Morphological changes of sintered polydopamine coatings

Polydopamine (PDA), produced from the self-polymerization of dopamine under alkaline conditions, is well known for its natural adhesive properties on a broad variety of surfaces. However, there is still ongoing controversy as to its growth, coverage and morphology characteristics. Here, we investigate the growth of PDA on a silicon substrate over various time periods (0-24 h) using a gentle rocking method. The samples were then post-heated at 150 °C under vacuum. Both the as-prepared and post-treated samples were examined with a combination of x-ray photoelectron, UV photoelectron, and neutral impact collision ion scattering spectroscopies, as well as atomic force microscopy. Results indicated that the PDA layer growth plateaus after 5 h, proceeding via island-growth, with incomplete coverage after 24 h. Heating PDA substrates resulted in sintering of the PDA islands to form a more homogenous surface coverage, indicating this is critical for the formation of smooth and homogenous coatings.