Solvent-induced Inversion of Colloidal Aggregation During Electrophoretic Deposition

Electrophoretic deposition of colloidal particles is a practical system for the study of crystallization and related physical phenomena. The aggregation is driven by the electroosmotic flow fields generated by the polarization of the electrode-particle-electrolyte interface. Here, we report on the electrochemical control of aggregation and repulsion in the electrophoretic deposition of colloidal microspheres. The nature of this transition depends solely on the composition of the solvent. The observed behavior switches between electrical field-driven aggregation in water to electrical field-driven repulsion in ethanol for otherwise identical systems of colloidal microspheres. This work uses optical microscopy-derived particle and a recently developed particle insertion method-approach to extract the effective interparticle potentials as a function of the solvent and electrode potential at the electrode interface. This approach can be used to understand the phase behavior of these systems based on the observable particle positions rather than a detailed understanding of the electrode-electrolyte microphysics.