Furcated droplet motility on crystalline surfaces

Directed liquid motion has been conventionally mediated by functionalizing chemical inhomogeneity or texturing topological anisotropy on target surfaces. Here we show the self-propulsion of droplets that furcated in well-defined directions on piezoelectric single crystals in the absence of any apparent asymmetry or external force. By selecting the crystal plane to interface with the droplets, the thermoelastic-piezoelectric interplay yields intricate electric potential profiles, enabling various forms of self-propulsion including unidirectional, bifurcated and trifurcated. This effect originates from an anisotropic crystalline structure that generates contrasting macroscopic liquid behaviours and is observed with cold/hot and volatile droplets. Intrinsically oriented liquid motions have broad applicability in processes ranging from soft matter engineering, autonomous material delivery and thermal management to biochemical analysis.