Chemical characterization of the coatings and polymerized polyphenol particles indicated the involvement of both physical and chemical interactions in the auto-oxidation reactions. Coating evaluation by ellipsometry and AFM confirmed the deposition kinetics determined by QCM-D and revealed maximum coating thicknesses of approximately 50 and 75 nm for TA and PG, respectively. The PG deposition was biphasic, starting with the adsorption of a nonrigid viscoelastic layer which was followed by layer stiffening upon further mass adsorption. TA coatings revealed a multiphasic layer formation: the deposition of an initial rigid layer was followed by the buildup of an increasingly dissipative layer, before mass adsorption stopped after approximately 5 h of coating time. The coating deposition was followed in real time over a period of 24 h using a quartz crystal microbalance with dissipation monitoring (QCM-D). We report the coating deposition kinetics of the polyphenol tannic acid (TA) and the simple phenolic compound pyrogallol (PG) on titanium surfaces. However, the mechanisms behind the coating deposition are poorly understood. Polyphenols can form functional coatings on a variety of different materials through auto-oxidative surface polymerization in a manner similar to polydopamine coatings.
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