Entropy-driven segregation of nanoparticles to cracks in multilayered composite polymer structures

Multilayer composites, which combine ductile polymers with brittle films, constitute vital components for optical communications, microelectronics and bio-engineering applications. However, crack formation is a critical problem in these materials; thus, designing layered systems that can respond to environmental changes and undergo self-healing is particularly important for a range of technologies. Here, nanoparticles dispersed in a polymer matrix were found to migrate to a crack generated at the interface between the polymer and a glassy layer. Segregation of the nanoparticles to the crack depended on both the enthalpic and entropic interactions between the polymer and nanoparticles. In particular, poly( ethylene oxide)- covered 5.2-nm spherical nanoparticles in a poly( methyl methacrylate) matrix diffused to cracks in the adjoining silicon oxide layer, whereas tri-n-octylphosphine oxide-covered nanoparticles did not. These results point to a simple means of fabricating systems that can self-heal, improving the durability of multilayered systems, or form the basis for auto-responsive materials.