Dr. Philippe Leroy (French Geological Survey (BRGM), Orléans, France) will deliver a seminar entitled "Investigating the electrochemical properties of colloids and porous media using electrokinetic and the complex resistivity methods and considering the key role of surface electrical conductivity" Friday, July 26th, 2019 at 10.00 am (mezzanine room)
Unveiling the electrochemical properties of interfaces is a topic of great interest in many scientific areas such as in biology, physical chemistry and hydrogeophysics. For instance, the surface electrical properties control adsorption and coagulation processes in colloidal chemistry and can be used in hydrogeophysics to better map soil and rock adsorption and transport properties. However, due to its microscopic nature, the characterization of the electrical double layer (EDL) compensating the surface charge at interface is very challenging. One way to indirectly characterize the EDL is to use electrokinetic methods such as electrophoresis for colloids and streaming potential for porous media and other electrical methods such as the complex resistivity, which is a dielectric spectroscopy method with a four-electrode system allowing measurements in the low-frequency range from mHz to kHz. When electrical current is induced by water flow dragging counter-ions in the EDL or when it is injected through the medium, an excess (or rarely a deficiency) of electrical conductivity named surface conductivity appears at interface. Surface conductivity is not often considered to relate the zeta potential located at the supposed shear plane to the electrokinetic measurement and can be described using the imaginary part of the complex resistivity as well as ion transport modeling from the interface and pore (nanometric to micrometric) scales to the laboratory (centimetric) scale. This presentation shows the importance of characterizing surface conductivity to describe the EDL properties from electrokinetic and other electrical measurements. As surface conductivity rises in importance when the surface to volume ratio increases, applications to the electrochemical properties of montmorillonite suspensions and titanium dioxide and amorphous silica nanoparticles are presented. In addition, our approach was also used to investigate the surface properties of inert gas bubbles, glass beads, calcite, and low-pH cement.
