ELECTROCHEMICAL CHARACTERIZATION OF LIQUID-VERTICAL-BAR-LIQUID MICROINTERFACE ARRAYS

Arrays of water-nitrobenzene microinterfaces have been realised by sep arating the two liquid phases with a polymer film, in which 100 microh oles were drilled using a UV laser photoablation technique. The microh oles were arranged in a square pattern with center-to-center separatio ns of 20 to 200 mu m. The diameter of the microholes was 10, 5 and sim ilar to 0.5 mu m. Cyclic voltammetry, chronoamperometry and measuremen ts in an electrochemical flow cell were used to characterise the elect rochemical behavior of the arrays. The dependence of the chronoamperom etric response on the center-to-center distance and diameter of the mi crointerfaces was investigated for times between 1 and 400 s after the application of the potential step. Unlike single microinterfaces, a s teady-state current is observed only for very long times and is attrib utable to natural convection processes as for electrodes of larger dim ensions. 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 pl ane of the array and by hemispheric diffusion to the individual microi nterfaces. A simple model is proposed which describes the chronoampero metric 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 logar ithm of the steady-state current depends linearly on the logarithm of the volume flow rate, as for conventional electrodes of large dimensio ns. The limiting value depends on distance and diameter of the microin terfaces and was of the order of 1 ml/min. (C) 1997 Elsevier Science S .A.