Abstract:

Contrary to everyday experience, where all liquid droplets assume rounded, near- spherical shapes, we have demonstrated that liquid droplets undergo temperature- controllable self-faceting shape transitions, with their bulk remaining liquid. These transitions occur for a wide range of different chemical compositions, for broad temperature ranges, and in droplets of sizes spanning an incredible 13 decades in volume, from nano- to yocto- liters, suggesting that these phenomena may play a role in a wide range of technologies. Furthermore, droplets’ solidification enabled the formation of icosahedral (and other complex-shape) micro- and nano- particles, promising for self- assembly of metamaterials, yet unachievable by any other method [1].

Our recent experiments have resolved the fundamental physical mechanism driving these phenomena. We have employed direct electron microscopy and other methods to demonstrate, that the effect is driven by a few-nm thick monolayer interfacial crystal, self- assembled at the surface of these liquid droplets. The closed-surface topology of this geometrically frustrated, quasi-two-dimensional hexagonal crystal dictates the formation of lattice defects, controlling the precise shapes adopted by the droplets. Similar physical mechanisms are suggested to play a fundamental role in shape formation in a wide range of biological systems: from viruses to living organisms [1].

Furthermore, taking advantage of crystalline monolayers’ self-assembly on surfaces of these droplets, we developed a strategy allowing the droplets to be decorated by precisely self-positioned molecules or nanoparticles. The achieved precise self-decoration is promising for multiple nanotechnological applications and opens new routes towards the self-assembly of complex higher-hierarchy liquid and solid structures [2].

[1] Marin et al., Curr. Opin. Colloid Interface Sci. 49, 107 (2020)

[2] Das et al., Nat. Phys. (in press, 2022)