Annealing Process Dependence of the Self-Assembly of Rod-Coil Block Copolymer Thin Films

Thermal annealing, solvent vapor annealing, and a two-step solvent plus thermal annealing are applied to a series of silicon-containing rod-coil thermotropic liquid crystalline (LC) block copolymer thin films with LC volume fractions of 0.42-0.85. Solvent vapor annealing using selective solvents of acetone and heptane produced a wide range of ordered nanostructures with small feature sizes, such as sub-10 nm cylinders, gyroids, and spheres. Subsequent thermal annealing yields final morphologies that depend on the initial morphology and the thermotropic LC phase transition. Combined thermal and solvent annealing as well as design of the rod and coil volume fractions provides an effective way to control the morphologies of rod-coil block copolymers.