Enhanced electrical conductivity of nylon 6 composite using polyaniline-coated multi-walled carbon nanotubes as additives

Aggregation in polymer composites is one of the major obstacles in the carbon nanotubes (CNTs) applications. Authentic CNTs are known to have very good electrical conductivity and mechanical strengths. Surface functionalization can avoid aggregation and help dispersion of CNTs, but reduces CNT’s electrical conductivities and mechanical strengths dramatically. It needs a good way to resolve the above dilemma situation; i.e., poor dispersion-good conductivity vs. good dispersion-poor conductivity. Herein, we demonstrate that in-situ polymerized polyaniline (PANI)-coated CNTs have good polymer matrix compatibility, and are superior electrically conductive fillers to nylon 6 composites. In this report, multi-walled CNTs (MWCNTs) were surface-modified with poly(acrylic acids) (PAA), followed by further coating with PANI. The electrical conductivity of (PANI-MWCNTs)-nylon 6 composite thin film was increased from 10⁻¹² to 7.3 × 10⁻⁵ S/cm in the presence of 1 wt% PANI-coated MWCNTs prepared by physical mixing of PANI and PAA-grafted MWCNTs. When in-situ polymerized PANI-coated MWCNTs were added, the electrical conductivity of MWCNTs-nylon 6 composite was further enhanced by 3 orders to be 3.4 × 10⁻² S/cm at the same 1 wt% loading of MWCNTs. Both Fourier-transformed infrared and uv-visible absorption spectra indicate that there exist very strong site-specific charge transfer interactions between the quinoid rings of PANI and MWCNTs, which results in the superior electrical conductivity of MWCNT-nylon 6 composite.     

The Band Gap of BaPrO3 Studied by Optical and Electrical Methods

We report on measurements of the electrical and optical properties of BaPrO₃. The temperature dependences of the electrical conductivity σ and the Seebeck coefficient α of polycrystalline samples were studied over a wide temperature range (300°C–1050°C). At lower temperatures, the observed charge transport can be described as thermally activated hopping of electron‐based small polarons with an activation energy of 0.37 eV. An observed change in temperature dependence of both σ and α around 700°C was observed and interpreted as a transition from extrinsic to intrinsic carrier transport. The intrinsic conduction can be modeled with an apparent electrical band gap of ~2 eV. Optical absorption and emission spectroscopy in the UV–VIS–NIR range revealed a series of characteristic absorption thresholds and the type of optical transitions was identified by combining transmittance and diffuse‐reflectance spectroscopy methods. An absorption edge of indirect type with onset at 0.6 eV is attributed to small polaron effects. The higher lying absorption thresholds of direct origin positioned at around 1.8 and 3.8 eV are correlated with thermal activation parameters from electrical measurements and discussed in terms of the band gap of BaPrO₃.     

A comparative study of the lattice structure,optical band gap,electrical conductivity and polarization at different stages of the heat treatment of chemical routed Al(OH)3

Aluminium hydroxide (Al(OH)₃) was prepared by chemical reaction of the Al(NO₃)₃ in alkaline medium. The as-prepared powder was heated in the temperature range 250 °C to 1250 °C for studying the structural phase transformation at different stages of the heat treatment. The synchrotron x-ray diffraction patterns confirmed a structural transformation of Al(OH)₃ through different (Boehmite, γ, θ, δ, and α) polymorphic phases of Al₂O₃ on increasing the heat treatment temperature. The samples in Boehmite (γ-AlOOH) and α- Al₂O₃ phases showed Raman active modes, whereas the intermediate (meta-stable) multi-phased structure showed weak Raman active peaks. The analysis of UV–visible spectra of the samples indicated two optical band gap energy values in the high energy range 4.50–4.73 eV and low energy range 3.06–3.84 eV. The voltage dependence of current, capacitance and electrical polarization were recorded to study electrical properties in heat treated samples. The capacitance value, derived from the polarization, showed a usual increasing trend on decreasing the measurement frequency (inverse of the time) of driving electric voltage. The measured electrical polarization in the samples was found to be highly correlated to their electrical conductivity and the results are helpful to understand the role of electrical conductivity on exhibiting the apparently ferroelectric properties in high conductive and low polarizable dielectric oxides.     

Effects of potassium incorporation on the structural,optical, vibrational and electrical properties of NiO sprayed thin films for p-type optical windows

Nickel oxide thin films were deposited on glass substrates by a simple mini spray technique at 460 °C. Alternatively, some of the obtained films were doped with potassium at the molar rates of: 1, 2 and 3% (K). In addition to the classical structural investigations including XRD, the opto-thermal studies, Raman spectroscopy and photoluminescence measurements were investigated.First, structural study by means of X-ray diffraction shows that all K-doped NiO thin films crystallized in cubic space group with some noticeable changes in terms of [K]/[Ni] ratio. In the same line, Raman spectroscopy reveals the principal NiO vibration’s mode with the shift related to K incorporation in NiO matrix. Second, some optical parameters, such as optical band gap, Urbach energy, refractive indices extinction coefficients and dielectric constant were studied in terms of K doping level. For all NiO:K prepared thin films, PL measurements show three large bands located at 405, 420, 485 and 529 nm.Furthermore, electrical properties were performed using impedance spectroscopy technique in the frequency range 5 Hz–13 MHz at various temperatures. DC conductivity is thermally activated showing a semiconductor behavior of NiO:K sprayed thin films. This study shows that the electrical conductivity is thermally activated. The calculated values of the activation energy show semiconductor behavior of such films.On the other hand AC conductivity is investigated through Jonscher law. The imaginary part of the complex impedance has a maximum whose relaxation frequency increases with temperature according to Arrhenius law.     

Characterization and physical properties of CoCl2 filled polyethyl‐methacrylate films

Pure polyethyl‐methacrylate (PEMA) and PEMA filled with CoCl₂ films were prepared by casting method. The structure and characterization of these film composites were investigated using Fourier transform infrared analysis (FTIR), optical spectra (UV), X‐ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and DC electrical conductivity. FTIR was used to identify the structural variations due to changing CoCl₂ concentration. The assigned conjugated double bonds suggested the presence of polarons and bipolarons in the polymeric matrix. The shift of some bands manifested the specific interaction in PEMA matrixes and the filler. XRD reveals the presence of some crystalline phase in PEMA matrixes. The degree of crystallinity increase with increasing CoCl₂ and there is no significant change on the halos center but it has become less obvious. Optical absorption measurements reveal that CoCl₂ filler influences the optical energy gap. TGA data clarified that addition of CoCl₂ to PEMA films enhances the thermal stability of PEMA. The activation energy decreases with increase in CoCl₂ content. The electrical properties were studied using DC electrical conductivity. The electrical measurements revealed a nearly monotonic behavior of electrical conductivity as CoCl₂ content increased. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Electromagnetic Interference Shielding Foams Based on Poly(vinylidene fluoride)/Carbon Nanotubes Composite

Polymeric electromagnetic interference (EMI) shielding foaming materials are found and applied in many frontier fields such as aerospace, transportation, and portable electronics. In this paper, a foam based on a composite system of poly(vinylidene fluoride) (PVDF) filled with carbon nanotubes (CNTs) is prepared for EMI shielding properties by using a solid-state supercritical CO₂ foaming strategy. PVDF is chosen as the matrix because of its excellent chemical resistance, thermal stability, and flame retardancy. The inclusion of CNTs renders this composite system enhanced complex viscosity and storage modulus by about two orders of magnitude. The electrical conductivity and EMI specific shielding effectiveness of obtained foams can be adjusted and reached the optimum value of 0.024 S m⁻¹ and 29.1 dB cm³ g⁻¹, respectively, originating from the gradual development of interconnected CNTs and conductive CNTs network as well as the introduction of cell structure in PVDF matrix. Interestingly, the reorientation of CNTs caused by foaming process results in electrical conductivity percolation threshold of PVDF/CNTs foams markedly decreases, in comparison to their unfoamed samples. This study provides a facile, efficient, green, and economic route for the preparation of EMI shielding foams consisted of fluorinated polymers and carbonaceous fillers.     

Optical, electrical and discharge profiles for (PVC + NaIO4) polymer electrolytes

A sodium ion conducting polymer electrolyte based on poly (vinyl chloride) (PVC) complexed with NaIO₄ was prepared using a solution-cast technique. Optical properties such as direct and indirect optical energy gap, and optical absorption edge were investigated in pure and doped PVC films from their optical absorption spectra in the 200–600 nm wavelength region. The direct optical energy gap for pure PVC lies at 3.14 eV while it ranges from 2.60 to 3.45 eV for different composition doped films. Similar behavior was observed for the indirect optical energy gap and absorption edge. It was found that the energy gaps and band edge values shifted to higher energies on doping with NaIO₄ up to a dopant concentration of 10 wt%. Measurements of ionic conductivity and transference number were made to investigate the order of conductivity and charge transport in this polymer electrolyte. Transference number values show that the charge transport in this polymer electrolyte is predominantly due to ions (t _ion = 0.93). The conductivity increases with increase in concentration of the salt and with temperature. Using this electrolyte, cells were fabricated and their discharge profiles were studied under constant load. Miscibility studies were performed using X-ray diffraction (XRD) and Fourier Transform Infrared analysis (FT-IR) measurements.     

Optical and electrical studies of borosilicate glass containing vanadium and cobalt ions for smart windows applications

Borosilicate glass with different concentrations of vanadium and cobalt of the composition (mol%) 40 Na₂B₄O₇- 40 SiO₂- (20–x) V₂O₅- x Co₂O_3, with x=0, 1, 3 and 5 mol% were prepared by melt quenching technique at 1373 K and investigated by X-ray diffraction (XRD) and FTIR spectroscopy. Optical properties of the obtained borosilicate glasses in the UV–vis range were also investigated. Urbach theory has been used to analyze the optical data. The dc electrical conductivity was investigated for all samples in the temperature range from 298 K to 700 K. The ac electrical conductivity was measured in the frequency range from 50 Hz to 2 MHz from 298 to 523 K. Guntini's theory has been used to analyze the electrical data. It was found that Urbach energy decreases with the increase of vanadium content, the sample with x=0 shows the highest absorption in the visible and IR region and an electrical conductivity in the order of 10⁻² Scm⁻¹. The frequency exponent was calculated. A semiconducting behavior has been assessed for the studied glasses. The sample with x=0 has the highest IR absorption, the highest conductivity, at 323 K at different frequencies, and the lowest activation energy; these features are promising for smart windows applications.     

A study of the electrical properties of carbon nanotube-NiFe2O4 composites: Effect of the surface treatment of the carbon nanotubes

Novel carbon nanotube-NiFe₂O₄ composite materials have been prepared for the first time by in situ chemical precipitation of metal hydroxides in ethanol in the presence of carbon nanotubes (CNTs) and followed by hydrothermal processing. The obtained composite powders were characterized using XRD, TEM and EDS. The effect of surface oxidation treatment of CNTs on their properties was investigated by FTIR, zeta potential and hydrodynamic radius distribution characterization. Electrical conductivity measurements show that surface oxidation treatment of CNTs can improve the electrical conductivity of the composites more pronouncedly than pristine CNTs do. With 10 wt.% addition of surface treated CNTs, the electrical conductivity is increased by 5 orders of magnitude. The surface oxidized CNTs are crucial for this significant increase in electrical conductivity, which provides strong adhesion between the nanotubes and the matrix to give a homogeneous carbon nanotube-NiFe₂O₄ composite.     

High-performance supercapacitors based on defect-engineered carbon nanotubes

Defect-engineered carbon nanotubes (CNTs) were prepared by KOH activation and subsequent nitrogen doping. Controlled KOH activation of the CNTs enlarged the specific surface area to 988 m² g⁻¹, which is about 4.5 times greater than that of pristine CNTs. In addition, a hierarchical pore structure and a rough surface developed at high degrees of activation, which are advantageous features for fast ion diffusion. The subsequent nitrogen doping changed the band structure of the CNTs, resulting in improved electrical properties. Symmetric supercapacitors fabricated using these nitrogen-doped and activated CNTs (NA-CNTs) successfully worked across a wide potential range (0–3.5 V) and exhibited a high capacitance of 98 F g⁻¹ at a current density of 1 A g⁻¹. Furthermore, a low equivalent series resistance (2.2 Ω) was achieved owing to the tailored nanostructure and electrical properties of the electrode materials. Over the voltage range from 0 to 3.5 V, supercapacitors based on NA-CNTs exhibited a high specific energy of 59 Wh kg⁻¹ and a specific power of 1750 W kg⁻¹. In addition, a specific power of 52,500 W kg⁻¹ with a 3-s charge/discharge rate was achieved with a specific energy of 26 Wh kg⁻¹. Moreover, the supercapacitors showed stable performance over 10,000 charge/discharge cycles.     

Synthesis and characterization of a new NLO-active donor–acceptor-type conjugated polymer derived from 3,4-diphenylthiophene

A new donor–acceptor-type conjugated polymer (P1) carrying 3,4-diphenylthiophene, 2,5-dihexyloxybenzene, and 1,3,4-oxadiazole units was synthesized through multistep reactions. The polymer was prepared using a polyhydrazide precursor route. The polymer has a well-defined structure and exhibits good thermal stability, with a decomposition onset temperature in nitrogen of 300 °C. Cyclic voltammetry experiments revealed that the polymer has low-lying LUMO (−3.68 eV) and high-lying HOMO (−5.78 eV) energy levels. The electrochemical band gap was found to be 2.10 eV. The UV-visible absorption spectrum of the polymer presented a maximum at 373 nm, and it displayed bluish-green fluorescence in dilute chloroform solution. The nonlinear optical properties of the new polymer were investigated at 532 nm using the Z-scan technique with nanosecond laser pulses. The polymer exhibited strong optical limiting behavior due to excited state absorption, which was phenomenologically similar to a three-photon absorption (3PA) process. The 3PA coefficient γ was found to be 7 × 10⁻²² m³/W². The studies show that the new polymer (P1) is a promising material for developing efficient photonic devices.     

Nanoarchitectonics of Niobium-Doped,Lead-Free BLT (Ba0.97La0.02Ti0.98Nb0.016O3) for Electrical Properties with Unusual d.c Bias Voltage Independence

Polycrystalline sample of Ba_0.97La_0.02Ti_0.98Nb_0.016O₃ (distinguished as BLTi_0.98Nb_0.016) has been prepared through Molten-Salt-Flux reaction route. The XRD, surface morphology, absorption spectra, impedance, and dielectric behaviors were employed to typify the prepared polycrystalline ceramic. The XRD analysis reflects that obtained perovskite having the pure-tetragonal structure with space group P4/mmm. As of the absorption spectra, the optical band gap (Eg), Urbach energy (Eu), and refractive index values have designed. The electrical properties of synthesized compound have been inspected via complex impedance spectroscopy vs. frequency (f) (10² Hz–10⁶ Hz) within the d.c-bias voltage range [0.5 V–5 V]. The fitting of the Nyquist plot exposes that both intra- and intra grains contribute to relaxation and the grain limits are more resistive and capacitive than the grains. Modulus analysis confirms that relaxation in our sample is of non-Debye nature and d.c-bias voltages dependent. Depending on the frequency, the change of ε′ can be discussed founded on the principle of interfacial polarization of the Maxwell–Wagner category. BLTi_0.98Nb_0.016 shows notable frequency independent relative studied properties, it is a potential candidate for devices.

     

Effect of carbon nanotubes with different lengths on mechanical and electrical properties of silica-filled styrene butadiene rubber compounds

Carbon nanotubes (CNTs) having three different lengths of 5, 30, and 100 μm were added to silica-filled styrene butadiene rubber (SBR) compounds in order to investigate the effect of the CNT addition on the dynamic and electrical properties. The amounts of CNTs were 1, 2, 4, and 7 phr, while the amount of silica was set high at 80 phr to clearly demonstrate the performance of the CNTs as fillers. The effect of CNTs on the silica-filled SBR compounds on the tensile properties is not significant, but the addition of longer CNTs with high loading severely deteriorated the dynamic properties, but considerably enhanced electrical conductivity. The medium loading of CNTs in silica-filled SBR compounds is suitable for the improvement of the electrical conductivity without severely sacrificing the dynamic properties.     

Sulphur doped DLC films deposited by DC magnetron sputtering

Diamond‐like carbon (DLC) and sulphur doped diamond‐like carbon (S‐DLC) films were synthesised at different sulphur molar percentage of 0%, 2%, 5%, 8% and 10% by direct current (DC) magnetron sputtering process using novel compressed sulphur‐graphite targets at relatively low power density. Films were characterised for their morphologies, structural, electrical and optical properties. Scanning electron microscope images reveal changes in the quality of the obtained films shown by the denser packing of DLC grains at different sulphur percentage. The conductivities of S‐DLC films were found to be in the range of 6.0 × 10^?3–0.6/Ω cm. The optical band gap energies were found to be in the range of ～1.4–2.0 eV. Both electrical and optical measurements exhibit nonlinear responses with optimum at around 5% sulphur molar percentage (minimum for conductivity and maximum for optical band gap energy). These trends of change in both conductivity and optical band gap energy are consistent with the variation in bond characters of the films indicated by Raman spectroscopy. © 2011 Canadian Society for Chemical Engineering     

Sub-micron calcium carbonate isolated carbon nanotubes/polyethylene composites with controllable electrical conductivity

The dispersion and distribution of carbon nanotubes (CNTs) on/in the polymer composites are greatly affected by the molding technology progress, which results in different electrical conductivity. The uncontrollable electrical conductivity has limited the application of conductive polymer composites, for example, sensor components. In this work, to enhance the dispersion stability of CNTs in polyethylene (PE) matrix, sub-micron calcium carbonate isolated CNTs (smCaCO₃@CNTs) were selected based on the fact that smCaCO₃ is much easier to disperse in polymer in comparison with CNTs. This good distribution of CNTs in smCaCO₃@CNTs/PE was characterized by transmission electron microscope and Raman mapping. The electrical performance test results show that when 0.5 wt% of CNTs filled in smCaCO₃@CNTs/PE, the percolation network begins to form; when CNTs filled increases to 1-2 wt%, the surface resistance of smCaCO₃@CNTs/PE ranges from 10⁶ to 10⁹Ω almost not affected by the molding technology process (compression molding or injection molding). The possible reason is that the isolated CNTs by smCaCO₃ in polymer matrix are favorable for the formation of the stable conductive network.     

Preparation-microstructure-property relationships in double-walled carbon nanotubes/alumina composites

Double-walled carbon nanotube/alumina composite powders with low carbon contents (2–3 wt.%) are prepared using three different methods and densified by spark plasma sintering. The mechanical properties and electrical conductivity are investigated and correlated with the microstructure of the dense materials. Samples prepared by in situ synthesis of carbon nanotubes (CNTs) in impregnated submicronic alumina are highly homogeneous and present the higher electrical conductivity (2.2–3.5 S cm⁻¹) but carbon films at grain boundaries induce a poor cohesion of the materials. Composites prepared by mixing using moderate sonication of as-prepared double-walled CNTs and lyophilisation, with little damage to the CNTs, have a fracture strength higher (+30%) and a fracture toughness similar (5.6 vs 5.4   MPa m^1/2) to alumina with a similar submicronic grain size. This is correlated with crack-bridging by CNTs on a large scale, despite a lack of homogeneity of the CNT distribution.     

Dual-Responsive Soft Actuator Based on Aligned Carbon Nanotube Composite/Graphene Bimorph for Bioinspired Applications

Nanocarbon-based polymer actuators have attracted significant attention because of their excellent actuation performance. In this study, a soft bimorph actuator composed of an anisotropic carbon nanotube (CNT)–polymer composite and reduced graphene oxide (rGO) film is fabricated by a simple blade-coating method. Owing to the excellent electrical, optical, and thermal properties of the CNT and rGO, the actuator exhibits dual-responsive actuation. It generates reversible bending deformation with a displacement of ≈13 mm under low electrical voltage stimulation or white light irradiation. Furthermore, because of the embedment of aligned CNTs in polymer matrix, this actuator exhibits excellent mechanical output compared with many of the reported nanocarbon-based actuators. It can lift a 2.048 g clip to a height of ≈5 mm under low electrical voltage stimulation. Based on this soft actuator with dual response and good mechanical output, various bionic devices are designed. A bionic eagle claw that grasps a soft object under electrical stimulation and an artificial flower blooming in response to light irradiation are constructed. Moreover, a light-driven smart curtain and a seagull robot are fabricated. These results reveal the great potential of the dual-responsive anisotropic soft actuator in soft robots and smart devices driven by electricity and light.     

Thermally induced phase separation in PαMSAN/PMMA blends in presence of functionalized multiwall carbon nanotubes: Rheology, morphology and electrical conductivity

The focus of this work is the evaluation and analysis of the state of dispersion of functionalized multiwall carbon nanotubes (CNTs), within different morphologies formed, in a model LCST blend (poly[(α-methylstyrene)-co-(acrylonitrile)]/poly(methyl-methacrylate), PαMSAN/PMMA). Blend compositions that are expected to yield droplet-matrix (85/15 PαMSAN/PMMA and 15/85 PαMSAN/PMMA, wt/wt) and co-continuous morphologies (60/40 PαMSAN/PMMA, wt/wt) upon phase separation have been combined with two types of CNTs; carboxylic acid functionalized (CNTCOOH) and polyethylene modified (CNTPE) up to 2 wt%. Thermally induced phase separation in the blends has been studied in-situ by rheology and dielectric (conductivity) spectroscopy in terms of morphological evolution and CNT percolation. The state of dispersion of CNTs has been evaluated by transmission electron microscopy. The experimental results indicate that the final blend morphology and the surface functionalization of CNT are the main factors that govern percolation. In presence of either of the CNTs, 60/40 PαMSAN/PMMA blends yield a droplet-matrix morphology rather than co-continuous and do not show any percolation. On the other hand, both 85/15 PαMSAN/PMMA and 15/85 PαMSAN/PMMA blends containing CNTPEs show percolation in the rheological and electrical properties. Interestingly, the conductivity spectroscopy measurements demonstrate that the 15/85 PαMSAN/PMMA blends with CNTPEs that show insulating properties at room temperature for the miscible blends reveal highly conducting properties in the phase separated blends (melt state) as a result of phase separation. By quenching this morphology, the conductivity can be retained in the blends even in the solid state.     

Enhancement of electrical conductivity and other related properties of epoxidized natural rubber/carbon nanotube composites by optimizing concentration of 3‐aminopropyltriethoxy silane

Carbon nanotube (CNT)‐filled epoxidized natural rubber (ENR) composites were prepared by mixing in an internal mixer and thereafter on a two‐roll mill. Silane coupling agent, namely 3‐aminopropyltriethoxy silane (APTES), was directly incorporated in the ENR‐CNT composites during mixing of rubber and CNTs in the mixer, to perform in situ functionalization. It was found that pre‐crosslinking of ENR and APTES occurred especially at high APTES concentrations, such as 0.06 mL/(g of CNTs) and caused strong CNT agglomeration in the ENR matrix. However, the pre‐crosslinking could be reduced or avoided by decreasing the APTES concentration. In the concentration range 0.01–0.015 mL/(g of CNTs) of APTES, the APTES molecules were grafted on the CNT surfaces and generated new chemical linkages with the ENR. This improved the CNT dispersion in the ENR matrix and enhanced the composite properties. A very low approximately 0.5 phr of CNT threshold concentration for electric percolation was achieved in this type of composites. Also, three‐dimensional connected CNT networks were found to form in the ENR matrix at very low APTES levels. Thus, the electrical conductivity achieved in these composites reached the level required of conductive materials. POLYM. ENG. SCI., 57:381–391, 2017. © 2016 Society of Plastics Engineers     

Effect of Composition on Electrical and Optical Properties of Thin Films of Amorphous GaxSe100?x Nanorods

We report the electrical and optical studies of thin films of a-Ga _x Se_100−x nanorods (x = 3, 6, 9 and 12). Thin films of a-Ga _x Se_100−x nanorods have been synthesized thermal evaporation technique. DC electrical conductivity of deposited thin films of a-Ga _x Se_100−x nanorods is measured as a function of temperature range from 298 to 383 K. An exponential increase in the dc conductivity is observed with the increase in temperature, suggesting thereby a semiconducting behavior. The estimated value of activation energy decreases on incorporation of dopant (Ga) content in the Se system. The calculated value of pre-exponential factor (σ₀) is of the order of 10¹ Ω⁻¹ cm⁻¹, which suggests that the conduction takes place in the band tails of localized states. It is suggested that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. On the basis of the optical absorption measurements, an indirect optical band gap is observed in this system, and the value of optical band gap decreases on increasing Ga concentration.