Exponential growth of layer-by-layer assembled coatings with well-dispersed ultrafine nanofillers: a facile route to scratch-resistant and transparent hybrid coatings

We report an innovative and straightforward method to well-disperse a low loading content of inorganic nanofillers of extremely small size in exponentially growing layer-by-layer (LbL) assembled micrometre-thick polymeric coatings. Complexes of poly(acrylic acid) (PAA) and in situ synthesized CaCO3 nanoparticles (noted as PAA-CaCO3) were alternately deposited with poly(allylamine hydrochloride) (PAH) to fabricate exponentially growing PAA-CaCO3/PAH coatings. The ultrafine CaCO3 nanofillers with a size of ∼2 nm were homogeneously dispersed in the hybrid PAA-CaCO3/PAH coatings because of the strong interaction of CaCO3 nanofillers with PAA and the “in-and-out” diffusion of the polyelectrolytes during the LbL assembly process. Thermogravimetric analysis indicates that the PAA-CaCO3/PAH coatings have a loading content of ∼4.2 wt% CaCO3 nanofillers. The thermally cross-linked PAA-CaCO3/PAH coatings, which have greatly enhanced hardness and Young's elastic modulus because of the well-dispersed CaCO3 nanofillers, are highly transparent and scratch-resistant. The transparent and scratch-resistant PAA-CaCO3/PAH coatings are further proved to be highly useful as scratch-protection layers of other functional film materials. The present study provides a convenient and rapid method to prepare mechanically robust and transparent coatings for various applications.