The dynamics of order–order phase separation

In multi-component soft matter, two microphase separated ordered phases such as lamellar and hexagonal phases coexist in equilibrium. We call such a macroscopic phase separation ‘order–order phase separation’. Based on a coarse grained single order parameter Ginzburg–Landau free energy, we investigate the dynamics of order–order phase separation. For this purpose, the equilibrium phase diagram is determined in three dimensions, including BCC and gyroid phases. Focusing on the phase separation between the lamellar and hexagonal phases, we study its dynamics using computer simulation in both two and three dimensions. We show that the microphase separation takes place in the early stage and the macrophase separation follows through the breaking and reconnection of microdomains. The observed epitaxial relation between the lamellar and hexagonal phases is compared with an analytical estimate of the interfacial energies of different mutual directions. (Some figures in this article are in colour only in the electronic version) 1