Controlled Synthesis of Dendritic Polyaniline Fibers with Diameters from Nanosize to Submicrometersize

Dendritic polyaniline nanofibers and submicrometer-sized fibers have been synthesized by chemical oxidative polymerization of aniline （An） doped with salicylic acid （SA）. The diameters of the fibers could be controlled easily from 30 to 400 nm by varying the concentration of aniline and salicylic acid at room temperature. Scanning electron microscopy （SEM） and typical transmission electron microscopy （TEM） were applied to investigate their morphologies. . Fourier transform infrared （FTIR） spectrum indicated that the state of the dendritic polyaniline fibers is emerialdine rather than solely the leucoemeraldine or permigraniline forms. The dendritic polyaniline fibers have potential applications as chemical sensors or actuators and neuron devices.     

Preparation of a nanowire-structured polyaniline composite and gas sensitivity studies

To obtain organic nanowire sensors with high sensitivity and rapid response times, based on the inducement effect of surfactants during in situ polymerization, nanostructured polyaniline composites are obtained by using a chemical oxidation method by adding a small amount of surfactant. A casting method is employed on interdigitated carbon electrodes. The gas sensitivity to a series of chemical vapors is examined at room temperature. The results indicate that polyaniline with regular nanowire structure is obtained when succinic acid is added. The gas sensitivity and response rates of a film with nanowire structure are much better than those of conventional polyaniline films produced by means of organic solution spin coating methods. The film described in this work shows good selectivity to trimethylamine and other related gases and, the reaction being reversible with the use of high-purity nitrogen.     

Self-Assembly Molecularly Imprinted Nanofiber for 4-HA Recognition

In this paper, we provided a self-assembly strategy to prepare surface molecularly imprinted polyaniline (PANI) nanofiber. The route provides simplicity, convenience, low cost, and high-productivity due to the omission of the template guided materials and their post-treatment. The molecularly imprinted PANI nanofibers could selectively bind the template (4-hydroxybenzoic acid) molecules, and the nanofibers have large adsorption capacity and fast uptake kinetics for target species. The PANI nanofibers could provide a good material for imprinting various organic or biological molecules toward applications in chemical/biological sensors and bioassay.     

Synthesis of polyaniline nanofibers by "nanofiber seeding"

Seeding a conventional chemical oxidative polymerization of aniline with even very small amounts of biological, inorganic, or organic nanofibers (usually <1%) dramatically changes the morphology of the resulting doped electronic polymer polyaniline from nonfibrillar (particulate) to almost exclusively nanofibers. The nanoscale morphology of the original seed template is transcribed almost quantitatively to the bulk precipitate. These findings could have immediate impact in the design and development of high-surface area electronic materials.     

Hydrogen sensors based on conductivity changes in polyaniline nanofibers

Hydrogen causes a reversible decrease in the resistance of a thin film of camphorsulfonic acid doped polyaniline nanofibers. For a 1% mixture of hydrogen in nitrogen, a 3% decrease in resistance is observed (DeltaR/R = -3%). The hydrogen response is completely suppressed in the presence of humidity. In contrast, oxygen does not inhibit the hydrogen response. A deuterium isotope effect on the sensor response is observed in which hydrogen gives a larger response than deuterium: (DeltaR/R)H/(DeltaR/R)D = 4.1 +/- 0.4. Mass sensors using nanofiber films on a quartz crystal microbalance also showed a comparable deuterium isotope effect: DeltamH/DeltamD = 2.3 +/- 0.2 or DeltanH/DeltanD = 4.6 +/- 0.4 on a molar basis. The resistance change of polyaniline nanofibers is about an order of magnitude greater than conventional polyaniline, consistent with a porous, high-surface-area nanofibrillar film structure that allows for better gas diffusion into the film. A plausible mechanism involves hydrogen bonding to the amine nitrogens along the polyaniline backbone and subsequent dissociation. The inhibitory effect of humidity is consistent with a stronger interaction of water with the polyaniline active sites that bind to hydrogen. These data clearly demonstrate a significant interaction of hydrogen with doped polyaniline and may be relevant to recent claims of hydrogen storage by polyaniline.     

Antioxidant activity of polyaniline nanofibers

Well-confined uniform polyaniline (PANI) nanofibers were synthesized by using photo-assisted chemical oxidative polymer- ization of aniline in the presence of different dopant acids,and the radical scavenging ability of the produced PANI nanofibers was determined by the DPPH assay.It was found that the antioxidant activity of PANI nanofibers was higher than conventional PANI, and increased with decreasing of averaged diameter of the nanofibers.The enhanced antioxidant activity was concerned with increased surface area of PANI nanofibers.     

Shape and aggregation control of nanoparticles: not shaken, not stirred

The aggregation of nanoparticles during synthesis, particularly the effect of mechanical agitation, is investigated from a viewpoint of nucleation using a conjugated polymer, polyaniline, as an example. Homogeneous nucleation of polyaniline results in nanofibers, while heterogeneous nucleation leads to granular particulates. Mechanical agitation, which is a common method for disrupting aggregates, instead dramatically triggers aggregation during the synthetic process and favors the formation of granular particulates. Correlating the shape and aggregation of polyaniline nanoparticles with the mode of nucleation, a new aggregation mechanism is proposed in which aggregation is triggered by heterogeneous nucleation. The mechanism may be quite general as indicated by experiments with other materials such as silica nanoparticles. Highly dispersible polyaniline nanofibers can now be reproducibly prepared from a conventional reaction simply by not mechanically agitating the reaction and carrying it out at an elevated temperature. This work may prove to be of great value in reproducibly synthesizing nanoparticles with well-controlled sizes and shapes and in effectively preventing aggregation in chemical, pharmaceutical, and materials production processes.     

Multifunctional chemical vapor sensors of aligned carbon nanotube and polymer composites

Partially coating perpendicularly aligned carbon nanotube arrays with an appropriate polymer thin film along their tube length provides a novel concept for developing new sensors of high sensitivity, good selectivity, and excellent environmental stability for the detection of a broad class of chemical vapors with low power consumption. The absorption and desorption of chemical vapors by the polymer matrix cause changes in the inter-tube distance and, hence, the surface resistance across the nanotube film. Simple measurements of the resistance change, therefore, constitute the nanotube-polymer chemical vapor sensors. These rationally designed, aligned carbon nanotube-polymer composite films are flexible and can be effectively integrated into many systems for a wide range of potential applications, including their use as multifunctional sensors for sensing chemical vapors, mechanical deformations, thermal and optical exposures.     

The intrinsic nanofibrillar morphology of polyaniline

Polyaniline nanofibers are shown to form spontaneously during the chemical oxidative polymerization of aniline. The nanofibrillar morphology does not require any template or surfactant, and appears to be intrinsic to polyaniline synthesized in water. Two approaches--interfacial polymerization and rapidly-mixed reactions--have been developed to prepare pure nanofibers. The key is suppressing the secondary growth that leads to agglomerated particles. The effects of different dopant acids and solvents are discussed. Changing the dopant acid can be used to tune the diameters of the nanofibers between about 30 and 120 nm. Changing the organic solvent in interfacial polymerization reactions has little effect on the product. A brief discussion of the processibility of the nanofibers is presented. The possibility of creating nanofibrillar structures for selected polyaniline derivatives is also demonstrated.     

Synthesis and electrochemical performance of sandwich-like polyaniline/graphene composite nanosheets

Sandwich-like polyaniline/graphene composite nanosheets have been synthesized by chemical oxidation polymerization of aniline monomer on the surfaces of reduced graphene oxide nanosheets in the absence of any surfactants. The influences of the mass ratios of aniline and reduced graphene oxide on the sizes and morphologies of polyaniline/graphene nanocomposites have been investigated. As the mass ratio of aniline and reduced graphene oxide is smaller than 12:1, polymerization reaction of aniline occurs on the surfaces of reduced graphene oxide by heterogeneous nucleation to form sandwich-like polyaniline/graphene composite nanosheets. However, besides sandwich-like polyaniline/graphene composite nanosheets, polyaniline nanofibers are formed by homogeneous nucleation. In comparison with reduced graphene oxide and polyaniline nanofibers, the obtained sandwich-like polyaniline/graphene composite nanosheets exhibit good electrochemical performances due to the synergistic effect between graphene and polyaniline.     

Spectral characteristics of polyaniline nanostructures synthesized by using cyclic voltammetry at different scan rates

The polyaniline nanofibers with different sizes were synthesized by using cyclic voltammetry at different potential scan rates, in the presence of ferrocenesulfonic acid. The potential scan rate controlled the formation and growth of polyaniline nuclei, which plays a key role in controlling nanofiber sizes. The average diameters of nanofibers decreased from about 130 nm to about 80 nm as the potential scan rate increased from 6 to 60 mV s (-1). We first observed an ordered change in the following spectra with the nanofiber sizes of polyaniline. The spectra of the X-ray diffraction indicated that the partially crystalline form existed in the polyaniline nanofibers and that the crystallinity of polyaniline increased with decreasing diameter of polyaniline nanofibers. The ESR spectra revealed the fact that the decrease in the intensity of the ESR signal was accompanied by the increase in the value of the peak-to-peak line width Delta H pp as the diameter of polyaniline nanofibers decreased. The (1)H NMR spectra showed that a peak in a triplet caused by the +/- NH free radical was split into two peaks with different intensities and that their relative intensity also changed with the diameter of the polyaniline nanofibers.     

Processable stabilizer-free polyaniline nanofiber aqueous colloids

Aqueous polyaniline colloids can be readily prepared by purifying polyaniline nanofibers and controlling the pH and self-stabilized via electrostatic repulsions without the need for any chemical modification or steric stabilizer, thus providing a simple and environmentally friendly way to process the conducting polymer in its conductive state both in bulk and at the nanometre level.     

The Naked‐Eye Detection of NH3–HCl by Polyaniline‐Infiltrated TiO2 Inverse Opal Photonic Crystals

A reversible color change of a polyaniline‐infiltrated TiO₂ inverse opal photonic crystal (PC) film can be obtained when the PC is switched from an acidic to alkali vapor environment. In a saturated NH₃ environment, the stopband of the as‐prepared PCs changes from 556 to 688 nm; such large shift of 132 nm could be observed, corresponding to a clear color change from green to red. After placing in HCl vapor, the stopband undergoes a blue‐shift and the color turns back to green. The result is ascribed to PANI being doped or dedoped by acid or base and the effective refractive index of the PC film varying accordingly. The naked‐eye detection of NH₃ and HCl vapors can be realized by the reversible color change of the PC film, which is of importance for chemical and biological sensors.     

New renewable resource amphiphilic molecular design for size-controlled and highly ordered polyaniline nanofibers

We demonstrate here, for the first time, a unique strategy for conducting polyaniline nanofibers based on renewable resources. Naturally available cardanol, which is an industrial waste and main pollutant from the cashew nut industry, is utilized for producing well-defined polyaniline nanofibers. A new amphiphilic molecule is designed and developed from cardanol, which forms a stable emulsion with aniline for a wide composition range in water (1:1 to 1:100 dopant/aniline mole ratio) to produce polyaniline nanofibers. The scanning electron microscopy and transmission electron microscopy analysis of the nanofibers reveals that the dopant/aniline ratio plays a major role in determining the shape and size of polyaniline nanofibers. The nanofiber length increases with the increase in the dopant/aniline ratio, and perfectly linear, well-defined nanofibers of lengths as long as 7-8 muM were produced. The amphiphilic dopant has a built-in head-to-tail geometry and effectively penetrates into the polyaniline chains to form highly organized nanofibers. Wide-angle X-ray diffraction (WXRD) spectra of the nanofibers showed a new peak at 2theta = 6.3 (d spacing = 13.9 A) corresponding to the three-dimensional solid-state ordering of polyaniline-dopant chains, and this peak intensity increases with increase in the nanofiber length. The comparison of morphology and WXRD reveals that high ordering in polyaniline chains results in the formation of long, well-defined nanofibers, and this direct correlation for the polyaniline nanofibers with solid-state ordering has been established. The conductivity of the polyaniline nanofibers also increases with increase in the solid-state ordering rather than increasing with the extent of doping. The polyaniline nanofibers are freely soluble in water and possess high environmental and thermal stability up to 300 degrees C for various applications.     

Electrospinning of Hyperbranched Poly-L-Lysine/Polyaniline Nanofibers for Application in Cardiac Tissue Engineering

Electrospun polyaniline nanofibers are one of the most promising materials for cardiac tissue engineering due to their tunable electroactive properties. Moreover, the biocompatibility of polyaniline nanofibes can be improved by grafting of adhesive peptides during the synthesis. In this paper, we describe the biocompatible properties and cardiomyocytes proliferation on polyaniline electrospun nanofibers modified by hyperbranched poly-L-lysine dendrimers (HPLys). The microstructure characterization of the HPLys/polyaniline nanofibers was carried out by scanning electron microscopy (SEM). It was observed that the application of electrical current stimulates the differentiation of cardiac cells cultured on the nanofiber scaffolds. Both electroactivity and biocompatibility of the HPLys based nanofibers suggest the use this material for culture of cardiac cells and opens the possibility of using this material as a biocompatible electroactive 3-D matrix in cardiac tissue engineering.     

Chemical Vapor Detection Using a Reconstituted Insect Olfactory Receptor Complex

The sensing of vapor odorants is highly demanded in the field of life and medical sciences. Although olfactory receptors (ORs) have potentials to recognize volatile organic compounds, the interaction of ORs, chemical vapors, and peptide components in olfactory mucus has yet to be analyzed to develop OR‐based sensors. A bioinspired electrophysiology technique is shown to record the response of reconstituted insect ORs to chemical vapors. To mimic the interface between ORs and olfactory mucus, OR expressing spheroids were loaded into a hydrogel microchamber array. A negative extracellular field potential shift of spheroids was successfully observed by the stimulation of their vapor cognate ligand. Importantly, the ligand repertoire of the OR of malaria vector mosquito examined by this method differed from that of in vivo studies. Our method is useful to develop protein‐based gas sensing techniques and to examine the binding of ORs and chemical vapors.     

Green synthesis of polymer nanofibers and their composites as flame‐retardant materials for polymer nanocomposites

Polyaniline nanofibers and their composites with carbon nanotubes were developed as an effective flame‐retardant material using a facile green method. Polyaniline nanofibers were used as a smart flame‐retardant for acrylonitrile–butadiene–styrene polymer. The polyaniline nanofibers were dispersed in polymer matrix forming well‐dispersed polymer nanocomposites. Effect of polyaniline nanofiber mass ratio on the polymer nanocomposite properties was studied. Polyaniline nanofiber composites with carbon nanotubes were also dispersed in polymer matrix. The thermal stability and flammability properties of the polymer nanocomposites were investigated. The rate of burning of polymer nanocomposites achieved 82.5% reduction (7.32 mm/min) compared with virgin polymer (42.5 mm/min). The reduction in peak heat release rate and total heat release of the polymer nanocomposites containing nanofibers achieved 74 and 34%, respectively. Interestingly, the average mass loss rate was significantly reduced by 58% and the emission of carbon monoxide and carbon dioxide gases were suppressed by 20 and 47%, respectively. The effect of polyaniline nanofibers composites on the flammability of polymer nanocomposites was also studied. Polyaniline nanofibers and their composites were characterized using Fourier transform infrared spectroscopy and transmission and scanning electron microscopy. The dispersion of polyaniline nanofibers in polymer nanocomposites was characterized using transmission electron microscopy. The different polymer nanocomposites were characterized using thermogravimetric analysis, UL94 flame chamber, and cone calorimeter tests. Copyright © 2016 John Wiley & Sons, Ltd.     

界面聚合法合成手性掺杂剂诱导螺旋形聚苯胺纳米纤维

以手性试剂D-樟脑磺酸(D-CSA)和L-樟脑磺酸(L-CSA)为掺杂剂和构象诱导剂,采用界面聚合法合成了螺旋形聚苯胺纳米纤维。通过FESEM、TEM、FTIR和UV-Vis吸收光谱等测试技术对螺旋形聚苯胺纳米纤维结构进行了表征。结果表明,所得聚苯胺纤维具有螺旋形构象,形貌均一,平均直径约为50nm,长度为300～600nm,具有较高的长径比(6:1～12:1)。在水溶液中,聚苯胺纳米纤维以伸展的螺旋形分子链构象存在,调节溶液的pH值,螺旋形聚苯胺纳米纤维表现出可逆的掺杂和脱掺杂性质。循环伏安(CV)测试表明,螺旋形聚苯胺纳米纤维在0.5mol/LHCl溶液中表现出良好的电化学活性。     

Application of Polyaniline Film as a Sensor for Stimulant Nerve Agents

Abstract

Methyl phosphonic dichloride (MPDC) and dimethyl methyl phosphonate (DMMP) are two important organophosphorus compounds used in the preparation of many toxic organophosphorus compounds such as nerve agents. This paper deals with the application of polyaniline coated on a glass slide surface as a sensor for the detection of some of the stimulant nerve agents such as MPDC and DMMP. The sensing behavior of polyaniline films toward MPDC and DMMP vapors via electrical conductivity changes of the polymer film using the standard four-point probe technique was investigated. The effects of the chemical concentration and the polymer thickness on the conductivity and conductivity stability of the polymer were also studied. The vapors of nerve agent stimulants affect the PANi film by the p-doping mechanism and lead to an increase in the conductivity of the polymer. The response times of the PANi film to MPDC and DMMP vapors are very fast, and the conductivity of the polymer increases with the increase in the concentration of the samples.     

Micro- and nanomechanical sensors for environmental, chemical, and biological detection

Micro- and nanoelectromechanical systems, including cantilevers and other small scale structures, have been studied for sensor applications. Accurate sensing of gaseous or aqueous environments, chemical vapors, and biomolecules have been demonstrated using a variety of these devices that undergo static deflections or shifts in resonant frequency upon analyte binding. In particular, biological detection of viruses, antigens, DNA, and other proteins is of great interest. While the majority of currently used detection schemes are reliant on biomarkers, such as fluorescent labels, time, effort, and chemical activity could be saved by developing an ultrasensitive method of label-free mass detection. Micro- and nanoscale sensors have been effectively applied as label-free detectors. In the following, we review the technologies and recent developments in the field of micro- and nanoelectromechanical sensors with particular emphasis on their application as biological sensors and recent work towards integrating these sensors in microfluidic systems.