Electrical and structural analysis of conductive polyaniline/polyacrylonitrile composites

Conducting composites of polyacrylonitrile (PAN) copolymer containing 10% mass ratio methylacrylate and dodecylbenzene sulfonic acid doped polyaniline (PANI-DBSA) were prepared by solution blending. Electrical properties of the blends were characterized by means of electrical conductivity measurements and the phase structures were investigated via scanning electron microscopy (SEM), X-ray diffraction (XRD), FT-IR spectroscopy, differential scanning calorimetry (DSC) and dynamical mechanical analysis (DMA). It was found that the electrical conductivity of the composites increased with the increase of PANI-DBSA content and the percolation threshold lay around 3.2 wt%. DSC and DMA measurements showed that there was only one T_g for each blend and the values of T_g varied with the PANI-DBSA content, implying that the PANI-DBSA/PAN blend was at least partially compatible. The formation of the hydrogen bonding between the carbonyl groups in PAN copolymer and the imine groups in PANI-DBSA was identified by the FT-IR spectra. XRD demonstrated that the intrinsic layered arrangement of PANI-DBSA was disaggregated in the blends. Nanosize network structure of PANI-DBSA dispersing in PAN matrix and the so-called phase reverse occurring in the skin layer of the film samples at low PANI-DBSA loading were observed by SEM.     

Template synthesis of polyaniline/Pd nanoparticle and its catalytic application

Pre-organization of Pd(II) species on polyaniline to form the corresponding d,π-conjugated complex provided a versatile route to a small and well-dispersed nanoparticle, which worked as an efficient redox catalyst for oxidative coupling reaction of 2,6-di-t-butylphenol.     

Pervaporation separation of water + isopropanol mixtures using novel nanocomposite membranes of poly(vinyl alcohol) and polyaniline

Novel nanocomposite polymeric membranes containing nanosized (30–100 nm) polyaniline (PANI) particles dispersed in poly(vinyl alcohol) (PVA) were prepared and used in the pervaporation separation of water–isopropanol feed mixtures ranging from 10 to 50 mass% of water at 30 °C. Of the three nanocomposite membranes prepared, the membrane containing 40:60 surface atomic concentration ratio of PANI:PVA produced the highest selectivity of 564 compared to a value of 77 observed for the plain PVA membrane. Flux of the nanocomposite membranes was lower than those observed for the plain PVA membrane, but selectivity improved considerably. Membranes were characterized by differential scanning calorimetry, dynamic mechanical thermal analyzer, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. The highest selectivity with the lowest flux was observed for 10 mass% water containing feed mixture. Flux increased with increasing amount of water in the feed, but selectivity decreased considerably. These results were attributed to the acid-doped PANI particles in the PVA membrane as a result of change in the micromorphology of the nanocomposite membranes. In addition, molar mass between cross-links and fractional free volume of the membranes are responsible for the varying membrane performance. Temperature effect on permeability was investigated for 10 mass% water containing feed with the membrane containing higher concentration of PANI particles, the presence of which could be responsible for varied effect of water permeation through the membrane. Membranes of this study could remove as much as 98% of water from the feed.     

Synthesis and characterization of red mud/polyaniline composites: Electrical properties and thermal stability

New types of conducting composites using red mud as an inorganic substrate and polyaniline as the conducting phase were prepared. Red mud/polyaniline (RM/PANI) composites were synthesized in acidic aqueous solution by the chemical oxidative polymerization of aniline using ammonium peroxydisulfate as the oxidant. The composites exhibit conductivities in the 0.42-5.2 S cm⁻¹ range, depending on the amount of polyaniline. They were characterized by infrared and UV-vis spectroscopy, scanning electron microscopy and X-ray diffraction. The IR and X-ray results show that PANI is deposited on the RM surface. The composites have a globular structure and the PANI globules synthesized on the surface of RM are smaller than those prepared under the same conditions without the substrate. Thermogravimetric analysis was used for investigation of the thermal stability of the composites. The thermal stability of the conductivity of RM/PANI composites was studied by ageing at 125 °C, the conductivity being measured in situ during this process.     

Electrochemical behavior of MF-4SK/polyaniline composites as investigated by membrane voltammetry

Membrane voltammetry was used to investigate composites consisting of perfluorinated MF-4SK membranes and polyaniline (PANI) and synthesized under various conditions. A theoretical analysis of the influence of transport-structure parameters of the ion-exchange membranes on their selectivity and limiting-current value is carried out. For MF-4SK/PANI composites, the increase in the exchange potential at the overlimiting state is found to be more than 2V compared to the original membrane. An analysis of how various factors influence the parameters of a current-voltage curve shows that the presence of anilinium and Fe³⁺ ions in the electromembrane system has no effect on the value of the potential at the onset of the overlimiting state. A phenomenological model is proposed to account for the increased plateau length at the limiting current through a change in the energetic state of water in the perfluorinated-membrane matrix resulting from the template synthesis of polyaniline.     

Effect of polyaniline on the stability of electrotransport characteristics and thermochemical properties of sulfocationite membranes with different polymer matrices

A comparative analysis of the electrotransport and thermochemical properties of homogeneous and heterogeneous sulfocationite membranes modified with polyaniline has been performed. The relationship between the conditions of polyaniline synthesis in the membrane matrix and their electric conductivity, electroosmotic permeability, and thermal stability was studied. The conditions of polyaniline synthesis on the surface of a heterogeneous MK-40 membrane had an insignificant effect on the amount of the introduced modifier, while the electric conductivity of the composites remained high enough. The absence of the effect of the polyaniline synthesis conditions on the electric conductivity of МK-40-based composites suggests that the heterogeneity of this membrane is a more significant factor than the polyaniline synthesis conditions. A thermogravimetric analysis of the thermochemical properties showed a significant increase in the thermal stability of the heterogeneous membrane after its modification with polyaniline. For perfluorinated membranes, the thermochemical properties changed less significantly, but the electrotransport of ions and water significantly decreased after modification.     

Influence of the preparation procedure on the properties of polyaniline based magnetic composites

A versatile process for the preparation of composite films consisting of magnetite (Fe₃O₄) nanoparticles embedded in a polyaniline (PANI) matrix is reported. Spectroscopic properties of polyaniline matrix (PANI-EB), polyaniline protonated with camphor sulfonic acid (PANI-CSA_0.5) PANI-ES and PANI/Fe₃O₄-CSA_0.5 composites were studied, both in the state of the solutions of m-cresol and in thin films processed from the same solvents. The results of these studies indicate that m-cresol can be used for PANI/Fe₃O₄ composite preparation. Such films show both reasonably high electrical conductivity and magnetic permeability. A controlled application of a magnetic field during the casting process resulted in the formation of the materials with an unusual combination of magnetic and transport properties. The obtained films show the behavior that can be explained by the presence of both ferromagnetic and paramagnetic phases. The superparamagnetic contribution, if any, is very small. Application of the external magnetic field during fabrication of the composites stimulates creation of the aggregates of magnetic particles which, although keeps conductivity at a relatively high level, leads to a small decrease of the conductivity value.     

Effects of the polymerization temperature on the structure,morphology and conductivity of polyaniline prepared with ammonium peroxodisulfate

Polyaniline (PANI) samples were prepared by the oxidation of aniline with ammonium peroxodisulfate in a reaction vessel placed in a bath thermostated to particular temperature, T_b, from −20 °C to 40 °C. Temperature–time profiles of reaction mixtures were monitored except for the reaction at −20 °C that proceeded in the solid state. The temperature regime was found to influence the molecular structure, morphology, crystallinity and electrical conductivity of PANI. The increase in T_b results in an increased content of meanwhile unspecified structure defects in the formed PANI chains (the presence of attached self-doping groups is improbable), decreased crystallinity, toughness and compactness of PANI microparticles and increased steepness of the temperature dependence of PANI conductivity. The PANI prepared in the solid-state polymerization at −20 °C shows, besides a rather high crystallinity, the unusually high position of the quinonoid band maximum: 643 nm, which suggests a high regularity of its chains. A correlation between the temperature dependence of PANI conductivity at low temperatures (range from 13 to 318 K) on one hand and the temperature regime of PANI preparation on the other hand, is reported for the first time. The dependences obtained only poorly meet the variable random hopping model.     

On the unusual solvent retention and the effect on the gas transport in perfluorinated Hyflon AD membranes

Dense membranes of Hyflon AD 60X were prepared by the solvent evaporation method and by melt pressing. The diffusion coefficient, solubility and permeability of the membranes were measured for six permanent gases using time lag and steady state permeation measurements. The thermal properties were determined by Differential Scanning Calorimetry (DSC) and the solvent content was measured gravimetrically and was estimated by the Fox equation. It was found that unusually strong solvent retention in the solution-cast membrane leads to considerable plasticization of the polymer, to possible foam formation upon drying and, most important, to significant changes in the permeation properties. The residual solvent increases the diffusion coefficient and permeability of the larger gas species up to almost one order of magnitude, and it reduces the permselectivity. For most gas species the solubility is about two times higher in the solvent-free melt-pressed film than in the solution-cast film. The relation between the residual solvent and the membrane properties is discussed.     

Effect of polyaniline (PANI) on Poly(vinylidene fluoride-co-hexaflouro propylene) (PVDF-co-HFP) polymer electrolyte membrane prepared by breath figure method

Poly(vinylidene fluoride-co-hexaflouro propylene) is a well-known material for polymer electrolyte membranes (PEMs) due to its low cost, high mechanical integrity and excellent chemical resistance; however, its pure form has limited characteristics that require further modification to achieve optimum results. Therefore, the different dosages of polyaniline (PANI) (10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt%) were incorporated into PVDF-HFP blend to fabricate PVDF-HFP/PANI polymer electrolyte membrane by using breath-figure method. The FTIR peaks of PVDF-HFP and PVDF-HFP/PANI membrane confirms the successful incorporation of PANI into PVDF-HFP blend, while TGA, DSC and XRD analysis shows the PANI effect on stability and ionic conductivity of PVDF-HFP membrane. The PVDF-HFP/PANI membrane with 30 wt% PANI found superior with the highest porosity of 83%, electrolyte uptake of 270% and ionic conductivity of 1.96 mS cm⁻¹; however, the other concentrations of PANI were also effective and enhanced the performance of PVDF-HFP membrane. This shows the improved performances of PVDF-HFP membrane were attributed to successful incorporation of PANI and the proposed membrane can be a suitable alternative PEM or a separator for energy devices.     

Optimisation and characterisation of biosensors based on polyaniline

With lower limits of detection and increased stability constantly being demanded of biosensor devices, characterisation of the constituent layers that make up the sensor has become unavoidable, since this is inextricably linked with its performance. This work describe the optimisation and characterisation of two aspects of sensor performance: a conductive polymer layer (polyaniline) and the immobilised protein layer. The influence of the thickness of polyaniline films deposited electrochemically onto screen-printed electrode surfaces is described in this work in terms of its influence on a variety of amperometric sensor performance characteristics: time to reach steady state, charging current, catalytic current, background current and signal/background ratios. The influence of polymer film thickness on the conductivity and morphology of finished films is also presented.

An electrostatic method of protein immobilisation is used in this work and scanning electron microscopy in conjunction with gold-labelled antibodies and back-scattered electron detection has enabled the direct visualisation of individual groups of proteins on the sensor surface. Such information can provide an insight into the performance of sensors under influence of increasing protein concentrations.     

Degradation and stability of polyaniline on exposure to electron beam irradiation (structure-property relationship)

Polyaniline (PAni) was prepared by electrochemical polymerization and subjected to different doses of electron beam (EB) irradiation. The effect of EB irradiation causes both chain scission and cross-linking process in PAni, which depends on irradiation dose. The degree of chain scission and cross-linking in PAni by EB irradiation is characterized through XRD, TGA, DSC, solubility, EPR and electrical properties measurement. The results reveal that with increase in EB irradiation dose from 0 to 150 kGy DC and AC conductivity and dielectric constant are found to increase mainly due to the chain scission or further doping in PAni. Due to irradiation there is change in the structure of PAni, such as decrease in the d-spacing, inter-chain separation, thermal stability and T_g but increase in the percent crystallinity and solubility. With further increase in the EB irradiation dose from 150 kGy onwards the DC and AC conductivity and dielectric constant are decreased due to the cross-link formation or dedoping in PAni, which causes the decrease in percentage of crystallinity and solubility and increase in d-spacing, inter-chain separation, thermal stability and T_g of PAni.     

Thermal and structural stability of composite systems based on polyaniline deposited on porous polyethylene films

Conducting composite systems containing polyaniline layers produced on the surface and inside the pores of polyethylene support have been prepared. Microporous polyethylene films were obtained by melt extrusion with subsequent annealing, uniaxial extension, and thermal fixation. Polyaniline layers were formed by in-situ polymerization of aniline onto polyethylene porous support placed into the aqueous reaction mixture. Structural and chemical transformations upon heating of these systems in air in free state and in vacuum under load have been investigated by thermo-mechanical tests, IR spectrometry, and electron microscopy. Changes in mechanical properties of composites after heating have been analyzed. Composite systems have been found to demonstrate a considerably lower shrinkage upon heating than microporous polyethylene substrates. It has been discovered that the composites preserve mechanical integrity on heating up to temperatures much higher than the polyethylene melting point. It is concluded that thermo-mechanical behaviour of the composites is determined by the space-continuous phase of polyaniline on the surface and in the bulk of polyethylene support.     

Poly(vinylidene fluoride)/polyaniline/carbon nanotubes nanocomposites: Influence of preparation method and oscillatory shear on morphology and electrical conductivity

Nanocomposites of poly(vinylidene fluoride) (PVDF)/polyaniline (PAni)/carbon nanotubes (CNT) were prepared through melt blending using three different methods. The PVDF, CNT and PAni were added into the internal mixer at the same time in method I. In method II, PAni was polymerized in the presence of different amounts of CNT, and then added to PVDF. In method III, PAni was obtained with half the CNT content, and then added to PVDF with the other half of CNT. The morphology, rheological behavior and electrical conductivity of these systems were investigated through transmission electron microscopy (TEM) and combined electro-rheological measurements. As expected, the preparation method strongly influenced the final morphology of the nanocomposites, as shown by TEM analysis. The deformation and destruction of PAni-PAni and CNT-CNT bonds during the oscillatory shear experiments strongly affected the electrical conductivity, probably in two different ways: it breaks the PAni into smaller domains and also disrupts the CNT percolated network. Concluding, a good correlation between the electrical, flow behavior and preparation method could be achieved for PVDF/PAni/CNT nanocomposites, mainly by means of the combined electro-rheological measurements.     

Gas transport in polyurethane-polystyrene interpenetrating polymer network membranes. I. Effect of synthesis temperature and molecular structure variation

The gas (oxygen and nitrogen) transport characteristics of the interpenetrating polymer network (IPN) membranes of polyurethane/polystyrene were studied. The effect of synthesis temperature, composition, molecular weight of the polyol and aromatic content (of MDI, TDI and HDI) on the gas permeability were analyzed. In the IPN synthesis, first polyurethane was polymerized thermally, and then polystyrene was polymerized by photolytic methods at different temperatures. The permeability coefficient decreased and the separation factor increased with decreasing synthesis temperature due to the miscibility increase. The permeability coefficient showed a minimum value and the separation factor showed a maximum value at ca.25 wt.% polyurethane composition. The permeability coefficient decreased and the separation factor increased with increasing aromatic content in polyurethane component. The morphology and density behavior of the IPN's agreed well with the permeability data. The tensile strength of the membrane increased with decreasing synthesis temperature and with increasing crosslink density and polystyrene content.     

Optimization of the thickness of a conducting polymer, polyaniline, deposited on the surface of poly(vinyl chloride) membranes: a new way to improve their potentiometric response

Repeated depositions of polyaniline (PANI) have been used to control the thickness of the polymeric film deposited on poly(vinyl chloride) (PVC) membrane surface. The oxidation of aniline was carried out in a dispersion mode, i.e. in the presence of poly(N-vinylpyrrolidone) (PVP). Two kinds of PVC were used for this purpose: a non-plasticized PVC for the study of PANI deposition and PVC, plasticized with nitrophenyl octyl ether (NPOE), as a prototype of a liquid membrane electrode. The results of UV-visible and FTIR spectroscopies and electron microscopy showed that (1) the film thickness increased by about equal increments of ∼40 nm after each polymerization, and (2) the interface with PVC was constituted by PANI film and adhering PANI-PVP colloidal particles.The various thicknesses of the deposited PANI films affected the potentiometric response of the NPOE/PVC membrane with and without an anion-exchanger. The potentiometric anionic response was observed with a minimal thickness of PANI film on the blank NPOE/PVC membrane. Sensitivity of the PANI film to pH occurred only with a blank NPOE/PVC membrane coated with a thick polymeric film, while it was strongly suppressed by the presence of a lipophilic anion-exchanger, tridodecylmethylammonium chloride (TDDMACl), in the membrane, regardless of the thickness of the polymer film. The thickness of the PANI film did not affect the anionic selectivity pattern of TDDMACl-based membranes to any great extent, but its presence improved and stabilized their potentiometric characteristics (sensitivity, linear-response range).     

Development of electrochemical biosensors based on sol-gel enzyme encapsulation and protective polymer membranes

Protective polymer coatings have been used to enhance the retention of enzymes in sol-gel films as immobilisation phases in electrochemical biosensors. Carbon film electrodes were electrochemically modified with poly(neutral red) (PNR). These electrodes were coated with oxysilane sol-gels incorporating glucose oxidase and an outer coating of carboxylated PVC (CPVC) or polyurethane (PU), with and without Aliquat-336 or isopropyl myristate (IPM) plasticizer, was applied. The biosensors were characterised electrochemically using cyclic voltammetry and amperometry, electrochemical impedance spectroscopy and scanning electron microscopy. Impedance spectra showed that the electrode surface is most active when the sol-gel–GOx layer is not covered with a membrane. However, membranes without plasticizer extend the lifetime of the biosensor to more than 2 months when PU is used as an outer membrane. The linear range of the biosensors was found to be 0.05–0.50 mM of glucose and the biosensor with PU outer membrane exhibited higher sensitivity (ca.117 nA mM⁻¹) in the region of linear response than that with CPVC. The biosensors were applied to glucose measurement in natural samples of commercial orange juice.     

Conductivity and solvent uptake of proton exchange membrane based on polystyrene(ethylene-butylene)polystyrene triblock polymer

Conducting membranes of polystyrene-block-(ethylene-ran-butylene)-block-polystyrene were obtained by sulphonation of the polymer using chlorosulphonic acid. The membranes were found to have an excellent conductivity in the order of 10⁻¹ S/cm in their fully hydrated condition at room temperature as measured by impedance spectroscopy. This value is several orders higher than what is reported in the literature for hydrocarbon based ionomers. Water and methanol absorption of both non-reinforced and reinforced membranes were studied. Maximum uptake of solvents, wet membrane porosity and uptake of solvent molecules per sulphonic acid group were calculated gravimetrically. Characterization of the membranes was performed by IR, DSC and TGA methods.     

掺杂和取代对聚苯胺导电性能影响机制的研究

在导电聚合物的研究中，聚苯胺及其衍生物一直是人们相当感兴趣的课题．此类聚合物既可用氧化剂掺杂，也可进行质子酸掺杂，掺杂后其电导率可提高约十个数量级｛1，’］；利用在主链上引入取代基等化学修饰方法，可方便地调节其溶解性、加工性等物理化学性能．已有的研究结果表明，主链的化学修饰往往给聚苯胺的导电性能带来不利影响＊．因此，如何使聚苯胶类导电聚合物保持高的电导率且同时具备优良的物理加工性能使成为此类导电聚合物研究中的一个亟待解决的问题一本文利用鼻子化学EHMO－CO方法对掺杂和取代影响聚苯胺及其衍生物导电性…