Control of Surface Properties Using Fluorinated Polymer Brushes Produced by Surface-Initiated Controlled Radical Polymerization

Abstract

Surface-grafted styrene-based homopolymer and diblock copolymer brushes bearing semifluorinated alkyl side groups were synthesized by nitroxide-mediated controlled radical polymerization on planar silicon oxide surfaces. The polymer brushes were characterized by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and time-dependent water contact angle measurements. Angle-resolved XPS studies and water contact angle measurements showed that, in the case of the diblock copolymer brushes, the second block to be added was always exposed at the polymer-air interface regardless of its surface energy. Values of z*/Rg were estimated based on the radius of gyration, Rg, of the grafted homopolymer or block copolymer chains for the grafted brushes and thickness of the brush, z*. The fact that z*/Rg > 1 suggests that all these brushes are stretched. These results support the idea that after grafting the first block onto the surface the nitroxide-end capped polymer chains were able to polymerize the second block in a "living" fashion and the stretched brush so formed was dense enough that the outermost block in all cases completely covers the surface. NEXAFS analysis showed a relationship between the surface orientation of the fluorinated side chains and brush thickness with thicker brushes having more oriented side chains. Time-dependent water contact angle measurements revealed that the orientation of the side chains of the brush improved the surface stability toward reconstruction upon prolonged exposure to water.

From Self-Assembled Monolayers to Coatings: Advances in the Synthesis and Nanobio Applications of Polymer Brushes

“…X-ray Photoelectron Spectroscopy (XPS) can also be used for surface characterization as it probes a depth of ~10 nm. Most often XPS is used to confirm brush growth, to study surface chemical composition of the brush and to determine surface densities of bound molecules on the brush [138][139][140][141][142]. XPS has also been used for initiator-coated surfaces, however most of these studies have been limited to qualitative confirmation of the presence of initiator groups [143][144][145][146].…”

Structural characterization of an elevated lipid bilayer obtained by stepwise functionalization of a self-assembled alkenyl silane film

“…For a melt brush the most common measure of whether it is in the brush or mushroom regime is the ratio of brush thickness ͑z͒ to radius of gyration ͑Rg͒. 38 The radius of gyration of the polymer as formed in solution is estimated as a͑N /6͒ 1/2 with a being the unit length of PEG 45 ͑0.52 nm͒ and N the degree of polymerization ͑45͒. So for a PEG 45 polymer Rg is equal to 0.52͑45/ 6͒ 1/2 = 1.42 nm.…”

Surface treatment and characterization: Perspectives to electrophoresis and lab‐on‐chips

“…The second block composed of styrene monomers, results in physicochemical changes, as studied by X-ray photoelectron spectroscopy (XPS) or water contact angle measurements. In addition, it demonstrated the living nature of NMRP after the first block synthesis [195]. Recently, using a similar strategy, this group realized the nitroxide-mediated polymerization of styrenic monomers containing oligo(ethylene glycol) side chains on silicon wafers.…”

“…Figure 11. Polymer brushes grown by nitroxide-mediated polymerization (adapted from reference [195]). [199]).…”