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Transport Properties in Ionic Media

Published online by Cambridge University Press:  21 March 2011

A.-L. Rollet
Affiliation:
Laboratoire LI2C, UniversitéPierre et Marie Curie Bat. F case 51, 4 place Jussieu, 75252 Paris cedex 05, France fax: 33144273834
M. Jardat
Affiliation:
Laboratoire LI2C, UniversitéPierre et Marie Curie Bat. F case 51, 4 place Jussieu, 75252 Paris cedex 05, France fax: 33144273834
J.-F. Dufrêche
Affiliation:
Laboratoire LI2C, UniversitéPierre et Marie Curie Bat. F case 51, 4 place Jussieu, 75252 Paris cedex 05, France fax: 33144273834
P. Turq*
Affiliation:
Laboratoire LI2C, UniversitéPierre et Marie Curie Bat. F case 51, 4 place Jussieu, 75252 Paris cedex 05, France fax: 33144273834
D. Canet
Affiliation:
Laboratoire de méthodologie RMN, Université Henri Poincaré BP 239, 54056 Vandoeuvre-les-Nancy, France
*
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Abstract

Transportcoe[ ]cients in charged media exhibit strong variations, according to the conditions of displacement of the particles. Electrical transport, characterized by the simultaneous displacement of positive and negative charges in opposite directions obeys Ohm's law, but its variation with concentration (non-ideality), depends on several types of interactions, whose time of establishment varies from picosecond to nanosecond. Several diffusion processes can occur: mutual diffusion, where ions move simultaneously in the same direction, keeping local elec- troneutrality, and self diffusion where individual ionic particles move separately. The variation of diffusion coefficients with concentration dependson non-ideality factors analogous to those occuring in conductance, and their experimental evidence is facilitated b y the availability of experimental tec hniquesowing different characteristic times of observation. This phenomenon is particularly noticeable for self-diffsuion coefficients, where the dynamical processes can be observed from the picosecond range (neutron quasi-elastic scattering), to millisecond (NMR) and to hour scale (radiactive tracers). The results are especially enhanced for porous charged media like ion exchanging membranes (nafions).

Those results are be explained here theoretically in the framework of contin uous solv en t model theories (brownian dynamics) and experimentally in the study of self-diffusion in nafion membranes.

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Type
Research Article
Copyright
Copyright © Materials Research Society 2001

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