Seminar Philippe Leroy

Abstract

Determining the electrochemical properties of particles and bubbles in aqueous solution is actually a great challenge due to the nanometric scale of investigation where physico-chemical reactions occur. A way to estimate particle and bubble electrochemical properties is to measure electrokinetic processes where water flow influences electrical phenomena at the pore scale and vice et versa. For instance, the zeta potential is an electrokinetic physical quantity defined as the electrical potential at the shear (or slipping) plane located at the nanometric scale of the electrical double layer (EDL) on the surface of particles and bubbles. The zeta potential is very useful to describe, e.g., adsorption reactions and electrostatic interactions in aqueous solutions. Nevertheless, this physical quantity is not necessarily accurately known because usually macroscopic centimetric scale laboratory measurements and poor transport models are used to estimate the zeta potential from electrokinetic measurements. Considering cross-coupling transport phenomena and interfacial physico-chemical reactions at the pore scale as well as pore space topology should be the key to unravel the zeta potential. This is particularly true for colloids that present a high surface to volume ratio compared to grains and where electrical double layer effects on transport are amplified. In this seminar, I present the effects of surface conductivity, which is due to the excess of electrical conductivity on the surface of particles or bubbles, on electrophoretic mobility and streaming potential measurements and the corresponding zeta potential estimates. Surface conductivity effects on these measurements are particularly strong when the surface conductivity is higher than the bulk conductivity, typically for dilute aqueous solutions (ionic strengths below 0.1 mol/L). This is a first step towards a better understanding of what is occurring at the pore and interfacial scales during electrokinetic measurements to characterize particle and bubble electrochemical properties.