  The rectification of electro-osmotic flows is important in micro/nano
fluidics applications such as micro-pumps and energy conversion devices. Here,
we propose a simple electro-osmotic diode in which colloidal particles are
contained between two parallel membranes with different pore densities. While
the flow in the forward direction just pushes the colloidal particles toward
the high-pore-density membrane, the backward flow is blocked by the particles
near the low-pore-density membrane, which clog the pores. Nonequilibrium
molecular dynamics simulations show a strong nonlinear dependence on the
electric field for both the electric current and electro-osmotic flow,
indicating diode characteristics. A mathematical model to reproduce the
electro-osmotic diode behavior is constructed, introducing an effective pore
diameter as a model for pores clogged by the colloidal particles. Good
agreement is obtained between the proposed model with estimated parameter
values and the results of direct molecular dynamics simulations. The proposed
electro-osmotic diode has potential application in downsized microfluidic
pumps, e.g., the pump induced under AC electric fields.
