Engineering Nitroxide Functional Surfaces Using Bioinspired Adhesion
Woehlk, H. / Steinkoenig, J. / Lang, C. / Michalek, L. / Trouillet, V. / Krolla, P. / Goldmann, A.S. / Barner, L. / Blinco, J.P. / Barner-Kowollik, C. / Fairfull-Smith, K.E. (2018)
Langmuir, 2018, 34, 10, 3264–3274, DOI: 10.1021/acs.langmuir.7b0375
- Date: Februar 2018
We pioneer a versatile surface modification strategy based on mussel-inspired oxidative catecholamine polymerization for the design of nitroxide-containing thin polymer films. A 3,4-dihydroxy-l-phenylalanine (l-DOPA) monomer equipped with a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-derived oxidation-labile hydroxylamine functional group is employed as a universal coating agent to generate polymer scaffolds with persistent radical character. Various types of materials including silicon, titanium, ceramic alumina, and inert poly(tetrafluoroethylene) (PTFE) were successfully coated with poly(DOPA-TEMPO) thin films in a one-step dip-coating procedure under aerobic, slightly alkaline (pH 8.5) conditions. Steadily growing polymer films (∼1.1 nm h–1) were monitored by ellipsometry, and their thicknesses were critically compared with those obtained from atomic force microscopic cross-sectional profiles. The heterogeneous composition of surface-adherent nitroxide scaffolds examined by X-ray photoelectron spectroscopy was correlated to that examined by in-solution polymer analysis via high-resolution electrospray ionization mass spectrometry, revealing oligomeric structures with up to six repeating units, mainly composed of covalently linked dihydroxyindole along the polymer backbone. Critically, the reversible redox-active character of the nitroxide-containing polymer scaffolds was investigated by cyclic voltammetric measurements, revealing a convenient and facile access route to electrochemically active nitroxide polymer coatings with potential application in electronic devices such as organic radical batteries.