Graphene oxide--polyelectrolyte nanomembranes.

Owing to its remarkable electrical, thermal, and mechanical properties, graphene, an atomic layer of carbon, is considered to be an excellent two-dimensional filler for polymer nanocomposites with outstanding mechanical strength along with the potential for excellent electrical and thermal properties. One of the critical limitations with conventional fillers is that the loading fraction required for achieving significant improvement in mechanical properties is relatively high, frequently reaching 50% for maximum strength. Here, we demonstrate that the mechanical properties of ultrathin laminated nanocomposites can be significantly enhanced by the incorporation of small amounts of a dense monolayer of planar graphene oxide (GO) flakes. Negatively charged functionalized graphene oxide layers were incorporated into polyelectrolyte multilayers (PEMs) fabricated in a layer-by-layer (LbL) assembly via Langmuir-Blodgett (LB) deposition. These LbL-LB graphene oxide nanocomposite films were released as robust freely standing membranes with large lateral dimensions (centimeters) and a thickness of around 50 nm. Micromechanical measurements showed enhancement of the elastic modulus by an order of magnitude, from 1.5 GPa for pure LbL membranes to about 20 GPa for only 8.0 vol % graphene oxide encapsulated LbL membranes. These tough nanocomposite PEMs can be freely suspended over large (few millimeters) apertures and sustain large mechanical deformations.