Mechanism of morphological transition from lamellar/perforated layer to gyroid phases

We investigated epitaxial relations of phase transitions between the lamellar (L), hexagonally perforated layers (HPL), and gyroid (G) morphologies in styrene-isoprene diblock copolymer (PSI) and polyisoprene (PI)/PSI blend using rheology and small angle X-ray scattering (SAXS) techniques. In HPL --> G transitions, six spot patterns of G phase were observed in two-dimensitional SAXS pattern. On the ocher hand, in direct L --> G transition without appearance of HPL phase, the polydomain patterns of G phase were observed. From present study, it was understood that direct L-G transition of blend may be suppressed by high-energy barrier of transition and mismatches in domain orientation between epitaxially related lattice planes.