Measuring the frequency dependent polarizability of colloidal particles from dielectrophoretic collection data

In a non-uniform ac electric field, dipole forces cause polarizable particles to experience ponderomotive forces. The particle velocity is a function of the dielectric properties of the particle, the suspending medium, particle volume and the electric field gradient. Measurement of the collection rate of particles can be used to estimate their dielectric polarizability. In this work we have measured the collection rate of sub-micrometer particles collecting at the edges of a planar interdigitated electrode array. The Fokker-Planck equation was used to simulate the spatial and temporal accumulation of particles at the electrodes. The experimental data shows that the collection rate decreases with increasing frequency of the applied field, in agreement with the predicted frequency-dependent reduction in the effective polarizability of the particles. Numerical simulations are in broad agreement with experimental results.