Electrochemical investigation of hemispherical microdroplets of N,N-didodecyl-N ',N '-diethylphenylenediamine immobilized as regular arrays on partially-blocked electrodes: A new approach to liquid vertical bar liquid voltammetry

A regular array of identically sized microdroplets of 2.5 mu m radius of the water-insoluble liquid N,N-didodecyl-N',N'-diethylphenylenediamine (DDPD) is immobilized on the nonconducting hydrophobic polymer blocks of a gold partially blocked electrode. Cyclic voltammetric and chronoamperometric measurements for the oxidation of the DDPD microdroplets immersed in an aqueous solution are then recorded for different electrolytes (NaClO4, NaCl, NaBr, NaNO3, Na2SO4, and NaF). Specifically, the cyclic-voltammetric measurements allow us for the first time ever to observe a pre-peak, which can be interpreted as the movement of charge across the surface of the hemispherical droplets before the bulk material of the droplets gets oxidized. Conversion of the whole bulk material in all droplets is obtained by chronoamperometry. The resulting current-time responses show Cottrellian diffusion at sufficiently short times and are modeled by simulating diffusion through the droplet revealing complex behavior, which is likely to be related to anion dehydration and/or tight and weak ion-pair formation.