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

Wed 711:10-14:00P5.7The role of boundary conditions on the low-frequencydielectric relaxation of concentrated colloidalsuspensionsFrancisco J. Arroyo, 1 Felix Carrique, 2 Silvia Ahualli, 3 Jose Horno, 1 and Angel V.Delgado 31 University of Jaen, Dep. Physics, Faculty of Experimental Sciences, 23071, Jaen,Spain2 University of Malaga, Malaga, Spain3 University of Granada, Granada, SpainThe presence of charged colloidal particles in suspension significantly changes the electricpermittivity of the system as compared to that of the pure dispersion medium. This is particularlytrue in the case of concentrated suspensions, in fact the most attractive from the applied viewpoint.There are theoretical models predicting the frequency-dependence of the relative permittivityof such suspensions using cell models [1], and most of them are based on the Kuwabara cellmodel [2] to allow for the hydrodynamic particle-particle interactions. Electrical interactionsare mimicked by setting boundary conditions on the field-induced perturbations on the electricpotential and ion concentrations on the cell limit [3]. As we demonstrated in [3] there is noeffect of the boundary condition choice (either Dirichlet or Neumann) for the potential, on thepredictions of the electrical conductivity of the suspension. However, this is not true when theconditions for ionic perturbation are changed. In this contribution, we will compare numericalresults on the dielectric spectra of suspensions with different volume fractions of solids for bothchoices of conditions. We will show that the spectra predicted can be different at low frequency,and that a critical frequency is found beyond which the differences are negligible. We will explainthe differences obtained in the context of the existence of a region where local electroneutrality isnot fulfilled [4].Acknowledgement : Financial support for this work by Junta de Andalucía, Spain (ProjectsPE2008-FQM3993 and P08-FQM-3779) and MICINN, Spain (Projects FIS2010-19493 andFIS2010-18972), co-financed with FEDER funds by the EU is gratefully acknowledged.[1] Carrique et al. , J. Chem. Phys. 118 (2003) 1945.[2] Kuwabara, J. Phys. Soc. Japan 14 (1959) 527.[3] Carrique et al. , Adv. Colloid Interface Sci. 118 (2005) 43.[4] López-García et al. , J. Phys. Chem B, 109, (2005) 5808.7