Imaging of the liquid-liquid interface under electrochemical instability using confocal fluorescence microscopy.

The onset of the electrochemical instability has been imaged at the 1,2-dichloroethane (DCE)|water (W) interface modified with a fluorescent phospholipid using confocal fluorescence microscopy (CFM). Heterogeneously fluorescent images are recorded successively under the transfer of dodecyl sulfate ions (DS-) across the interface, which induces the irregularly increased current in a voltammogram. The commencement of the hydrodynamic movement of the solutions due to the electrochemical instability has been detected as the appearance of dark domains at the edge of the interface, that is, the three-phase contact of the DCE-W-glass wall confining the interface. In the potential region around the midpoint potential of the transfer of DS-, the area of the dark domains fluctuates and gradually grows with time. These locally confined unstable domains give rise to slightly augmented current in the simultaneously recorded voltammogram. The interface in this potential range appears to be globally stable at the expense of small unstable domains. In the potential region where the irregularly increased current is visible in the voltammogram, the entire interface becomes unstable and the dark and bright regions move vertiginously due to the Marangoni convection of the adjacent solution phases.