Effect of fluorination on electrical properties of single walled carbon nanotubes and C60 peapods in networks

We present a comparative study of fluorinated single wall carbon nanotubes and C₆₀ peapods. The fluorination was carried out by xenon difluoride treatment at moderate temperature (100 °C). The fluorination level was determined by EDX. In empty nanotubes a fluorination level of 0.8 at.% was obtained, whereas the same treatment leads to 18 at.% in peapods (corresponding to a gross stoichiometry of C₄F). TEM images show that this fluorination procedure does not affect the peapod structure. The elemental mapping carried out by EELS reveals homogenous distribution of fluorine along the carbon nanotube bundle. This chemical treatment is found to change the electrical properties of carbon nanotubes in bucky papers. Four-probe measurements indicate a conductivity decrease by up to two orders of magnitude at room temperature. The temperature dependence of the conductivity indicates a significant change in the charge carrier density of this system. Moreover, a non-linear behavior of the I–V characteristic is observed below 50 K in fluorinated peapods.     

Aggregation kinetics of single walled carbon nanotubes influenced by the frequency of ultrasound irradiation in the aquatic environment

The colloidal stability of single-walled carbon nanotubes (SWNTs) sonicated at three different ultrasonication (US) frequencies (28, 580, and 1000 kHz) were investigated under environmentally relevant conditions. In particular, correlations between surface chemistry, electrokinetic potential, interaction energy, and the aggregation kinetics of the aqueous SWNTs were studied. We observed that H₂O₂ production is negatively correlated with the yield of hydroxylation and carboxylation of SWNTs, which was dependent on the generation of ultrasonic energy by cavity collapse during US process. The SWNTs sonicated at relatively high US frequencies (580 and 1000 kHz) aggregated rapidly in synthetic surface water, whereas alkalinity affected the stability of SWNTs insignificantly. This was because the SWNTs became less negatively charged under such conditions and were captured in deep primary energy wells, according to the Derjaguin-Landau-Verwey-Overbeek theory. Critical coagulation concentration values for the ultrasonicated SWNTs were determined to be 102 mM NaCl for 28 kHz, 22 mM NaCl for 580 kHz, and 43 mM NaCl for 1000 kHz. Suwannee River humic acid decreased the aggregation rate of SWNTs due to the steric hindrance, because of adsorbed macromolecules. Our findings show that the aggregate stability of SWNTs is controlled largely by a complex interplay between the evolution of surface functional groups on the SWNTs during US and solution chemistry.     

Comparison of two different carbon nanotube-based surfaces with respect to potassium ferricyanide electrochemistry

This paper describes the electrochemical investigation of two multi-walled carbon nanotube-based electrodes using potassium ferricyanide as a benchmark redox system. Carbon nanotubes were fabricated by chemical vapor deposition on silicon wafer with camphor and ferrocene as precursors. Vertically-aligned as well as islands of horizontally-randomly-oriented carbon nanotubes were obtained by varying the growth parameters. Cyclic voltammetry was the employed method for this electrochemical study. Vertical nanotubes showed a slightly higher kinetic. Regarding the sensing parameters we found a sensitivity for vertical nanotubes almost equal to the sensitivity obtained with horizontally/randomly oriented nanotubes (71.5 ± 0.3 μA/(mM cm²) and 62.8 ± 0.3 μA/(mM cm²), respectively). In addition, values of detection limit are of the same order of magnitude. Although tip contribution to electron emission has been shown to be greatly larger than the lateral contribution on single carbon nanotubes per unit area, the new findings reported in this paper demonstrate that the global effects of nanotube surface on potassium ferricyanide electrochemistry are comparable for these two types of nanostructured surfaces.     

Polyphosphazene based composite polymer electrolytes

Composite salt-in-polymer electrolyte membranes were prepared from poly[(bis(2-methoxyethyl)amino)_1−x(n-propylamino)_x-phosphazene] (BMEAP) with dissolved LiCF₃SO₃ and dispersed Al₂O₃ nanoparticles (40 nm). Membranes with good mechanical stability were obtained. Low ionic conductivities were found in particle free membranes with maximum conductivities at 10 wt.% LiCF₃SO₃ ranging from 3.1 × 10^− 7 S/cm at 30 °C to 1.8 × 10^− 5 S/cm at 90 °C. For the composite membranes, addition of 2 wt.% Al₂O₃ nanoparticles leads to a steep increase of the conductivity by almost two orders of magnitude as compared to the homogeneous membranes. The highest room temperature conductivity for the investigated BMEAP–LiCF₃SO₃–Al₂O₃ composite systems was 10^− 5 S/cm.     

Effect of solvent on the characteristics of nanostructured composites of poly (1-naphthylamine) with poly (vinyl alcohol)

Efficient utilization of inherently conducting polymers in nano technological applications faces the challenge to assemble them into highly ordered structures which may yield novel properties. The present study reports for the first time the synthesis and characterization of nanostructured poly (1-naphthylamine) (PNA) dispersed polyvinyl alcohol (PVA) composites. The composites were prepared by loading PNA from 2 wt% to 10 wt% in PVA in aqueous as well as nonaqueous media. The composites were characterized by UV–visible spectroscopy, TEM, stress–strain studies, electrical conductivity measurements and moisture absorption studies under controlled humidity. A discrete but uniform distribution of nanoparticles was obtained in PNA/PVA composites synthesized in water having particle size between 5 and 30 nm. A self assembled network of nanostructured PNA particles was obtained in case of PNA/PVA composites synthesized in N-methylpyrolidone (NMP) with particle sizes between 10 and 65 nm. The variation in the nanostructured morphology of PNA particles in PVA matrix in the two cases resulted from the pronounced interaction of PVA with NMP through hydrogen bonding. This leads to the formation of a homogeneous matrix that facilitates the formation of a self assembled network of PNA nano particles. In case of PNA/PVA composites synthesized in water, lower affinity of PVA towards water was responsible for a discrete, agglomerate free distribution of PNA particles. We have found that the PNA/PVA nano composite synthesized in water exhibited good mechanical properties and electrical conductivity (8.1 × 10⁻¹ S/cm) as well as lowest moisture absorption (4 wt%) which holds potential for use in semiconductor and biomedical devices.     

Fabrication of thin-film transistor based on self-assembled single-walled carbon nanotube network

Thin-film transistor based on controllable electrostatic self-assembled monolayer single-wall carbon nanotubes (SWNTs) network has been fabricated by varying the density of nanotubes on the silicon substrate. The densities of SWNTs network have been investigated as a function of concentration and assembly time. It has been observed that the density of SWNTs network increases from 0.6 µm⁻² to 2.1 µm⁻², as the average on-state current (I_on) increases from 0.5 mA to 1.47 mA. The device has a current on/off ratio (I_on/I_off) of 1.3×10⁴ when I_on reaches to 1.34 mA.     

Synthesis of CdS nanostructures using template-assisted ammonia-free chemical bath deposition

CdS micro- and nano-structures (micro/nanotubes and nanostructured films) were obtained by ammonia-free chemical bath deposition using polymer templates (ion track-etched polycarbonate membranes and poly(styrene-hydroxyethyl methacrylate) nanosphere arrays). The semiconductor structures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), optical absorption, photoluminescence and electrical measurements. The diameters of CdS tubes are between 300 nm and few microns and the lengths are up to tens of micrometers. The SEM images prove that the CdS films are nanostructured due to the deposition on the polymer nanosphere arrays. For both CdS structures (tubes and films) the XRD patterns show a hexagonal phase. The optical studies reveal a band gap value of about 2.5?2.6 eV and a red luminescence at ～1.77 eV. A higher increase of conductivity is observed for illuminating the CdS nanostructured film when compared to the simple semiconductor film. This is a consequence of the periodic patterning induced by the polymer nanosphere array.     

Electrical conductivity of (Ba0.3Sr0.2La0.5)(In1−xFex)O3−δ

We have synthesized the perovskite oxides of the (Ba_0.3Sr_0.2La_0.5)(In_1−xFe_x)O_3−δ system and measured the total electrical conductivity as a function of temperature and oxygen partial pressure. It was found that the single-phase composition region extended from x = 0.0 to x = 1.0, and that the Fe valence increased from 3.06 to 3.50 in that region. The electrical conductivity was semiconducting from x = 0.0 to x = 0.40 and metallic from x = 0.50 to x = 1.0. The total electrical conductivity at 800 °C also increased with the Fe content and achieved a maximum value of 140 (S/cm) at x = 1.0. From the dependence of the electrical conductivity on the oxygen partial pressure, we conclude that above x = 0.50, the majority carriers are holes. The estimated hole conductivity increased exponentially with the amount of Fe⁴⁺ cation present. The oxide ion conductivity was dependent on the oxygen vacancy content.     

Entropy-driven adsorption of carbon nanotubes on (0 0 1) and (1 1 1) surfaces of CeO2 islands grown on sapphire substrate

According to the aim to compose combinatorial material by adsorption of carbon nanotubes onto the structured CeO₂ surface the interaction of the armchair (5,5) and zigzag (8,0) nanotubes with the (0 0 1) and (1 1 1) surfaces of CeO₂ islands have been investigated by theoretical methods. The thermodynamics of the adsorption were studied at the low surface coverage region. The interaction energy between the nanotube and the different CeO₂ surfaces shows significant increase when the size of the interface reaches 7–8 unit cells of CeO₂ and it remains unchanged in the larger interface region. However, the entropy term of the adsorption is significantly high when the distances of CeO₂ islands are equal to 27 nm (adsorption of armchair (5,5) nanotube) or 32 nm (adsorption of zigzag (8,0) nanotube). This property supports adsorption of nanotubes onto CeO₂ surfaces which possesses a very specific surface morphology. A long-wave vibration of nanotubes was identified as background of this unexpected phenomenon. This observation could be applicable in the development of such procedures where the nanotube adsorption parallel to the surface is aimed to perform.     

Preparation and characterization of conductive nanostructured particles based on polyaniline and cellulose nanofibers

Conducting polyaniline (PANI) and cellulose coated PANI (PANI-NC) nanostructures with sizes of about 80–100 nm, doped with hydrochloric acid were synthesized by a sonochemical method. Both type of particles resulted electrically conductive (direct current conductivity of 0.059 and 0.075 S/cm for PANI and PANI-NC structures, respectively) and could be dispersed easily in water, leading to green colored suspensions that remain stable for more than 4 h. The morphology, crystallinity, electrical conductivity (σ) and thermal stability of the obtained PANI based structures were investigated and compared. Furthermore, UV–Vis spectroscopy and rheology of water suspensions were used to explain the measured properties. Although the concentration of cellulose fibers used to synthesize the PANI-NC structures was very low, important differences respect to the neat PANI fibers regarding the microstructure, electrical conductivity and suspension behavior were found.     

Oxygen nonstoichiometry and transport properties of strontium substituted lanthanum cobaltite

Oxygen nonstoichiometry, structure and transport properties of the two compositions (La_0.6Sr_0.4)_0.99CoO_3−δ (LSC40) and La_0.85Sr_0.15CoO_3−δ (LSC15) were measured. It was found that the oxygen nonstoichiometry as a function of the temperature and oxygen partial pressure could be described using the itinerant electron model. The electrical conductivity, σ, of the materials is high (σ > 500 S cm^− 1) in the measured temperature range (650–1000 °C) and oxygen partial pressure range (0.209–10^− 4 atm). At 900 °C the electrical conductivity is 1365 and 1491 S cm^− 1 in air for LSC40 and LSC15, respectively. A linear correlation between the electrical conductivity and the oxygen vacancy concentration was found for both samples. The mobility of the electron-holes was inversely proportional with the absolute temperature indicating a metallic type conductivity for LSC40. Using electrical conductivity relaxation the chemical diffusion coefficient of oxygen was determined. It was found that accurate values of the chemical diffusion coefficient could only be obtained using a sample with a porous surface coating. The porous surface coating increased the surface exchange reaction thereby unmasking the chemical diffusion coefficient. The ionic conductivity deduced from electrical conductivity relaxation was determined to be 0.45 S cm^− 1 and 0.01 S cm^− 1 at 1000 and 650 °C, respectively. The activation energy for the ionic conductivity at a constant vacancy concentration (δ = 0.125) was found to be 0.90 eV.     

The interfacial effect on ionic conduction of AgI–anatase TiO2 composites

AgI–anatase TiO₂ nanoparticle composites, (x)AgI–(1 ? x)anatase, with different porosities were fabricated over a wide range of 0–1 of AgI content. The electrical conductivity was measured at room temperature as function of AgI content (x) and porosity (p). The conductivity varies considerably with both x and p. In the vicinity of x = 0.4 and p = 0.31, the conductivity attains a maximum (2.5 × 10^? 3 S/cm). The conductivity is enhanced by three orders of magnitude in comparison with that of pristine AgI. The mechanism of the observed conductivity enhancement is discussed in the light of the scanning electron microscope images and X-ray diffraction patterns of the different (x)AgI–(1 ? x)anatase composites.     

Electrical and dielectric properties of β-BaB2O4 (BBO) and CsLiB6O10 (CLBO) crystals

In barium borate (BBO) crystals, sodium and potassium ions, inherited due to the preparation technique, are dominant charge carriers. The conductivity between layers is higher; the conductivity activation energy and the conductivity at 350 °C being equal to 1.01±0.05 eV and (1.3±0.2)×10⁻⁸ S/cm, respectively. The conductivity activation energy and the conductivity at 350 °C along the channels are equal to 1.13±0.05 eV and to (4±0.2)×10⁻⁹ S/cm, respectively. Relative static permittivity is almost isotropic, and equal to 7.65±0.05. Upon storing of cesium–lithium borate (CLBO) crystals, pre-heating to 600 °C eliminates the influence of surface humidity. At 500 K, the ionic conductivity ranges from 4×10⁻¹² to 2×10⁻¹⁰ S/cm; the conductivity activation energy ranges from 1.01 to 1.17 eV. Relative static permittivity is equal to 7.4±0.3.     

Proton-conducting composite membranes derived from poly(2,6-dimethyl-1, 4-phenylene oxide) doped with phosphosilicate gels

Proton-conducting composite membranes were prepared by doping phosphosilicate gels into SPPO polymer matrix. The structure of gels was examined by ³¹P MAS-NMR. The composite membranes were characterized in terms of TGA, mechanical property, water uptake and conductivity. It was found that the composite membranes were thermally stable up to 150 °C, and possessed higher mechanical strength than Nafion112, either in dry state or in wet state. The conductivity of composite membranes increased with the increase of the ion exchange capacity (IEC), relative humidity (R.H.) and doping amounts. The water uptakes of composite membranes are much higher than Nafion112 in weight percent form at room temperature, and the highest conductivity value of 0.216 S cm^− 1 was achieved for water equilibrated membranes, 2.5 times higher than 0.0871 S·cm^− 1 for Nafion112 measured under the same condition. It is suggested that the composite membranes should be the promising candidates used in PEMFC.     

Mesopore size dependence of the ionic diffusivity in alumina based composite lithium ionic conductors

Ordered-mesoporous Al₂O₃ was synthesized by a sol–gel method using neutral copolymer surfactants as structure-directing agents. The pore size was controlled over the 3–15 nm range by the use of various surfactants. Composites composed of the synthesized mesoporous Al₂O₃ and a lithium ion conductor (LiI) were prepared. The maximum dc electrical conductivity, 2.6 × 10^− 4 S cm^− 1 at 298 K, was observed for 50 LiI·50 Al₂O₃ composite with 4.2 nm average mesopore size, which was considerably higher than the previously reported LiI-alumina composites. A systematic dependence of conductivity upon pore size was observed, in which conductivity increased with decreasing pore size, except for samples with a pore size of 2.8 nm. The lithium ion diffusion coefficient determined by the ⁷Li pulsed field gradient nuclear magnetic resonance (PFG-NMR) showed excellent agreement with the measured conductivity calculated by the Nernst-Einstein equation. On the other hand, lithium migration activation energies obtained by quasielastic neutron scattering (QENS) and ⁷Li NMR spin-lattice relaxation time (T₁) were considerably smaller than those obtained from electrical conductivity and PFG-NMR. This could be explained by the ion migration mechanism in heterogeneous composites and a possible enhancement of conductivity in mesoscopically confined spaces.     

Proton conducting membranes from sulfonated poly[bis(phenoxy)phosphazenes] with an interpenetrating hydrophilic network

Proton conducting membranes have been prepared using sulfonated poly[bis(phenoxy)phosphazene] (s-BPP) trapped in a cross-linked interpenetrating hydrophilic network of hexa(vinyloxyethoxyethoxy)cyclotriphosphazene (CVEEP). Membranes with good mechanical and thermal stabilities were obtained exhibiting high ion exchange capacities in the range of 1.62–1.79 mmol/g. The proton conductivity was measured as a function of water partial pressure in nitrogen (0 mbar to 25 mbar) in the temperature range 25 °C to 75 °C. At 25 mbar water partial pressure and 75 °C, a conductivity of 2.2 × 10^− 4 S/cm was obtained for s-BPP with a network made of 50 wt.% CVEEP. After immersion in water, the conductivity increased up to 0.013 S/cm at 25 °C. The hydrophilic nature of the CVEEP network stabilizes the water content and enhances the proton conductivity at elevated temperatures.     

Ultrasound-assisted synthesis of poly(MMA–co–BA)/ZnO nanocomposites with enhanced physical properties

The present study reports synthesis and characterization of poly(MMA–co–BA)/ZnO nanocomposites using ultrasound-assisted in-situ emulsion polymerization. Methyl methacrylate (MMA) was copolymerized with butyl acrylate (BA), for enhanced ductility of copolymer matrix, in presence of nanoscale ZnO particles. Ultrasound generated strong micro-turbulence in reaction mixture, which resulted in higher encapsulation and uniform dispersion of ZnO (in native form – without surface modification) in polymer matrix, as compared to mechanical stirring. The nanocomposites were characterized for physical properties and structural morphology using standard techniques such as XRD, FTIR, particle size analysis, UV–Visible spectroscopy, electrical conductivity, TGA, DSC, FE-SEM and TEM. Copolymerization of MMA and BA (in presence of ZnO) followed second order kinetics. Thermal stability (T_10% = 324.9 °C) and glass transition temperature (T_g = 67.8 °C) of poly(MMA-co-BA)/ZnO nanocomposites showed significant enhancement (35.1 °C for 1 wt% ZnO and 15.7 °C for 4 wt% ZnO, respectively), as compared to pristine poly(MMA–co–BA). poly(MMA–co–BA)/ZnO (5 wt%) nanocomposites possessed the highest electrical conductivity of 0.192 μS/cm and peak UV absorptivity of 0.55 at 372 nm. Solution rheological study of nanocomposites revealed enhancement in viscosity with increasing ZnO loading. Maximum viscosity of 0.01 Pa-s was obtained for 5 wt% ZnO loading.     

Polymer electrolytes based on cross-linked cyclotriphosphazenes

Substituted cyclotriphosphazenes were used to prepare lithium ion conducting polymer networks. Two types of compounds were synthesized starting with the precursor hexachlorocyclotriphosphazene (HCCP): Type I (CVEEP) in which all the chlorine atoms in HCCP were replaced by vinyloxyethoxyethoxy groups (VEE = –OCH₂CH₂OCH₂CH₂OCHCH₂), and type II (CVMEEP) in which half of the chlorine was replaced by VEE and the other half by methoxyethoxyethoxy groups (MEE = –OCH₂CH₂OCH₂CH₂OCH₃). The terminal vinyl groups were used to build up a network by a thermally initiated cross-linking of lithium salt containing membranes. Polymer electrolytes with dissolved LiSO₃CF₃ and LiN(SO₂CF₃)₂ were investigated by impedance measurements. The ionic conductivity of CVMEEP with 10 wt.% LiSO₃CF₃ was 3.2 × 10^− 5 S/cm at 30 °C and 4.1 × 10^− 4 S/cm at 90 °C. Lower conductivity values in the range 10^− 8–10^− 9 S/cm were obtained at 30 °C for the highly crosslinked CVEEP. An interesting polymer electrolyte with good mechanical properties and a good conductivity of 1.3 × 10^− 5 S/cm (30 °C) was obtained from a solution of MEEP (= poly[bis(methoxy–ethoxy–ethoxy)phosphazene]) and LiSO₃CF₃ in CVEEP as an interpenetrating network.     

Sonocatalytical degradation enhancement for ibuprofen and sulfamethoxazole in the presence of glass beads and single-walled carbon nanotubes

Sonocatalytic degradation experiments were carried out to determine the effects of glass beads (GBs) and single-walled carbon nanotubes (SWNTs) on ibuprofen (IBP) and sulfamethoxazole (SMX) removal using low and high ultrasonic frequencies (28 and 1000 kHz). In the absence of catalysts, the sonochemical degradation at pH 7, optimum power of 0.18 W mL⁻¹, and a temperature of 15 °C was higher (79% and 72%) at 1000 kHz than at 28 kHz (45% and 33%) for IBP and SMX, respectively. At the low frequency (28 kHz) H₂O₂ production increased significantly, from 10 μM (no GBs) to 86 μM in the presence of GBs (0.1 mm, 10 g L⁻¹); however, no enhancement was achieved at 1000 kHz. In contrast, the H₂O₂ production increased from 10 μM (no SWNTs) to 31 μM at 28 kHz and from 82 μM (no SWNTs) to 111 μM at 1000 kHz in the presence of SWNTs (45 mg L⁻¹). Thus, maximum removals of IBP and SMX were obtained in the presence of a combination of GBs and SWNTs at the low frequency (94% and 88%) for 60 min contact time; however, >99% and 97% removals were achieved for 40 and 60 min contact times at the high frequency for IBP and SMX, respectively. The results indicate that both IBP and SMX degradation followed pseudo-first-order kinetics. Additionally, the enhanced removal of IBP and SMX in the presence of catalysts was because GBs and SWNTs increased the number of free OH radicals due to ultrasonic irradiation and the adsorption capacity increase with SWNT dispersion.     

Synthesis of oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)] and anomalous proton conductivities of the thin films

New proton-conductive polyamide oligomers, oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)], were synthesized to investigate the proton transport properties of bulk and thin films. The obtained oligomers were characterized by the X-ray diffraction, FT-IR spectra, ¹H NMR, Matrix Assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) mass spectrum, and electrical conductivity measurements. The bulk proton conductivity is 3.0 × 10^? 4 S cm^? 1 at the relative humidity (RH) of 80%. The proton conductivity of thin film is relatively higher than that of bulk sample. Thickness dependence of the proton conductivity was observed in these thin films. The maximum proton conductivity of the thin film is 4.0 × 10^? 3 S cm^? 1 at the relative humidity (RH) of 80%, which is higher one order magnitude than that of the bulk sample. The activation energies of bulk and 200 nm thick film are 1.0 and 0.69 eV at the RH of 60%, respectively.