Thermal Annealing Treatment to Achieve Switchable and Reversible Oleophobicity on Fabrics
by Chhatre, S., Tuteja, A., Choi, W., Reveaux, A., Smith, D., Mabry, J.M., McKinley, G.H. and Cohen, R.E.

Surfaces which are strongly non-wetting to oil and other low surface tension liquids can be realized by
trapping microscopic pockets of air within the asperities of a re-entrant texture and generating a solid liquid-
vapor composite interface. For low surface tension liquids like hexadecane (γ_lv = 27.5 mN/m),
this composite interface is metastable due to the low value of the equilibrium contact angle.
Consequently pressure perturbations can result in an irreversible transition of the metastable composite
interface to the fully-wetted interface. In this work, we use a simple dip-coating and thermal annealing
procedure to tune the liquid wettability of commercially available polyester fabrics. A mixture of 10 %
1H,1H,2H,2H-heptadecafluorodecyl polyhedral oligomeric silsesquioxane (fluorodecyl POSS) and
90 % polyethyl methacrylate (PEMA) is used to uniformly coat the fabric surface topography. Contact
angle measurements show that a robust metastable composite interface with high apparent contact
angles can be supported for hexadecane (γ_lv = 27.5 mN/m) and dodecane (γ_lv = 25.3 mN/m). To tune the
solid surface energy of the coated surface, we also developed a reversible treatment using thermal
annealing of the surface in contact with either dry air or water. The tunability of the solid surface energy
along with the inherent re-entrant texture of the polyester fabric result in reversibly switchable
oleophobicity between a highly non-wetting state and a fully wetted state for low surface tension liquids
like hexadecane and dodecane. This tunability can be explained within a design parameter framework
which provides a quantitative criterion for the transition between the two states, as well as accurate
predictions of the measured values of the apparent contact angle (θ*) for the dip-coated polyester
fabrics.