8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P5.94Wed 711:10-14:00Influence of variable permittivity constrains on theequilibrium electric double layer of colloidal suspensionsJosé Juan López García, 1 Miguel Jesús Aranda Rascón, 1 and José HornoMontijano 11 Universidad de Jaén, Edificio A3, Campus Las Lagunillas s/n, Universidad de Jaén 23009,Jaén, SpainIn the macroscopic electric treatment of the interface between two different dielectric media, it iswell know that both the electric potential and the normal component of the electric displacementvector are continuous, while that the electric field intensity is discontinuous at the interface. Whenthe region of study is of the order of a few solvent molecules in the interface, it is more suitable toassume a continuous spatial variation for both the dielectric permittivity and the electric field. Thisis particularly true in the liquid phase of solid-liquid interfaces, and for aqueous solutions wherethe macroscopic permittivity near the interface is smaller than in the solution due to the boundwater effects. If the solid phase is charged and the liquid phase is an ionic solution, a region with adistribution of electric charge and potential known as Electric Double Layer (EDL) appears. T hePoisson-Boltzmann equation (PBE), widely accepted as a good model of this region, is obtainedby the inclusion of a series of simplifying assumptions: finite sizes of ions are neglected, thepermittivity of the medium is assumed to be constant, etc. According to this theoretical model thethickness of the EDL is inversely related with the square root of the ionic concentration in the bulksolution and can be of the order of a nanometer for high ionic concentrations (1M) and the electricpotential drop across the EDL increases with the square root of the solution permittivity for a givensurface charge influencing strongly the capacity, impedance, electrokinetic phenomena, dielectricproperties, etc, of the system. In this work we propose a theoretical model including a variablepermittivity of the electrolyte solution to take into account the gradual change of electric field in asolid-liquid interface. Financial support by MICINN (FIS2010-19493), FEDER funds, and Juntade Andalucía (PE-2008 FQM-3993), of Spain, is gratefully acknowledged.94