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