(19f) Biphasic Liquid Systems with Reversible Shape-Memory Domains

Liquids comprising two coexisting phases can form a range of stable and metastable states, including wetting films, droplets and threads. Processes that permit rapid and reversible transformations between such morphologies, however, have been difficult to realize because physical properties required for rapid shape change (e.g., low interfacial tension or viscosity) provide pathways for relaxation that result in short-lived states. In this presentation, I will report the discovery of shape-shifting pathways and shape-memory behaviors of microdomains of a biphasic liquid system comprised of an isotropic oil and a liquid crystalline oil (LC). The isotropic oil forms stable wetting films (“original” shape) between solid surfaces and an overlying LC phase and, when exposed to a transient (< 1 s) AC electric field at low frequency (10 Hz), transforms into long-lived (> 24 hr) spherical domains (“temporary” shape) stabilized by topological defects in the LC. Subsequent application of an AC electric field of high frequency (1 kHz) triggers solitons to form in the LC, creating kinetic pathways that lead to remarkably rapid (< 3 s) coalescence of the dispersed spherical domains and recovery of the original shape (wetting film). I will show rapid and reversible switching between distinct optical states of the biphasic system, with each state persisting without continuous application of the field, thus providing a combination of optical properties long sought in thin liquid films. The fully reversible and long-lived emulsion formation to be described in this presentation appears promising for materials synthesis, microchemical systems and tunable optical metamaterials (e.g., to control visibility and transmittance of light through windows).