From superhydrophilic to superhydrophobic surfaces by means of polymeric Layer-by-Layer films

In this paper a nanocoating that shows a superhydrophilic behavior (with a contact angle close to 0 degrees) is transformed into a superhydrophobic nanofilm (whose contact angle is 165 degrees) following a procedure that needs no nanoparticles to generate the nano-roughness required for superhydrophobicity. The superhydrophilic nanocoating was fabricated using poly (allylamine hydrochloride) (PAH) and poly (sodium phosphate) (PSP) combined by means of the Layer-by-Layer (LbL) technique. Seven different nanocoatings were constructed with different number of bilayers (4, 8, 12, 16, 20, 30 and 40) being the concentration of both polymers 10(-3) M. The analysis was conducted studying three different features: roughness, thickness and contact angle. The results show that initially, the contact angle of the nanofilms above 20 bilayers is close to 0 degrees, that is, the minimum value for a superhydrophilic coating. These surfaces were functionalized using 1H,1H,2H,2H-Perfluorodecyltriethoxsilane to transform them into hydrophobic coatings by Chemical Vapor Disposition (CVD). Thereafter, the nanofilms showed a superhydrophobic behavior with a contact angle of 165 degrees for the 40 bilayers films. The results of roughness and the images of AFM prove that the morphology of the nanocoating is preserved. (C) 2015 Elsevier B.V. All rights reserved.