MEASURING THE CONDUCTIVITY OF SUB-MICRON SIZED POLYSTYRENE PARTICLES BY CAPILLARY ELECTROPHRESIS AND DIELECTROPHORESIS
Christian M. White
The apparent surface properties of commercially available polystyrene particles can vary due to inhomogeneous sample populations and differences in quality control testing conditions and actual use conditions. Capillary electrophoresis is used to characterize four different types of fluorescent polystyrene particles. The electrophoretic mobility of the particles during a capillary electrophoresis run can be used to calculate the zeta potential, surface charge density, and surface conductance of the particles. Suppression of the electroosmotic flow via polymer-based capillary coatings is used to reduce a significant source of variability allowing for more precise measurements. Dielectrophoresis is used as an orthogonal method to verify the surface conductance measurements. A miniaturized dielectrophoresis chip containing patterned gold quadrupole electrodes is used to observe the change in dielectrophoretic behavior of the particles in response to changing the frequency of an applied AC electric field. For a given particle and a suspending medium with a known conductivity, the frequency at which the particle changes its dielectrophoretic behavior is directly related to the surface conductance of the particle. The measured surface conductance values ranged from 0.21 x 10-2 S/m to 2.1 x 10-2 S/m, and values obtained from capillary electrophoresis and dielectrophoresis measurements agreed to within 0.3 x 10-3 S/m of each other.