Mechanically Responsive Films of Variable Hydrophobicity Made of Polyelectrolyte Multilayers

Mechanically responsive surfaces that allow to switch reversibly from a hydrophobic to a hydrophilic substrate are reported. The surfaces are constituted of polyelectrolyte multilayers deposited on modified charged silicone sheets. n bilayers of poly(allylamine)-Nafion (PAH−Naf) and m bilayers of poly(allylamine)−poly(acrylic acid) (PAH−PAA) composed the multilayers. A (PAH−Naf)_n film possesses a water contact angle of around 105°, whereas the contact angle of a (PAH−Naf)₄−(PAH−PAA)_m multilayer is around 50°. When such a film with m < 5 and terminated by PAA is stretched out, its water contact angle increases up to around 100°. Successive elongation/retraction cycles allow the water contact angle to alternate reversibly between 100 and 57° indicating the reversible mechanical responsive nature of the film.