Reversible Transition between Superoleophobic and Superoleophilic States on Titania Coated Substrates by UV Irradiation

TL;DR

This study presents a reversible method to switch between superoleophobic and superoleophilic states on titania-coated surfaces using UV irradiation, enabling controllable liquid repellency for potential applications.

Contribution

It introduces a simple, repeatable process to reversibly alter surface wettability by UV-induced decomposition and re-grafting of monolayers on titania-coated substrates.

Findings

Spray coating creates micro-particles that repel lower surface tension liquids.

UV irradiation decomposes FDTS, switching to superoleophilic state.

Surface wettability can be restored by annealing and re-grafting FDTS.

Abstract

We demonstrate that tunable superoleophobic surfaces fabricated by a simple spin and spray coating methods of titania on silicon (Si) wafers and stainless steel (SS) mesh, which possess a hierarchical re-entrant structure consisting of nano meter sized particles on top of micron sized particle, are able to induce superoleophobicity on an oleophilic self assembled monolayer of 1H,1H,2H,2H-perflurodecyltrichlorosilane (FDTS). Though comparison between different coating methods, we show that spray coating on Si substrate and SS mesh can repel lower surface tension liquids than spin coating on Si substrates due to formation of half spherical micro-particles on the spray coated substrates which is confirmed by FESEM images. Subsequently, superoleophobic surfaces changes its super repellent property to complete wetting of any liquids under UV illumination by decomposing the FDTS molecules via photo catalytic property of titania particles. The superoleophobic property was regained by annealing followed by grafting of FDTS on the UV treated surface and the total process is repeatable over number of cycles.