Polyaniline–sodium montmorillonite clay nanocomposites: effect of clay concentration on thermal, structural, and electrical properties

A simple and facile method was used to synthesize polyaniline (PANI) nanocomposites with sodium montmorillonite clay (Na⁺-MMT) using in situ intercalative oxidative polymerization. Aniline was admixed with Na⁺-MMT at various concentrations, keeping the aniline monomer in the reaction mixture constant. The intercalation of PANI into the clay layers was confirmed by X-ray diffraction studies in conjugation with electron microscope techniques and FTIR spectra, particularly by the narrowing of the Si–O stretching vibration band confirmed the interaction between PANI and the clay. The employed route offers the possibility to improve the thermal properties with simultaneously controlled electrical conductivity. Thermal studies show an improved thermal stability of the nanocomposites relative to the pure PANI. Depending on the loading of the clay, the room temperature conductivity values of these nanocomposites varied between 2.0 × 10⁻⁴ and 7.4 × 10⁻⁴ S cm⁻¹, with the maximum at 44 wt% PANI concentration. The decrease of electrical conductivity at high PANI concentration was ascribed to the decrease of the structural ordering of PANI in the nanocomposite.     

CNT–CdSe QDs nanocomposites: synthesis and photoluminescence studies

In this study, synthesis of carbon nanotube (CNT)–CdSe Quantum dots (QDs) nanocomposites has been investigated. CdSe QDs were synthesized via hydrothermal process. The chemical tendency of CNT and QDS was increased by precipitation after surface functionalization of CNTs (by carboxylated groups) and CdSe QDs (by silane groups), separately. The structure of nanocomposites was amorphous with a little amount of nanocrystalline cubic CdSe. The Fourier-transform infrared (FTIR) spectra and Raman spectrum revealed the strong chemical tendency of linkage between CNTs and QDs after functionalization on the surface of them. The morphology of nanocomposites depended on the QDs concentration and changed from aggregates of CNTs to the marvelous decoration of quantum dots on the ropes of CNTs. Transmission electron microscope (TEM) and atomic force microscope (AFM) images confirmed the adorable coatings of CNTs with CdSe QDs. The nanocomposites emitted in blue–green region with a maximum peak at 490 nm under the exposure of Ultraviolet (UV) light. Below 50 wt% QDs, the emission was quenched completely.     

Electrical and optical studies in polyaniline nanofibre–SnO2 nanocomposites

Polyaniline nanofibre–tin oxide (PAni-SnO₂) nanocomposites are synthesized and mixed with polyvinyl alcohol (PVA) as stabilizer to cast free-standing films. Composite films are characterized by X-ray diffraction studies (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence spectroscopy (PL) and UV-visible spectroscopy. XRD confirms the formation of PAni nanofibre–SnO₂ nanocomposite. From TEM images, diameter of the polyaniline nanofibre and SnO₂ nanoparticles in the PAni-SnO₂ nanocomposite are found to be 20–60 nm. SEM results show fibrous morphology of the PAni nanofibre and spherical morphology of polyaniline-SnO₂ composites. The nanocomposites exhibit high relative photoluminescence intensity in violet as well as green–yellow region of visible spectrum. From electrical conductivity measurement, it is confirmed that PAni nanofibre–SnO₂ nanocomposite follows Mott’s one-dimensional variable range hopping (VRH) model.     

Nitrogen effect on spin-coated ZnO-based p–n homojunctions: structural,optical and electrical characteristics

In this work, ZnO:Al–N/ZnO:Al and ZnO:Ag–N/ZnO:Al homojunctions were deposited by means of spin coating method using precursors obtained by sol gel chemistry. The optical, structural and electrical properties of spin coated undoped and M-doped ZnO thin films (M?=?Al, Ag–N and Al–N) using ammonium hydroxide as a nitrogen source are reported. The films showed the wurtzite type structure with a c-axis (002) preferential orientation. The films showed a surface morphology consisting of wrinkles, which were constituted of nanocrystals in the range of ～?20 nm. The thin films were highly transparent in the visible region of the electromagnetic spectrum. The optical band gap of the films was close to 3.30 eV. Hall Effect measurements indicated that undoped and Al doped ZnO thin films showed an n-type conductivity, whereas ZnO:Al–N and ZnO:Ag–N thin films exhibited p-type conductivity, probably related to the formation of dual acceptor complexes related to nitrogen. Two types of p–n homojunctions (ZnO:Al–N/ZnO:Al and ZnO:Ag–N/ZnO:Al) were fabricated by means of sol–gel spin-coating method. In both cases, a rectifying behavior was observed, as revealed by current–voltage measurements.     

Synthesis,characterization and studies on optical properties of hierarchical ZnO–CdS nanocomposites

Cadmium sulfide coated zinc oxide hierarchical nanocomposites have been synthesised at room temperature by a simple solution based method. CdS nanoparticles were deposited on the surface of ZnO without using any surfactant, ligand or chelating agents. The nanocomposites were synthesised using different concentrations of thioacetamide, cadmium salts, and also by varying the reaction time. After characterization of the nanocomposites, optical properties were investigated by UV–visible diffuse reflectance and photoluminescence spectroscopy techniques. It was found that band gap of the ZnO–CdS nanocomposites is tunable between 2.42 and 3.17 eV.     

Growth,structural, thermal,optical, and electrical properties of potassium succinate–succinic acid crystal

Potassium succinate–succinic acid (KSSA), semi-organic single crystals were grown by slow evaporation growth technique using water solvent. Single crystal X-ray diffraction study revealed that the KSSA crystal belongs to monoclinic system. FT-IR and FT-Raman spectral studies were performed to identify the vibrations of functional groups. TGA/DTA analyses were carried out to characterize the melting behavior and stability of the title compound. The UV–Vis–NIR spectrum showed that the grown crystal is transparent in the entire visible region. Fluorescence studies were carried out in the range of 200–700 nm. The optical nonlinearity of KSSA was investigated at 532 nm using 7 ns laser pulses, employing the open aperture Z-scan technique. The photoconductivity study was carried out to know the conducting nature of the crystal. The laser damage threshold was measured using Q-switched Nd:YAG laser (1064 nm). Electrical properties of the crystal are studied using Hall Effect measurement.     

Preparation of sol–gel-based nanostructured hybrid coatings; part 1: morphological and mechanical studies

Attempts have been made using sol–gel-based precursors to produce hybrid organic–inorganic clearcoats. To this end, a typical automotive acrylic/melamine clearcoat with tetramethyl ortosilicate (TEOS) and methacryoloxy propyltrimethoxysilane (MEMO) were used to obtain nanostructured silica clusters produced in situ embedded in the polymeric matrix. Microscopic techniques including scanning electron microscope (SEM), atomic force microscope (AFM), and transmission electron microscope (TEM) were utilized to investigate the morphology of coatings. The effect of each precursor on coating mechanical properties was also studied using dynamic mechanical thermal analysis (DMTA) as well as micro and nanoindentation techniques. It was found that using TEOS and MEMO (in non-hydrolyzed state), the mechanical properties of the resulting films were negatively influenced. The decreased hardness, lower T _g and cross-linking density, and reduced elastic modulus were observed with non-hydrolyzed precursors. In addition, the phase separation of organic and inorganic domains occurred in the presence of pristine sol–gel precursors. However, using hydrolyzed precursors (HTEOS and HMEMO), the mechanical properties were notably improved. While HTEOS resulted in an increase in coating T _g, and cross-linking density as well as improved elastic modulus and hardness, HMEMO caused an increase in coating hardness but lowered coating T _g and cross-linking density.     

Effect of alloy composition on structural, optical and morphological properties and electrical characteristics of GaxIn1−xP/GaAs structure

The structural, optical and morphological properties of Ga-rich Ga_xIn_1?xP layers with various gallium compositions grown on epi-ready semi-insulating (100)-oriented GaAs substrates by using Molecular Beam Epitaxy technique are presented in this study. The Ga_xIn_1?xP/GaAs structures (S1, S2 and S3) have been evaluated by means of high resolution X-ray diffraction, photoluminescence (PL) and atomic force microscopy measurements at room temperature. Experimental forward and reverse bias current–voltage (I–V) characteristics of structure S3 was investigated at room temperature due to its better characteristics when compared to the other two samples. The main electrical parameters such as ideality factor (n), barrier height (Φ _b ) and series resistance (R _s ) were extracted from forward bias I–V characteristics and Cheung’s function. In addition, Hall measurements were carried out as a function of temperature (30–300 K) and at a magnetic field of 0.4 T were presented for structure S3.     

Thermal evolution of morphological,optical, and photocatalytic properties of Au–Cu2O–CuO nanocomposite thin film

Plasmonic nanocomposite thin films find exciting applications in environmental remediation and photovoltaics. We report on thermal annealing driven development of morphology, structure and photocatalytic performance of Au–Cu₂O–CuO nanocomposite thin film. Nanocomposite thin film coatings of Au–Cu₂O–CuO, prepared by radio frequency (RF) magnetron co-sputtering, were annealed at different temperatures. Thermal annealing driven evolution of morphology of Au–Cu₂O–CuO nanocomposite was studied by field emission scanning electron microscopy (FESEM), which revealed significant growth in size of nanostructures from 10 nm to 69 nm upon annealing. X-ray diffraction (XRD) together with Raman studies confirmed the nanocomposite nature of Au–Cu₂O–CuO film. UV-visible diffuse reflectance spectroscopy (UV-vis-DRS) studies showed band gap variation from 2.44 eV to 1.8 eV upon annealing at 250 °C. Nanocomposite thin film annealed at 250 °C exhibited superior photocatalytic activity for organic pollutants [methylene blue (MB) and methyl orange (MO)] decomposition. The origins of thermal transformation of morphological, optical and photocatalytic behaviour of the Au–Cu₂O–CuO nanocomposite coating are discussed.

     

Polyaniline–MWCNT nanocomposites for microwave absorption and EMI shielding

Highly conducting polyaniline (PANI)–multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by in situ polymerization. The FTIR and XRD show systematic shifting of the characteristic bands and peaks of PANI, with the increase in MWCNT phase, suggesting significant interaction between the phases. The SEM and TEM pictures show thick and uniform coating of PANI over surface of individual MWCNT. Based on observed morphological features in SEM, the probable formation mechanism of these composites has been proposed. The electrical conductivity of PANI–MWCNT composite (19.7 S cm^?1) was even better than MWCNT (19.1 S cm^?1) or PANI (2.0 S cm^?1). This can be ascribed to the synergistic effect of two complementing phases (i.e. PANI and MWCNT). The absorption dominated total shielding effectiveness (SE) of ?27.5 to ?39.2 dB of these composites indicates the usefulness of these materials for microwave shielding in the Ku-band (12.4–18.0 GHz). These PANI coated MWCNTs with large aspect ratio are also proposed as hybrid conductive fillers in various thermoplastic matrices, for making structurally strong microwave shields.     

Polymer matrix–clay interaction mediated mechanism of electrical transport in exfoliated and intercalated polymer nanocomposites

We report significant results on charge transport phenomena in the exfoliated and intercalated phase of polymer nanocomposite (PNC). X-ray diffraction and transmission electron microscopy results have provided convincing evidence of exfoliation at lower clay loading (x < 5 wt%) and intercalation at higher clay loading (x > 5 wt%) in the PNC. Fourier transform infrared (FTIR) spectrum indicated lowering of anion symmetry from O_h to C_4ν/C_2ν/C_3ν (depending on mode of cation interaction with counter ion). Substantial jump in electrical conductivity (~110 times) at room temperature has occurred on nanocomposite formation in sharp contrast to that of the polymer salt (PS) complex film. Large conductivity enhancement (10⁻³ S cm⁻¹) is attributed to clay-induced interaction with PS matrix whose origin lies in polymer–ion, ion–ion, ion–clay, and polymer–ion–clay interaction evidenced in the FTIR results. An excellent correlation of conductivity with fraction of free anion and polymer glass-transition temperature agrees well with conductivity enhancement at specific clay loading. A model for charge transport phenomena is proposed to explain clay-induced ion dynamics. The conceptual basis of the model seems consistent with experimental results.     

In situ prepared polypyrrole–Ag nanocomposites: optical properties and morphology

Polypyrrole–silver (PPy–Ag) nanocomposites with various silver contents have been synthesized via a kinetically favorable one-step chemical oxidative polymerization process. The oxidant, ammonium persulfate, was used to oxidize pyrrole monomer for growing chains of PPy. And AgNO₃ was used as a precursor for metallic silver nanoparticles. The detailed characterization techniques, UV–Vis–NIR, fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy (TEM), have been used to reveal electronic environment, structure, and morphology of composites as well as as-synthesized PPy. The synthesis environment prior to polymerization has also been investigated by absorption spectroscopy. The TEM images of PPy–Ag nanocomposites reveal that silver nanoparticles are deeply embedded into the polymer matrix in addition to surface adsorption. It is observed that the size distribution of inorganic nanoparticles (ca. 4–10 nm, depending on the metal ion concentrations) as well as structural morphology is altered by the initial concentrations of silver ions.     

One-step synthesis of Co–Ni ferrite/graphene nanocomposites with controllable magnetic and electrical properties

Co_1−xNi_xFe₂O₄/graphene nanocomposites were synthesized through a one-step solvothermal method. The as-synthesized products were characterized by X-ray powder diffraction, field emission scanning microscopy, transmission electron microscope, and high-resolution transmission electron microscope. The results show that the Co_1−xNi_xFe₂O₄ nanoparticles are uniformly dispersed on graphene sheets. The dependence of structure, magnetic and electrical properties of Co_1−xNi_xFe₂O₄/graphene nanocomposites on the Ni²⁺ concentration and the graphene content were also studied. The saturation magnetization and electrical conductivity of the as-prepared products reached 51.82 emu/g and 1.00 × 10² S/m, respectively.     

Electrical transport,optical and thermal properties of polyaniline–pumice composites

In this study, electrical conductivity, photoconductivity, absorbance and thermal properties of polyaniline (PANI) and polyaniline–pumice composites were investigated. Temperature dependent conductivity and photoconductivity measurements were carried out in the temperature range of 80–400 K. The measurements revealed that the dominant conduction mechanisms in polyaniline and 15% pumice doped composite were hopping conduction. The low activation energies calculated for 36% pumice doped composite indicated that this sample has highly defective and degenerate structure due to the high pumice content. Polyaniline and pumice doped composites showed semiconductor behavior with the exponential variation of inverse temperature dependence of electrical conductivity. Photoconductivities of the PANI and PANI–pumice composites under various illumination intensities were studied and it was found for all samples that the conductivity increased with increasing temperature and light intensity, but decreased with increasing pumice content in the structure. Absorbance spectrum has been determined in the wavelength range of 300–700 nm and it was found that the band gap values decreased as the pumice content was increased. Thermogravimetric analysis have shown for all samples that the mass loss has started above around 300 K due to the loss of moisture from the structures. As a result of this work, it was found that polyaniline and polyaniline–pumice composites had low resistivity and high band gaps and could be used as a window layer semiconductor in heterojunction solar cell applications.     

Synthesis,structural and optical studies of sol–gel Gd2O3:Eu3+, Tb3+ films

Eu³⁺ and Tb³⁺ co-doped Gd₂O₃ films were elaborated by sol–gel process and dip-coating technique. The films were synthesized by hydrolysis of gadolinium pentanedionate. A homogeneous and stable sol was obtained by the reaction with acetylacetone. Gd₂O₃:Eu³⁺, Tb³⁺ films were crystallized around 500 °C; at an increase of temperature up to 700 °C, oriented growth of (4 0 0) face was observed. The obtained transparent Gd₂O₃: 2.5 at.% Eu³+, 0.005 at.% Tb³⁺ waveguide films at 700 °C display significant optical properties. Different crystallographic properties can be obtained in Gd₂O₃:Eu³⁺, Tb³⁺ films with varying sintering temperatures.     

New diketopyrrolopyrrole based D–A–D π-conjugated molecules: Synthesis,optical, electrochemical,morphological and photovoltaic properties

Two solution processable donor–acceptor, π-conjugated molecules that consist of diketopyrrolopyrrole (DPP) central acceptor unit with dibenzofuran (DPP-DBF) or acenaphtene (DPP-ACN) donor substituents, were prepared by Suzuki coupling reaction. The optical, electrochemical and film forming properties of these D–A–D molecules were investigated and used as active materials in bulk heterojunction solar cells.     

Characterization of Ge–Bi–S glass by thermal, electrical, switching and optical measurements

A study of the synthesized Ge22.5Bi7S70.5 glassy system has been carried out. Differential thermal analysis data indicate the retention in the as-quenched sample of two amorphous phases. Thermal conductivity, , measurements on bulk sample reveal that the main contribution to is due to phonon thermal conductivity. Thermal evaporation of the synthesized ingot gives films with Ge20.7Bi6.8S72.5 as composition. The values of the activation energy and the pre-exponential factor calculated from the direct current electrical conductivity above 53 °C suggest that carrier conduction occurred between extended states in these films. The I–V characteristics in the off-state and the switching phenomenon are investigated. A memory switch with a threshold voltage decreasing with temperature is detected for the studied films. Optical parameters such as absorption coefficient, optical gap and refractive index are also determined. Comparison with binary Ge–S glass reveals that the addition of Bi introduces additional absorbing states at band edges. © 1998 Kluwer Academic Publishers     

Design and synthesis of inorganic–organic hybrid microstructures

Vanadium oxide–polypyrrole (V₂O₅–PPy) hybrid aerogels were prepared using three different strategies. These approaches were focused on either sequential or consecutive polymerization of the inorganic and organic networks. The hybrid microstructure differed greatly depending on which synthesis approach was used. Microcomposite aerogels were synthesized by encapsulating a dispersion of preformed PPy in a V₂O₅ gel. In the second approach, pyrrole was polymerized and doped within the pore volume of a preformed V₂O₅ gel. The hybrid microstructure of these materials was nanometer scaled but inhomogeneous. When the inorganic and organic precursors were allowed to polymerize simultaneously, the resulting gels exhibited a nanometer-scaled microstructure with a homogeneous distribution of the PPy and the V₂O₅. Through this route, a suitable microstructure and composition for a lithium secondary battery cathode were obtained. Undoped material with a composition of [PPy]_0.8V₂O₅ exhibited a lithium intercalation capacity comparable to that of V₂O₅ aerogel. For the full benefit of the PPy phase to be achieved, a suitable doping procedure is still required to oxidize the PPy into its high conductivity state while preserving the inorganic structure.