Study on self-healing behavior of the layer-by-layer assembled polyethylenimine/poly(acrylic acid) film

Many studies have demonstrated that intrinsic self-healing polyelectrolyte coatings can be fabricated by exponentially growing Layer-by-Layer (LbL) assembled polyelectrolyte multilayers. However, due to the lack of controlled self-healing evaluation methods, the researches on self-healing properties have remained at some simple qualitative characterization. In our study, a self-healing branched polyethylenimine (bPEI)/poly(acrylic acid) (PAA) films is successfully prepared by LbL and a new systematical self-healing evaluation method is developed. The cuts with controllable depth, width, and period can be easily fabricated on bPEI/PAA films through the colloidal lithography and photolithography. Colloidal lithography, as a facile, low-cost, and versatile unconventional technique, can realize precise and repetitive fabrication of cuts at the same sample and in the same area, which will be beneficial to the systematic study and evaluate self-healing behavior. The self-healing behaviors on the different cuts are observed by scanning electron microscope (SEM). The SEM results reveal that bPEI/PAA film could realize damage/healing process for multiple times at the same sample and in the same area. In addition, the self-healing abilities of the LbL films are related to the damage number, depth, and width of cuts. With the increase of damage number, depth, and width of cuts, the loss of polyelectrolyte was also increased, which lead to the flow of remaining polyelectrolytes were not enough to heal the cuts. This work provides a new route to systematically characterize the self-healing ability of bPEI/PAA films as well as other polyelectrolyte films.