M A Gonzalez

Publications (3)0 Total impact

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

  M. Bée, D. Djurado, P. Rannou, B. Dufour, A. Pron, J. Combet, M. A. Gonzalez
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  ABSTRACT: Using the quasielastic neutron scattering technique on the 10−12 s 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.
  Philosophical Magazine. 05/2004; 84(13-16):1547-1554.
• Article: Dynamics of camphor sulphonic acid: a quasielastic neutron scattering study

  M. Bée, D. Djurado, J. Combet, M.A. Gonzalez
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  ABSTRACT: Molecular motions in mono-hydrated racemic camphor sulphonic acid (±)-10-C10H16O4S−–H3O+ which is abbreviated as (CSA–H2O) 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 . 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.
  Chemical Physics. 277(2):211-224.
• Article: Force field based molecular dynamics simulations in highly conducting compounds of poly(aniline). A comparison with quasi-elastic neutron scattering measurements

  M Sniechowski, D Djurado, M. Bée, M A Gonzalez, M R Johnson, P Rannou, B Dufour, W Luzny