3D analysis of the lattice defects in the gyroid network structure of a block copolymer/homopolymer blend – The line-like defects in the gyroid network structure

The line-shaped defects formed in the gyroid bicontinuous microdomain structures in the solution-casting process of a blend of polystyrene-block-polyisoprene (SI) diblock copolymer and homopolystyrene (HS) were investigated using 3D electron tomography. The inclusion-type lattice defects composed of segregated HS formed during the morphological transition from the preexisted sponge phase to the stable gyroid phase induced by the phase separation between SI and HS. The gyroid grains grew by consuming the sponge phase and expelling excess HS as well as by impinging each other. Consequently, some expelled HS was trapped as the line-like inclusions in the gyroid grains. Structural rearrangement occurred so that low energy planes of the gyroid phase are facing the HS inclusions while the gyroid structure became continuous across/around the inclusions.