Mussel-inspired polydopamine (PDA) and its derivative materials have exhibited a huge potential as a facile and versatile route to fabricate multifunctional coatings on virtually any substrate surface. However, their performance and applicability are frequently obstructed by limited optical absorption in visible regions of PDA and poor surface adhesion persistence of dopamine solutions. Herein, we report a facile strategy to improve these problems by rationally regulating the dopamine polymerization pathway through mixed-solvent-mediated periodate oxidation of dopamine. The spectral analysis, ultrahigh-performance liquid chromatography coupled with high-resolution mass spectrometry, and density functional theory simulations systematically demonstrate that the mixed-solvent reaction systems can effectively accelerate the periodate-induced formation of cyclized moieties in the PDA microstructure and inhibit their further oxidative cleavage, thus contributing to narrowing the inherent energy band gap of PDA and improving the long-lasting surface deposition performance of aged dopamine solutions. Moreover, the newly constructed cyclized species-rich PDA coatings have excellent surface uniformity and significantly enhanced chemical stability. Benefiting from these fascinating properties, they have been further used for permanent dyeing of natural gray hair with remarkably improved blackening effect and excellent practicability, which exhibited their promising prospect in real-world applications.
Keywords: hair dyeing; intrinsic light absorption; mixed-solvent; polydopamine coatings; surface adhesion persistence.