Hierarchical nanoflake surface driven by spontaneous wrinkling of polyelectrolyte/metal complexed films.

A mechanical or physical change observed in nanocomposite thin films has recently offered new opportunities to generate intriguing nanostructures. In this study, we present a novel means of creating a hierarchically developed nanoflake structure by exploiting surface wrinkles that occur during the incorporation process of metallic nanoparticles into layer-by-layer assembled polyelectrolyte multilayer (PEM) thin films. The PEM film composed with linear polyethylenimine (LPEI) and poly(acrylic acid) (PAA) allows for facilitated cationic exchange reaction within the film even after the electrostatic complexation and chemical cross-linking reaction. The subsequent reduction process induces an in situ complexation of metallic nanoparticles with a PEM matrix, causing an accumulation of lateral compressive stress for surface wrinkling. The wrinkling characteristics of the complexed films can be theoretically interpreted by employing the gradationally swollen film model, whereby a gradual change in the elastic pr...