EPD of Metal Oxide Nanoparticles from Polyol-Based Colloidal Suspensions

Microwave-assisted synthesis of nanoparticles in polyols is a well-established technique for the production of colloidal suspensions. In this technique, metal precursors are dispersed in polyols, and nanoparticles are then synthesised by microwave-heating the mixture. Microwave-assisted synthesis of nanoparticles in polyols produces suspensions of extremely fine particles (~10 nm), characterized by exceptional colloidal stability. Furthermore, flexible functionalization of the particles' surface can be performed, allowing the fine-tuning of key colloidal parameters, like zeta potential and particle size distribution. Both the exceptional colloidal stability of such suspensions and the outstanding physico-chemical properties of nanosized metallic and oxidic materials render polyol-based suspensions very attractive systems for EPD applications. Despite the abovementioned properties, in most cases EPD from polyol-based suspensions did not appear to be straightforward, even though high values of the zeta potential were measured and no sedimentation of the particles was observed to take place over several months. Since such high stability was to some extent preserved after adding controlled amounts of solvents to the suspensions, modifications of the composition by dilution were attempted, which in some cases led to successful EPD. This empirical observations, besides leading to successful EPD from some polyol-based suspensions, may provide some insights on the fundamental mechanisms through which the two main steps of EPD, i.e. mass transport and coagulation, take place in these systems. In this presentation, we report about the practical results of EPD trials from some of these system and the possible explanations of either success or failure in achieving the formation of the EPD films.