In situ synthesis and characterization of polyaniline–CaCu3Ti4O12 nanocrystal composites

High dielectric constant (ca. 2.4 × 10⁶ at 1 kHz) nanocomposite of polyaniline (PANI)/CaCu₃Ti₄O₁₂ (CCTO) was synthesized using a simple procedure involving in situ polymerization of aniline in dil. HCl. The PANI and the composite were subjected to X-ray diffraction, Fourier transform infrared, thermo gravimetric, scanning electron microscopy and transmission electron microscopy analyses. The presence of the nanocrystallites of CCTO embedded in the nanofibers of PANI matrix was established by TEM. Frequency dependent characteristics of the dielectric constant, dielectric loss and AC conductivity were studied for the PANI and the composites. The dielectric constant increased as the CCTO content increased in PANI but decreased with increasing frequency (100 Hz–1 MHz) of measurement. The dielectric loss was two times less than the value obtained for pure PANI around 100 Hz. The AC conductivity increased slightly up to 2 kHz as the CCTO content increased in the PANI which was attributed to the polarization of the charge carriers.     

Synthesis,characterization and low frequency AC conduction of polyaniline/niobium pentoxide composites

New types of conducting polyaniline–niobium pentoxide (PANI/Nb₂O₅) nanocomposites have been synthesized by in situ deposition technique by placing fine grade powder of Nb₂O₅ during in situ polymerization of aniline. The composites formed were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). XRD and TEM indicated the dominant role-played by Nb₂O₅ particles, whereas XPS indicated incomplete protonation of imine moieties. SEM images indicated a systematic morphological variation of particles aggregated in the composite matrix as compared to the pristine PANI. Three step decomposition patterns were observed for PANI and its composites. AC conductivity and dielectric response of the composites were investigated in the frequency range, 10²–10⁶ Hz. AC conductivity obeyed the power law index, which decreased with increasing wt.% of Nb₂O₅. PANI showed high dielectric constant, which could be related to conductivity relaxation phenomenon. Both dielectric constant and dielectric loss decreased with increasing wt.% of Nb₂O₅. Variations in measured AC response parameters with increasing Nb₂O₅ contents of the composite followed systematic trends that are similar to those observed with decreasing temperature and level of doping.     

Synthesis and characterization of polyaniline–ZnO composite and its dielectric behavior

Films of polyaniline (PANI) and PANI–zinc oxide (ZnO) composites have been synthesized by solution cast and spin coating technique. The ZnO powder of particle size 100–200 nm was synthesized by sol–gel technique and the polyaniline was synthesized by chemical oxidative polymerization of aniline. The composite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infra red (FTIR) and the results were compared with polyaniline films. Dielectric properties of PANI and PANI–ZnO composite films have been investigated between frequency ranges of 8.5 and 13.0 GHz. The ‘a’ lattice parameter of ZnO was found to increase and the ‘c’ lattice parameter was found to decrease after ZnO–PANI composite formed. The characteristic FTIR peaks of PANI were found to shift to higher wave number in ZnO–PANI composite. These observed effects have been attributed to interaction of ZnO particles with PANI molecular chains. Dielectric constant of PANI–ZnO composite film was found to be smaller than the PANI film. The decrease of dielectric constant in PANI–ZnO films as compared to PANI was attributed to the interfaces formed between ZnO particles and PANI.     

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.     

One-step reverse micelle polymerization of organic dispersible polyaniline nanoparticles

Organic solvent dispersible dodecylbenzenesulfonic acid (DBSA)-doped polyaniline (PANI) was prepared from DBSA micelles with ammonium persulfate (APS) as an oxidant in hexane by one-step polymerization. Morphology observation showed PANI–DBSA powder polymerized with 0.0375 mol DBSA consisting of spherical particles having diameters of 40–60 nm that formed irregular aggregates with about 1 μm diameter. Polymerization was carried out in the hydrophilic aqueous microdomains of micelle dissolved reactants. The experimental conditions were optimized for direct synthesis of DBSA-doped PANI with high electrical conductivity by adjusting various reaction conditions. This research showed the importance of adjusting reaction conditions such as DBSA, aniline, ammonium persulfate, and acidity for polymerization. It was also found that a portion of an electrically neutral anilinium–DBSA complex could be assembled into reverse micelles together with DBSA molecules, where DBSA and anilinium–DBSA acted as both surfactants and doping agents to achieve nano-scaled DBSA-doped PANI with high conductivity. The doping level of DBSA in PANI particles was studied by UV–vis spectroscopy and X-ray diffraction (XRD). From TG/DTA/mass spectrometry, it was found that the PANI–DBSA was doped with both free and bound DBSA.     

Formation and properties of nano- and micro-structured conducting polymer host–guest composites

Process of formation of polyaniline (PANI) at the surface of SiC and CdS nanoparticles or submicron- and micron-sized particles of poly(vinylidene fluoride) (PVDF), polycarbonate and polyamides-11, 12 and properties of the prepared composites are considered. Beginning of the formation of the PANI shell at the particle surface was evaluated. This important result opens the possibility to control properties of the final hybrid composite. In case of CdS nanoparticles PANI was synthesized in the form of nanofibers embedding these nanoparticles. Films of the PANI–polymer composites showed the conductivity of up to ～0.4 S/cm. The planar heterojunction of the compression molded PVDF/PANI–DBSA film with bulk CdS displayed photovoltaic activity.     

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.     

Dependence of dielectric properties on BT particle size in EP/BT composites

The polymer-ceramic composites of epoxy resin (EP) and barium titanate (BT) were prepared.BT powders of different BT particle sizes from 100 nm to 1 μm were used in the preparation.The dielectric properties, such as dielectric constant, dielectric loss and electrical breakdown strength, of the EP/BT composites were studied.The morphology of the composites was characterized by the means of scanning electron microscopy (SEM).The results show that the dielectric constant of the composites is much higher than the epoxy matrix at frequency range from 1 kHz to 10 MHz, and it is also obviously dependent on the size of BT particles.The electrical breakdown strength of the composites decreases with the increase of the BT content.The dependence of electrical breakdown strength on BT particle sizes was also discussed.     

Preparation and characterization of polyaniline nanoparticles synthesized from DBSA micellar solution

Chemical oxidative polymerization of aniline was performed in a micellar solution of dodecylbenzene sulfonic acid (DBSA, anionic surfactant) to obtain conductive nanoparticles with enhanced thermal stability and processability. DBSA was used to play both the roles of surfactant and dopant. The polymerization kinetics and optimum polymerization conditions were determined by UV–VIS spectra. The optimum molar ratio of oxidant to aniline was 0.5 and DBSA content was the most important factor in the formation of polyaniline (PANI) salt. The polymerization rate was increased with increasing DBSA concentration. The reaction model was proposed on the basis of the roles of DBSA. The electrical conductivity varied with the molar ratio of DBSA to aniline and the highest conductivity of particles was 24 S/cm. The layered structure due to PANI backbone separated by long alkyl chains of DBSA was observed and it seems to facilitate the electrical conduction. The doping level of particle was fairly high and was dependent on the preparative conditions. The average size of the PANI particles determined by Guinier plot of small-angle X-ray scattering (SAXS) measurement was 20–30 nm, which was well coincidence with scanning electron microscopy (SEM) results     

The influence of magnetic and dielectric loss on the noise absorption of iron particles-rubber composites attached to a microstrip line

Magnetic and dielectric loss are systematically controlled by using iron flake powders with various initial sizes (7 μm and 70 μm) as the absorbent fillers in the rubber matrix, and their noise absorbing characteristics have been investigated as a function of frequency and sheet thickness. Flake iron particles were prepared by the mechanical forging of spherical powders using an attrition mill. Composite sheets (thickness=0.2 mm-1.0 mm) were prepared with a mixture of iron particles and silicone rubber. Attaching the composite sheets to a microstrip line of 50 Ω, a network analyzer was used to measure the reflection and transmission parameters (S₁₁ and S₂₁, respectively). A nearly constant value of S₁₁ (about −10 dB) was observed, irrespective of particle size. However, S₂₁ is strongly dependent upon initial particle size. For the composites of 7 μm particles (with high magnetic loss), S₂₁ is reduced below −20 dB in the frequency range of 1 GHz to 10 GHz, and the corresponding bandwidth of noise absorption is not so greatly diminished by reducing the sheet thickness as low as 0.2 mm. For the composites of 70 μm particles (with high dielectric loss), however, the bandwidth is greatly reduced with a decrease in sheet thickness. It is concluded that the attenuation of conduction noise through the microstrip line is primarily controlled by the magnetic loss of the iron particles due to strong magnetic field around the microstrip line.     

Polyaniline synthesis: influence of powder morphology on conductivity of solution cast blends with polystyrene

Synthesis of polyaniline (PANI) was performed under different conditions followed by dedoping, redoping with dodecyl benzene sulfonic acid (DBSA) and then blending with PS. The morphologies of the as-polymerized, doped and blended PANI were studied. The main polymerization stages seem to include: PANI oligomers assembling into nuclei, nuclei growing into primary particles (10 nm), primary particles assembling into aggregates (≈0.5 μm) and aggregates assembling into agglomerates (≈10 μm). The morphology of the as-polymerized PANI was found to be strongly related to the rate of oxidant addition, synthesis duration and synthesis temperature. This morphology dominates the effects of DBSA doping and dispersing the resulting PANI–DBSA in the matrix polymer. A fine PANI–DBSA powder with weakly bound aggregates is likely to disperse well in a solvent and hence promote the formation of the desired fine-network morphology and yield a low percolation threshold and high conductivity. Synthesis at a high oxidant addition rate, an excess of oxidant, a relatively high polymerization temperature and a short synthesis duration should diminish the tendency to form dense complex structures. These dense structures prevent efficient DBSA doping, deaggregation and the desired fine-network dispersion of PANI–DBSA in the blends.     

Polymerization of pyrrole derivatives on polyacrylonitrile matrix,FTIR–ATR and dielectric spectroscopic characterization of composite thin films

Oxidative polymerization of acrylonitrile (AN) initiated by Ce(IV)–oxalic acid redox system in the aqueous medium was performed and polyacrylonitrile (PAN)/polypyrrole (PPy) composite thin films were prepared by polymerization of pyrrole on polyacrylonitrile matrix. Effect of concentration of pyrrole derivatives on the resulting polymeric film properties was investigated. The influence of the pyrrole derivative type and content on the dielectric permittivity, dielectric loss and electrical properties of the composite films were analyzed in the frequency range from 0.05 Hz to 10 MHz. For a selected concentration of 200 μl of composite films at 10⁷ Hz, the conductivity was found to be in the following order: PAN–PPy < PAN–PNMPy < PAN–PNPhPy. Dielectric constant increase of the composite films was more obvious when the quantity of n-phenyl pyrrole was increased. A linear relationship was observed between the absorbances (FTIR–ATR) and conductivities (dielectric spectroscopy).     

Electrical conductivity of polyaniline–dodecylbenzene sulphonic acid complex: thermal degradation and its mechanism

Polyaniline (PANI) doped with dodecylbenzene sulphonic acid (DBSA) and methylbenzene sulphonic acid (MBSA) were used as model compounds to investigate thermal degradation mechanisms of electrical conductivity of PANI salts. The effects of high temperature annealing on the conductivity, thermal stability and morphology of the doped PANI were studied. Within a period of 2 h, the conductivity of the two PANI salts decreases continuously with the annealing time. The conductivity reduction also increases significantly with the annealing temperature. Both polymers show significant weight loss during the annealing, especially at 200 °C. The weight loss of PANI–MBSA is more pronounced than that of PANI–DBSA, while the conductivity reduction shows an opposite trend. Scanning electronic microscopy (SEM) study reveals a significant morphology change caused by the annealing. Fourier transformed infrared (FT-IR) results indicate that some dopants are converted to free acids due to the annealing. It is, therefore, suggested that in addition to cross-linking of PANI and evaporation and degradation of the dopants, the segregation of the dopants from the polymers is also an important mechanism responsible for the conductivity degradation observed.     

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.     

CaCu3Ti4O12／NiCuZn铁氧体基磁电复合材料研究

将CCTO（CaCu3Ti4O12）与NiCuZn铁氧体进行复合,系统地研究了组分变化对这种新型磁电复合材料的烧结性能、晶相结构、显微结构和磁电性能的影响。随后,为了实现复合材料的低温烧结以及综合考虑复相陶瓷的磁电性能,选取80％（质量分数,下同）NiCuZn铁氧体／20％CCTO组分,以BBSZ（Bi2O3-H38O3-SiO2-ZnO）玻璃作为助熔剂,研究了CCTO／NiCuZn铁氧体基复合材料的烧结行为和磁电性能。结果表明,掺杂BBSZ后,900℃下烧结的所有样品的密度均达到了复相陶瓷理论密度的95％,且复相陶瓷的介电常数和磁导率在1～30MHz范围内均不依赖于频率的变化。在10MHz的频率下,当BBSZ的含量从0增加到3％时,复相陶瓷磁导率μ从13．2增加到47．9,磁损耗tanδμ从0．022下降到0．017,同时,样品的谐振频率从10^9Hz左右移动到3．2×10^8Hz。相应地,复相陶瓷的介电常数F从9．2增加到16,介电损耗tanδε从0．069下降到0．012。这一优异的整体性能使其有望实际应用。     

Dielectric characteristics and nonlinear properties of ZnO–polypyrrole composites

The nonlinear properties and frequency characteristics of ZnO–polypyrrole composites were investigated at 200 Hz–5 MHz frequency interval with different zinc oxide contents. Samples were prepared using hot press method at 130 °C. Results show an optimum point for breakdown voltage at ZnO content of 70%. Breakdown voltage decreases from 590 to 380 V and after that tends to increase from 450 to 740 V due to the absence of polypyrrole at grain boundaries. No matter how breakdown voltage behaves, nonlinear coefficient increases from 4.2 to 9 by increasing ZnO content because of the increase in acceptor-like states at grain boundaries by increasing ZnO content. The electrical parameters such as dielectric constant, dielectric loss and series resistance of samples show a strong dependence on frequency especially below 1 kHz. These parameters fall off by increasing frequency up to 1 kHz, which is related to charge transportation through the Schottky barrier at grain boundaries. The high dielectric constant of samples below 1kHz is related to the Maxwell–Wagner polarization at grain boundaries. The presence of different anomalies at different frequency intervals is related to interfacial polarization because of different structures of grains and intergranular layer with a huge difference in conductivity.     

Dielectric properties of eight-harness-stain fabric glass fiber reinforced polyimide matrix composite in the THz frequency range

Electromagnetic wave transmittances of eight-harness-stain fabric glass fiber reinforced polyimide matrix composite with ≈1.1 mm thickness were measured in a terahertz (THz) frequency range using a terahertz time-domain spectroscopy (THz-TDS) system. The transmittance value is nearly zero at a frequency of 1.0 THz. The real part of the complex dielectric constant is 3.87 in the frequency range from 0.2 to 1.0 THz, and it is almost frequency independent. Conversely, the imaginary part of the dielectric constant linearly increases with increase of the frequency from 0.12 (0.2 THz) to 0.33 (1.0 THz). The dielectric properties of the eight-harness-stain fabric glass fiber reinforced polyimide matrix composite were also estimated from those of the E-glass fabric and matrix using a series model for the dielectric constant and the dielectric loss tangent.     

Composite films of nanostructured polyaniline with poly(vinyl alcohol)

The uniform composite films of nanostructured polyaniline (PANI) (e.g. nanotubes or nanorods with 60–80 nm in diameter) were successfully fabricated by blending with water-soluble poly(vinyl alcohol) (PVA) as a matrix. The PANI nanostructures were synthesized by a template-free method in the presence of β-naphthalene sulfonic acid (β-NSA) as a dopant. The molecular structures of PANI–β-NSA and the related composite films were characterized by UV–Vis absorption spectrum, FTIR spectrum and X-ray diffraction. It was found that the electrical, thermal and mechanical properties of the composite films were affected by the content of nanostructured PANI–β-NSA in the PVA matrix. The composite film with 16% PANI–β-NSA showed the following physical properties: room-temperature conductivity is in the range 10⁻² S/cm, tensile strength ∼603 kg/cm², tensile modulus ∼4.36×10⁵ kg/cm² and ultimate elongation ∼80%.     

Conducting polyaniline–montmorillonite composites

Polyaniline (PANI)–montmorillonite (MMT) composites were prepared in two ways: (a) by the polymerization of aniline hydrochloride with ammonium peroxydisulfate (APS) in aqueous suspensions of MMT, (b) by the intercalation of aniline hydrochloride into MMT in aqueous suspension followed by the oxidation with APS, i.e. by the surface and intercalative polymerizations of aniline. The products were analyzed by SEM, XRD, TGA, FTIR and Raman spectroscopies. The formation of red coloration after interaction of MMT with aniline is discussed. The conductivity of PANI–MMT composites increased to units S cm^?1 as the content of PANI reached 50–60 wt.%. The intercalation of aniline into MMT before the polymerization had no marked effect on the conductivity of resulting composites, which was determined mainly by the PANI present at the MMT particles surfaces.     

Microwave study of chemically synthesized conducting polyaniline on alumina

Polyaniline (PANI) thin film on alumina was prepared by the chemical oxidation of aniline with ammonium peroxydisulphate in acidic aqueous medium. DC conductivity, microwave transmission and reflection, microwave conductivity, shielding effectiveness and microwave dielectric constant of the conducting PANI films are reported. DC conductivity was between 0.15 × 10^?3 and 3.13 × 10^?3 S/cm. Microwave conductivity was between 0.2 and 10 S/cm. The PANI films coated on alumina gave shielding effectiveness value of ?1 to ?4 db. The ?′ was between 2 and 350 whereas ?″ was between 437 and 60. Measurements have been carried over the frequency range of 8.2–18 GHz.