Reversible tuning of wetting behavior of polymer surface with responsive polymer brushes

We develop the route to fabricate mixed brushlike layers on polyamide substrates (PA-6, PA-6I, PA-66) by the "grafting from" approach. The PA substrates were functionalized by NH3 plasma. The azo initiator of radical polymerization was covalently bound to the functionalized PA surface. A two-step grafting procedure was applied to graft polystyrene in the first step and poly(2-vinylpyridine) in the second step. We found remarkable differences between grafting on Si wafers and on the PA substrates. "Grafting from" the PA surface results in a dramatic increase of the surface roughness of the film which can be explained by grafting in a swollen surface layer of PA. Because of this effect, we found a substantial amount of grafted polymers even on not functionalized PA substrates, which was explained by grafting via chain transfer reaction. The synthesized mixed polymer brushes form responsive coatings which switch their morphology due to the interplay between lateral and vertical phase segregation upon exposure to selective solvent. The switching of morphology affects the change of the surface composition of the brushes and their surface energetic state. We performed the same grafting procedure on the surface of PA fabric. In this case the switching behavior was amplified by the texture of the material: wettability of the fabric with the mixed brush was switched from complete wetting to highly hydrophobic state (150degrees water contact angle).