KES4-1050
On-Demand Formation, Ordering and Erasure of Emulsions using AC Electric Fields
Topic
S4. Colloids, Interfaces, and Molecular Assemblies for Functional Soft Materials
When and Where
Sep 29, 2026
10:50 - 11:15
Room 106
Session Chairs
Chan-Jin KIM
Presenter(s)
Nicholas Abbott (Cornell University)
Co-Author(s)
Abstract
AC electric fields can induce instabilities that deform, undulate, and elongate liquid-liquid interfaces via dielectric stresses. This presentation will describe how these AC electric field effects and others can provide the basis of fresh approaches to on-demand formation, ordering and erasure of emulsions.
First, I will describe how AC electric fields can, via dielectric and capillary instabilities, emulsify immiscible oils to produce arrays of droplets with well-defined number densities and narrow size distributions. The emulsions form through a pathway that involves capillary bridges that result from a dielectric instability; the capillary bridges break up into droplets via a Plateau-Rayleigh instability. Significantly, we find that the droplets formed via this process exhibit a size distribution that is narrower (and more asymmetric) than the capillary bridge diameters. To provide insight into this finding, we quantified the effects of AC field strength and electrode geometry on the capillary instability and discovered a non-monotonic relationship between capillary bridge diameter and droplet size, contrasting to the monotonic scaling typically found to describe the capillary break-up of an infinite liquid jet. The origin of the non-monotonic relationship was determined to reflect a competition between draining and instability of the confined capillary bridge. I will also describe how electrode surfaces micropatterned with topography can template the emulsification pathway at defined locations. Finally, when one of the oils is a nematic liquid crystal, I will discuss how the emulsification pathway produces droplets with uniformly oriented topological defects that lead to ordered emulsions.
Second, I will describe our discovery of a new droplet coalescence pathway that arises when isotropic liquids are dispersed as droplets within a continuous liquid crystalline phase. We found that relatively weak AC electric fields can generate spatially-localized regions of strain (called solitons) that are templated by topological defects accompanying droplets dispersed in a liquid crystal. The solitons can “lasso” multiple microdroplets to drive a rapid coalescence process. In contrast to dipolar forces that act primarily along field lines (causing chaining), the soliton-mediated coalescence pathway is “three dimensional” and thus highly efficient at driving coalescence of emulsions.
Overall, the results to be discussed in this presentation provide approaches that permit rapid formation of emulsions, manipulation of their organization, and subsequent erasure.
First, I will describe how AC electric fields can, via dielectric and capillary instabilities, emulsify immiscible oils to produce arrays of droplets with well-defined number densities and narrow size distributions. The emulsions form through a pathway that involves capillary bridges that result from a dielectric instability; the capillary bridges break up into droplets via a Plateau-Rayleigh instability. Significantly, we find that the droplets formed via this process exhibit a size distribution that is narrower (and more asymmetric) than the capillary bridge diameters. To provide insight into this finding, we quantified the effects of AC field strength and electrode geometry on the capillary instability and discovered a non-monotonic relationship between capillary bridge diameter and droplet size, contrasting to the monotonic scaling typically found to describe the capillary break-up of an infinite liquid jet. The origin of the non-monotonic relationship was determined to reflect a competition between draining and instability of the confined capillary bridge. I will also describe how electrode surfaces micropatterned with topography can template the emulsification pathway at defined locations. Finally, when one of the oils is a nematic liquid crystal, I will discuss how the emulsification pathway produces droplets with uniformly oriented topological defects that lead to ordered emulsions.
Second, I will describe our discovery of a new droplet coalescence pathway that arises when isotropic liquids are dispersed as droplets within a continuous liquid crystalline phase. We found that relatively weak AC electric fields can generate spatially-localized regions of strain (called solitons) that are templated by topological defects accompanying droplets dispersed in a liquid crystal. The solitons can “lasso” multiple microdroplets to drive a rapid coalescence process. In contrast to dipolar forces that act primarily along field lines (causing chaining), the soliton-mediated coalescence pathway is “three dimensional” and thus highly efficient at driving coalescence of emulsions.
Overall, the results to be discussed in this presentation provide approaches that permit rapid formation of emulsions, manipulation of their organization, and subsequent erasure.
