Nanoparticles Induce Polymer Patterns

Nanoparticles can cause radially concentric patterns to form in thin films of block copolymers, according to researchers at NIST (ACS Nano, DOI: 10.1021/nn9002133). The study deepens understanding of polymer properties and may lead to a new way to gauge stresses present in thin films during polymer processing. Differences in the properties of the chemically distinct segments of block copolymers can cause these materials to assemble into nanosized cylinder-shaped domains. For years, researchers have used various "handles" including electric fields and temperature gradients to control the microscopic order in block copolymers by orienting the cylinders. The NIST team, which includes Xiaohua Zhang, Jack F. Douglas, and coworkers, reports a new way to induce such ordering. Introducing immobilized nanoparticles that span the copolymer film thickness causes domains of aligned cylinders to adopt concentric ring patterns, the team reports. Similarly, they observe undulating height patterns in nanoparticle-modified homopolymer films. The patterns arise from stresses that build up in the film during thermal treatment and could serve as a diagnostic to evaluate those stresses, the group proposes.