Local concentrations of salts by means of a scanning electrochemical microscope with microspheres

点击翻译按钮获取中文摘要

We disperse microspheres composed of polystyrene sulfonate in water and deionize it exhaustively by means of ion exchange resins. This suspension is not allowed to make conventional electrochemical measurements because it is highly resistive. However, a microelectrode technique can permit to obtain reduction waves of hydrogen ions. Since most of hydrogen ion is immobilized electrostatically by the microsphere, the current is very small. If salt is added to the suspension, the current increases dramatically because of a release of hydrogen ion from the microsphere. In other words, the current in the suspension is quite sensitive. This sensitivity can be applied to local detection of salts at a microelectrode.This project deals with the detection of current of hydrogen ions released from polystyrene sulfonic microspheres at several concentrations of salts at the scanning electrochemical microscope. When this technique was applied to a weak acid, the current at a microelectrode was not pr … More oportional to the concentrations because of the participation in dissociation of the acid. The resistance of the suspension under the reduction of hydrogen ion was obtained by ac impedance. Then it showed higher resistance than that estimated from the molar conductance of acid, probably because of contribution of the dissociation. Microspheres were synthesized, of which diameter was 0.7 μm with a very narrow dispersion in size. Steady-state current was observed in the suspension at various distance between the electrode and an insulating wall. When the microelectrode was scanned over the a metal mounted on the wall to which a dissolution potential was applied, it could detect the reduction current of the dissolved ions. It was possible to make an image of the metal from the analysis of the current vs. three-dimensional positions. During this course, we found that the polyaniline-coated polystyrene particles showed synchronized currents. In order to pursue reasons of the synchronization, the scanning electrochemical microscope was used for changing the distance between the electrode and the wall. This advanced research is still going on. Less