Robust PEDOT:PSS Wet‐Spun Fibers for Thermoelectric Textiles

To realize thermoelectric textiles that can convert body heat to electricity, fibers with excellent mechanical and thermoelectric properties are needed. Although poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is among the most promising organic thermoelectric materials, reports that explore its use for thermoelectric fibers are all but absent. Herein, the mechanical and thermoelectric properties of wet‐spun PEDOT:PSS fibers are reported, and their use in energy‐harvesting textiles is discussed. Wet‐spinning into sulfuric acid results in water‐stable semicrystalline fibers with a Young's modulus of up to 1.9 GPa, an electrical conductivity of 830 S cm^?1, and a thermoelectric power factor of 30 μV m^?1 K^?2. Stretching beyond the yield point as well as repeated tensile deformation and bending leave the electrical properties of these fibers almost unaffected. The mechanical robustness/durability and excellent underwater stability of semicrystalline PEDOT:PSS fibers, combined with a promising thermoelectric performance, opens up their use in practical energy‐harvesting textiles, as illustrated by an embroidered thermoelectric fabric module.     

Ordered and ultrathin reduced graphene oxide LB films as hole injection layers for organic light-emitting diode

In this paper, we demonstrated the utilization of reduced graphene oxide (RGO) Langmuir-Blodgett (LB) films as high performance hole injection layer in organic light-emitting diode (OLED). By using LB technique, the well-ordered and thickness-controlled RGO sheets are incorporated between the organic active layer and the transparent conducting indium tin oxide (ITO), leading to an increase of recombination between electrons and holes. Due to the dramatic increase of hole carrier injection efficiency in RGO LB layer, the device luminance performance is greatly enhanced comparable to devices fabricated with spin-coating RGO and a commercial conducting polymer PEDOT:PSS as the hole transport layer. Furthermore, our results indicate that RGO LB films could be an excellent alternative to commercial PEDOT:PSS as the effective hole transport and electron blocking layer in light-emitting diode devices.     

Electrical conductivity of polymer blends of poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate): N-methyl-2-pyrrolidinone and polyvinyl alcohol

The goal of this study is to determine the electrically conductivity of the polymers poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate): N-methyl-2-pyrrolidinone (PEDOT: PSS: NMP) and PEDOT: PSS when blended with polyvinyl alcohol (PVA). While the conducting polymers have high conductivity when not blended with PVA, they are brittle and difficult to spin-coat. Thus, the motivation for this study is to develop blends of these two conducting polymers with PVA to produce a material with optimized mechanical properties and that can also be spin-coated. The blends are produced using aqueous preparations of these materials. Mixtures of various weight percentages (wt %) of PEDOT: PSS: NMP and PEDOT: PSS are prepared and spin-coated on glass slides to form thin films. In the blends, the film conductivity increases with increasing content of either PEDOT: PSS: NMP or PEDOT: PSS. For example, 100 wt % of PEDOT: PSS: NMP and 60 wt % of PEDOT: PSS: NMP blended with PVA exhibit conductivities of, respectively, 10 and 4.02 S/cm. In contrast, conductivities of only 0.0525 and 0.000506 S/cm are observed, respectively, for 100 wt % of PEDOT: PSS and 60 wt % of PEDOT: PSS content in the PEDOT: PSS/PVA blends (No NMP). The addition of the NMP enhances the electrical conductivity by two to five orders of magnitude (depending on the amount of PVA in the blend) due to conformational change of PEDOT chains. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Research progress on polymer-inorganic thermoelectric nanocomposite materials

A thermoelectric (TE) material is a material where a potential difference is generated as a result of a temperature difference or the corollary of this where a temperature difference is generated when a voltage is applied. These phenomena can be used to generate electricity and/or control temperature. Traditionally, thermoelectric materials are inorganic semiconductors which have been limited in their application by low efficiency and high cost. Since the 1990s, both theoretical and experimental studies have shown that low-dimensional TE materials, such as superlattices and nanowires, can enhance the value of the TE figure of merit (ZT) which is an indicator of TE thermodynamic efficiency. To date it has not been feasible to apply these materials in large-scale energy-conversion processes because of limitations in both their heat transfer efficiency and cost. When compared to inorganic materials, organic conducting polymers possess some unique features, such as low density, low cost, low thermal conductivity, easy synthesis and versatile processability and their use in preparing polymer-inorganic TE nanocomposites appears to have great potential for producing relatively low cost and high-performance TE materials. Recently, an increasing number of studies have reported on polymeric and polymer-inorganic TE nanocomposite materials. The purpose of this paper is to review the research progress on the conducting polymers and their corresponding TE nanocomposites. Its main focus is the TE nanocomposites based on conducting polymers such as polyaniline (PANI), polythiophene (PTH), poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS), as well as other polymers such as polyacetylene (PA), polypyrrole (PPY), polycarbazoles (PC) and polyphenylenevinylene (PPV). Typically, polymer-inorganic TE nanocomposites are produced by physical mixing, solution mixing and in situ polymerization. The key factors that limit the use of these polymers and their polymer-inorganic TE nanocomposites as TE materials are their low ZT values. More recent developments designed to overcome the limitation including, for example, the use of carbon nanotubes and graphenes and the use of computational modelling to accelerate the selection of suitable pairs of conductive polymer and inorganic TE materials to achieve best possible nanocomposites are reviewed.     

Preparation and characterization of graphene composites with conducting polymers

We report a new route for preparing electro‐conductive composites based on reduced graphene oxide (RG‐O) and poly(3,4‐ethylenedioxythiophene) (PEDOT). The composites were prepared by in situ polymerization of EDOT in aqueous mixture containing RG‐O platelets modified with poly(sodium 4‐styrenesulfonate) (PSS). In the synthetic process, PSS molecules stabilize RG‐O in the aqueous phase and function as a polymerization template to hybridize PEDOT chains along RG‐O platelets. Compared with the RG‐O platelets, the resulting composites show an enhanced electrical conductivity of 9.2 S cm^?1 with good thermal stability. Copyright © 2011 Society of Chemical Industry     

Enhanced thermoelectric performance by alcoholic solvents effects in highly conductive benzenesulfonate‐doped poly(3,4‐ethylenedioxythiophene)/graphene composites

Benzenesulfonate‐doped poly(3,4‐ethylenedioxythiophene) (PEDOT‐Bzs)/graphene thermoelectric (TE) composites with various graphene filler contents were synthesized in five different kinds of solvents. Dodecylbenzenesulfonic acid (DBSA) was used to achieve good dispersion of graphene into the PEDOT matrix. Among the synthesized PEDOT materials, the one synthesized in methanol (PEDOT‐MeOH) had the highest electrical conductivity. X‐ray photoelectron spectroscopy (XPS) analysis showed almost the same charge carrier concentration for all PEDOT materials. However, the X‐ray diffraction (XRD) analysis highlighted the enhancement of PEDOT chain stacking by shorter‐chain alcoholic solvents, as a result of which the carrier mobility and electrical conductivity were increased. The electrical conductivity and the Seebeck coefficient of the PEDOT/graphene composites were significantly improved with increasing the graphene content, which strongly depended on increased carrier mobility. The thermal conductivity of the composites exhibited relatively small changes, attributed to phonon scattering effects. The maximum TE efficiency of the PEDOT‐MeOH/graphene composite with 75 wt % graphene showed a substantially improved value of 1.9 × 10^?2, higher than that of the other PEDOT/graphene composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42107.     

Flexible polymer thermoelectric device based on PEDOT:PSS and surface treated pyromellitic dianhydride-oxydianiline polyimide substrate

Flexible polymer thermoelectric devices based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and pyromellitic dianhydride-oxydianiline polyimide polyimide (PI) were fabricated and investigated in this work. PI was selected as a substrate for PEDOT:PSS to secure from repeated bending cycles of flexible device. To enhance the interfacial adhesion between PEDOT:PSS and PI, oxygen plasma treatment was used on the surface of PI substrate. The effect of the surface treatment with oxygen plasma on the synthesized PI substrate was significant. The polar component of surface free energy of PI was increased from 2.8 to 31.8 mJ/m². The power factor of PEDOT:PSS on the PI substrate was increased from 25.86 to 43.78 μW m⁻¹ K⁻². Also, as a result of 10 k times of bending test, the electrical performance consistency and the mechanical stability of the fabricated devices were confirmed. This verified fabricated flexible polymer thermoelectric devices based on PEDOT:PSS and PI are suitable for the various applications.     

Heteroatom-doped reduced graphene oxide/polyaniline nanocomposites with improved n-type thermoelectric performance

Polyaniline (PANI) is a potential candidate for n-type thermoelectric (TE) materials owing to its intrinsic electrical conductivity, low thermal conductivity, and facile synthesis techniques. However, its low Seebeck coefficient and power factor have limited its widespread usage. In this study, nitrogen-doped, and sulfur-nitrogen co-doped reduced graphene oxide (rGO) were used for tuning the TE properties of PANI. Doped rGO and PANI/doped-rGO nanocomposites were prepared via hydrothermal technique and chemical oxidative polymerization respectively and thereafter characterized. The TE properties of the nanocomposites were also studied and an optimized Seebeck coefficient, power factor and zT value of −1.75 mV K⁻¹, 95 μW m⁻¹ K⁻² and 0.06, respectively were reported for the PANI nanocomposite containing 1 wt% sulfur-nitrogen co-doped rGO. These results suggest that PANI/heteroatom-doped rGO can serve as promising candidates for n-type based TE applications.     

Cold-sintered V2O5-PEDOT:PSS nanocomposites for negative temperature coefficient materials

A low temperature sintering method, namely cold sintering process, was used to prepare 97 vol%V₂O₅-3 vol% PEDOT:PSS (Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate ceramic-polymer nanocomposites. The density, phase purity, microstructure, elemental distribution and electrical properties of sintered tape-cast films were investigated. The composition with 97 vol%V₂O₅-3 vol% PEDOT:PSS ceramic-polymer nanocomposites can be densified (∼90%) after a cold sintering of 140 °C for 45 min under a uniaxial pressure of 300 MPa. The Transmission Electron Microscopy (TEM) microstructure shows that a ∼10 nm thick intergranular polymer of PEDOT:PSS has been distributed around the V₂O₅ grains after cold sintering. The resistivity decreases with temperature increasing, indicating a typical negative temperature coefficient (NTC) characteristic. The resistivity at 25 °C, temperature coefficient α at 25 °C, and B coefficient (material constant) are 6.34 Ωm, −2.4% K⁻¹ and 2153 K, respectively. The V₂O₅-PEDOT:PSS nanocomposite materials are suitable for new NTC devices, with properties that are comparable to traditional NTC materials that are sintered at much higher temperatures and with much more complexed process and compositions.     

Highly Stretchable and Sensitive Flexible Strain Sensor Based on Fe NWs/Graphene/PEDOT:PSS with a Porous Structure

With the rapid development of wearable smart electronic products, high-performance wearable flexible strain sensors are urgently needed. In this paper, a flexible strain sensor device with Fe NWs/Graphene/PEDOT:PSS material added under a porous structure was designed and prepared. The effects of adding different sensing materials and a different number of dips with PEDOT:PSS on the device performance were investigated. The experiments show that the flexible strain sensor obtained by using Fe NWs, graphene, and PEDOT:PSS composite is dipped in polyurethane foam once and vacuum dried in turn with a local linearity of 98.8%, and the device was stable up to 3500 times at 80% strain. The high linearity and good stability are based on the three-dimensional network structure of polyurethane foam, combined with the excellent electrical conductivity of Fe NWs, the bridging and passivation effects of graphene, and the stabilization effect of PEDOT:PSS, which force the graphene-coated Fe NWs to adhere to the porous skeleton under the action of PEDOT:PSS to form a stable three-dimensional conductive network. Flexible strain sensor devices can be applied to smart robots and other fields and show broad application prospects in intelligent wearable devices.     

High‐performing dye‐sensitized solar cells based on reduced graphene oxide/PEDOT‐PSS counter electrodes with sulfuric acid post‐treatment

Four kinds of counter electrodes are prepared with polystyrene‐sulfonate doped poly(3,4‐ethylenedioxythiophene) (PEDOT‐PSS) as basic material, reduced graphene oxide (rGO) sheets as additives and H₂SO₄ as treating agent. The cyclic voltammetry and Tafel polarization are measured to evaluate catalytic activity of these counter electrodes for /I^? redox couple. It is found that H₂SO₄ treated rGO and PEDOT‐PSS hybrid counter electrode (S/rGO/PEDOT‐PSS counter electrode) has the highest catalytic activity among these counter electrodes. Power conversion efficiency of the dye‐sensitized solar cell with S/rGO/PEDOT‐PSS counter electrode can attain to 7.065%, distinctly higher than that of the cells with the other three ones, owing to the great enhanced fill factor and short‐circuit current density. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42648.     

Thermoset/graphene polymer composites—A review of processing and properties

Polymer-carbon nanocomposites incorporate the exceptional properties of both the polymer matrices, such as low cost and simple processing, with the distinctive features of the carbon-based fillers, such as high electrical and thermal conductivities, and excellent mechanical properties. Various fillers like carbon black (CB), graphite, expanded graphite (EG), and carbon nanotubes (CNTs) are being used to produce materials with advanced properties. However, at high filler loading, these filler materials have some major challenges such as filler agglomeration. Recently, graphene has gained increased interest as an alternative filler to produce polymer nanocomposites with advanced characteristics. Thermosetting polymer composites with graphene fillers are being considered for multiple applications and are a subject of interest for researchers because of enhanced properties like excellent corrosion resistance and low density. This review outlines studies to improve the mechanical, electrical, and thermal properties of thermoset/graphene composites.     

Graphene-Based Sensors for the Detection of Bioactive Compounds: A Review

Over the last years, different nanomaterials have been investigated to design highly selective and sensitive sensors, reaching nano/picomolar concentrations of biomolecules, which is crucial for medical sciences and the healthcare industry in order to assess physiological and metabolic parameters. The discovery of graphene (G) has unexpectedly impulsed research on developing cost-effective electrode materials owed to its unique physical and chemical properties, including high specific surface area, elevated carrier mobility, exceptional electrical and thermal conductivity, strong stiffness and strength combined with flexibility and optical transparency. G and its derivatives, including graphene oxide (GO) and reduced graphene oxide (rGO), are becoming an important class of nanomaterials in the area of optical and electrochemical sensors. The presence of oxygenated functional groups makes GO nanosheets amphiphilic, facilitating chemical functionalization. G-based nanomaterials can be easily combined with different types of inorganic nanoparticles, including metals and metal oxides, quantum dots, organic polymers, and biomolecules, to yield a wide range of nanocomposites with enhanced sensitivity for sensor applications. This review provides an overview of recent research on G-based nanocomposites for the detection of bioactive compounds, providing insights on the unique advantages offered by G and its derivatives. Their synthesis process, functionalization routes, and main properties are summarized, and the main challenges are also discussed. The antioxidants selected for this review are melatonin, gallic acid, tannic acid, resveratrol, oleuropein, hydroxytyrosol, tocopherol, ascorbic acid, and curcumin. They were chosen owed to their beneficial properties for human health, including antibiotic, antiviral, cardiovascular protector, anticancer, anti-inflammatory, cytoprotective, neuroprotective, antiageing, antidegenerative, and antiallergic capacity. The sensitivity and selectivity of G-based electrochemical and fluorescent sensors are also examined. Finally, the future outlook for the development of G-based sensors for this type of biocompounds is outlined.     

Enhanced thermoelectric properties of poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate)/copper phthalocyanine disulfonic acid composite films

A series of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/copper phthalocyanine disulfonic acid (PEDOT: PSS/CuPc-[SO₃H]₂) composite films were prepared by using CuPc-(SO₃H)₂ as the dopant. EG treatment was applied to further improve the thermoelectric properties of PEDOT: PSS/CuPc-(SO₃H)₂ composites. Structural analyses indicated the strong π − π interactions existed between PEDOT: PSS and CuPc-(SO₃H)₂, and led to more ordered regions in the composite films, and benefit the conductivity. CuPc-(SO₃H)₂ can greatly improve the thermoelectric properties of PEDOT: PSS/CuPc-(SO₃H)₂ composite films, which have a Seebeck coefficient of 13.2 μV K⁻¹ and a conductivity of 2.8 × 10⁵ S/m with 20 wt% CuPc-(SO₃H)₂ at room temperature, and the corresponding power factor is 48.8 μW m⁻¹ K⁻², which is almost 6.83 times higher than the PEDOT: PSS films without CuPc-(SO₃H)₂.     

Effects of solvents on thermoelectric performance of PANi/PEDOT/PSS composite films

Organic thermoelectric materials based on conducting polymers, especially for polyaniline (PANi) and poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS), have attracted great concern due to their tunable electron transport properties by controlling doping level. Here, the solvent effects of deionized H₂O and NH₃·H₂O were investigated on the electrical conductivity and Seebeck coefficient of PANi/PEDOT/PSS composite films. The introduction of PEDOT/PSS can not only effectively improve the quality of pure PANi film, but also enhance the electrical conductivity of PANi film. The different volumes of deionized H₂O as dilution have a great influence on the electrical conductivity of PANi/PEDOT/PSS composite thin film with a maximum electrical conductivity value of 63.5 S cm^?1, which is much higher than pure PANi and pristine PEDOT/PSS. The introduction of NH₃·H₂O shows a positive effect on Seebeck coefficient with a large decline on electrical conductivity of PANi/PEDOT/PSS. The Raman spectroscopy, scanning electron microscopy (SEM), and UV-vis spectroscopy were used to obtain the morphology and structure information of PANi/PEDOT/PSS.     

Advances in Biologically Applicable Graphene-Based 2D Nanomaterials

Climate change and increasing contamination of the environment, due to anthropogenic activities, are accompanied with a growing negative impact on human life. Nowadays, humanity is threatened by the increasing incidence of difficult-to-treat cancer and various infectious diseases caused by resistant pathogens, but, on the other hand, ensuring sufficient safe food for balanced human nutrition is threatened by a growing infestation of agriculturally important plants, by various pathogens or by the deteriorating condition of agricultural land. One way to deal with all these undesirable facts is to try to develop technologies and sophisticated materials that could help overcome these negative effects/gloomy prospects. One possibility is to try to use nanotechnology and, within this broad field, to focus also on the study of two-dimensional carbon-based nanomaterials, which have excellent prospects to be used in various economic sectors. In this brief up-to-date overview, attention is paid to recent applications of graphene-based nanomaterials, i.e., graphene, graphene quantum dots, graphene oxide, graphene oxide quantum dots, and reduced graphene oxide. These materials and their various modifications and combinations with other compounds are discussed, regarding their biomedical and agro-ecological applications, i.e., as materials investigated for their antineoplastic and anti-invasive effects, for their effects against various plant pathogens, and as carriers of bioactive agents (drugs, pesticides, fertilizers) as well as materials suitable to be used in theranostics. The negative effects of graphene-based nanomaterials on living organisms, including their mode of action, are analyzed as well.     

Energy harvesting and temperature sensing thermoelectric devices based on the carbon template method

A series of self-supporting carbon nanomaterial films with different morphologies were employed as conductive templates for n-junction after polyethyleneimine (PEI) doping by taking advantages of the entanglement between carbon nanotubes. With the assistance of dimethyl sulfoxide (DMSO)-treated poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) films as p-junction, flexible and light-weight thermoelectric generators (TEGs) were assembled. The effect of the morphology of the carbon nanomaterial, including multi-walled carbon nanotube (MWCNT), whisker carbon nanotube (WSCNT), and graphene on the electrical conductivity, mechanical properties and morphology of n-junction was investigated, on basis of which thermoelectric properties of TEG were evaluated. The properties of the three carbon-based self-supporting films show significant differences. The MWCNT/PEI film exhibits a tensile strength of up to 36.23 ± 0.57 MPa due to the high entanglement network density of MWCNT. The entanglement of WSCNT/MWCNT/PEI provides an ideal conductive template for PEI to prepare n-junction material. TEGs with PEDOT:PSS-DMSO and WSCNT/MWCNT/PEI as p- and n-junctions show high power generation performance and cyclability. The output power density is up to 4.6 nW/cm² at ΔT = 42.0 K, matched to a suitable load. With its fast response and slow recovery, this TEG is expected to be used for human health monitoring and energy storage.     

Progression from Graphene and Graphene Oxide to High Performance Polymer-Based Nanocomposite: A Review

In this article, various types of carbon nanofiller and modification of graphene oxide and graphene for the preparation of polymer-based nanocomposites are reviewed. Recently, polymer/graphene and graphene oxide-based materials have attracted tremendous interest due to high performance even at low filler content. The property enhancement is due to the high aspect ratio, high surface area and excellent electrical, thermal and mechanical properties of nanofiller. Different techniques have been employed to fabricate polymer/graphene and graphene oxide nanocomposite with uniform dispersion due to fine matrix/nanofiller interaction. Here we discuss the structure, properties and preparation of these nanocomposites.     

The effect of graphene nanofiller on the crystallization behavior and mechanical properties of poly(vinyl alcohol)

The effect of graphene on the crystallization behavior of graphene/poly(vinyl alcohol) (PVA) nanocomposites is investigated in terms of the heterogeneous nucleation effect using Fourier transform infrared spectroscopy and differential scanning calorimetry. Nanometer‐sized graphenes with disc‐type shape are successfully fabricated by transversal cutting of platelet carbon nanofibers, and the graphene/PVA nanocomposites are prepared by varying the concentration of graphene using a solution‐casting method. The graphene/PVA nanocomposites exhibit an enhanced degree of crystallization, increasing to 18.8% at a graphene concentration of 0.5 wt%. The graphene acts as an effective nucleating agent during the crystallization process, enhancing the degree and rate of crystallization. In addition, the graphene/PVA nanocomposites with a high graphene content have markedly improved mechanical properties. Mechanical properties, including hardness and elastic modulus, of the prepared graphene/PVA nanocomposites are analyzed using an atomic force microscopy nanoindentation method. The graphene plays a key role in increasing the crystallinity by acting as an effective nucleating agent at low concentrations (<1.0 wt%) and in enhancing the mechanical properties by acting as a nanofiller at high concentrations (>1.0 wt%).     

Synthesis of PEDOT:PSS (poly(3,4‐ethylenedioxythiophene))/poly(4‐styrene sulfonate))/ ngps (nanographitic platelets) nanocomposites as chemiresistive sensors for detection of nitroaromatics

Polymer nanocomposites (NCs) are a special class of materials having unique properties and wide application potential in electronics and other diverse areas. In this study, NCs consisting of poly(3,4‐ethylenedioxythiophene)/poly(4‐styrene sulfonate) (PEDOT:PSS) matrix reinforced with graphite nanosheets were fabricated by solution method. The graphite used was functionalized before fabrication of NCs. The functionalized graphite was characterized by transmission electron microscopy (TEM) and Fourier transform Infrared spectroscopy (FTIR) technique. The NCs prepared were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and FTIR technique. The conductivity studies of the prepared NCs were carried out. The prepared NCs films were investigated for the detection of nitrobenzene vapors. The detection mechanism is based on measuring resistivity changes that occur in a NC due to the absorption of nitrobenzene vapors by PEDOT:PSS film. These sensors exhibited excellent response at room temperature when exposed to vapors of nitrobenzene. Sensitivity as high as 18.5% was observed for PEDOT:PSS/NGPs composite. The chemresistor exhibits a fast response (～1.14 min) and good recovery time (～1–2 min). The response of NC to the nitrobenzene vapors is reproducible. POLYM. ENG. SCI., 53:2045–2052, 2013. © 2013 Society of Plastics Engineers