Fine Switching between Underwater Superoleophilicity and Underwater Superoleophobicity while Maintaining Superhydrophobicity

Switching
between superhydrophobicity/underwater superoleophilicity
and superhydrophilicity/underwater superoleophobicity has been widely
designed. Recently, superwettability is subdivided into multiple extreme
wetting states for oil, water, and air as wetting and medium phases.
However, fine switching among the multiple superwettability is rare.
Here, a pH-responsive case is presented to demonstrate the fine switching
between underwater superoleophilicity and underwater superoleophobicity
while maintaining superhydrophobicity. The surface chemistry of silver-roughened
copper coatings is elaborately manipulated by water-repellent perfluoroalkyl
and alkyl chains and the smart terminal carboxyl group. By adjusting
the pH value of water, the completely opposite extreme wetting states
for oil in water are precisely controlled. Simultaneously, the extreme
repellence for water in the air can be kept owing to the fairly low
surface energy of the perfluoroalkyl chain. This discovery accelerates
the subdivision of superwettability and the achievement of unusual
superwetting switching.