Grain boundaries and stacking faults in a Pm3n cubic mesophase

A monodendron that over a broad temperature range self-assembles in quasi-spherical supramolecular aggregates organized on a thermotropic cubic Pm3n lattice was examined by TEM. Grain boundaries were found parallel to the (1 0 0) and (3 2 0) planes. In well annealed specimens, in which grain boundaries are rare, two types of stacking fault were numerous, suggesting their relatively low energy. In the original Pm 3n lattice and in the two stacking fault arrangements, the supramolecular aggregates are distorted to an oblate shape, which is likely to be favoured by a crowded microscopic interface between core and tail moieties. Symmetry and phase selection for the ordered arrangement of amphiphilic molecules is discussed.