Frc. Chang et G. Sposito, THE ELECTRICAL DOUBLE-LAYER OF A DISK-SHAPED CLAY MINERAL PARTICLE - EFFECTS OF ELECTROLYTE PROPERTIES AND SURFACE-CHARGE DENSITY, Journal of colloid and interface science, 178(2), 1996, pp. 555-564
The purpose of present study was to investigate, using a disk model, t
he effects of charge density and 1-1 electrolyte properties on the dif
fuse portion of the electrical double layer near a 2:1 clay mineral pa
rticle, Numerical solutions for the inner potential and anion exclusio
n volume were obtained by solving a Poisson-Boltzmann equation with va
rying parameter values for electrolyte ion radius, electrolyte concent
ration, basal plane charge density, and edge surface charge density. A
lthough the negative electrostatic potential of the basal planes may s
pill over to dominate a positively charged edge surface at low electro
lyte concentrations because of the typically large particle radius-to-
thickness ratio, the simulation results suggested that the spillover e
ffect diminishes with an increase in 1-1 electrolyte concentration, Th
e electric potential surrounding the edge surface is more positive for
large (0.4 nm) hardsphere electrolyte ions than for small (0.2 nm) or
point-charge ions, Reducing the basal plane charge density does not s
ignificantly affect the anion exclusion volume over a wide range of el
ectrolyte concentration, A highly positive edge surface, however, may
spill over to dominate the basal plane and thereby adsorb significant
amounts of anions at low electrolyte concentrations. The disk model pr
edictions of anion adsorption or exclusion behavior for 2:1 clay miner
al particles were consistent with available experimental observations.
(C) 1996 Academic Press, Inc.