Disordered Nanoparticle Interfaces for Directed Self-Assembly
Yager, K.G.; Berry, B.C.; Page, K.; Patton, D.; Karim, A.; Amis, E.J. "Disordered Nanoparticle Interfaces for Directed Self-Assembly" Soft Matter 2009
We present a unique methodology for controlling substrate surface energy and roughness, and use these surfaces to bias the self-assembly of block-copolymers. In particular, we show that rough substrates cause an oscillation of orientation, between horizontal and vertical (with respect to the substrate), as a function of film thickness.
Self-assembly is a promising route for controlling the nanoscale structure and material properties of coatings, yet it remains difficult to control the microstructure of these systems. In particular, self-assembling materials typically have complex and delicate energy landscapes, which are sensitive to defects, making it difficult to control morphology or orientation. We present a simple and robust strategy for modulating the film-substrate interaction, which can bias the self-assembly energy landscape and thus enforce a desired microstructure. The technique uses nanoparticles with tunable surface energy to generate a rough interface with controlled properties. The intentionally disordered interface is tolerant to variation in substrate preparation. We apply this technique to block-copolymer lamellae, and demonstrate a remarkable thickness-dependence to the induced orientation, consistent with theoretical predictions. The simultaneous control of substrate energy and topography enables expression of the vertical lamellae state without rigorous control of the preparation conditions. We measure an 8-fold increase in surface energy tolerance compared to flat substrates.