(230b) Hierarchical Emulsion Networks from Endoskeletal Droplets

The shape of liquid-liquid interfaces at small length scales is dictated by surface tension. In the colloidal size regime, isotropic interfaces are highly favorable to anisotropic ones due to the large energy cost of increasing interfacial area. As a result, emulsions consist of spherical droplets that coarsen through coalescence into larger spheres and eventually a fully phase-separated system. The coarsening behavior of emulsions implies that they are intrinsically incapable of building larger structures, limiting them to forming isotropic, discontinuous dispersions.

Producing emulsion droplets that resist coarsening requires a structural scaffold to be introduced to counteract surface tension. In endoskeletal droplets, the scaffold consists of an internal network of intercalated wax crystallites with a yield stress strong enough to resist the driving force for droplet collapse. As a result, the droplets can be molded into anisotropic shapes. However, the internal elasticity is not insurmountable; multiple droplets can partially coalesce with others, forming larger suprastructures that retain the shapes of the component droplets. Many droplets can be coalesced into linear secondary structures akin to polymer chains, which can then assemble tertiary folded structures similar to electrospun fiber networks, resulting in hierarchical assemblies of bicontinuous fluids that preserve a continuous, anisotropic liquid interface. The size scales of these networks can be tuned during formation or once formed by applying external fields or tuning coalescence between droplets, allowing diverse networks to be formed. We present a microfluidic method for producing droplet suprastructures continuously and demonstrate control of three-dimensional structures during and after production.