The present study prepared a size-controllable, uniform, and surfactant-free emulsification to investigate the ζ potential of the solvent effect. The results showed that the ratio of electrophoretic mobility changed with droplet diameter, and the correct factor of the ζ potential was determined. The effect of functional groups on the ζ potential was further studied in the presence of an organic hydrophilic solvent. The study characterized the effects of pH, ionic strength, and ionic type on the ζ potential and indicated that the solvents were able to modulate the local electrochemical environment, thus leading to the redistribution of interface charges.