Electrochemical characterisation of liquid|liquid microinterface arrays

Arrays of water-nitrobenzene microinterfaces have been realised by separating the two liquid phases with a polymer film, in which 100 microholes were drilled using a UV laser photoablation technique. The microholes were arranged in a square pattern with center-to-center separations of 20 to 200 mu m. The diameter of the microholes was 10, 5 and similar to 0.5 mu m. Cyclic voltammetry, chronoamperometry and measurements in an electrochemical flow cell were used to characterise the electrochemical behavior of the arrays. The dependence of the chronoamperometric response on the center-to-center distance and diameter of the microinterfaces was investigated for times between 1 and 400 s after the application of the potential step. Unlike single microinterfaces, a steady-state current is observed only for very long times and is attributable to natural convection processes as for electrodes of larger dimensions. The plot of the inverse current versus the square root of the time reveals, that the chronoamperometric response for medium times (about 1 to 20 s) is governed both by planar diffusion normal to the plane of the array and by hemispheric diffusion to the individual microinterfaces. A simple model is proposed which describes the chronoamperometric response for the medium time range. When the arrays are used in a flow-through electrochemical cell, no dependence of the current on the flow rate is observed as long as the volume flow rate is less than a limiting value. For flow rates above this limiting value, the logarithm of the steady-state current depends linearly on the logarithm of the volume flow rate, as for conventional electrodes of large dimensions. The limiting value depends on distance and diameter of the microinterfaces and was of the order of 1 ml/min. (C) 1997 Elsevier Science S.A.