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°) is transformed into a superhydrophobic nanofilm (whose contact angle is 165°) 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°, 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° for the 40 bilayers films. The results of roughness and the images of AFM prove that the morphology of the nanocoating is preserved.