Effect of electrostatic heterocoagulation of PVM/MA grafted carbon black and attapulgite nanorods on electrical and mechanical behaviors of waterborne polyurethane nanocomposites

In our previous report, poly(methyl vinyl ether-alt-maleic anhydride) grafted CB (GCB) with stable dispersion in water was successfully prepared. In the present study, waterborne polyurethane (WPU) nanocomposites including GCB and attapulgite (ATT) were prepared by liquid mixing method. Anionically charged GCB nanoparticles were heterocoagulated on the surface of cationically charged ATT nanorods at low pH value and improved the stabilization of ATT nanorods in water as a dispersing aid. The microstructure development in matrix that depended on various weight ratios of the nanoparticles ultimately influenced the electrical conductivity and mechanical properties of WPU nanocomposites. Composites containing equal concentrations of GCB and ATT showed reduced electrical conductivity, but significant increase in storage modulus. When the weight ratio of GCB to ATT was 5:1, both electrical conductivity and storage modulus of composite were improved simultaneously. The percolation threshold of composites containing a 5:1 (w/w) GCB/ATT ratio was lower than that of composites with GCB alone. The proposed mechanism for the effect of GCB and ATT on electrical or mechanical behaviors in composite was discussed in details. The clear evidence of microstructure development was also observed by transmission electron microscope.     

A Robust Electrochemical Sensor Based on Butterfly-shaped Silver Nanostructure for Concurrent Quantification of Heavy Metals in Water Samples

Heavy metals in drinking water have become a severe threat to human health. Detection of heavy metals has been achieved by electrochemical sensors that are modified with complex nanocomposites; however, reproducibility of these sensors is still a big challenge when applied in commercial settings. Here, a simple, very robust, and sensitive electrochemical sensor based on a screen-printed carbon electrode modified with butterfly-shaped silver nanostructure (AgNS/SPCE) has been developed for the concurrent determination of cadmium (II), lead (II), copper (II), and mercury (II) in water samples. The electrochemical behavior of the modified electrodes was investigated using cyclic voltammetry and differential pulse anodic stripping voltammetry. The AgNS/SPCE showed distinct peak potentials and a significant increase in the peak currents for all heavy metals, attributed to the high electrical conductivity and electrocatalytic activity of the synthesized butterfly-shaped AgNS. Moreover, the excellent stability and sensitivity towards simultaneous quantification of heavy metals have been obtained with detection limits of 0.4 ppb, 2.5 ppb, 7.3 ppb, and 0.7 ppb for Cd (II), Pb (II), Cu (II), and Hg (II), respectively. Besides, the constructed sensor was successfully applied to simultaneously quantify target heavy metals in spiked water samples. Owing to excellent sensitivity, high robustness, affordability, and fast response, the presented electrochemical sensor could be incorporated into a portable and miniaturized potentiostat device, making it a promising method for on-site water analysis.     

Magnetic,Electrical and Thermal Studies of Polypyrrole-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanocomposites

This research paper comprises of the synthesis of polypyrrole (PPy)-Fe₂O₃ nanocomposites by employing the in situ chemical oxidative polymerization method. The concentration of the filler material was adjusted between 10–50 wt % of PPy. The synthesized nanocomposites were characterized by using X-ray diffraction (XRD). Magnetic analysis and DC electrical conductivity of the samples were carried out using vibrating sample magnetometer (VSM) and two probe DC conductivity method, point towards magnetically active and electrically conductive samples. The magnetic parameters under applied magnetic field demonstrated that the values of coercivity (H _c ), saturation magnetization (M _s ) and remanence (M _r ) can be tailored by carefully controlling the amount of dopant material into the nanocomposites indicating their suitability for controllable switching devices and microwave absorption applications. The DC electrical conductivity showed an increase up to 20 wt % of filler material and thereafter a decrease in the conductivity of nanocomposites with increase in filler content is observed. Thermogravimetric analysis (TGA) showed an increase in thermal stability with an increase in ferrite content in nanocomposites.     

Preparation and characterization of water-in-oil decane/AOT microemulsions containing silver and gold nanoparticles and large amounts of water

Stable microemulsions with water contents as high as 10 vol % have been obtained, including those additionally containing silver and gold nanoparticles. Especial attention has been focused on the influence of water and stabilizer contents on the structure of adsorption layers on nanoparticles. The properties of nanoparticles obtained via the traditional microemulsion synthesis have been compared with the properties of nanoparticles that have preliminarily been concentrated with the help of electrophoresis and dried. The electrophoretic concentration and drying of nanoparticles have been shown to improve the stability of their microemulsions. Microemulsions with the highest content of water have been studied to determine the occurrence of percolation and the influence of nanoparticles on their percolation temperature and electrical conductivity.     

Synthesis and evaluation of lead telluride/bismuth antimony telluride nanocomposites for thermoelectric applications

Heterogeneous nanocomposites of p-type bismuth antimony telluride (Bi_2−xSb_xTe₃) with lead telluride (PbTe) nanoinclusions have been prepared by an incipient wetness impregnation approach. The Seebeck coefficient, electrical resistivity, thermal conductivity and Hall coefficient were measured from 80 to 380 K in order to investigate the influence of PbTe nanoparticles on the thermoelectric performance of nanocomposites. The Seebeck coefficients and electrical resistivities of nanocomposites decrease with increasing PbTe nanoparticle concentration due to an increased hole concentration. The lattice thermal conductivity decreases with the addition of PbTe nanoparticles but the total thermal conductivity increases due to the increased electronic thermal conductivity. We conclude that the presence of nanosized PbTe in the bulk Bi_2−xSb_xTe₃ matrix results in a collateral doping effect, which dominates transport properties. This study underscores the need for immiscible systems to achieve the decreased thermal transport properties possible from nanostructuring without compromising the electronic properties.     

Novel conductive nanocomposites from perfluoropolyether waterborne polyurethanes and carbon nanotubes

The exceptional electrical conductivity of carbon nanotubes (CNTs) has been exploited for the preparation of conductive nanocomposites based on a large variety of insulating polymers. Among these, perfluoropolyether‐polyurethanes (PFPE‐PUs) represent a class of highly performing fluorinated materials with excellent water/oil repellency, chemical resistance, and substrate adhesion. The incorporation of highly conductive fillers to this class of highly performing materials allows them to be exploited in new technological and industrial fields where their unique properties need to be combined with the electrical conductivity or the electrostatic dissipation properties of carbon nanotubes. However, no studies have been presented so far on nanocomposites based on PFPE‐PUs and CNTs. In this work, polymer nanocomposites based on waterborne PFPE‐PUs and increasing amounts of carboxylated multiwall CNTs (COOH‐CNTs) were prepared and characterized for the first time. The effect of increasing concentration of COOH‐CNTs on the physical, mechanical, and surface properties of the nanocomposites was investigated by means of rheological measurements, dynamic mechanical analysis, thermal characterization, optical contact angle measurements, and scanning electron microscopy. In addition, electrical measurements showed that the highly insulating undoped PFPE‐PU system undergoes substantial modifications upon addition of COOH‐CNTs, leading to the formation of conductive nanocomposites with electrical conductivities as high as 1 S/cm. The results of this study demonstrate that the addition of COOH‐CNTs to PFPE‐PU systems represents a promising strategy to expand their possible use to technological applications where chemical stability, water/oil repellence and electrical conductivity are simultaneously required. Copyright © 2014 John Wiley & Sons, Ltd.     

Optimization of the solution composition for laser-induced chemical liquid phase deposition of copper

Optimal compositions of autocatalytic solutions for laser-induced deposition of copper were established. The copper salt concentration range in which the process gives the best results was determined. It is shown that optical microscopy, as a means of controlling the topology of the deposited structures, has limited applicability. The results obtained by this method should be verified by alternative techniques, e.g., electron microscopy or measurements of the electrical conductivity of deposited structures.     

Cooperative interactions of metal nanoparticles in the ion-exchange matrix with oxygen dissolved in water

The kinetics of the reduction of molecular oxygen dissolved in water with nanocomposites consisting of an ion-exchange matrix and copper nanoparticles deposited in it in various amounts was studied. As the metal content in the polymer increased, the amount of reduced oxygen initially increased and then reached the limiting value. At a certain metal content, ionization of individual particles with formation of metal counterions changes to the oxidation of particles assembly giving layers of oxide products. The mechanism changes at the percolation threshold of the electron conductivity of the nanocomposite and determines the maximum amount of absorbed oxygen.     

Enhancement of tensile,electrical and thermal properties of epoxy nanocomposites through chemical hybridization of polypyrrole and graphene oxide

This paper presents the properties of epoxy nanocomposites, prepared using a synthesized hybrid Polypyrrole-Graphene Oxide (PPy-GO) filler, via in-situ chemical polymerization, at various filler loadings (i.e., 0.5–2 w. t %). The microstructures and properties of the PPy-GO hybrids and epoxy nanocomposites were studied via Fourier transform infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), mechanical (Tensile Properties), electrical, Dynamic mechanical thermal analysis (DMTA) and thermogravimetric analyses (TGA). Morphological study demonstrated that varying the nanofiller nature (PPy-GOs, PPy or GO) lead to different states of dispersion. Mechanical, electrical and thermal analysis demonstrated that the hybrid concentration and its architecture (PPy:GO ratio) are interesting factors significantly affected the properties of the epoxy based nanocomposites. On the other hand, the mechanical performance of the cured nanocomposites outperformed the PPy-GO, with enhancements of 78% and 51% of Young's modulus and strength, respectively. Here it has been established that the embedding of PPy-GO hybrids into pristine epoxy endows optimum dispersion of PPy and GO as well as better interfacial adhesion between the fillers and matrix, which results in a significant improvement in load transfer effectiveness. Electrical conductivity measurements showed that conductivity of epoxy filled nanocomposites increased up 10⁻⁴ S/cm for Epoxy/PPy-GO nanocomposites. DMTA test indicated that incorporation of PPy-GO resulted in a significantly increase in Tg of the resultant nanocomposites, which is attributed to the highly exfoliation structure and the stronger interfacial interaction. The PPy-GO particles enhanced electrical, thermal and mechanical properties of nanocomposites, confirming the synergistic effect of PPy-GO as multifunctional filler.     

Enhanced magnetoconductivity and electrical property of MWCNT-CdS nanocomposite embedded in polyaniline

PANI/MWCNT-CdS nanocomposites with different content of CdS wt.% has been synthesized by the chemical oxidative in-situ polymerization reaction of aniline in the presence of multi-walled carbon nanotubes (MWCNT). TEM, XRD, FTIR, and TGA studies were done for the structural and thermal characterization of the samples respectively. The particle size of CdS nanoparticles distributes in between 2.7 and 4.8 nm. XRD spectrum reveals that the co-existence of MWCNT, CdS in PANI matrix, where CdS forms a hexagonal structure. TGA result shows that nanocomposite becomes more thermally stable with the increase in CdS content. The dc electrical transport property of PANI/MWCNT-CdS nanocomposites has been investigated within a temperature range 77 ≤ T ≤ 300 K. The dc conductivity follows a 3D variable range hopping (VRH) model. A large magnetoconductivity change (19%) is observed for 2 wt% CdS content in PANI/MWCNT-CdS, which is explained by the wave function shrinkage model.     

Electrometric monitoring of water adsorption by porous glass modified with copper(II) oxide

Modification of porous glass with copper(II) oxide with planar structure does not change the run of the water-adsorption isotherm, whereas in the case when nanoparticles are formed from the supported oxide, a cluster-type adsorption mechanism is operative when a relative pressure p/p ₀ > 0.5 is reached. These specific features are reflected in the different dependences of the electrical resistance of the samples on humidity. It was shown that a porous glass with distributed copper(II)oxide planar layer can be used as a sensitive element of a resistive humidity sensor.     

Isotactic polypropylene/carbon nanotube composites prepared by latex technology: Electrical conductivity study

Several series of nanocomposites were prepared using a latex-based process, the main step of which consisted of mixing an aqueous suspension of exfoliated carbon nanotubes (CNTs) and a polymer latex. In the present work, a systematic study on the electrical properties of fully amorphous (polystyrene - PS) as well as semi-crystalline (isotactic polypropylene - iPP) nanocomposites containing either single-wall (SWCNTs) or multi-wall carbon nanotubes (MWCNTs) has been conducted. Percolation thresholds as low as 0.05 wt.% or 0.1 wt.% were observed for SWCNT/iPP and MWCNT/iPP nanocomposites, respectively. The formation of a conductive percolating network at such a low CNT concentration is favored by the high intrinsic conductivity and the low viscosity of the polymer matrix. The electrical percolation threshold of the iPP-based system was found to be lower than its rheological percolation threshold. Beyond the percolation threshold, MWCNT-based nanocomposites generally exhibited higher conductivity levels than those based on SWCNTs, most probably due to the higher intrinsic conductivity of the MWCNTs as compared to that of the SWCNTs. These excellent electrical properties, associated with the strong nucleating effect of the CNTs reported earlier [1] and [2], render this type of nanocomposites extremely attractive from a technological point of view.     

Electrical percolation in micellar sodium dodecyl sulfate solutions. a phenomenological consideration

Effects of electrical percolation accompanying variations in overall surfactant concentration с have been studied by the example of micellar sodium dodecyl sulfate solutions. It has been found that, in the studied concentration range of 0.001–1.2 M, dependences of electrical conductivity K on c may exhibit at least three break points, with the dK/dc derivatives changing in the vicinities of these points. At two of these points, which are reliably identified and correspond to critical micelle concentrations (CMC₁ and CMC₂), they decrease. At the third concentration, lying between CMC₁ and CMC₂, the dK/dc derivative increases. A substantiated assumption has been put forward that this break point, at which the dK/dc derivative increases, results from the clustering of micelles and the appearance of channels with a higher specific conductivity, which is provided by the contribution from the electrical conductivity of the diffuse and dense parts of micelle electrical double layers, upon the formation of clusters. The ionic surfactant concentration that corresponds to the break point at which the dK/dc value increases has been denoted as the critical percolation concentration.     

Simultaneous large enhancements in thermopower and electrical conductivity of bulk nanostructured half-Heusler alloys

Large reductions in the thermal conductivity of thermoelectrics using nanostructures have been widely demonstrated. Some enhancements in the thermopower through nanostructuring have also been reported. However, these improvements are generally offset by large drops in the electrical conductivity due to a drastic reduction in the mobility. Here, we show that large enhancements in the thermopower and electrical conductivity of half-Heusler (HH) phases can be achieved simultaneously at high temperatures through coherent insertion of nanometer scale full-Heusler (FH) inclusions within the matrix. The enhancements in the thermopower of the HH/FH nanocomposites arise from drastic reductions in the "effective" carrier concentration around 300 K. Surprisingly, the mobility increases drastically, which compensates for the decrease in the carrier concentration and minimizes the drop in the electrical conductivity. Interestingly, the carrier concentration in HH/FH nanocomposites increases rapidly with temperature, matching that of the HH matrix at high temperatures, whereas the temperature dependence of the mobility significantly deviates from the typical T(-α) law and slowly decreases (linearly) with rising temperature. This remarkable interplay between the temperature dependence of the carrier concentration and mobility in the nanocomposites results in large increases in the power factor at 775 K. In addition, the embedded FH nanostructures also induce moderate reductions in the thermal conductivity leading to drastic increases in the ZT of HH(1 - x)/FH(x) nanocomposites at 775 K. By combining transmission electron microscopy and charge transport data, we propose a possible charge carrier scattering mechanism at the HH/FH interfaces leading to the observed anomalous electronic transport in the synthesized HH(1 - x)/FH(x) nanocomposites.     

Design of New Water Receptors Based on Oligomeric Complexes of Copper(II) and Nickel(II)

The interaction of mono- and oligomacromolecular complexes of copper(II) and nickel(II) with water vapor has been studied on a piezoquartz microbalance. It has been established that the effectiveness of adsorption is determined by the nature of the metal ion to a larger extent than the quantity of macrocyclic ligand in the receptor molecule. Oligomacrocyclic complexes of copper(II) are shown to have prospects for use as active coverings of moisture meters working over a wide range of relative humidity.     

Synthesis and characterization of C60/polyaniline composites from interfacial polymerization

C₆₀/polyaniline (PANI) nanocomposites have been synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in the presence of C₆₀ by using an interfacial reaction. When compared with the pure PANI nanofibers from the similar process, the diameter of the obtained C₆₀/PANI nanofibers was increased because of the encapsulation of C₆₀ into PANI during aniline polymerization, which resulted from the charge‐transfer interactions between C₆₀ and aniline fragment in PANI. In addition, the resulting C₆₀/PANI nanocomposites synthesized from the low initial C₆₀/aniline molar ratio (less than 1:25) showed the homogenous morphology composed of fiber network structures, which has an electrical conductivity as high as 1.1 × 10^?4 S/cm. However, the C₆₀/PANI nanocomposites from the higher initial C₆₀/aniline molar ratio (more than 1:15) showed the nonuniformly distributed morphology, and the electrical conductivity was decreased to 3.5 × 10^?5 S/cm. Moreover, the C₆₀/PANI nanocomposites from the interfacial reaction showed a higher value of electrical conductivity than the mechanically mixed C₆₀/PANI blends with the same C₆₀ content, because of the more evenly distributed microstructures. FTIR, UV–vis, and CV data confirmed the presence of C₆₀ and the significant charge‐transfer interactions in the resultant nanocomposites, which was responsible for the morphology development of the C₆₀/PANI and the variation of the electrical conductivity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Electroconductive Green Metal-polyaniline Nanocomposites: Synthesis and Application in Sensors

Polyaniline (PANI) is one of the most extensively used conducting polymer due to its fascinating properties including conducting, thermal, optical, magnetic and electrochemical properties, simple synthesis procedure and low cost of monomer. It has attracted major attention in a variety of applications including electrochemical sensors, catalysts, supercapacitors and biosensors. However, its limitations such as insolubility in common solvents, low process-ability and poor mechanical properties have led to the development of new approaches to improve it properties. Metal nanoparticles (MNPs) such as silver, gold, copper and palladium have been combined with PANI to improve on its properties which has led to a new class of materials known as metal/PANI nanocomposites. These hybrid nanocomposites incorporate advantages of both MNPs and polymers which effectively improves the properties of the individual materials. Various synthesis techniques including in situ polymerization, ɤ-radiolysis, electrodeposition, complexation, vacuum deposition and interfacial polymerization have been used in the formation of metal/PANI nanocomposites. These nanocomposites have been used in various sensor and biosensor applications due to their excellent conductivity, ease of synthesis, excellent redox potentials, chemical and thermal stability. This review highlights the various metal/PANI nanocomposites, their various synthesis techniques and their application in sensors and biosensors. The importance of these nanocomposites in sensing and signaling various toxic heavy metals such as mercury, lead and silver and toxic gases such as hydrogen sulphide, ammonia and chloroform has been discussed. In addition the review covers the applications of metal/PANI nanocomposites in biosensor systems for the detection of glucose, DNA, protein, cholesterol, drugs and hydrogen peroxide.     

Preparation and properties of conductive silver/photosensitive polyimide nanocomposites

A new electrically conductive photoresist has been developed. It is based on the dispersion of silver nanoflakes in a negative‐tone photosensitive polyimide (PSPI) precursor. 2‐Mercaptopropionic acid was used as the surfactant to modify the silver nanoflake surface for the dispersion of silver nanoflakes in the polymer. The silver/PSPI nanocomposites showed electrical conductivity at a low silver content of 10 wt %. The electrical conductivity of the silver/PSPI nanocomposites ranged from 10 to 10⁴ S/cm, which was dependent on the silver weight fraction in the resist formulation. Patterns with a resolution of 30 μm were obtained from the silver/PSPI nanocomposites. The silver/PSPI nanocomposites had excellent thermal properties. Their glass transition temperatures were above 360 °C and thermal decomposition temperatures were over 420 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1575–1583, 2009     

Electrical transport properties of semiconducting lithium molybdate glass nanocomposites

We have reported the formation of lithium molybdate glass nanocomposites embedded with lithium molybdate nanophases from the x-ray diffraction and transmission electron microscopic studies. We have investigated the dc electrical conductivity in a wide temperature range for these glass nanocomposites, which exhibit semiconducting behavior. We have analyzed the dc electrical data in the light of polaronic conduction models of Mott and Schnakenberg. We have also studied ac electrical conductivity of these glass nanocomposites in wide temperature and frequency ranges. The experimental ac results have been analyzed with reference to various theoretical models based on quantum-mechanical tunneling and hopping over the barrier. We have observed that the temperature dependence of the dc conductivity is consistent with the polaronic hopping models, while the temperature and frequency dependence of the ac conductivity is consistent with the polaronic tunneling models.     

Pseudolattice theory of charge transport in ionic solutions: Corresponding states law for the electric conductivity

A statistical mechanical framework for charge transport in ionic liquid–solvent mixtures based on the existence of a statistical lattice structure (pseudolattice) throughout the whole range of concentration is reported. The ion distribution is treated in a mean-field Bragg–Williams-like fashion, and the ionic motion is assumed to take place through hops between cells of two different types separated by non-random-energy barriers of different heights depending on the cell type. Assuming non-correlated ion transport, the electrical conductivity is shown to have a maximum, arising from the competition between the concentration of charge carriers in the bulk medium and their mobilities in the pseudolattice. An explicit expression for the concentration at which this maximum occurs is given in terms of microscopic parameters, and the electrical conductivity normalized by its maximum value (κ/κ_max) is shown to follow rather closely a universal corresponding states law in concentration space when represented against the ionic concentration scaled by its value at the conductivity maximum (?_α/?_max). Ion–ion and ion–solvent interactions are explicitly considered combining the path probability method for charge transport in solid electrolytes and the Bragg–Williams approximation for interparticle interactions, and their impact on the deviations of experimental data from the universal behavior of non-correlated transport analyzed. The theoretical predictions are shown to satisfactorily predict experimental values of electrical conductivity of aqueous solutions of conventional electrolytes and of mixtures of room temperature molten salts with typical solvents.