Controlling and Patterning Polyelectrolyte Liquid Droplets with Electric Field

Control and manipulation of colloidal 'particles' using external electric fields have been of much interest for their potential uses in many applications, including drug delivery. Much of this work has focused on solid particles, with less emphasis on liquid droplets, due to the ease of manufacturing those materials. From a materials point of view, a surfactant stabilized oil droplet in water could serve this purpose. However, it is a non-trivial task to encapsulate biomolecules in an oil phase. To over this challenge, we have made a water-in-water emulsion of a phase-separated polyelectrolyte blend and stabilized the liquid droplets against coalescence. These droplet can serve as field responsive bio-capsules. The capsules are electrostatically charged, and can be simply manipulated using a 9V battery. We found that the droplets exhibit controlled mobility under the E-field in a 2D plane. Moreover, due to the high polarizability of polyelectrolytes, these polyelectrolyte capsules can be patterned into parallel, pearl-like chains - typical of an electrorheological fluid of conventionally solid particles - albeit at orders of magnitude lower E-field strengths. As a demonstration, we encapsulated and transported protein molecules of various kinds in these field-driven capsules.