ELECTROCHEMICAL STUDIES OF OCTADECANETHIOL AND OCTANETHIOL FILMS ON VARIABLE SURFACE-AREA MERCURY SESSILE DROPS

Octadecanethiol (ODT) and octanethiol (OT) films at the mercury-electr olyte interface are examined using cyclic voltammetry and differential capacitance measurements at a single frequency. A mercury flow-system is used to alter the volume, and therefore, the surface area and surf ace pressure of the mercury electrode. Manipulation of the mercury ele ctrode's volume enables the introduction and removal of defects in the insulating thiol films. OT and ODT film behavior are contrasted under conditions of expansion and contraction. ODT forms extremely impermea ble layers that allow 1000 time less redox probe current than seen on uncoated drops. Expansion of the mercury electrode to increase the ele ctrode surface area produces defects and pinholes in the thiol film. T hese defects are almost completely removed when the drop is compressed back to its initial surface area. OT also forms insulating films on m ercury sessile drops, however these films contain more defects than OD T films. While expansion of an OT-coated mercury drop increases redox probe current, recompression of the drop does not return the film to i ts initial condition. Pinholes and defects in the OT and ODT films can also be produced by cycling to negative potentials, which produce abr upt stripping peaks.