Phase behavior of complex diblock copolymer blends: A transmission electron microscopy study

Diblock copolymers consist of two long contiguous sequences (''blocks'') of chemically dissimilar monomer species. If the blocks are sufficiently incompatible, these materials can microphase-order into periodic morphologies measuring on the order of tens of nanometers. While previous efforts to control the microstructural characteristics of these materials have relied upon chemically tailored copolymers, only recently have studies shown that miscible blends of diblock copolymers behave as single-component copolymers of intermediate molecular weight and composition. In this work, we have investigated several series of poly(styrene-b-isoprene) (SI) diblock copolymer blends, some with other diblock copolymers and others with higher-order multiblock copolymers, to (i) discern the extent of phase miscibility and (ii) quantitate microstructural dimensions with transmission electron microscopy (TEM). Three-dimensional features of interest (e.g., defects due to lattice mismatch) are also examined at relatively high spatial resolution using electron microtomography (3-D imaging).