Order-order transition in gyroid forming block copolymer in thin films.

Block copolymers provide an attractive route for the definition of well-defined nanostructures. Intense efforts are currently being devoted for their directed self-assembly to extend the performances of conventional lithography. Consequently, we have designed polycarbosilane-based block copolymers that are suitable for next-generation lithography thanks to the high segregation strength and the high etching contrast provided by the Si-containing block¹. Here, we chose to focus on the gyroid phase, as it has shown potential for 3D complex-ordered structures. We present a study on the self-assembly of thermally-annealed gyroid films. We demonstrate a transition from the (211) plane of the gyroid oriented parallel to the free surface to in-plane cylinders with increasing annealing time. This transition was correlated to the evaporation of the remaining solvent in the film during the annealing process, thus driving the mesostructure towards the cylindrical window of the phase diagram. The morphological assignments were confirmed using SAXS measurements in bulk as well as AFM and GISAXS characterizations in thin film. Such gyroid could be used in nanotechnologies as templates for bulk heterojunction solar cells or as filtration membranes.
¹K. Aissou et al., Adv. Mater., 27, 261-265.