Mechanical Enhancement of Polydopamine Nano-Coatings via Thermal Annealing

Inspired by the adhesive proteins of mussels, polydopamine (pDA) has become one of the most widely employed methods for functionalizing material surfaces, powered in part by the versatility and simplicity of pDA film deposition. Despite the widespread adoption of pDA as a multifunctional coating for surface modification, it exhibits poor mechanical performance and it still remains a challenge to improve its mechanical properties without sacrificing functionality and versatility of pDA. Here, we demonstrate thermal annealing at a moderate temperature (130 C) as a facile route to enhance mechanical robustness of pDA coatings. Chemical spectroscopy, x-ray scattering, molecular force spectroscopy and bulk mechanical analyses indicate that monomeric and oligomeric species undergo further polymerization during thermal annealing, leading to fundamental changes in molecular and bulk mechanical behavior of pDA. Considerable improvements in scratch resistance and elastic modulus were noted for the annealed pDA coating, indicating the enhanced ability of the annealed coating to resist mechanical deformations, possibly due to cross-linking and increased intermolecular and cohesive interactions in the pDA structure.