Surfactant-controlled shape change of organic droplets using polypyrrole

Control of the shape and position of organic droplets has been investigated using polypyrrole doped with the surfactant dodecylbenzenesulfonate (PPy center dot DBS). Ex-situ contact angle measurements of electrochemically-reduced PPy center dot DBS revealed a dramatic increase in wettability compared to the oxidised polymer, attributable to dopant reorientation and cation incorporation during the reduction process. In-situ studies showed that droplets of dichloromethane resting upon PPy center dot DBS electrodes and immersed in an aqueous electrolyte changed shape dramatically upon electrochemical reduction of the polymer. A mechanism for the unusual and unexpected changes in drop shape is presented. Controlled release of the surfactant dopant into the electrolyte upon reduction of PPy center dot DBS and subsequent doping of the polymer upon oxidation were found to affect the droplet shape. (C) 2011 Elsevier B.V. All rights reserved.