All-in-liquid 3D printed structures: Arresting oil-water interfacial layers with emulsions

All-in-liquid devices have broad potential applicability in processes ranging from energy storage to drug delivery and tissue engineering. Conventionally, they are produced by the jamming of nanoparticle-polymer at the oil-water interface, where one liquid is arrested in a desired non-equilibrium shape in the second liquid phase. Such structures lack the multiscale porosity that exits in equivalent solid hierarchies. Remarkably, we report on printing spongy all-in-liquid materials utilizing the direct ink writing technique. Stable liquid columns of nanoparticle dispersions are produced inside micellar solutions due to the rapid formation of a highly viscoelastic emulsion phase at the interface. The diffusion time of the generated emulsified zone into the micellar solution is longer than the convection time scale. Thus, emulsions remain at the interface during the injection period. The printed aqueous phase becomes an emulsion zone, creating a porous texture in the oil phase. Consequently, a 3D structure with flexible walls consisting of layered emulsions is achieved, which is counterintuitive to the current liquid-based printed structures. We show the applications of emulsion-based 3D printed all-in-liquid materials in liquid lab-on-chip devices and natural gas/hydrogen storage.