Poly-catecholamines have received significant attention for their versatile properties and straightforward fabrication methods. In this work, we present the results of investigations conducted on films comprising one such polymer, namely, polydopamine (PDA). The polymer’s monomer, dopamine, comprises a benzene ring with two adjacent hydroxyl side groups, called catechol, further connected to an amine group through an ethyl chain. The same groups co-occur in the adhesive proteins found in mussels, possessing a unique ability to stick their bodies to a wide variety of surfaces, including adhesion underwater. In the search for membranes thicker than electropolymerization would normally allow for nonconductive polymers, multiple ≈20 nm thick PDA layers were stacked, utilizing PDA’s analogous adhesive qualities. This resulted in samples consisting of 1-4 PDA layers of up to ≈58 nm total thickness. The samples possess great elasticity (characterized by Young Modulus values of 7.3-9.3 GPa), which we assessed utilizing Brillouin Light Scattering (BLS). These results indicated that the stacked PDA films can be effectively treated as a single thick layer. The membranes absorb visible light, similarly to the various photosynthetic pigments found in algae in plants. Red laser light (λ = 660 nm) irradiation measurements resulted in obtaining the extinction coefficient of PDA, whose value was magnitudes larger than that of classical polymers. These exceptional absorptive qualities allow for finely tuned control of the membrane morphology. Applying heat induced by a laser beam causes water desorption from the sample, manifesting as the flattening of the membrane surface, analogous to the contractions of muscle tissue. This process was found to be reversible, with the removal of the stimulus resulting in the spontaneous wrinkling of the surface due to water resorption. The laser light-induced motion investigations lead to the characterization of PDA as a ultra-thin actuator characterized by relaxation times of the order of ≈1-10 ms.
References:
[1] A. Krysztofik et al., “Multi-responsive poly-catecholamine nanomembranes,” Nanoscale, 2024, doi: 10.1039/D4NR01050G.
[2] A. Krysztofik et al., “Fast Photoactuation and Environmental Response of Humidity-Sensitive pDAP-Silicon Nanocantilevers,” Advanced Materials, 2024, doi: 10.1002/adma.202403114.
Z. K., A. K., M. P., and B. G. acknowledge the National Science Centre of Poland (NCN) for the OPUS grant UMO-2021/41/B/ST5/03038.
