Creation of robust cupric stearate coated liquid marbles for droplet manipulations

Liquid marbles which can be created by encapsulating water droplets using superhydrophobic powders have attracted extensive attention for their various promising application prospects. Cupric stearate coated liquid marbles was created by encapsulating water droplet using cupric stearate powders in a droplet rolling process. Hierarchies of robustness have been constructed which showed that the cupric stearate coated liquid marbles survived on surfaces with different wettabilities and could keep intact after impact, manipulation, transportation and mechanical compression. To evaluate robustness of the liquid marbles in manipulation processes, the mass of superhydrophobic powders per unit area on the surface of liquid marbles (powder surface density) was investigated. Powder surface density was decreased with the increase of water volume in the liquid marble. Moreover, water volume of the liquid marble was adjusted in situ, and the critical powder surface density was obtained via increasing or decreasing water volume of the liquid marble. By analyzing the critical surface density upon rupture or collapse of the liquid marble, the dependence of the critical surface density on the water volume of the liquid marble was predicted, which agrees well with experimental results.