A frustrated packing model for the B6-B1-SmAPA sequence of phases in banana shaped molecules.

A vast majority of compounds with bent core or banana shaped molecules exhibit the phase sequence B6-B1-B2 as the chain length is increased in a homologous series. The B6 phase has an intercalated fluid lamellar structure with a layer spacing of half the molecular length. The B1 phase has a two dimensionally periodic rectangular columnar structure. The B2 phase has a monolayer fluid lamellar structure with molecules tilted with respect to the layer normal. Neglecting the tilt order of the molecules in the B2 phase, we have developed a frustrated packing model to describe this phase sequence qualitatively. The model has some analogy with that of the frustrated smectics exhibited by highly polar rod like molecules.