Surface patterning of micron-sized aluminum flakes by seeded dispersion polymerization: Towards waterborne colored pigments by gold nanoparticles adsorption

The concomitant polymer embedding and surface patterning of micron-sized aluminum flakes by dispersion polymerization of styrene is reported. The aluminum pigments coated by a thin silica layer were modified by trimethoxysilylpropyl acrylate grafting (TMSPA-grafted Al@silica). Dispersion polymerization of styrene was further performed in alcoholic or hydro-alcoholic media in the presence of the organically modified TMSPA-grafted Al@silica pigments as a seed and poly(N-vinylpyrrolidone) (PVP) as a steric stabilizer to lead to hybrid aluminum flakes. The weight fraction of polymer onto the aluminum pigment surface was tuned from 14 to 29 wt.% by the hydro-alcoholic continuous phase composition and from 19 to 38 wt.% by the initiator content. The chemical nature of the initiator plays an important role in the surface patterning of the hybrid aluminum flakes as 2,2′-azobis(isobutyronitrile) initiator provided polymer nodules, i.e. due to a pattern of polymer protrusions with nodules shape at the surface of the inorganic substrate, while a flat and continuous polymer layer was obtained with 2,2′-azobis(2-amidinopropane) dihydrochloride initiator. Moreover, the introduction of ammonium groups at the surface of the polymer particles was possible by the delayed addition of a cationic acrylate co-monomer ([2-(acryloyloxy)ethyl]-trimethylammonium chloride) rendering the pigments dispersible in water. Finally, gold nanoparticles were successfully deposited onto the micro-patterned aluminum flakes to open the way towards new colored aluminum pigments. Both location of cationic ammonium function in the polymer nodule and nature of gold nanoparticles ligands were investigated with the aim to evaluate the amount of adsorbed gold nanoparticles. The final hierarchically patterned aluminum pigments dispersed in water exhibited an intense purple color.