Salt concentration and particle density dependence of electrophoretic mobilities of spherical colloids in aqueous suspension.
Using laser Doppler velocimetry in the superheterodyne mode, we conducted a systematic study of the electrophoretic mobility of dispersions of small silica spheres (a=18 nm) suspended in water at different salinities and particle concentrations. The concentration of NaCl was varied from 40 microM up to 16 mM, while the particle concentrations were varied between 4.2x10(18) and 2.1x10(20) m-3. We find a decrease of mobility with increasing salt concentrations and an increase with increased particle number densities. The latter observation is not backed by the standard cell model of electrophoresis with Shilov-Zharkikh boundary conditions. Rather, if the experimental data are interpreted within that model, an unexpected change of the zeta potential at constant added salt concentration results. Interestingly, all experimental data collapse onto a single master curve, if plotted versus the ratio C* of particle counterions to added salt ions. We obtain a logarithmic increase of mobility for C*<1 and a plateau for C*>1. This may indicate a change of the Stern layer structure not yet included in the theoretical model.
Reiber
Holger
H
Institut für Physik, Johannes Gutenberg Universität, 55099 Mainz, Germany. hreiber@uni-mainz.de
Köller
Tetyana
T
Palberg
Thomas
T
Carrique
Felix
F
Ruiz Reina
Emilio
E
Piazza
Roberto
R
D003102:Colloids / Q000737:chemistry*; D004586:Electrophoresis; D017078:Laser-Doppler Flowmetry; D008956:Models, Chemical; D010316:Particle Size; D012822:Silicon Dioxide / Q000737:chemistry*; D012965:Sodium Chloride / Q000737:chemistry*; D013535:Suspensions / Q000737:chemistry; D014867:Water / Q000737:chemistry
D003102:Colloids; D013535:Suspensions; D014867:Water; D012965:Sodium Chloride; D012822:Silicon Dioxide