D. Djurado

Annealing effect in polyaniline-CSA upon moderate heating*

Abstract Heating of polyaniline-CSA films in ambient air usually results in accelerated ageing, as evidenced by a progressive disappearance of the crystallinity and of the metallic features. However, after moderate heating (typically for 30 min at 135 °C), an annealing effect is observed: X ray diffraction shows an increase of the crystallinity, while low temperature dc conductivity, NIR reflectance and magnetoresistance data reveal that the transport properties are improved, with a more metallic behaviour.

Dynamics of camphor sulfonic acid in polyaniline (PANI-CSA): a quasielastic neutron scattering study

Abstract PolyAniline (PANI) doped by camphor sulphonic acid (CSA) exhibits an electronic conductivity of several hundreds of S/cm. All the authors agree to invoke in various extents the role of disorder in the evolution of the transport properties as a function of temperature. The IRIS spectrometer at the Rutherford–Appleton Laboratory was used to remove uncertainties of previous IN6–IN16 experiments at Institut Laue-Langevin. The rigidity of the PANI chains was confirmed, in both a conducting and a partially doped sample. All the observable quasielastic scattering occurs from the CSA dynamics. However, this contribution is too weak in the case of the partially doped specimen to conclude about the coupling of the counter-ion disorder with the electronic transport properties.

Ageing in PANI-HCl: a grain size story

X-ray diffraction and conductivity measurements carried out on series of aged HCl-doped-polyaniline samples have shown that pristine material is made of conducting grains separated by insulating barriers and that ageing results in a nibbling of the grains.

Dynamics of camphor sulphonic acid: a quasielastic neutron scattering study

Abstract Molecular motions in mono-hydrated racemic camphor sulphonic acid (±)-10-C 10 H 16 O 4 S − –H 3 O + which is abbreviated as (CSA–H 2 O) were investigated using incoherent neutron scattering techniques. Analysis of the intensity of the purely elastic scattering over a wide temperature range (4–340 K) carried out with a high-resolution backscattering spectrometer revealed the onset of molecular motions at ca. 100 K which could be observed on the 10 −10 s time-scale up to T =180 K. These motions were identified as 120° jumps of the methyl groups. Quasielastic measurements using both the backscattering and the time-of-flight techniques enabled to study this movement from 150 to 340 K. The corresponding characteristic time was found to follow an Arrhenius law with an activation energy ΔH=12.0±0.2 kJ mol −1 . All the methyl groups appear as dynamically equivalent. That result is at contrast with earlier studies on conducting polymers where CSA was introduced as a counter-ion and for which the intermolecular effects were found to strongly influence the dynamics. Inspection of the low frequency part of the vibrational spectrum evidences deformations of the C–C–S angle and rotational oscillations of the hydration molecules.

Dynamics of counter-ions in a conducting rigid polymer matrix: the relation with electrical properties

Using the quasielastic neutron scattering technique on the 10−12u2009s time scale, the dynamics of highly conducting free-standing films of doped polyaniline have been studied in detail. The latter are protonated with sulphonated organic acids made of flexible molecules which also play the role of plasticizer of the system. While polymer chains appeared immobile, the study of the dynamics of these counter-ions reveals a glass transition temperature which corresponds to the change in the electronic conductivity of the film. Competing interactions in between the counter-ions and between polymer chains and counter-ions limit the available space for alkyl chains to move around. A description of the dynamics is proposed on the basis of a model where protons undergo a local diffusion inside individual spheres whose radii depend explicitly on their position on the molecule. When the temperature is decreased, only protons attached to the aliphatic tails explore a significant space while the others are progressively frozen. Refinement of the neutron data permit one to access the radii of the sphere and the diffusion constant as functions of temperature.

Structural and dynamical aspects of solid sulpholan in the temperature range 160–300 K II. — Incoherent quasielastic neutron scattering study

Abstract The dynamics of the sulpholan molecules in their high (I and II) and low-temperature (III and IV) phases is studied using the incoherent quasielastic neutron scattering technique (IQNS). The experiments were carried out on polycrystalline samples using the time-of-flight time-focussing neutron spectrometer IN6 at the Institut Laue-Langevin in Grenoble, with a temperature ranging from 160 to 298 K. The results are compared with the conclusions of previous NMR studies and examined in terms of several models. It is shown that on the 10−11 1 s time-scale accessible to the experiment, the molecular motions in the two high-temperature phases essentially consist of a uniaxial rotation about the twofold symmetry axis. In the low-temperature phase IV no quasielastic broadening was observed. Conversely, in the other low-temperature phase III, restricted angular oscillations of molecules about their equilibrium positions are responsible for a distinct quasielastic broadening of the spectra. Another paper (paper I) deals with the structural aspects of the phase transitions.

Structural and dynamical aspects of solid sulpholan in the temperature range 160-300 K. I. - X-ray powder diffraction study

Abstract The X-ray diffraction study of polycrystalline sulpholan has been carried out in the T = 200–300 K temperature range, in order to compare with previous NMR results about the existence of two high-temperature phases I and II and of two low-temperature phases III and IV. The transition I–II could be evidenced by the temperature evolution of the relative intensities of the observed diffraction lines. The crystalline phases III and IV were identified as monoclinic, with a = 12.29(1) A , b = 10.23(1) A , c = 9.27(1) A , β = 97.49(5)°, space group P21/c, Z = 8 at T = 230 K. The transition III–IV was observed only as a discontinuity in the temperature evolution of lattice parameters.

Preliminary SANS studies of PANI-CSA films

Abstract Small Angle Neutron Scattering (SANS) studies were carried out on (deuterated-PANI)-CSA films with different doping levels. Scattering curves show a bump around Q≈5×10 −2 A −1 which follows a sharp low angle Q −4 decay. These features suggest that the films are heterogeneous and exhibit 30–100A domains related to the doping procedure.