(421i) Reversible Emulsification and Demulsification of Oil-in-Oil Emulsions Using Electric Fields

This presentation will describe the results of an experimental investigation demonstrating emulsification and demulsification of oil-in-oil emulsions using AC electric fields. When an AC electric field at low frequency (<10 Hz) is applied to oil-in-oil emulsions, we observe droplet break-up, consistent with electrohydrodynamic (EHD) flows that deform the droplets such that capillary instabilities drive droplet break-up. In contrast, AC electric fields at high frequency (> 1kHz) are observed to drive attractive interactions between droplets which end with droplet coalesce. The observations at high frequency are attributed to electric field-induced dipolar interactions and the cessation of EHD effects. Overall, by manipulating the frequency and amplitude of AC fields, we show that the competing effects of EHD flows and dipolar attractive interactions can provide the basis of methods for precise and reversible control over droplet size and size distributions. The technological potential of these fundamental finding will be discussed.