Abstract
Polydopamine (PDA) is a simple and versatile conformal coating material that has been proposed for a variety of uses; however in practice its performance is often hindered by poor mechanical properties and high roughness. Here, we show that blue-diode laser annealing dramatically improves mechanical performance and reduces roughness of PDA coatings. Laser-annealed PDA (LAPDA) was shown to be >100-fold more scratch resistant than pristine PDA and even better than hard inorganic substrates, which we attribute to partial graphitization and covalent coupling between PDA subunits during annealing. Moreover, laser annealing provides these benefits while preserving other attractive properties of PDA, as demonstrated by the superior biofouling resistance of antifouling polymer-grafted LAPDA compared to PDA modified with the same polymer. Our work suggests that laser annealing may allow the use of PDA in mechanically demanding applications previously considered inaccessible, without sacrificing the functional versatility that is so characteristic of PDA.
Highlights
Polydopamine (PDA) is a simple and versatile conformal coating material that has been proposed for a variety of uses; in practice its performance is often hindered by poor mechanical properties and high roughness
Considering the current understanding of the formation and molecular structure of PDA10–12, this deficiency could be attributed to the relatively weak noncovalent intermolecular bonds between PDA building blocks[13,14,15]. Another significant problem is the unavoidable spontaneous deposition of PDA particles ranging from hundreds of nanometers to a few microns on top of the PDA layer, producing high roughness that may be undesirable from a surface engineering perspective
Considering that the light absorption of PDA is in the range of blue-diode laser wavelength (440 nm)[15], we inferred that blue-diode laser annealing (BLA) could be employed to efficiently anneal and improve PDA properties
Summary
Polydopamine (PDA) is a simple and versatile conformal coating material that has been proposed for a variety of uses; in practice its performance is often hindered by poor mechanical properties and high roughness. The level of graphitization can be controlled by adjusting the laser power to achieve a balance between the wear resistance and the catechol functionality of the PDA film.
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