Streaming potentials near a rotating disk bearing a thick fuzzy surface layer
Dennis Prieve (Carnegie Mellon University), Paul Sides (Carnegie Mellon Univ.)
Electrohydrodynamics and electrokinetics of fluid systems
Mon 10:45 - 12:15
Barus-Holley 161
In Langmuir 22, 9765-9769 (2006) we present a model for predicting the streaming-potential profile near a rotating disk immersed in a dilute aqueous electrolyte. This geometry represents a promising new method for determining the zeta potential of flat surfaces (e.g. silicon wafers). We call this new technique ZetaSpin. Since then we have measured streaming potentials which are an order of magnitude larger than for flat surfaces when a 2 mm thick and 2 cm in diameter, highly porous sample (e.g. Velcro) is affixed to the rotating disk. In this paper, we present a simple model which predicts the enhanced streaming potential arising when a porous layer is affixed to the disk. The main result is that flow through the porous media causes convection of charge and the apparent space-charge density of the fluid in the porous media is given by –epsilon*zeta/k, where epsilon is the permittivity of the fluid, zeta is the zeta potential of the solid and k is the Darcy-law constant of the porous media.