Highly oriented and ordered double-helical morphology in ABC triblock terpolymer films up to micrometer thickness by solvent evaporation

A triblock terpolymer, polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (SBM), formed a double-helical nanoscale structure, composed of polybutadiene (PB) helical microdomains around hexagonally packed polystyrene (PS) cores in a poly(methyl methacrylate) matrix. The orientation of double-helical morphologies at various film thicknesses were studied using transmission electron microtomography, following solvent annealing and drying at a controlled solvent evaporation rate. The evaporation rate of the solvent and the film thickness were important factors in whether the double-helical microdomains were oriented parallel or perpendicular with respect to the substrate. In some cases, the perpendicularly aligned double-helical morphology extended several micrometers from the substrate to the air surface. A similar experiment using polystyrene-block-poly(methyl methacrylate) diblock copolymer proved that the presence of helical PB microdomains around PS cylinders is the key factor in achieving a uniform orientation over several micrometers throughout the film thickness.