Characterizing the Solvent-Induced Inversion of Colloidal Aggregation During Electrophoretic Deposition

Electrophoretic deposition (EPD) 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 and induced dipole moments generated by the polarization of the electrode-particle-electrolyte interface. Here, the electrochemical control of aggregation and repulsion in the electrophoretic deposition of colloidal microspheres is reported. The nature of the observed transition depended on the composition of the solvent, switching from electrode-driven aggregation in water to electrical field-driven repulsion in ethanol for otherwise identical systems of colloidal microspheres. This work uses optical microscopy-derived particles and a recently developed particle insertion method approach to extract model-free, effective interparticle potentials to describe the ensemble behavior of the particles 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. This approach enables simple predictability of the static and dynamic behaviors of functional colloid-electrode interfaces.