Highly Transparent, Nanofiller-Reinforced Scratch-Resistant Polymeric Composite Films Capable of Healing Scratches

Integration of healability and mechanical robustness is challenging in the fabrication of highly transparent films for applications as protectors in optical and displaying devices. Here we report the fabrication of healable, highly transparent and scratch-resistant polymeric composite films that can conveniently and repeatedly heal severe damage such as cuts of several tens of micrometers wide and deep. The film fabrication process involves layer-by-layer (LbL) assembly of a poly(acrylic acid) (PAA) blend and branched poly(ethylenimine) (bPEI) blend, where each blend contains the same polyelectrolytes of low and high molecular weights, followed by annealing the resulting PAA/bPEI films with aqueous salt solution and incorporation of CaCO3 nanoparticles as nanofillers. The rearrangement of low-molecular-weight PAA and bPEI under aqueous salt annealing plays a critical role in eliminating film defects to produce optically highly transparent polyelectrolyte films. The in situ formation of tiny and well-dispersed CaCO3 nanoparticles gives the resulting composite films enhanced scratch-resistance and also retains the healing ability of the PAA/bPEI matrix films. The reversibility of noncovalent interactions among the PAA, bPEI, and CaCO3 nanoparticles and the facilitated migration of PAA and bPEI triggered by water enable healing of the structural damage and restoration of optical transparency of the PAA/bPEI films reinforced with CaCO3 nanoparticles.