Successive four-phase liquid separation using hierarchical microcube-nanohole structure and controlled surface wettability meshes.

The chemical industry needs filter systems with selective wetting properties for environmental protection and effective liquid separation. Current liquid-separation systems are mainly based on the surface energy of the meshes used to separate liquid particles; the smaller the difference between the surface tension of the liquids to be separated, the lower the separation efficiency of these systems. Sophisticated control of the surface wettability of a separation system is necessary to separate liquids with small differences in their surface tension. We precisely adjusted the surface-energy threshold of aluminium meshes used for separation by simply coating their hierarchical microcube and nanohole structures with different materials. We also applied patterning technology to create a single mesh with a heterogeneous distribution of surface tension to successively separate four liquids. Under the force of gravity, the hybrid system of meshes effectively separated the mixture of four liquids, yielding a perfect collection rate (≥98%) and high content ratio (≥96%). Even multiphase mixtures of immiscible liquids with surface tension differences as small as 10.4 mN/m could be effectively separated. Thus, multiphase liquid-separation systems can be used for the efficient and economical separation of various liquid mixtures in many industrial and environmental fields.