Nanoparticle type-dependent regulation of polydopamine coating formation and wettability

Polydopamine (PDA) has emerged as a versatile surface modification material because of its universal adhesion and ability to tailor surface properties. However, although various nanomaterials have been incorporated into PDA coatings, the influence of nanoparticle morphology on dopamine polymerization, coating formation, and the resulting surface wettability has not been systematically investigated. In this study, four nanoparticles representing three structural dimensionalities, namely carbon quantum dots (CQDs) and silica nanoparticles (SiO₂) as 0D nanomaterials, halloysite nanotubes (HNTs) as 1D nanomaterials, and graphene oxide (GO) nanosheets as a 2D nanomaterial, were comparatively evaluated as regulators of PDA coating formation. Dopamine oxidation in the solution phase was monitored by UV-vis spectroscopy, while the resulting coatings were characterized using colorimetry as an indicator of film thickness, field-emission scanning electron microscopy (FESEM) to examine the morphology of the films, atomic force microscopy (AFM) to measure surface roughness, and static water contact angle (WCA) measurements to investigate the interaction of water droplets with the surface of the resulting coatings. The results demonstrate that nanoparticle morphology markedly influences dopamine polymerization, PDA deposition, and coating morphology. Among the investigated systems, CQD-PDA coatings exhibited the largest surface aggregates (323 ± 65 nm) and the highest surface roughness (R _a = 114 ± 5.5 nm, R _q = 163 ± 19 nm), indicating enhanced coating growth. Subsequent deposition of a thin polydimethylsiloxane (PDMS) layer on the optimized CQD-PDA coating increased the WCA to 119°, while maintaining a WCA of approximately 90° after five ultrasonication cycles and 103° after five water-impact cycles, demonstrating good coating durability. These findings establish nanoparticle morphology as a key parameter governing PDA coating formation and provide a simple, morphology-directed strategy for fabricating functional coatings with controllable wettability.