Phase transitions of 4'-n-hexacosyloxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC-26; "26" means the number of carbons in the alkoxy group) were studied by differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), polarizing optical microscopy (POM) and so on. The results showed that this compound, which has a very long alkoxy chain of n=26, forms two types of cubic phases, one with Im3m symmetry and the other with Ia3d symmetry, where the Im3m cubic phase(Cub I) is transformed into the Ia3d cubic phase(Cub II) at 161.9℃ on heating. This is the first example of the thermotropic cubic-cubic phase transition in one-component systems.
