Microphase separation during binary electrophoretic deposition of particles with dissimilar polarizabilities

We describe a two-dimensional, microphase separation in a binary mixture of yeast cells and colloidal polystyrene particles driven by the electrophoretic deposition (EPD) process. Self-organized core-shell clusters with predominantly yeast cores surrounded by shells of polystyrene (PS) particles were observed after applying uniform 5 Hz, 10 V/cm ac electric fields to initially randomly mixed monolayers adjacent to an ITO electrode. Depending on the type, size and ζ-potential of the colloids, the interplay between an aggregative electrohydrodynamic (EH) force and a repulsive induced-dipole–induced-dipole (ID) force produced either particle separation, aggregation or a combination of both in single component experiments conducted at 5Hz, 10 V/cm. In binary systems, the PS particle size and ζ-potential had only a secondary effect on the microphase structure, and the yeast–PS binary cluster morphology was frequency dependent. Differences in the particle dielectric response, characterized by the induced-dipole strength for PS and yeast, and in their relative vertical displacements during an alternating field cycle gave rise to the different self-organized morphologies observed in binary systems, while differences in the vertical motions of the assembling particles were directly observed to play a critical role in the binary sorting process.