Hydrophobic and hydrophlic interactions are now relatively well understood as regards their origin and their thermodynamic and structural consequences. The dynamic aspect i.e. their influence on transport and time dependent properties are less familiar. For ions, colloids and particle in suspension, the key parameter is the solvation of the particle, explaining the variation of the hydrodynamic friction factor from 4 pi to 6 pi, for slipping to sticking particles. For the dynamics in porous materials a large variety of phenomena occurs, from electrokinetic phenomena to surface conductance, all related to the slipping (hydrophobic) or sticking (hydrophilic) character of the surface. As a result all details of interactions are required in order to explain quantitatively the observed phenomena. Dynamic properties appear then as a discriminative and severe test of theoretical models for surface interactions.For the viscocity of electrolyte solutions, despite numerous efforts, no real progresses have been performed since the pioneering works by Debye, Huckel, Onsager and Falkenhagen. Contrary to further transport properties (such as the electrical conductivity or the diffusion coefficients), it is not possible to predict the viscosity of electrolyte solutions beyond the limiting law from a microscopic point of view. The well-known Jones-Dole coefficient that characterizes the concentration dependance of the viscosity cannot be simply calculated from an extended Brownian model. Using Mode-Coupling Theory (MCT), we propose such an attempt, in the case of simple dissociated electrolyte solutions. We show that it is possible to quantify a breaking structure effect for the ions. Molecular dynamics indicate that this effect slghtly depends on the nature of the ions. Then we propose a new simple model for the description of viscosity based on the MCT. It appears to be in agreement with experimental values for most of the simple electrolyte. The concentration dependance of viscosity appears to be a subtle consequence of opposite effects: Coulombic forces, solvent structure breaking, hydrophobicity and hydrophilicity.

Viscosity of aqueous electrolyte solutions: The dynamic point of view for hydrophobicity and hydrophilicity

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.