FIG. 13.

When the Debye length ${\kappa }^{-1}$ exceeds the pore radius $a$, the cloud of counterions associated with the charged cylindrical wall of the pore spills out of the ends of the pore. Since the strongest electric field is localized primarily within the pore, the “spilled” charge is unavailable for driving the flow which results in a greatly decreased fluid flux as seen in Fig. 12.