S. Wilke et al., ELECTROCHEMICAL CHARACTERIZATION OF LIQUID-VERTICAL-BAR-LIQUID MICROINTERFACE ARRAYS, Journal of electroanalytical chemistry [1992], 436(1-2), 1997, pp. 53-64
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.