Double Emulsions Droplets with Thermally Reconfigurable Shells as Micro-Lenses*

Complex emulsions, serving as micro-lenses, offer a unique and versatile material platform for innovative applications in optics, photonics and beyond. Multi-phase droplets, with the versatility to manipulate light at microscale dimensions, are ideal candidates for designing tunable lenses. For example, triple-phase emulsions, consisting of three distinct phases with different refractive indices, have demonstrated promise in correcting optical aberrations. Here we introduce a novel kind of tri-phase emulsions with thermally reconfigurable shells. Water-oil-water double emulsions featuring a shell made of hydrocarbon and fluorocarbon components, which exhibit temperature-dependent miscibility, are rendered stable with specially tailored surfactants to form solid-like W/O interfaces, whose viscoelasticity is then characterized with the droplet flow in patterned sinusoidal channels as a rheometer in PDMS devices. Upon temperature change, the two components in the oil shell phase separate; therefore, the droplets reconfigure into a new morphology resembling an egg with double yolks. The morphologies of the droplets are tuned by changing the hydrocarbon-to-fluorocarbon ratio and the small surfactants used in the outer aqueous phase, forming exotic structures. 2D simulations of ray tracing passing through different droplet morphologies are further performed in order to calculate the longitudinal and transverse spherical aberrations for informative fluid lens design and selection.