The aggregation structures of Ia3d and Im3m cubic phases formed by rod-shaped mesogens ANBC and BABH

This article focuses on thermotropic cubic phases with bicontinuous type constructed by rod-shaped molecules such as 4'-n-alkoxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC) and 1,2-bis (4'-n-alkoxybenzoyl)hydrazine (BABH). Their phase diagrams as functions of temperature and terminal alkyl chain length were fully established. The common feature of the two series is the Ia3d to Im3m to Ia3d phase sequence on lengthening the terminal chains. The formations are usually understood in analogy with lyotropic cases, but one of the highlighted differences is the structure of the Im3m phase. The structure contains two types of aggregates, spherical shells and a 3-by-3 network, within a lattice. The presence of the two distinguished sites in their dynamically ordered structure is very surprising. Another interesting point in their phase diagram is the Ia3d phase region, which is separated into two. The structures of the two Ia3d regions were also investigated. It was revealed that the network is composed of central core parts of the constituent molecules in both chain regions. This is another interesting feature probably only observed in thermotropic system because in the case of lyotropic system a replacement of location between the two chemically incompatible parts is usually observed. Analogies and differences between the thermotropic and lyotropic cubic phases are discussed.