Transport Phenomena in Nanofluidic Channels

摘要

It is well known that surface charges induce electrostatic ion screening and electrokinetic effects such as electroosmosis, electrophoresis, streaming potentials and streaming currents in micro- nano-fluidic channels. Schasfoort et al. [1] have reported that electrdosmotic flow can be controlled by modifying the surface potential inside a microfluidic channel using a gate electrode. In nanofluidic channels, the surface charges may have large effects on ionic flow rather than fluid flow. At high bulk concentration of ion, where the channel height, h, is much larger than the Debye length, λ{sub}D (=1/κ), (κh1), the ion concentration inside the channel is almost the same to the bulk concentration. While at low bulk concentration, where κh1, a unipolar solution of counterions is created inside the channel and the average concentration is determined by the requirement of electroneutrality. The authors [2] have proposed that ionic flow can be regulated by locally modifying the surface charge density through a gate electrode when the electrical double layers are overlapped. However, in this condition, only counterion flow can be controlled and the ionic current is small. If the electrical double layer is not overlapped, counterion and coion flows can be controlled at the same time and the fluidic channels may have various current-potential characteristics such that semiconductor diodes and transistors have, besides, the ionic current may become larger. The objective of this study is to confirm theoretically that the ionic current can be controlled by locally modifying the surface charge density when the electrical double layers are not overlapped and to clarify the current-potential characteristics for nanofluidic diode and transistor.