Low-Frequency Dielectrophoretic Response of a Single Particle In Aqueous Suspensions

Alpha-relaxation, the counterion diffusion in the electric double layer, has been used to describe the anomalous low frequency dielectric dispersion of aqueous suspensions of colloidal particles. A microscopic theory describing this relaxation process proposed by Schwarz, however, has not been investigated systematically. We use an optical tweezers-based single-particle dielectrophoretic (DEP) force spectroscopy to study the relaxation mechanism as a function of particles size, temperature and solvent viscosity. Specifically, we measure the dependence of the DEP crossover frequency and compare results with predictions by Schwarz.