INVESTIGADORES
LONGINOTTI Maria Paula
artículos
Título:
Fractional Walden Rule for Electrolytes in Supercooled Disacharide Aqueous Solutions
Autor/es:
M. PAULA LONGINOTTI; HORACIO R. CORTI
Revista:
JOURNAL OF PHYSICAL CHEMISTRY B
Editorial:
American Chemical Society
Referencias:
Lugar: Washington; Año: 2009 vol. 113 p. 5500 - 5507
ISSN:
1089-5647
Resumen:
The electrical conductivity of CsCl, KCl, Bu4NBr and Bu4NI was studied in stable and supercooled (metastable) sucrose and trehalose aqueous solutions over a wide viscosity range. The results indicate that large positive deviations from the Walden rule occur in these systems due to the higher tendency of the ions to move in water-rich regions, as previously observed for NaCl and MgCl2. The electrical molar conductivity viscosity dependence can be described with a fractional Walden rule (Lha= constant), where a is a decoupling parameter which increases with ionic size and varies between 0.61 and 0.74 for all the studied electrolytes. Using the electrical molar conductivity dependence on ion-ion interactions an effective dielectric constant was calculated for a trehalose 39 wt% aqueous solution as a function of temperature. Above 278 K the effective and the bulk solution dielectric constants are similar but, at lower temperatures, where the carbohydrate becomes less mobile than water, the effective dielectric constant approaches the dielectric constant of water. We also conclude that the solute-solvent dielectric friction contribution can be neglected, reinforcing the idea that the observed breakdown of the Walden rule is due to the existence of local microheterogeneities. The Walden plots for the studied ionic solutes show a decoupling similar to that found for the diffusion of water in the same solutions.