Co-Electrophoretic Deposition of Composites: Understanding Deposition Mechanisms

Electrophoretic deposition (EPD) is a process in which a suspension of colloidal particles is driven to deposit onto the surface of an electrode under an applied electric field. EPD has been used industrially for decades as a coating process, for instance, to deposit ceramic on metal for thermal and diffusion barriers. Recently, EPD has been employed to fabricate functional and functionally graded materials. These applications entail depositing a composite of at least two different materials. A method for accomplishing this is to co-suspend the materials of interest in a solvent and deposit both simultaneously. However, it has been observed that, in general, the composition of the coating does not match the composition of the suspension. Two mechanisms have been proposed account for this: each material has a different electrophoretic mobility and hence deposits at a different rate, or the materials form agglomerates in the bulk, which then deposit by EPD. Here, we present a study in which we systematically vary the composition of the suspension and deposition parameters to determine the effects on final deposit composition in an attempt to differentiate between the two mechanisms.