High-Toughness, Hierarchically Structured Polyurethane Films from Exponential Lbl Assembly

Nanostructured thin films prepared with the layer-by-layer (LBL) assembly process have shown remarkable versatility in transferring the unique properties of nanomaterials into functional, macroscale structures. The daunting problem of the LBL method is the slow speed of film growth, which is especially important for the preparation of ultra-strong nanocomposites. A recently discovered mode of the LBL assembly, the “exponential LBL” (e-LBL), offers a solution to this problem by greatly increasing the growth speed. Here we show the first preparation of high-toughness multilayered polymer films from water-born polyurethanes by the e-LBL process. We further describe a simple and general method for consolidating the thin films into hierarchical laminates which brings about a change in the paradigm for thin LBL films. The laminated structures show great improvement of mechanical properties: 4x in modulus, 4x in yield strength, 2.5x in ultimate strength, 3x in and toughness when compared to the base polyurethane. Further ability to incorporate functional materials into individual layers of the laminate allows for preparation of multifunctional polymeric materials with multi-level hierarchical organization.