Environ. Sci. Technol. 2002, 36, 343-348
Influence of Metal Ion Sorption on Colloidal Surface Forces Measured by Atomic Force Microscopy
particles and, as a consequence, the colloidal surface forces (e.g., refs 3 and 4). A quantitative understanding of the changes in colloidal forces caused by chemical interactions between the particles and their chemical environment is therefore critical for the prediction and control of colloidal processes.
CHING-JU CHIN,† S O T I R A Y I A C O U M I , * ,† A N D COSTAS TSOURIS‡ School of Civil and Environmental Engineering, Georgia Institute of Technology, 200 Bobby Dodd Way, Atlanta, Georgia 30332-0512, and Separations and Materials Research Group, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831-6181
The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which includes van der Waals and electrostatic forces, has been widely used to explain the interactions between colloidal particles. Traditionally, to quantify the interparticle forces in a system, it is necessary to determine particle properties, such as ζ-potential and Hamaker constant, and to employ existing theories (e.g., DLVO) to calculate the various forces. Recent advancements in technology have made direct force measurements possible by surface force apparatus (5, 6), total internal reflection microscopy (TIRM) (7), optical tweezers (8, 9), differential electrophoresis (10), and atomic force microscopy (AFM) (11, 12).
Atomic force microscopy (AFM) is employed to directly measure colloidal surface forces between a silica particle and a smooth glass plate in an aqueous solution with or without the presence of copper ions. Without the presence of copper ions, results show that the force between these two surfaces is repulsive and that its magnitude decreases with increasing ionic strength and decreasing pH. The surface forces are calculated based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for constant surface charge and are then compared with AFM force measurements. A good agreement between theory and experimental data is reported except at very small separation distances (
