Research of silver plating nano-graphite filled conductive adhesive

In this paper, silver plating nano-graphite (Ag plating nano-G) was developed by electroless plating method using nano-graphite prepared from expanded graphite. The silver plating nano-graphite filled conductive adhesive prepared was composed of 66 wt% of epoxy resin E-51, 20 wt% of Ag plating nano-graphite as conductive filler, 9 wt% of triethanolamine as curing agent and 5 wt% of other additives. It took 180 min for the adhesive to be cured completely at 120 °C. The electrically conductive adhesives exhibited two percolation threshold values which were 7 wt% and 17 wt%, respectively. The electrical resistivity of the conductive adhesive decreased to 1.50 × 10^?3 Ω cm and the tensile lap strength remained at a high level (about 13.2 MPa) when the content of the conductive filler was 20 wt%. TGA indicated that the conductive adhesive exhibited good thermal stability.     

Optical,mechanical, and electrical studies of polymer composites based on charge transfer complex of phenothiazine–iodine with poly(vinyl chloride)

Charge transfer complex (CTC) of phenothiazine and iodine (1:2 molar ratio) was prepared by solvent evaporation method in diethyl ether and its composite with poly(vinyl chloride) was prepared in benzene by diffusion method. Infra-red spectra showed overlapped peaks for both components and intensity of individual component was proportional to feed ratio. Optical photographs and scanning electron microscopy of composites showed template growth and connectivity in insulator matrix was proportional to wt% of CTC. Mechanical strength of composites was found to increase with wt% of PVC. The current–voltage study showed percolation threshold of 8 wt% of CTC. The temperature dependence of conductivity showed semiconducting nature of the materials. Transport property of charges were explained by regression analysis of σ_dc vs. T^?1/1+n data and meets the basis for the Mott's 2D, 3D variable range hopping or thermoionic emission model, depending on temperature and wt% of CTC content. The impedance spectroscopy was performed between 40 Hz–100 kHz range. Circuit elements consists only combination of resistance and capacitance, which showed homogeneous nature of composites. Thermoelectric factor ‘S’ was also evaluated and has value of <1 at 303 K in all cases.     

Properties of single-walled carbon nanotube-based aerogels as a function of nanotube loading

Here, we present the synthesis and characterization of low-density single-walled carbon nanotube-based aerogels (SWNT-CA). Aerogels with varying nanotube loading (0–55 wt.%) and density (20–350 mg cm^?3) were fabricated and characterized by four-probe method, electron microscopy, Raman spectroscopy and nitrogen porosimetry. Several properties of the SWNT-CAs were highly dependent upon nanotube loading. At nanotube loadings of 55 wt.%, shrinkage of the aerogel monoliths during carbonization and drying was almost completely eliminated. Electrical conductivities are improved by an order of magnitude for the SWNT-CA (55 wt.% nanotubes) compared to those of foams without nanotubes. Surface areas as high as 184 m² g^?1 were achieved for SWNT-CAs with greater than 20 wt.% nanotube loading.     

Effect of impingement angle and WC content on high temperature erosion behavior of SiC-WC composites

Hot pressed dense SiC-(0, 10, 30 or 50 wt%)WC composites were subjected to erosion against SiC particles at 800 °C. Effects of WC content and angle of impingement (30°, 60° or 90°) on the erosion performance of composites were evaluated. Erosion rate ranged from 2.1 × 10² mm³/kg to 7.7 × 10² mm³/kg with varying WC content or angle of impingement. The erosion rate of the composites increased with increasing the impingement angle from 30° to 90°, and decreased with WC content up to 30 wt%. Minimum and maximum erosion wear rates were obtained for SiC-30 wt% WC composites at 30° and for SiC-50 wt% WC composites at normal impact, respectively. Grain fracture and pull-out were observed as major mechanisms of material removal for the composites. Decreased angle of impingement led to reduced grain fracture and pull-out, and hence reduction in material removal. Owing to increased fracture toughness with incorporation of WC particles, the composites showed less fracture and removal of WC particles up to 30 wt% reinforcement.     

Effect of silver doped MWCNTs on the electrical properties of conductive MWCNTs/PMMA thin films

The transmittance and electrical properties of conductive multi-walled carbon nanotubes (MWCNTs)/poly(methyl methacrylate) (PMMA) films were investigated as a function of MWCNT content. The effect of silver doped MWCNTs (Ag-MWCNTs) on the surface resistance of the films was also determined. The surface characteristics of acid-treated MWCNTs were confirmed using FT-Raman. The dispersion and formation of a conductive network of MWCNTs in PMMA were observed by SEM and AFM analyses. The transmittance of the films observed by UV–vis–NIR was decreased from 89% to 64%, and the surface resistance of the films was decreased from 392 MΩ/sq to 293 kΩ/sq while increasing the MWCNT content due to the increase of the electron conductive pathway. The Ag-MWCNTs/PMMA films showed a lower surface resistance about 2–4 times than that of MWCNTs/PMMA films. This was probably due to the synergic effect induced between MWCNTs and Ag.     

Antistatic coating and electromagnetic shielding properties of a hybrid material based on polyaniline/organoclay nanocomposite and EPDM rubber

Thermal, mechanical, electrical and microwave radiation absorbing properties of conductive composites based on dodecylbenzenesulfonate doped polyaniline/organoclay nanocomposites and propylene–ethylidene–norbornene rubber have been investigated with special interest on the effect of the nanocomposite concentration. Composites were prepared by melt blending using an internal mixer. Morphology studies by scanning electron microscopy of cryofractured surfaces indicated that the conducting nanocomposites produced heterogeneously distributed aggregates in the continuous elastomeric matrix. The composites exhibit high conductivities, up to 10⁻³ S cm⁻¹ for 40 wt.% of conducting nanocomposite, and good mechanical properties. They also present high microwave attenuation values, in the frequency range of 8–12 GHz. This property depends on the concentration of the conductive nanocomposite and on the film thickness. The composites can be used for antistatic coatings or for electromagnetic shielding.     

Viscoelastic and conductivity properties of thermoreversible polyaniline–DNNSA gel in m-cresol

The rheological behavior of polyaniline (PANI)–dinonylnaphthalene sulfonic acid (DNNSA) in m-cresol is studied for different weight percent (w/v) of PANI–DNNSA_0.5. From rheological viewpoint the sample behaves like viscous fluid at low concentration (2 wt%) and gel at the concentration ≥8 wt%. The 4 wt% PANI–DNNSA_0.5 in m-cresol is at typical viscoelastic percolation region which is sol in the absence of shear but show invariant storage modulus with frequency at 30 °C. SEM picture indicates fibrillar network structure in the gel and the doped polyaniline remain as nanofiber at ≤2 wt% concentrations. The complete doping of PANI in all the systems is confirmed from UV–vis spectra. The dc conductivity of the gel increases with increasing the concentration of PANI–DNNSA_0.5 in m-cresol showing a jump at ～4% concentration (percolation threshold). ac-Conductivity increases with increase in PANI–DNNSA_0.5 concentration studied here for each frequency. At lower frequency (<10⁵ Hz) ac-conductivity increase slowly with frequency but at higher frequency (>10⁵ Hz) the increase is large having a curve like behavior. The gel state shows an increase of module by ～5 orders and also an increase of ～3 orders in ac-conductivity at the same frequency. The impedance spectroscopy results suggest the formation of combined resistance and capacitance (R–C) circuits in the gel and the increase of PANI–DNNSA_0.5 in the gel increases the capacitive feature more dominantly though the path becomes less resistive. The process also signifies the preparation of DNNSA doped PANI nanofiber in the gel medium.     

Evaluation of dispersion state and thermal conductivity measurement of carbon nanotubes/UV-curable resin nanocomposites

We describe (i) the evaluation of bundled degrees of single-walled carbon nanotubes (SWNTs) in SWNT/UV-curable resin composite films based on the intensity change in the radial breading mode (RBM) of their Raman spectra at a 785-nm excitation, and (ii) the thermal conductivity measurements of the composites films using the temperature wave analysis method. The homogeneous dispersion of the SWNTs produced a gradual increase in the thermal conductivity with an increase in the SWNT loading up to 5.0 wt%. This observed behavior is quite different from that of the electric conductivity of the composite films, in which the electric conductivities dramatically decrease at around only a 0.05 wt%-SWNT loading as previously reported.     

Structural interpretations of deformation and fracture behavior of polypropylene/multi-walled carbon nanotube composites

The deformation and crack resistance behavior of polypropylene (PP) multi-walled carbon nanotube (MWNT) composites have been studied and their interrelation to the structural attributes studied by transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and polarization light microscopy has been discussed. The composites were produced from industrial available MWNT by extrusion melt-mixing and injection-molding. In stress–strain measurements a strong increase in the yield stress and the Young’s modulus at low MWNT contents has been observed, which was attributed to an efficient load transfer between the carbon nanotubes and polypropylene matrix through a good polymer–nanotube adhesion as indicated by SEM. The extent of enhancement in mechanical properties above 1.5 wt.% of MWNT decreased due to an apparently increased tendency of clustering of carbon nanotubes. Several theoretical models have been taken into account to explain the mechanical properties and to demonstrate the applicability of such models to the system under investigation. The crack resistance behavior has been studied with the essential work of fracture (EWF) approach based on post-yield fracture mechanics (PYFM) concept. A maximum in the non-essential work of fracture was observed at 0.5 wt.% MWNT demonstrating enhanced toughness compared to pure PP, followed by a sharp decline as the MWNT content was increased to 1.5 wt.% reveals a ductile-to-semi-ductile transition. Studies on the kinetics of crack propagation aspects have revealed a qualitative picture of the nature of such a transition in the fracture modes.     

The preparation and properties of sodium and organomodified-montmorillonite/polypyrrole composites: A comparative study

Two montmorillonites, an inorganic sodium montmorillonite (NaMMT) and an organo-modified montmorillonite (OMMT), were used for the preparation of montmorillonite/polypyrrole (MMT/PPy) composites. MMT particles were modified by the in situ polymerization of pyrrole in water, in aqueous solution of dodecylbenzenesulfonic acid (DBSA) used as anionic surfactant, and in water/methanol. Ferric chloride was used as oxidant in each case. Wide angle X-ray scattering (WAXS) measurements proved the intercalation of PPy into the galleries of NaMMT regardless the reaction media. In contrast, for OMMT/PPy composites, the increase of interlayer spacing depends on the preparation conditions, the highest increase in interlayer spacing was achieved in water/DBSA solution. The WAXS patterns of OMMT/PPy composites synthesized in methanol/water showed no change in interlayer spacing and the electrical conductivity of these composites was low, similar to that of NaMMT/PPy composites prepared under the same conditions. Conductivity about 1.1 S cm⁻¹ was reached for OMMT/PPy composites containing 13.3 wt% PPy prepared in the presence of DBSA. The NaMMT/PPy composite containing 15.6 wt% PPy and prepared under the same conditions showed a conductivity of 0.26 S cm⁻¹. X-ray photoelectron spectroscopy (XPS) proved that the surface of NaMMT/PPy composites is rich in MMT, whereas more PPy was found on the surface of OMMT/PPy composites. The conductivity of composites correlated with the N/Si atomic ratio determined from XPS results, which was taken as a semi-quantitative measure of the PPy surface fraction.     

PMMA-based patternable gate insulators for organic thin-film transistors

In order to prepare patternable polymer gate insulators, two methods of photo-crosslinking the polymer insulator were investigated. In the first method, poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) [poly(MMA-co-HEMA)] functionalized with cinnamate groups was synthesized and photo-crosslinked. In the second method, a semi-interpenetrating PMMA network was prepared using a 25 wt% solution of PMMA/dipentaerythritol hexa-acrylate (DPEHA)/diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) by photo-crosslinking. Both of the photo-crosslinked insulator layers showed a high pattern resolution, indicating that physically and chemically stable crosslinking was accomplished. The field-effect mobilities of the pentacene-based OTFTs fabricated with the functionalized poly(MMA-co-HEMA) (60/40) and PMMA/DPEHA as gate insulators were 0.98 and 0.71 cm²/V s, respectively. It was found that patternable polymer gate insulators having good electrical properties could be prepared by using the functionalized poly(MMA-co-HEMA) and the PMMA/DPEHA solution.     

Electrical conductivity and dielectric response of poly(vinylidene fluoride)–graphite nanoplatelet composites

Poly(vinylidene fluoride)/graphite nanoplatelets (PVDF/GNP) composites were fabricated using solution mixing followed by compression molding. The electric conducting and dielectric behavior of such nanocomposites were determined over a wide frequency range from 10² to 10⁷. The results showed that the electrical behavior of PVDF/GNP nanocomposites can be well described by the percolation theory. Both conductivity and dielectric constant were found to be greatly enhanced at the percolation threshold. A large dielectric constant of 173 and low loss tangent of 0.65 were observed in the PVDF/2.5 wt% GNP nanocomposite at 1 kHz. Moreover, dynamic mechanical analysis was also used to characterize the relaxations of polymers in PVDF/GNP nanocomposites. Dielectric and mechanical relaxations of PVDF/GNP nanocomposites showed strong dependence with frequency and temperature. The activation energy for glass transition determined from mechanical relaxation is considerably higher than that evaluated from the dielectric analysis. This resulted from different operating mechanisms for dielectric and mechanical relaxation processes.     

Synthesis and characterization of novel conducting composites of polyaniline prepared in the presence of sodium dodecylsulfonate and several water soluble polymers

Various conductive composites were prepared by in situ chemical polymerization of aniline in the presence of several water soluble polymers [alginic acid (2a, AA), poly(acrylic acid) (2b, PAA), and poly(vinyl alchol) (2c, PVA)] and/or anionic surfactants [dodecylbenzenesulfonic acid (1a, DBSA) and sodium dodecylsulfate (1b, SDS)] under various polymerization conditions. As a result, the corresponding composites having good film forming property were readily obtained even in the cases with SDS, although PANI prepared in the presence of SDS (PANI/SDS) generally shows extremely poor film forming property due to its low solubility/miscibility and processability in the similar manner as PANI doped with HCl (PANI/HCl). Among the resulting composites, the conductivities of the composites synthesized with SDS tended to be higher than those of the similar composites prepared with DBSA or without anionic surfactants. In particular, the composite prepared by using PVA bearing high molecule weight (PVA-H) and 20 mmol of SDS to aniline monomer was found to show the highest conductivity among the present investigations (32 S/cm), although the conductivity of typical conductive polyaniline doped with HCl, which was synthesized under the similar polymerization conditions, was ca. 3 S/cm at the best. The present PANI composites were characterized by spectroscopic and thermal analysis. Formation of oxidation states of PANIs in these composites was confirmed by the spectroscopic (UV–vis and FT-IR) analysis. The thermal stability of the resulting composite was somewhat lower than those of PANI/SDS itself and PANI/HCl.     

VC and Cr3C2 doped WCoB-TiC ceramic composites prepared by hot-pressing

The grain growth inhibitors (GGIs) VC and Cr₃C₂ doped WCoB-TiC ceramic composites were fabricated by hot-pressing. The microstructure, hardness, transverse rupture strength (TRS), fracture toughness (K_IC) and wear-resistance of WCoB-TiC ceramic composites were investigated. The results reveal that the grains can obviously become refined and the densification temperature of WCoB-TiC ceramic composites will be increased due to the VC and Cr₃C₂. The typical microstructure of WCoB-TiC ceramic composites mainly consist of bright W₂CoB₂ grains, gray TiC particles, dark TiB₂ and pores. WCoB-TiC ceramic composites doped with 0.3 wt% VC and 0.3 wt% Cr₃C₂ hot-pressing at 1420 °C show the optimum mechanical properties (hardness, TRS and K_IC are 92.6 HRA, 1976 MPa and 14.8 MPa m^1/2, respectively) and the best dry sliding wear-resistance.     

Electrical,structural and magnetic properties of polyaniline/pTSA-TiO2 nanocomposites

Polyaniline (PANI)/para-toluene sulfonic acid (pTSA) and PANI/pTSA-TiO₂ composites were prepared using chemical method and characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The electrical conductivity and magnetic properties were also measured. In corroboration with XRD, the micrographs of SEM indicated the homogeneous dispersion of TiO₂ nanoparticles in bulk PANI/pTSA matrix. Conductivity of the PANI/pTSA-TiO₂ was higher than the PANI/pTSA, and the maximum conductivity obtained was 9.48 (S/cm) at 5 wt% of TiO₂. Using SQUID magnetometer, it was found that PANI/pTSA was either paramagnetic or weakly ferromagnetic from 300 K down to 5 K with H_C ≈ 30 Oe and M_r ≈ 0.015 emu/g. On the other hand, PANI/pTSA-TiO₂ was diamagnetic from 300 K down to about 50 K and below which it was weakly ferromagnetic. Furthermore, a nearly temperature-independent magnetization was observed in both the cases down to 50 K and below which the magnetization increased rapidly (a Curie like susceptibility was observed). The Pauli susceptibility (χ_pauli) was calculated to be about 4.8 × 10^?5 and 1.6 × 10^?5 emu g^?1 Oe^?1 K for PANI/pTSA and PANI/pTSA-TiO₂, respectively. The details of these investigations are presented and discussed in this paper.     

Conducting polymer functionalized multi-walled carbon nanotubes with noble metal nanoparticles: Synthesis,morphological characteristics and electrical properties

We report the synthesis of conducting polyaniline-functionalized multi-walled carbon nanotubes (MWCNTs-f-PANI) containing noble metal (Au and Ag) nanoparticles composites (MWCNTs-f-PANI-Au or Ag-NC). MWCNTs-f-PANI was initially synthesized by functionalizing acyl chloride terminated carbon nanotubes (MWCNTs-COCl) with 2,5-diaminobenzenesulphonic acid (DABSA) via amide bond formation, followed by surface initiated in situ chemical oxidative graft polymerization of aniline in the presence of the ammonium persulphate (APS) as an oxidizing agent. MWCNTs-f-PANI was then dispersed into an aqueous Au or Ag metal salt solution followed by the addition of sodium citrate, which acted as a reducing agent. The resulting composite contained a high level of well dispersed Au or Ag nanoparticles (MWCNTs-f-PANI/Au-NC or MWCNTs-f-PANI-Ag-NC). Morphological and structural characteristics, as well as electrical conducting properties of the hybrid nanocomposites were characterized using various techniques including high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV–visible spectroscopy (UV–vis) and four-probe measurements. FT-IR spectra confirmed that PANI was covalently bonded to MWCNTs. TEM images revealed the presence of Au or Ag nanoparticles finely dispersed in the composites with a size of <15 nm. XRD analysis revealed the presence of strong interactions between the metal nanoparticles and MWCNTs-f-PANI, where the metal particles were present in a phase-pure crystalline state with face centered cubic (fcc) structure. The room temperature electrical conductivity of the MWNCTs-f-PANI/Au or Ag composites was 4.8–5.0 S/cm, respectively, which was much higher than that of CNTs-f-PANI (0.18 S/cm) or pure PANI (2.5 × 10^?3 S/cm). A plausible mechanism for the formation of nanocomposites is presented. We expect that the new synthesis strategy reported here will be applicable for the synthesis of other hybrid CNTs–polymer/metal nanocomposites with diverse functionalities. This new type of hybrid nanocomposite material may have numerous applications in nanotechnology, gas sensing, and catalysis.     

Preparation and photovoltaic property of a new polyfluorene derivative/ZnO nanoparticles hybrid composites

A new kind of polyfluorene copolymers, poly(2,7-(9,9-dioctyl-fluorene)-alt-5,5 -(4′,7′-di-2-thienyl-2′,1′,3′,-benzothiadiazole) (PFDTBT), was prepared. The introduction of ZnO nanoparticles with perfect wurtzite crystal character into PFDTBT makes the resulted single-layer photovoltaic device to perform a significant photovoltaic response. Among the tested devices, the best performance is observed for that containing 60 wt% of ZnO nanoparticles, which has a photocurrent density of 1.17 μA/cm², an open circuit voltage of 0.81 V, a fill factor of 0.09 and a power conversion efficiency of 0.009%. The results show that the polyfluorene derivatives/ZnO nanoparticles hybrid composites are excellent fluorescence and photovoltaic materials.     

Unidirectional solidification of Zn-rich Zn–Cu peritectic alloys—II. Microstructural length scales

Experimental results are presented of solidification microstructure length scales including η-phase cell spacing, primary ε secondary dendrite arm spacing, size of nonaligned dendrite of primary ε, and volume fraction of primary ε, as functions of alloy concentration (containing up to 7.37 wt% Cu) and growth velocity (ranging from 0.02 to 4.82 mm/s) in the unidirectional solidification of Zn-rich Zn–Cu peritectic alloys. Intercellular spacing (λ) of two-phase cellular structure decreases with increasing growth velocity (V) such that λV^1/2 is constant at a fixed alloy concentration in parametric agreement with the KGT and Hunt–Lu models. The value of λV^1/2 varies from 216±10 to 316±55 μm^3/2/s^1/2 with decrease in alloy concentration from 4.94 to 2.17 wt% Cu. These values are much greater than for normal eutectic systems but comparable with monotectic alloys. Dendritic secondary arm spacing (λ₂) of primary ε decreases with increasing V such that λ₂V^1/3 is constant ranging 14.9±0.9 to 75.6±8.1 μm^4/3/s^1/3 with increase in alloy concentration (C₀) from 2.17 to 7.37 wt% Cu, which is in parametric agreement with predictions of arm-coarsening theory. The volume fraction (f_ε) of primary ε increases with increasing V for Zn-rich Zn–3.37, 4.94 and 7.37 wt% Cu hyperperitectic alloys. Predictions of the Scheil and Sarreal–Abbaschian models show good agreement with the observed f_ε for Zn–4.94 wt% Cu at moderate V from 0.19 to 2.64 mm/s, but fail at low V of less than 0.16 mm/s and at high V of greater than 3.54 mm/s. The measured average size, Λ, of nonaligned dendrites of primary ε decreases with increasing V such that ΛV^1/2 is constant for a given alloy, increasing from (0.98±0.04)×10³ to (7.2±0.7)×10³ μm^3/2/s^1/2 with increase in alloy concentration from 2.17 to 4.94 wt% Cu.     

Preparation and properties of conducting composites of polypyrrole and porous cross-linked polystyrene with and without supercritical carbon dioxide

Composites of polypyrrole (PPy) and porous cross-linked polystyrene (PCPS) were prepared using a two-step batch method proposed by Ruckenstein and Park. However, the solvent employed by Ruckenstein and Park (methanol) in the polymerization step of their method was replaced with supercritical CO₂. For comparison purposes, PPy/PCPS composites were also prepared using no solvent in the polymerization step. Conductivities as high as 10⁻² S cm⁻¹ were obtained, with or without the use of supercritical CO₂. Uniformity of conductivity was determined via surface and bulk conductivity measurements, as well as by a new volume conductivity measurement that provides a measure of spatial (three-dimensional) distribution of the conducting component in the composite.The conductivity of composites prepared with or without the use of supercritical CO₂ conformed to the same percolation behavior with respect to the amount of PPy formed. The percolation threshold in all cases was as low as 4 wt.%. The mechanical strength of the composites was found to be about the same as that of the host PCPS, as was the thermal stability. Therefore, the conductive component did not appear to adversely affect these properties of the host. Finally, the temperature behavior of the conductivity could be correlated with Mott's variable-range hopping (VRH) model for three-dimensional electronic transport.     

Preparation of poly (hydroxymethyl EDOT)/nano-silver composite films by oxidative polymerization with low-baking temperature,low resistance and good adhesion on PET substrate

Low-resistance films were prepared by polymerization of hydroxymethyl EDOT along with nano-Ag at low-baking temperature (below 120 °C) and low-silver contents (below 20 wt%) on PET substrate. The poly (hydroxymethyl EDOT)/nano-Ag composite films showed low resistance at 21 Ω/□ by spin-coating and at 196 m Ω/□ by drop-casting. We also compared the conductive inks of EDOT, AI4083, nano-Ag and hydroxymethyl EDOT/nano-Ag, and investigated their conductivity, film-forming property and adhesion property. The viscosity of hydroxymethyl EDOT/nano-Ag conductive ink was 12.2 cP at 25.9 °C and suitable for application in flexible plastic devices and inkjet printing technology.