Polydopamine (PDA) is one of the most commonly used materials for the preparation of protective adhesive layers for biomedical and tribological applications. Despite its widespread use, the way in which the polymer binds to the substrate is yet to be fully understood. At the nanometre level, the spatial arrangement of individual molecules and the initial growth of PDA layers are expected to be influenced by the utilized substrate material and PDA deposition time. To investigate these hypotheses, we have prepared PDA layers with various times of deposition on surfaces of gold and oxygen-terminated materials (silicon/silicon dioxide and nitrogen-doped titanium oxide). The prepared samples were subsequently analysed using a scattering-type scanning near-field optical microscope utilizing four irradiation energies in the mid-infrared region to detect the chemical contrast originating from vibrational modes of selected chemical moieties. It was found that the polymerization process leads to a formation of a surface confluent PDA layer and deposition of PDA nanoaggregates. The differences in the optical contrast observed at irradiation energies corresponding to the vibrations of indole units of PDA and quinoid groups of polymerization intermediates indicated a slightly different composition of the nanoaggregates and the surrounding confluent layer.

Department of Chemistry and Physics of Surfaces and Interfaces Institute of Macromolecular Chemistry Czech Academy of Sciences 162 06 Prague 6 Czech Republic

Department of Physical Chemistry Faculty of Chemical Engineering University of Chemistry and Technology 166 28 Prague 6 Czech Republic

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