ac Electrokinetic phenomena over semiconductive surfaces: effective electric boundary conditions and their applications.

Electrokinetic boundary conditions are derived for ac electrokinetic phenomena over leaky dielectric (i.e., semiconducting) surfaces. Such boundary conditions correlate the electric potentials across a semiconductor-electrolyte interface (consisting of an electric double layer inside the electrolyte solution and a space charge layer inside the semiconductor) in an ac electric field with arbitrary wave forms. The presented electrokinetic boundary conditions allow for evaluation of the induced ζ potential contributed by both bond charges (due to electric polarization) and free charges (due to electric conduction) from the leaky dielectric materials. Two well-known limiting cases, (i) the conventional insulating boundary condition and (ii) the perfectly polarizable boundary condition, can be recovered from the generalized electrokinetic boundary conditions derived in the present paper. Subsequently, we demonstrate the implementation of the derived boundary conditions for analyzing the ac induced-charge electrokinetic flow around a semiconducting cylinder. The results show that the flow circulations exist around the semiconducting cylinder and become stronger in the ac field with a lower frequency and around the semiconducting cylinder with a higher conductivity.