Superhydrophobicity and superoleophobicity from hierarchical silica sphere stacking layers

The present study demonstrates the creation of a stable superhydrophobic and superoleophobic surface using a hierarchical nano/submicron silica sphere stacking layer with a thin fluorination coating on the surface of the spheres. The super repellent surface not only repels the liquids with surface tension, ranging from 23.4 to 73.2 mN m−1, but also shows a stable superoleophobicity toward sunflower oil at least for 3 days. The deposition of nanospheres provides the nanoscale cavity to repel the oil penetration, referring to the Cassie state. Thus, there is an existing thin air film that is capable of protecting each submicron spheres from oil contamination, subsequently leading to the superoleophobicity. The significant enhancement of superoleophobicity can be attributed to the following facts: (i) surface fluorination (low surface tension), (ii) surface topography (roughness), and (iii) creation of bionic surface hierarchically combined with nano/submicron architecture. Accordingly, designing of the surface geometry with two-tier roughness acts as the key factor in inducing superoleophobicity.