univariate and multivariate analyses revealed that none of the pretreatment factors were significantly associated with VR. Conclusions: TDF monotherapy was as effective as TDF–LAM combination therapy for maintaining viral suppression in the vast majority of patients with LAM-resistant CHB, which suggests that TDF add-on therapy with LAM is unnecessary.

Recently, triboelectric nanogenerators (TENGs) have been widely utilized to address the energy demand of portable electronic devices by harvesting electrical energy from human activities or immediate surroundings. To increase the surface charge and surface area of negative TENGs, previous studies suggested several approaches such as micro-patterned arrays, porous structures, multilayer alignment, ion injections, ground systems and mixing of high dielectric constant materials. However, the preparation processes of these nanocomposite TENGs have been found to be complex and expensive. In this work, we report a simple, efficient and inexpensive modification of poly(dimethylsiloxane) (PDMS) using graphene nanoplatelets (GNPs) fillers and a Na2CO3 template. This GNP-PDMS was chemically bonded using 3-aminopropylethoxysilane (APTES) as a linker with an electrode multilayer made by layer-by-layer deposition of polyvinyl alcohol (PVA) and poly(4-styrene-sulfonic acid) (PSS)-stabilized GNP (denoted as [PVA/GNP-PSS]n). A 33 wt.% Na2CO3 and 0.5 wt.% of GNP into a PDMS-based TENG gives an open-circuit voltage and short-circuit current density of up to ~270.2 V and ~0.44 &mu, A/cm2, which are ~8.7 and ~3.5 times higher than those of the pristine PDMS, respectively. The higher output performance is due to (1) the improved surface charge density, 54.49 &mu, C/m2, from oxygen functional moieties of GNP, (2) high surface roughness of the composite film, ~0.399 &mu, m, which also increased the effective contact area, and (3) reduced charge leakage from chemical bonding of GNP-PDMS and [PVA/GNP-PSS]3 via APTES. The proposed TENG fabrication process could be useful for the development of other high-performance TENGs.

Recently, with the miniaturization of electronic devices, problems with regard to the size and capacity of batteries have arisen. Energy harvesting is receiving significant attention to solve these problems. In particular, the thermoelectric generator (TEG) is being studied for its ability to harvest waste heat energy. However, studies on organic TEGs conducted thus far have mostly used conductive polymers, making the application range of TEGs relatively narrow. In this study, we fabricated organic TEGs using carbonaceous nanomaterials (i.e., graphene nanoplatelet (GNP) and single-walled carbon nanotube (SWNT)) with polyelectrolytes (i.e., poly(vinyl alcohol) (PVA) and poly (diallyldimethyl ammonium chloride) (PDDA)) via layer-by-layer (LbL) coating on polymeric substrates. The thermoelectric performance of the carbonaceous multilayer structure was measured, and it was confirmed that the thermoelectric performance of the TEG in this study was not significantly different from that of the existing organic TEG fabricated using the conductive polymers. The 10 bilayer SWNT thin films with polyelectrolyte exhibited a thermopower of &minus, 14 &mu, V&middot, K&minus, 1 and a power factor of 25 &mu, W&middot, m&minus, 1K&minus, 2. Moreover, by simply changing the electrolyte, p- or n-type TEGs could be easily fabricated with carbonaceous nanomaterials via the LbL process. Also, by just changing the electrolyte, p- or n-type of TEGs could be easily fabricated with carbonaceous nanomaterials with a layer-by-layer process.

Because of their outstanding electrical and mechanical properties, graphene strain sensors have attracted extensive attention for electronic applications in virtual reality, robotics, medical diagnostics, and healthcare. Although several strain sensors based on graphene have been reported, the stretchability and sensitivity of these sensors remain limited, and also there is a pressing need to develop a practical fabrication process. This paper reports the fabrication and characterization of new types of graphene strain sensors based on stretchable yarns. Highly stretchable, sensitive, and wearable sensors are realized by a layer-by-layer assembly method that is simple, low-cost, scalable, and solution-processable. Because of the yarn structures, these sensors exhibit high stretchability (up to 150%) and versatility, and can detect both large- and small-scale human motions. For this study, wearable electronics are fabricated with implanted sensors that can monitor diverse human motions, including joint movement, phonation, swallowing, and breathing.

The toughening effects of graphene and graphene-derived materials on thermosetting epoxies are investigated. Graphene materials with various structures and surface functional groups are incorporated into an epoxy resin by in situ polymerization. Graphene oxide (GO) and GO modified with amine-terminated poly(butadiene-acrylonitrile) (ATBN) are chosen to improve the dispersion of graphene nanosheets in epoxy and increase their interfacial adhesion. An impressive toughening effect is observed with less than 0.1 wt% graphene. A maximum in toughness at loadings as small as 0.02 wt% or 0.04 wt% is observed for all four types of graphene studied. An epoxy nanocomposite with ATBN-modified GO shows a 1.5-fold improvement in fracture toughness and a corresponding 2.4-fold improvement in fracture energy at 0.04 wt% of graphene loading. At such low loadings, these graphene-type materials become economically feasible components of nanocomposites. A microcrack mechanism is proposed based on microscopy of the fracture surfaces. Due to the stress concentration by graphene nanosheets, microcracks may be formed to absorb the fracture energy. However, above a certain graphene concentration, the coalescence of microcracks appears to facilitate crack propagation, lowering the fracture toughness. Crack defl ection and pinning likely contribute to the slow increase in fracture toughness at higher loadings.

With the growth of the wearable electronics industry, structural modifications of sensing materials have been widely attempted to improve the sensitivity of sensors. Herein, we demonstrate patterned graphene strain sensors, which can monitor small-scale motions by using the simple, scalable, and solution-processable method. The electrical properties of the sensors are easily tuned via repetition of the layer-by-layer assembly, leading to increment of thickness of the conducting layers. In contrast to nonpatterned sensors, the patterned sensors show enhanced sensitivity and the ability to distinguish subtle motions, such as similar phonations and 81 beats per minute of pulse rate.

Poly(ethylene terephthalate) (PET)-based nanocomposites with graphene or multi-wall carbon nanotubes (MWCNT) were prepared by melt mixing. Aspect ratio, A f , and interparticle distance, λ , of graphene in the nanocomposites were obtained from melt rheology and transmission electron microscopy respectively. λ of PET/graphene nanocomposites was much smaller than λ in PET/MWCNT. For PET/graphene with highest A f , λ became

The interfacial adhesion between polymer and nanofiller plays an important role in affecting the properties of nanocomposites. The detailed relationship between interfacial adhesion and bulk properties, however, is unclear. In this work, we developed an atomic force microscopy (AFM)-based abrasive scanning methodology, as applied to model laminate systems, to probe the strength of interfacial adhesion relevant to poly(ethylene terephthalate) (PET)/graphene or clay nanocomposites. Graphite and mica substrates covered with ∼2 nm thick PET films were abrasively sheared by an AFM tip as a model measurement of interfacial strength between matrix PET and dispersed graphene and clay, respectively. During several abrasive raster-scan cycles, PET was shear-displaced from the scanned region. At temperatures below the PET glass transition, PET on graphite exhibited abrupt delamination (i.e., full adhesive failure), whereas PET on mica did not; rather, it exhibited a degree of cohesive failure within the shear-displaced layer. Moreover, 100-fold higher force scanning procedures were required to abrade through an ultimate "precursor" layer of PET only ∼0.2-0.5 nm thick, which must be largely disentangled from the matrix polymer. Thus, the adhesive interface of relevance to the strength of clay-filler nanocomposites is between matrix polymer and strongly bound polymer. At 90 °C, above the bulk PET glass transition temperature, the PET film exhibited cohesive failure on both graphite and mica. Our results suggest that there is little difference in the strength of the relevant interfacial adhesion in the two nanocomposites within the rubbery dynamic regime. Further, the bulk mechanical properties of melt mixed PET/graphene and PET/clay nanocomposites were evaluated by dynamic mechanical analysis. The glassy dynamic storage modulus of the PET/clay nanocomposite was higher than that of PET/graphene, correlating with the differences in interfacial adhesion probed by AFM.

Aqueous reduction of graphene oxide is a low energy and hazardous-chemical free method to produce graphene. In this article, we report the first polymer nanocomposites with aqueous reduced graphene (ARG). Dispersion of ARG in polymer can be challenging because of the aggregation and stacking of single sheets during the removal of water. A novel co-solvent process to blend ARG into thermoplastic polyurethane (TPU) avoids drying ARG by adding an organic solvent before water is completely removed from the aqueous reduction mixture. The dispersion of ARG in TPU was significantly improved using the co-solvent process compared to conventional solvent blending as demonstrated by the mechanical and electrical properties of ARG/TPU composites. Moreover, properties of the co-solvent blended ARG composite are similar to those of the composites of thermally reduced graphene (TRG), which are the best reported to date. We believe that using solvent exchange to avoid aggregation during drying is a general strategy applicable to other nanocomposite preparations.

In contrast to conventional hydrophobic Conductive Polymer nanoComposites (CPCs) used to design vapor sensors, which are mostly soluble in organic solvents, monodispersed acrylate copolymer latexes present the double advantage of being more sensitive and selective towards polar vapors such as water. A hierarchically structured latex based CPC film was obtained by co-dispersion of an aqueous acrylic emulsion with multiwalled carbon nanotubes (CNTs), followed by spray layer by layer (sLbL) assembly. The analysis of CPC films morphology by AFM and TEM show that a segregated network of CNT as been achieved by partial coalescence of latex nanoparticles and homogeneously assembled in 3D. Transducer sensitivity was investigated as a function of CNT content, latex glass transition temperature (Tg), organic vapor nature and vapor concentration. The source of the high sensitivity and selectivity observed for these latex-based composites towards water vapor is assumed to mainly result from ionic interaction of SDS with water molecules offering interesting perspectives of development. The different diffusion regimes through the CPC transducer are visualized, modeled and interpreted with the Langmuir–Henry-Clustering (LHC) model, showing that only water is reaching a clustering mode at high vapor concentration. Finally it is believed that the unique hierarchical architecture of BA latex–CNT sensors is responsible for their quick, stable and reproducible responses to vapors.

Transparent electrodes made from metal oxides suffer from poor flexibility and durability. Highly transparent and electrically conductive thin films were assembled as a potential indium tin oxide (ITO) replacement using layer-by-layer (LbL) assembly of single-walled carbon nanotubes (SWNTs), stabilized with negatively charged deoxycholate (DOC), and positively charged poly(diallyldimethylammonium chloride) [PDDA]. Ellipsometry, quartz crystal microbalance, and UV-vis were used to measure the linear growth of these films as a function of the number of bilayers deposited, while TEM and SEM were used to visualize the morphology of these films. The PDDA/(SWNT + DOC) system produced transparent (>82% visible light transmittance) and electrically conductive (∼160 S cm−1) 20-bilayer films with a 38.4 nm thickness. Moreover, a series of post-treatments, involving heating and nitric acid doping, were used to increase conductivity to 1430 S cm−1 (Rs ≈ 300 Ω sq−1), with no change in transparency, owing to the removal of PDDA and the charge transfer doping. This study demonstrates high visible light transmittance and electrical conductivity of SWNT-based thin films, which are potentially useful as flexible transparent electrodes for a variety of optoelectronic applications.

Layer-by-layer (LbL) assembly was used to generate transparent, highly conductive thin films containing carbon nanotubes. Three different types of nanotubes were used, (1) multiwalled carbon nanotubes (MWNTs), (2) a mixture of single, di-, and triwalled nanotubes, also known as few-walled carbon nanotubes, and (3) purified single-walled carbon nanotubes (SWNTs). Thin films, less than 100 nm thick, were created by alternately exposing a substrate to aqueous suspensions of nanotubes stabilized by deoxycholate (DOC) and a solution of poly(diallyldimethylammonium chloride) [PDDA]. SWNTs produced the most transparent (>85% visible light transmittance) and electrically conductive (∼ 150 S/cm) 20 bilayer films with a 41.6 nm thickness. With just two bilayers of PDDA/(SWNT+DOC), these films have an electrical conductivity of 40 S/cm (3.8 nm thick with a sheet resistance of 65 kΩ/sq) and transmittance greater than 97% at 550 nm. MWNT-based films are much thicker and more opaque as a function of PDDA/(MWNT+DOC) bil...

Conducting polyaniline (PaN) was synthesized onto single-wall carbon nanotubes (SWNTs) by using the in situ polymerization method. Elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), field emission scanning electron microscope (FE-SEM), thermal gravimetric analysis (TGA), electron spin resonance (ESR), X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to characterize the resulting complex nanotubes (SWNTs–PaN) structure. We observed no significant interaction chemically between the PaN and SWNTs. The physical properties of the complex nanotubes were measured and also showed that the SWNTs were modified by conducting polyaniline.

International audience; Volatile organic compounds (VOC) sensors have recently extended their field of application to medical area as they are considered as biomarkers in anticipated diagnosis of diseases such as lung cancer by breath analysis. Conductive polymer nanocomposites (CPC) have already proved their interest to fabricate sensors for the design of electronic noses (e-noses) but, for the first time to our knowledge, the present study is showing that electrostatic layer by layer assembly (eLbL) is bringing an interesting input to tailor the sensitivity of carbon nanotubes (CNT)-polyelectrolyte sensors. By this technique transducers are progressively built in 3D alternating dipping into sodium deoxycholate (DOC)-stabilized SWNT and poly(diallyldimethyl-ammonium chloride) [PDDA] solutions, respectively anionic and cationic. The precise control of transducers thicknesses (between 5 and 40 nm) resulting from this process allows a fine tuning of multilayer films resistance (between 50 and 2 kΩ) and thus of their sensitivity to VOC. Interestingly the surfactant used to disperse CNT into water, DOC is also found to enhance CNT sensitivity to vapors so is it for the polyelectrolyte PDDA. Finally it is found that transducers with 16 bilayers of PDDA/DOC-CNT provide optimum chemo-resistive properties for the detection and discrimination of the eight vapors studied (chloroform, acetone, ethanol, water, toluene, dichloromethane, tetrahydrofuran and methanol).

Layer-by-layer (LbL) assembly was used to deposit transparent, highly conductive thin films using aqueous solutions of nanotubes stabilized by deoxycholate (DOC) and poly(diallyl-dimethylammonium chloride) (PDDA). Three different types of carbon nanotubes (CNTs) were used: (1) multi-walled carbon nanotubes (MWNTs), (2) a mixture of single, di- and tri-walled nanotubes (XM grade) and (3) purified HiPCO single-walled carbon nanotubes (SWNTs). SWNTs produced the most transparent (> 85 %T across visible spectrum) and electrically conductive (˜ 150 S/cm) 20-bilayer films with 42 nm thickness. Moreover, optoelectronic performance of SWNT-based thin films was improved with heat treatment due to the removal of PDDA. A 20-bilayer SWNT LbL film achieved a conductivity of 369 S/cm with a 5 min exposure to 400 °C. This study demonstrates the ability of the LbL technique to produce highly transparent and conductive nanotube-based thin films, which may be useful for a variety of large area electronics applications.

Transparent electrodes made from metal oxides, of which indium tin oxide (ITO) is most common, suffer from poor mechanical flexibility and electrochemical stability. Highly transparent and electrically conductive thin films based on double-walled carbon nanotubes (DWNTs) were assembled layer-by-layer (LbL) as a potential replacement for ITO. The alternate deposition of positively charged poly(diallyldimethyl ammonium chloride) [PDDA] and DWNTs, stabilized with negatively charged deoxycholate (DOC), exhibits linear film growth. A five bilayer (BL) assembly exhibits a sheet resistance of 309 Ω sq−1, and visible light transmittance of 84%. In an effort to further reduce sheet resistance, these thin films were exposed to HNO3 vapor. Sheet resistance of the 5 BL film was reduced to 104 Ω sq−1 (4200 S cm−1 conductivity, 22.9 nm thickness), with no change in transparency. Single-walled carbon nanotube assemblies show an even greater change when exposed to HNO3 vapor, with a 5 BL assembly (%T > 85) decreasing from 1236 to 237 Ω sq−1. The DWNT-based assemblies maintained their low sheet resistance after repeated bending and also showed excellent electrochemical stability relative to ITO. This work demonstrates the excellent optoelectronic performance, mechanical flexibility, and electrochemical stability of nanotube-based assemblies, which are potentially useful as transparent electrodes for a variety of flexible electronics.