(311c) Manipulation of Coacervate Droplets with an Electric Field

Many biopolymers are highly charged, and as in the case of many polymer mixtures, they tend to phase separate as a natural consequence of chain connectivity and an associated relatively low entropy of polymer mixing. Recently, it has become appreciated that the phase-separated structures formed by such blends, called polyelectrolyte coacervates, underlie numerous biological structures and processes essential to living systems, and there has been intense interest in understanding the unique physical features of this type of phase separation process. In the present work, we are particularly concerned with the field responsiveness of stabilized coacervate droplets formed after phase separation of polyelectrolytes and then exposed to distilled water, making the droplet interfacial layer acquire an elastic character that strongly stabilizes them against coalescence. We show that we can precisely control the positions of individual droplets and arrays of them with relatively low voltage electric fields (on the order of 10 V/cm) and that the imposition of an oscillatory field gives rise to chain formation with coarsening of these chains into long fibers. Such a phase separation-like process is generally observed in electrorheological fluids of solid colloidal particles subjected to much larger field strengths. The key to these novel coacervates’ electrorheological properties is the altered interfacial viscoelastic properties when the droplets are introduced into distilled water and the associated high polarizability of the droplets, similar to the properties of many living cells. Since many different molecular ‘payloads’ can be incorporated into these stable droplets, we anticipate many applications.