Distinctive electrokinetic behavior of nanoporous silica particles treated with cationic polyelectrolyte

In this study we show, for the first time, that the streaming potential of aqueous suspensions of nanoporous silica gel, after treatment with the ationic polyelectrolyte poly-diallyldimethylammonium chloride (poly-DADMAC), can depend very strongly on the concentration of background lectrolyte. An increase in the electrical conductivity from 60 to 1000 S/cm resulted in an approximately 1000-fold increase in the amount of oly-DADMAC that was required to reach an endpoint of zero streaming potential. Results were explained by two contributions to the overall lectrokinetic behavior—one due to the outer surfaces and another due to the interior surfaces of nanopore spaces that were inaccessible to the olyelectrolytes. Experiments with cyclical changes in salt content revealed a high degree of reversibility; such observations help to rule out xplanations based on salt-induced desorption or enhancement of pore penetration. Supplementary tests with non-porous glass fibers showed o evidence of the distinctive electrokinetic behavior observed in the case of nanoporous particles. Effects of polymer molecular mass and pH, valuated under similar experimental conditions, agreed with well-established trends. 2006 Elsevier B.V. All rights reserved.