19 nm-Thick Grafted-To Polymer Brushes onto Optimized Poly(Dopamine)-Coated Surfaces

Grafting-to polymer coatings are typically easy to apply, but the thickness of such coatings is typically limited to a few nanometers, which may hamper applications. This paper presents a grafting-to coating approach that yields polymer brushes up to an unprecedented thickness of 19 nm. To this aim, an easy-to-apply poly(dopamine) (PDA) primer layer is optimized. PDA is an easy-to-apply, but highly complex and chemically not well understood primer layer. In this study, PDA is deposited on silicon substrates using several deposition protocols (pH 4-7 in presence of NaIO4, and from Tris solution at pH 8.5). The modified surfaces are characterized using X-ray photoelectron spectroscopy, spectroscopic ellipsometry, static water contact angle measurements, and atomic force microscopy. Subsequently, block copolymers of poly(glycidyl methacrylate)(20)-b-poly(N-isopropylacrylamide)(n) are attached onto the PDA films using a grafting-to approach. The results indicate that the conditions of PDA deposition and the PDA film thickness strongly influence the stability and grafting efficiency of the block copolymers. PDA films deposited at pH 7 with NaIO4 are stable, and yield the most efficient grafting, with grafted polymer layers as thick as 19 nm. Polymer layers of such thickness are rarely achieved using grafting-to procedures from solution.