A simple electrokinetic nanorotor

The phenomenon of dielectric particles tumbling spontaneously in low-conductivity fluids under strong DC electric fields is known as Quincke rotation. For this to happen, the charge relaxation time of the particle must typically be longer than that of the liquid, which normally requires that the particle be less conductive than the surrounding medium. Here, we show that semiconducting nanowires in deionized water, when subject to high-frequency AC field, can also exhibit Quincke rotation. We explain the tumbling by analyzing the torque balance between the moments of the electroosmotic flows, the electric force on the induced dipole, and the Stokes drag. In addition, we suggest that this Quincke rotation starts at a critical field strength and frequency. This work demonstrates a simple concept for a continuous nanorotor in aqueous solution using a stationary, linearly polarized electric field.