Differential anomalous scattering studies of amorphous hbr-doped polyaniline (original) (raw)

Synthetic Metals

https://doi.org/10.1016/S0379-6779(96)04119-7

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Abstract

The local molecular structure of amorphous HBr-doped polyaniline has been probed using conventional and differential anomalous scattering in conjunction with a single chain modelling analysis. Initial results identify a probable Br-ion site along the polymer chain approximately 3.3A above (or below) the average polyaniline molecular plane and situated, on average, 3.7A from the closest neighboring amine nitrogen.

EPR and charge-transport studies of polyaniline

Physical Review B, 1997

The study of dc and microwave ͑140 GHz͒ electrical conductivities using multifrequency electron-spin resonance in undoped and HCl-doped polyaniline is reported. The accidental quasi-three-dimensional ͑3D͒ charge hopping between the pinned and mobile small polarons dominates the bulk conductivity of the emeraldine base form of polyaniline. The increase in mobility and the number of excitations upon light doping of the polymer leads to the isoenergetic interpolaron charge hopping between the polaron and bipolaron states. 1D variable-range hopping of a charge between conducting islands, which correlates with a superslow torsional dynamics of the polymer chains, dominates bulk conductivity of heavily doped polyaniline at low temperatures. Intrinsic microconductivity is determined by the interaction of the charge with the lattice phonons at high temperatures. Following Epstein and MacDiarmid we propose that emeraldine salt of polyaniline represents a 1D disordered conducting compound consisting of metal-like islands of well coupled chains with 3D delocalized charge carriers. ͓S0163-1829͑97͒00524-9͔

Polyaniline Emeraldine Salt in the Amorphous Solid State: Polaron versus Bipolaron

The Journal of Physical Chemistry B, 2014

The polaronic and bipolaronic forms of polyaniline emeraldine salt (PAni-ES) in the amorphous solid state have been simulated using classical molecular dynamics (MD) and hybrid quantum mechanical/molecular mechanical-molecular dynamics (QM/MM-MD) approaches. It should be remarked that the electronic state of PAni-ES has been theoretically investigated in the gas phase, solution phase, and crystalline state, but this is the first study in the amorphous solid state, which is the most typical for this conducting polymer. MD simulations were carried out using force-field parametrizations explicitly developed for polaronic and bipolaronic models. QM/MM-MD calculations were performed using a quantum mechanical zone defined by four repeat units. In addition of the structural and electronic characteristics of the two forms of PAni-ES, MD and QM/MM-MD simulations indicate that the bipolaronic is the most stable state of amorphous PAni-ES. Complementary studies have been carried out using different experimental techniques. Although the morphology and topography of doped and undoped PAni are very similar, comparison of their UV−vis spectra supports the preference toward the bipolaronic form of PAni-ES.

Investigation of fundamental molecular parameters of polyaniline films

Journal of Polymer Science Part B: …, 1999

The effects of fabrication process and solvent on the structure of polyaniline (PANI) emeraldine base films and their intrinsic properties are examined. Freestanding films of PANI base fabricated from N,NЈ-dimethyl propylene urea (DMPU) and N-methyl-2-pyrrolidone (NMP) solutions, by casting and spin-coating procedures and subsequently drawn to different draw ratios, are examined. X-ray diffraction studies show that the PANI films processed from DMPU solution have a noncrystalline structure, whereas the PANI films cast from NMP solution are partially crystalline. The crystal structure is in conformity with the orthorhombic unit cell (EB-II) reported earlier. However, the c parameter of the unit cell was found to be slightly lower than the literature values. A near-infrared waveguide technique was used to determine the three-dimensional refractive indices of the processed and drawn PANI films. The anisotropies developed by the different fabrication and deformation procedures were compared and found to differ. Coupling birefringence and quantitative infrared dichroism measurements yields the intrinsic birefringence and transition moment angles of the infrared absorption bands of PANI.

Spectroscopic Study of Electronically - Doped Polyanilines

"Polyanilines namely emeraldine, nigraniline and pernigraniline were prepared by chemical method and were electronically-doped with organic acceptors such as, TCNE, TCNQ, DDQ, Chloranil and KI-I2. The FTIR spectra of 20% and 50% doped polyanilines were obtained and analyzed using small polaron model which connected electrical conductivity with IR absorption. Emeraldine prepared by standard method and pure emeraldine as readily obtained wee used. The absorption profiles as experimentally obtained and as calculated using small-polaron model were compared. This comparison leads to frequency -dependence of the real part of refractive index which shows dispersion shape as desired. Hitesh Parmar | R.K.Shah | Vishal.R.Jain""Spectroscopic Study of Electronically - Doped Polyanilines"" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-1 | Issue-2 , February 2017, URL: http://www.ijtsrd.com/papers/ijtsrd64.pdf Article URL: http://www.ijtsrd.com/other-scientific-research-area/physics/64/spectroscopic-study-of-electronically---doped-polyanilines/hitesh-parmar"

Charge transport and structural morphology of HCl-doped polyaniline

Journal of Materials Science, 2000

The d.c. and a.c. (100 Hz-1 MHz) conductivities of HCl-doped polyaniline have been measured in the temperature range 77-300 K. At 77 K, the a.c. conductivity data, ( ), can be described by the relation ( )"A s, where the parameter s lies close to unity and decreases with increase in the doping level. The ratio of measured a.c. to d.c. conductivity shows dispersion at 77 K, which decreases with increase in the doping level. This decrease is found to be sharp around pH&3.0. In the temperature range 77-150 K, the observed d.c. conductivity data can be described by Mott's three dimensional variable range hopping (VRH) model. Scanning electron microscopy studies reveal a sharp change in structural morphology of HCl-doped polyaniline at a pH&3.0. A strikingly remarkable structural morphology has been observed in the form of a channel at this pH value. This change is accompanied by a rapid increase in d.c. conductivity, dielectric constant, along with sharp changes in structural morphology, which indicates the existence of a doping-induced structural conductivity correlation in this system.

Solvent effect on the electronic absorption spectra of polyaniline

Synthetic Metals, 1989

The electronic absorption peak at around 2 eV of polyaniline (in the emeraldine base form) solution is found to be highly sensitive to the dielectric constant of the solvent, showing a bathochromic shift. An increase in electron density on the imine nitrogen of the polymer, on '2 eV' excitation, has been concluded.

A 13C CP-MAS NMR investigation of polyaniline

Journal of Polymer Science: Polymer Letters Edition, 1985

Polyaniline, synthesized by the chemical or electrochemical oxidation of aniline, (C6H5)NHz, has a long history (see, e.g., ref. 1) in a variety of uncharacterized forms such as "aniline black," "emeraldine," "nigraniline," etc. Recently considerable attention has been focused on polyaniline with respect to its potential as a conducting polymer.1-8 If aniline is oxidized electrochemically or by a chemical oxidant such as sodium peroxydisulfate in an acidic medium, a conducting form of polyaniline is obtained.'-395-6 By alkali/acid treatments and oxidatiodreduction it is possible to reversibly convert the material into several forms with different properties. The following scheme has been proposed for these procease&*:

Direct analysis of lamellar structure in polyaniline protonated with plasticizing dopants

Synthetic Metals, 2004

Structural disorder in polyaniline (PANI) protonated with plasticizing dopants, namely diesters of 4-sulfophthalic acid containing linear alkyl or alkoxy subsituents (so-called plastdopants), has been investigated by both wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) measurements. Based on the experimental data we propose, in all cases studied, a lamellar-like structure in which a bilayer of plastdopant anions alternates with a layer of PANI chains. In order to account for the shape of the diffraction profiles obtained experimentally, we use a model in which statistical fluctuations of the electronic density are introduced along the stacking direction of the lamellae. The model enables us to calculate several structural parameters and in particular the average number of stacked layers constituting a crystallite. We also demonstrate that the disorder is principally governed by the structural features of the plastdopant bilayer. In particular strong interdigitation of long alkyl (alkoxy) tails of the plastdopant anions favors the formation of more ordered supramolecular domains.

Optical studies of polyaniline nanostructures

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007

An investigative infrared spectroscopic study is undertaken of nano polyaniline (PANI) samples differing in size and morphology in order to explore the sensitivity of spectral behavior on these factors. IR spectroscopy is used for studying the changes in the interaction between polymeric molecules as parts of nanodimensional structures. A time dependent interfacial oxidative polymerization of aniline monomer is conducted in order to obtain the desired nano PANI samples in doped form. The morphological changes in samples so obtained are characterized using scanning electron microscopy (SEM). The SEM images of samples obtained using the time dependent interfacial polymerization show preferential formation of 1D nano/micro structures with dimensions varying with reaction time intervals, which is also confirmed by transmission electron microscopy (TEM). X-ray diffraction study is undertaken to assess the crystalline nature of the samples. The IR spectra and the X-ray diffraction pattern of samples reflect these morphological variations. A comparative study of bulk polyaniline sample obtained using standard procedures is also undertaken. Significant variations in the conductivity of different polyaniline samples are also observed. The 10 min sample shows significantly enhanced conductivity as compared to the 20 min and 24 h. PANI samples having well defined nanofibers.

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References (16)

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Determination of the local molecular structure in amorphous polyaniline

Physical review. B, Condensed matter, 1996

The short-range order within amorphous polyaniline ͑a-PANI͒ has been studied through use of a pairdistribution-function analysis of x-ray scattering data in combination with quantitative refinements of model structure functions. Both the emeraldine base and salt ͑ES͒ forms of a-PANI are less planar than their crystalline counterparts. Direct evidence for appreciable interchain hydrogen bonding is seen. A probable position of the dopant ions in hydrohalogenic-acid-doped ES has also been ascertained. The intrachain structure and the ion location are such that the effective -conjugation length is lowered and the chain-to-chain packing is frustrated. These characteristics hinder charge transport through the polymer matrix and prevent evolution towards a metallic state.

Functionalization-induced changes in the structural and physical properties of amorphous polyaniline: a first-principles and molecular dynamics study

Scientific reports, 2016

In this paper, we present a first-principles and molecular dynamics study to delineate the functionalization-induced changes in the local structure and the physical properties of amorphous polyaniline. The results of radial distribution function (RDF) demonstrate that introducing -SO3(-)Na(+) groups at phenyl rings leads to the structural changes in both the intrachain and interchain ordering of polyaniline at shorter distances (≤5 Å). An unique RDF feature in 1.8-2.1 Å regions is usually observed in both the interchain and intrachain RDF profiles of the -SO3(-)Na(+) substituted polymer (i.e. Na-SPANI). Comparative studies of the atom-atom pairs, bond structures, torsion angles and three-dimensional structures show that EB-PANI has much better intrachain ordering than that of Na-SPANI. In addition, investigation of the band gap, density of states (DOS), and absorption spectra indicates that the derivatization at ring do not substantially alter the inherent electronic properties but ...

On the molecular properties of polyaniline: A comprehensive theoretical study

Polymer, 2008

A comprehensive study about the molecular and electronic properties of the different forms of polyaniline has been developed using quantum mechanical calculations. Initially the performance of different ab initio and DFT quantum mechanical methods has been evaluated by comparing the results provided for small model compounds containing two repeating units. After this, calculations on the emeraldine base, leucoemeraldine base, pernigraniline base and emeraldine salt (monocationic and dicationic) forms of oligoanilines with n repeating units, where n ranged from 5 to 13, have been performed using the BH&H/6-31G(d) method, which was found to be a very suitable theoretical procedure. Interestingly, calculations indicate that the distribution in blocks of the repeating units containing amine and imine nitrogen is largely preferred for the emeraldine base form. On the other hand, the molecular structure and band gap of the emeraldine base, leucoemeraldine base and pernigraniline base forms have been rationalized according to their differences in the conjugation of the C 6 H 4 rings. Calculations on cationic oligoanilines indicate that, when the emeraldine salt form presents a doublet electronic state, the positive charge and the spin density are located in the middle of the chain extending through five consecutive repeating units.

Polyaniline–water interactions: A theoretical investigation with the polarisable continuum model

Synthetic Metals, 2010

The simulations of emeraldine hydrochloride tetramers were performed for the first time in implicit water solvent using the polarisable continuum model (PCM) with the density functional theory (DFT) method. This approach should be more appropriate for the study of the conducting form of polyaniline as all known processes of synthesis and further transformations take place in polar medium. Our results confirm this hypothesis and clearly indicate that the geometry and electronic structure of the emeraldine salt depend on the dielectric properties of the medium. In polar environment the protons are bound tighter to the chains compared to vacuum and this leads to stronger impact of the dopant on the structural parameters of PANI. As a consequence, the density distribution in the emeraldine hydrochloride obtained by PCM is more realistic compared to vacuum estimates. The stability in polar medium of two possible salt configurations with respect to counterions position is assessed. Each configuration is simulated in singlet and triplet state (bipolaron and polaron). The results show that at the tetramer level the bipolaron form is always preferred in accordance to available experimental results.

Conductivity and structure of DBSA-protonated polyaniline

Solid State Communications, 1994

The discovery of a processable and conducting polyaniliie complexes includii functionalized sulphonic acids is an important discovery in the field of conjugated polymers. The conductivity, electronic and crystalline structure properties of polyaniline protonated with dodecylbenzenesulphonic acid are proportional to the molar concentration of the acid. The protonation leads to a layer structure evident in X-ray diffraction patterns and the crystallinity follows a growth as a function of the acid concentration similar to the conductivity increase. The electronic structure measured by UV-VIS spectroscopy shows an increase in the polaron concentration up to an acid concentration of 0.35 after which a broadening of the peak indicates the formation of a polaron band.

An overall view of the structure of an heterogeneous medium: the conducting polyaniline

Synthetic Metals, 1999

The structures of free standing films of polyaniline (PAni) protonated by camphorsulfonic acid (CSA) are characterized by different scattering techniques: WAXD, IINS, SANS and SEM. In this way, we could investigate the complex structural arrangement of these films at different length scales. It is shown that a unique description of structure and microstructure of such films is not realistic since they tightly depend on the conditions of preparation and processing. This contribution gives an account of the most important structural data obtained on films prepared in Grenoble (France) during the four last years.

Calculations of Band Gaps in Polyaniline from Theoretical Studies of Oligomers

The Journal of Physical Chemistry B, 2000

Geometries and band gaps of polyaniline oligomers up to decamer have been systematically calculated and analyzed using various computational techniques such as molecular mechanics, semiempirical, and ab initio methods. On the basis of fully optimized geometries of neutral and charged forms of polyaniline oligomers, excitation energies are calculated at the semiempirical ZINDO (INDO/S) level and extrapolated to the band gap value of the infinite chain. Band gaps are also approximated by extrapolating the HOMO/LUMO difference calculated at the density functional level (B3LYP/6-31G*). The ZINDO//AM1 band gaps in the reduced and oxidized form of polyaniline (4.3 and 2.7 eV) are in good agreement with experimental values (3.8 (2 and 1.8 (3 eV, respectively). The doped form of polyaniline (two positive charges per four aniline units) has been computed with a spin-unrestricted method (UAM1) and the band gap approximated from an extrapolation of the tetramer and octamer. The calculated band gap of 1.3 eV (UZINDO//UAM1) is in good agreement with experiment (1.5 eV). The influence of ring torsional angle and interchain interaction on the band gap of the polyaniline system are also discussed.

Doping-Induced Layered Structure in N-Alkylated Polyanilines

Polymer Journal, 1996

The influence of various organic dopants on the structure of N-alkylated polyanilines substituted with alkyl side chains of different lengths and at different degrees of alkylation has been studied by FT-IR, UV-Visible spectroscopies, and X-ray diffraction. The results show that the protonation as seen for polyaniline emeraldine base can be achieved successfully through the doping method in our experiments. The conductivities of the doped polymers decrease with increasing the length of side chains and the degree of alkylation. The polyanilines doped with methanesulfonic acid (MSA), toluenesulfonic acid (TSA), and dodecylbenzenesulfonic acid (DBSA) induce a cooperative effect with the alkyl side chains on the formation of layer order. Small dopants distort the layered structure and prevent the crystallization of the side chains. The interaction of the alkyl side chains and alkyl group in DBSA assist in the development of the layered structure. KEY WORDS Polyaniline I Doping I Layer Formation I

Charge transport in the “emeraldine” form of polyaniline

Synthetic Metals, 1989

The conductivity and the dielectric constant of the "emeraldine" form of polyanillne is studied in a wide range of frequency (de, 101-105 Hz, 6.5x109 Hz), temperature (20K-340K) and protonation level (x-[C1]/[N] :0.0-0.5). Two distinct behaviors are observed: Firstly, for low protonation (x < 0.13), hopping of charges between polarons and bipolarons leads to dipolar relaxation (opt(T)). Oscillation of polarons around pinning centers is suggested to be responsible for the high frequency dielectric constant of low protonated samples. Secondly, for intermediate to highly protonated samples (x > 0.22), the presence of "metallic islands" is apparent. Oscillation of charge carriers within the coherence length contributes to Et,~(T=0). The intrinsic conductivity within the islands is estimated to be of the order of 250 S/era. The T-dependence of the dielectric constant indicates an increase of the coherence length with increasing temperature. The role of localization and the nature of "textured metallic islands" are discussed.

Raman dispersion in polyaniline base forms

2007

Raman spectra of polyaniline in its emeraldine (EB) and pernigraniline (PB) base forms were obtained using several excitation laser lines and Raman dispersion of the bands was measured. Only the νC N band value depends on excitation wavelength for both polymeric forms. These changes of vibrational frequencies with excitation wavelength were analyzed using amplitude mode model (AMM). n (ω R n /ω 0 n) 2 versus excitation photon energies plot was linear in the electronic absorption transition region, for EB at ca. 640 nm and for PB at ca. 620 nm. The dispersion values, D (slope of n (ω R n /ω 0 n) 2 versus excitation photon energies plot) were 0.058 and 0.038 eV −1 for EB and PB, respectively, which indicate that EB has the first excited state of even parity presenting lower energy when comparing to that of PB.