Linear Polyaniline Research Articles

Interfacial growth of free-standing PANI films: toward high-performance all-polymer supercapacitors.

Along with high power capability and energy density, long cycle life is regarded an essential performance requirement for energy storage devices. The rapid capacitance decline of conducting polymer-based electrodes remains a major technical challenge and precludes their practical applications in supercapacitors. In this work, a polyaniline (PANI) network is synthesized via interfacial Buchwald–Hartwig polymerization for the first time, facilitating the construction of covalently connected PANI networks by ligand-promoted C–N bond formation. Particularly, the interfacial synthesis and subsequent gas release from pre-anchored protecting groups allow bottom-up and efficient access to porous cross-linked PANI (PCL-PANI) films that are free-standing and solvent-resistant. Upon assembling into supercapacitors, the PCL-PANI material enables an unprecedent long-term charge–discharge cycling performance (>18 000 times) without clear capacitance loss for an additive-free pseudocapacitive system. In addition, this synthesis affords electrodes entirely consisting of conducting polymers, yielding highly reversible gravimetric capacitance at 435 F gelectrode−1 in a two-electrode system, and a high gravimetric energy of 12.5 W h kgelectrode−1 while delivering an outstanding power density of 16 000 W kgelectrode−1, which is 10-fold higher than those of conventional linear PANI composite supercapacitors. This synthetic approach represents a novel and versatile strategy to generate additive/binder-free and high-performance conducting thin-films for energy storage.

Influence of Acidity and Oxidant Concentration on the Nanostructures and Electrochemical Performance of Polyaniline during Fast Microwave-Assisted Chemical Polymerization.

Polyaniline (PANI), a typical conducting polymer, has attracted great interest as an electrode material. A series of PANIs were prepared through fast microwave-assisted chemical oxidative polymerization with varying HCl and APS concentrations here. It was found that the microwave synthesized PANIs had ~4 times higher for the yields and 7~10 times higher for the electrical conductivity in comparison to PANI samples prepared using conventional method. PANI nanosheets could easily be fabricated in weakly acidic solution due to their oligomeric structure, which contained flat phenazine rings. By contrast, linear PANI chains produced in highly acidic solutions formed nanofibers. The APS concentration did not significantly affect the molecular structures of PANIs under the conditions here. However, increasing the concentration of APS produced nanofibers with shorter branches, which may be due to secondary nucleation during chain growth resulting from increases in active initiation centers. The electrical conductivity and electrochemical performance of PANIs were both improved with increasing HCl and APS concentrations. Improvements due to increases in HCl concentration may be attributed to additions in conjugation length and enrichment of doping levels, while improvements due to increases in APS concentration could be attributed to the increased crystallinity of PANI, which facilitates ion transport.

Novel capacitance properties of polyaniline with branch-like chains

A novel capacitance performance of polyaniline (PANI) with branch-like chains is investigated firstly at the molecular level in this paper. The PANI with branch-like molecular chains has been synthesized by a simple template-free polymerization method. The morphology and structure of the PANI have been studied by using scanning electron microscopy (SEM) and Fourier transform infra-red spectroscopy (FTIR). The results indicate that the branch-like chains disintegrate into small linear fragments during galvanostatic charge-discharge cyclings, with a concomitant increase of conductivity and decrease of the internal resistance (IR), which is consistent with a stronger π-π molecule conjugation inside the small linear PANI fragments. Therefore, the branch-like PANI exhibits a novel capacitance property with the specific capacitance rises up to 73-fold (from 4 to 294 F g−1) after 107 charge-discharge cycles. This work provides a new pathway to design and prepare high-quality PANI-based supercacitors with novel molecular chain structures.

Preparation and characterization of conducting hydrogels composite made of polyaniline, polyacrylamide and kaolin

In this work, clay minerals such as kaolin particles were embedded within the network of poly(acrylamide) hydrogel (PAAm) using free radical solution polymerization method. Aniline monomer was absorbed in the network of PAAm/Kaolin composite hydrogel and followed using free radical solution polymerization at room temperature. The novel semi-interpenetrating network was comprised of linear polyaniline immersed in PAAm/Kaolin composite. Electrical conductivity of the hydrogels was measured using four-probe technique. The conductivity for the prepared new semi-interpenetrating polymer network (s-IPN) is found to be 1.1×10-4 S.cm-1. The s-IPN hydrogel systems were employed for swelling experiments in water. The drug uptake and release properties of the prepared hydrogels were also studied. Methylene Blue (MB) was selected as a model drug. The incorporation of Kaolin and PAN lead to an increase in electrostatic interaction between charge sites on carboxylate ions and cationic MB molecules. It is to be emphasized that the addition of Kaolin and PAN in the gel structure improved mechanical and electrical properties and the adsorption capability of the new composite hydrogels.

Exploration on the microwave‐assisted synthesis and formation mechanism of polyaniline nanostructures synthesized in different hydrochloric acid concentrations

ABSTRACTUnder microwave‐assisted synthesis, polyaniline (PANI) products with multiple nanostructures were synthesized by the oxidative polymerization of aniline and ammonium peroxodisulfate in the different concentrations of hydrochloric acid solutions. The structural analysis of PANI using FTIR, UV, and XPS indicated that phenazine‐like oligomers were produced in acid‐free and low acidic systems. Moreover, long linear PANI chains were obtained in the presence of highly acidic solutions. The morphology of PANI observed by SEM and TEM showed that nanoscale structures, including stacked sheets, nanotubes, branched nanofibers, and uniform nanofibers, occurred respectively in acid‐free solution, low acidity, medium and high acidity systems, effectively regulating by acidity. The formation mechanism of PANI nanostructures was explored here. The sheets were formed by the oligomers containing flat phenazine rings that can be stacked together with strong π–π interactions. Furthermore, nanotubes were fabricated by the self‐curling of thin sheets consisted of phenazine‐like oligomers with numerous linear units in the chains. The nanofibers are supposed to form by the linear PANI chains and the secondary growth during aniline polymerization caused the branch formation on the nanofibers. All results indicate that acidity, rather than microwave assistance, is the critical factor that determines the polymerization mechanism and the final nanostructure. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3357–3369

Conducting hydrogels based on semi‐interpenetrating networks of polyaniline in poly(acrylamide‐co‐itaconic acid) matrix: synthesis and characterization

In this work, acrylamide/itaconic acid copolymeric hydrogels are prepared by free radical polymerization initiated by redox initiators of potassium persulfate and N,N,N′,N′‐tetramethyl ethylene diamine; N,N′methylene bisacrylamide was employed as a crosslinking agent. Aniline monomer was absorbed in the network of poly(acrylamide‐co‐itaconic acid) P(AAm‐co‐IA) hydrogel and followed by gamma radiation induced polymerization at room temperature. The novel semi‐interpenetrating network was comprised of linear polyaniline immersed in P(AAm‐co‐IA) matrix. Electrical conductivity of the hydrogels was measured using four‐probe technique. The conductivities for the prepared hydrogels are found to increase from 5.5 × 10−7 S cm−1 for P(AAm‐co‐IA) alone to 4.4 × 10−3 S cm−1 for semi‐interpenetrating polymer network P(AAm‐co‐IA)/polyaniline. Thus, a new composite hydrogel with good conductive properties also displaying enhanced mechanical strength and pH sensitivity was prepared. Copyright © 2017 John Wiley & Sons, Ltd.

Two-dimensional polyaniline (C3N) from carbonized organic single crystals in solid state

The formation of 2D polyaniline (PANI) has attracted considerable interest due to its expected electronic and optoelectronic properties. Although PANI was discovered over 150 y ago, obtaining an atomically well-defined 2D PANI framework has been a longstanding challenge. Here, we describe the synthesis of 2D PANI via the direct pyrolysis of hexaaminobenzene trihydrochloride single crystals in solid state. The 2D PANI consists of three phenyl rings sharing six nitrogen atoms, and its structural unit has the empirical formula of C3N. The topological and electronic structures of the 2D PANI were revealed by scanning tunneling microscopy and scanning tunneling spectroscopy combined with a first-principle density functional theory calculation. The electronic properties of pristine 2D PANI films (undoped) showed ambipolar behaviors with a Dirac point of -37 V and an average conductivity of 0.72 S/cm. After doping with hydrochloric acid, the conductivity jumped to 1.41 × 10(3) S/cm, which is the highest value for doped PANI reported to date. Although the structure of 2D PANI is analogous to graphene, it contains uniformly distributed nitrogen atoms for multifunctionality; hence, we anticipate that 2D PANI has strong potential, from wet chemistry to device applications, beyond linear PANI and other 2D materials.

Size-Controlled Fabrication of Polyaniline Microfibers Based on 3D Hydrodynamic Focusing Approach.

Owing to the relatively high conductivity and unique redox behavior, polyaniline (PANI) has been one of the most technologically promising conducting polymers. Although various methodologies have been developed, fabrication of PANI microfibers has been a challenging task owing to the poor solubility in most organic solvents. By taking advantage of a microfluidic technology and organic soluble acid labile t-Boc-protected PANI (t-Boc-PANI) as the conducting polymer precursor, fabrication of PANI microfibers in a size-controlled manner is possible. Introduction of a THF solution containing t-Boc-PANI, and dodecylbenzenesulfonic acid (DBSA) as a core flow, and water as a sheath flow into a microfluidic channel with a 3D hydrodynamic focusing effect results in crystallization of the polymer fiber. By changing the flow rate, linear PANI microfibers that range from 16.2 to 39.4 μm in diameter are readily obtained.

Improvements to the photocatalytic efficiency of polyaniline modified TiO2 nanoparticles

Polyaniline/TiO2 nanocomposite powders were successfully synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in water without the addition of acid, in the presence of colloidal TiO2 nanoparticles (d∼4.5nm). The morphological, structural, and optical properties of the synthesized nanocomposites prepared at initial TiO2/aniline mole ratios of 50, 100, and 150 were studied using transmission electron microscopy, X-ray powder diffraction, Raman and UV–vis spectroscopies. The presence of emeraldine salt and the base form of linear polyaniline (PANI) chains as well as the presence of phenazine units, branched PANI chains, oligomeric structures and short PANI chains in PANI/TiO2 nanocomposites was confirmed by Raman spectroscopy. The anatase crystal structure of TiO2 nanoparticles in all the nanocomposites was confirmed by X-ray powder diffraction measurements and by Raman spectroscopy. The photocatalytic activities of PANI/TiO2 nanocomposites were evaluated using the photocatalytic degradation of Rhodamine B and Methylene blue as model compounds and compared with the activity of bare colloidal TiO2 nanoparticles. Enhanced degradation efficiencies in the dyes used were observed. A possible explanation for the PANI/TiO2 photocatalytic activities was suggested, taking into account the influence of the molecular structures of the used dyes and PANI in PANI/TiO2 nanocomposites.

Improved electrocatalytic behavior of ascorbic acid by crosslinked polyaniline with enhanced conductivity

A newly designed crosslinked polyaniline (CPAN) was developed and preliminarily used to fabricate a sensor for determination of ascorbic acid (AA). The nanostructured copolymer was confirmed through surface morphology studies (SEM). The amperometric response of electrodes toward AA based on crosslinked polyaniline (CPAN) is far more than that of linear polyaniline (LPAN), which exhibits improved electrocatalytic oxidation of AA. The linear range of the promising sensor is from 5.0 × 10−6 to 1.13 × 10−2 M with a lower detection limit of 1.67 × 10−6 M (S/N = 3) as well as good selectivity, stability and reproducibility.

Conformations of Polyaniline Molecules Adsorbed on Au(111) Probed by in Situ STM and ex Situ XPS and NEXAFS

In situ scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure (NEXAFS) have been used to examine the conformation of a monolayer of polyaniline (PAN) molecules produced on a Au(111) single-crystal electrode by anodization at 1.0 V [vs reversible hydrogen electrode (RHE)] in 0.10 M H(2)SO(4) containing 0.030 M aniline. The as-produced PAN molecules took on a well-defined linear conformation stretching for 500 A or more, as shown by in situ and ex situ STM. The XPS and NEXAFS results indicated that the linear PAN seen at 1.0 V assumed the form of an emeraldine salt made of PAN chains and (bi)sulfate anions. Shifting the potential from 1.0 to 0.7 V altered the shape of the PAN molecules from straight to crooked, which was ascribed to restructuring of the Au(111) electrified interface on the basis of voltammetric and XPS results. In situ STM showed that further decreasing the potential to 0.5 V transformed the crooked PAN threads into a mostly linear form again, with preferential alignment and formation of some locally ordered structures. PAN molecules could be reduced from emeraldine to leucoemeraldine as the potential was decreased to 0.2 V or less. In situ STM showed that the fully reduced PAN molecules were straight but mysteriously shortened to approximately 50 A in length. The conformation of PAN did not recuperate when the potential was shifted positively to 1.0 V.

Controlled Synthesis of Linear Polyaniline Tubes and Dendritic Polyaniline Fibers with Stearic Acid

One dimensional linear polyaniline (PANI) tubes (with cavity about 2-3 nm) and three dimensional dendritic PANI fibers (with different length) have been synthesized by chemical oxidation polymerization of aniline doped with stearic acid at room temperature. The shape of the as-prepared PANI could be easily tuned from line to dendriform and to network simply by controlling the concentrations of aniline and stearic acid. Scanning electron microscopy and transmission electron microscopy were applied to investigate the various kinds of morphologies. UV-vis absorption spectra and Raman spectra suggested these as-prepared PANI were in conductive emeraldine state and the various kinds of structures could affect their property.

Direct Visualization of an Aniline Admolecule and Its Electropolymerization on Au(111) with in Situ Scanning Tunneling Microscope

In situ scanning tunneling microscopy has been used to examine the structure of the aniline adlayer and the conformation of polyaniline molecules produced electrochemically on a Au(111) electrode in 0.1 M sulfuric acid containing 30 mM aniline. As evidenced by the high-resolution STM imaging, a simple method of potential step triggered electropolymerization of aniline molecules. This reaction propagated preferentially in the 〈121〉 directions to produce mostly linear polyaniline molecules. Molecular resolution STM yielded the internal structure of polyaniline molecules.

Synthesis of polyaniline derivatives via biocatalysis

Three structurally different aniline monomers, which can not be polymerized by chemical methods, have been polymerized with horseradish peroxidase. Enzymatic synthesis of linear polyaniline requires template molecules to minimize branching in the polyaniline backbone. Monomers having methoxy and methyl blocking groups at the ortho or meta position could induce the conducting form of para-linked polyaniline without the use of an anionic template, such as SPS. A new mild peroxide, peroxyacetic acid, was identified and used to oxidize horseradish peroxidase in water.

High Dielectric Hyperbranched Polyaniline Materials

New organic materials for the purpose of high speed capacitor applications are discussed. The effect of the microcrystalline size dependence of different polyaniline polymeric systems on the dielectric constant is investigated. Two different methods are described for the preparation of the polyaniline dielectric materials. By sonication polymerization, the prepared polyaniline with a suggested hyperbranched structure showed much larger microcrystalline domains in comparison to the conventional linear polyaniline. Investigations of the dielectric constant and capacitance at a relatively high frequency (>100 kHz) suggested that the system with the larger microcrystalline domains (hyperbranched) gives rise to a larger dielectric constant. The mechanism of the increased dielectric response at higher frequencies is investigated by EPR spectroscopy, and these results suggest that delocalized polarons may provide a way to enhance the dielectric response at high frequency.

ENZYMATICALLY SYNTHESIZED POLYANILINE IN THE PRESENCE OF A TEMPLATE POLY(VINYLPHOSPHONIC ACID): A SOLID STATE NMR STUDY

Template guided enzymatic synthesis of conducting polyaniline (PANI) is a one-step reaction and more importantly, it is an environmentally friendly process. Understanding of the reaction and coupling mechanism at the molecular level is of paramount significance to improve its processability and conductivity. Solid-state NMR techniques are useful to investigate molecular structures of enzymatically synthesized polyaniline (PANI). The PANI sample in three different forms i.e., (a) as-synthesized, self-doped conducting form; (b) dedoped, base form and; (c) redoped, conducting form, are investigated by solid-state 13C and 15N CP/MAS NMR techniques. Solid-state NMR data analysis shows that the structural features of enzymatically synthesized PANI are similar to that of chemically synthesized PANI. The solid-state 13C CP/MAS NMR spectrum of the base form of PANI confirmed that benzenoid-quinoid repeating units are present in the backbone of the PANI polymer chain. The poly(vinylphosphonic acid) (PVP) template provides charge compensation during the chain growth of linear polyaniline. After the completion of template-guided synthesis of PANI, it is now possible that the PVP template can be completely removed from the complex by dedoping with aqueous NH4OH. The detached PANI from the PANI-PVP complex can then be redoped to conducting form without the presence of the template. The conductivity of the PANI and PANI-PVP complex are of the same order of magnitude. The solid-state 15N CP/MAS NMR chemical shifts are sensitive to charge distribution on the nitrogens in the backbone. The solid-state 15N CP/MAS NMR spectrum of the base form of the enzymatically derived PANI sample showed the clear signature for benzenoid-quinoid repeating units in the polymer backbone. †Deceased.

Degradation of copolymers of aniline and metanilic acid

The degradation of aniline-metanilic acid copolymer (PMA) by potentiostatic anodic polarisation was compared with the degradation of polyaniline (PAn) in order to understand the function of the pendant groups in polymer degradation. The degradation of PMA was believed to follow the same reaction pathway as the unmodified PAn, namely by attack of water molecules on oxidised polymer in the bipolaronic state. The presence of sulphonate curtailed the bipolaron production and increased the steric hindrance in degradative hydrolysis, so that the degradation of polymer was inhibited as a result. It is concluded that the pendant groups on the PAn backbone only moderated the electroactivity of the linear PAn chains in degree but not in kind.

Electrochemical synthesis of linear polyaniline in aqueous solutions

An attempt was undertaken to prepare polyaniline with a fine linear structure in aqueous media. Comparable electrochemical polymerization was carried out in solutions of the following acids: hydrochloric, sulfuric, perchloric and tetrafluoroboric. Spectroelectrochemical measurements have revealed the presence of an intermediate product (nitrenium cation) in the initial stage of aniline polymerization carried out in these media. The polymerization starts after an induction period which depends on the final potential for cyclic voltammetry and the nature of the medium. The number of spins as a function of the applied potential was a criterion to determine the linearity of the polymer chain. In polymers with linear structure (without ortho-bindings and cross-linking effects), polarons formed during the doping process in the presence of double-charged anions undergo a recombination process to form bipolarons. As a result no EPR signal is observed between the two redox systems of polyaniline. This kind of polymer can be formed only by voltammetric polymerization in a 5 M solution of tetrafluoroboric acid. The other media mentioned lead to formation of more or less cross-linked chains. The measurements performed suggest that the mechanism of aniline polymerization in aqueous media is analogous to that in non-aqueous solutions for a eutectic mixture of NH 4F; 2.35 HF.

Band structure and limiting behavior of linear polyanilines

AbstractThe band structure of an infinite linear polyaniline is investigated by using the HCO approximation. The degree of modelling of the limiting structure for the series by the linear oligomers so far synthesized is investigated. The upper bound of the wave‐length of the long‐wave ultraviolet absorption band for the limit is found, and the possibility of estimation of the conduction properties of its complex with iodine is indicated. The problem of replacement of the NH group in the chains by a more general group X is dealt with, and the dependence of the energy gap between the highest occupied and the lowest unoccupied band on the parameters of this group is determined.

Polyaniline compounds. II. The linear oligoaniline derivatives tri‐, tetra‐, and hexaanilinobenzene and their conductive complexes

AbstractOligomeric oligoaniline derivatives of diethyl Δ1,4‐dihydroterephthalate (V–VIb–d) of diethyl terephthalate (VIIb–d) and linear oligoanilines (Ib–d) were synthesized. Ultraviolet spectra and polarographic half‐wave potentials corresponding to the first degree of oxidation of linear oligoanilines of type (I) were studied, their iodine complexes prepared, and their electric and magnetic properties studied. Increase of chain length of the base causes increase of λmax of ultraviolet bands, decrease of ionization potential, and increase of electric conductivity of iodine complexes in solid state. The properties of the five‐membered oligomer (Ic) differ only slightly from analogous properties of the seven‐membered oligomer (Id); the same holds in the case of their iodine complexes. Such substances may be regarded as in some respects models of a linear polyaniline polymer or its complexes.