Article Dans Une Revue Molecular Motions in liquids Année : 1974

Etude, Par Relaxation Dielectrique, Du Mouvement Brownien des Ions dans les Liquides Simples

Résumé

The motion of ions in an electrolyte solution can be related to the observed dielectric relaxation by means of correlation functions. When the dynamic variables are chosen as the velocities, the results of the Onsager and Debye-Falkenhagen (ODF) theories can be found. The ionic part of the complex permittivity shows then an asymmetrical distribution of relaxation time, when described phenomenologically in dielectrics language. Unfortunately, these theories are restricted to dilute solutions, too dilute for any experimental verification to be made. If the dynamic variables of the correlation function are chosen as the positions of the ions an a priori separation has to be made between a static conductivity σ(0) and an ionic complex permittivity Δε(ω). Only the latter can be deduced from the corresponding correlation function, and it represents the permittivity of a non-conductive medium. Within this frame, a dielectric model is built. The ions are first assumed to be gathered in complex aggregates which undergo deformations when an electric field is applied. These deformations are then assumed to come from a brownian linear motion of the ions, interrupted by collisions, and can be described by stochastic laws involving a diffusion coefficient and a mean collision time. The magnitude of both quantities can be estimated a priori, as well as the molecular part of the complex permittivity. This model fits fairly well the experimental data obtained between 137 MHz and 34 GHz with solutions of lithium perchlorate (0.6 M l–1) in tetrahydrofuran-benzene mixtures.
L’étude de la relaxation diélectrique des solutions électrolytiques permet d’accéder au mouvement brownien des ions par l’intermédiaire des fonctions de corrélation temporelles. Toutefois, suivant que l’on considère le liquide comme étant ou non conducteur, ces fonctions portent sur des variables dynamiques différentes. Nous comparons ici les deux approches actuellement proposées et nous illustrons les problèmes posés à partir de résultats expérimentaux récents.

Domaines

Chimie

Dates et versions

hal-04888000 , version 1 (15-01-2025)

Identifiants

Citer

Jean-Pierre Badiali, Hubert Cachet, Alain Cyrot, Jean-Claude Lestrade. Etude, Par Relaxation Dielectrique, Du Mouvement Brownien des Ions dans les Liquides Simples. Molecular Motions in liquids, 1974, Molecular Motions in Liquids, pp.179-186. ⟨10.1007/978-94-010-2177-7_15⟩. ⟨hal-04888000⟩
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