New Research


Non-equilibrium ion transport phenomena in micro- and nanospaces

Prof. Satoyuki Kawano, Assoc. Prof. Kentaro Doi, Assist. Prof. Itsuo Hanasaki and Testuro Tsuji

   A principle of energy conversion due to ion transports between a pair of electrodes can be seen in batteries. Recently, novel technologies associated with rechargeable batteries and capacitors have been developed by using micro/nano-fabrication processes. Realizing efficient ion transports in a narrow confined space, a high energy density and reduction of Joule heating can be achieved and result in developing high performance electric devices.


   We treat electrokinetic transport phenomena of electrolyte ions from the viewpoint of molecular fluid mechanics and are particularly conducting non-equilibrium ion flows from both theoretical and experimental aspects. For example, when an electric potential is applied on a pair of tiny electrodes in a reservoir which is filled with NaCl aqueous solution, a transient response of ionic current can be observed (schematically shown in the upper right figure). By using very small electrodes, one can detect very weak electrical signals. Theoretically, it is explained that ions at very near an electrode rapidly respond to screen the surface immediately after applying an electric potential and that an equilibrium distribution of ions is broadly disturbed in accordance with the change of electric fields. As shown in the lower right figure, the response of ionic currents with noise can be expressed by our theoretical model. The screening of electrode surfaces causes to a drastic increase in ionic current when an electric potential is applied and a successive slow decay is also observed due to a broad response of electrolyte ions. This result well explains the experimental observations.


   Developments of single molecule detection technologies are also one of the hottest research topics. Particularly, identification of single base molecules of deoxyribonucleic acid (DNA) is tackled by using the tiny electrodes. Our study has contributed to such a pioneering research project.


   Please see the website of our laboratory for more details.

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