Certain lipids form bicontinuous cubic phase nanostructures upon hydration. Among them, double diamond type lattices consist of two intertwined networks of aqueous channels that are separated by a continuous lipid bilayer. Theoretically, the cubic bilayer membrane is found to fold like an infinite periodic minimal surface. In real soft-matter self-assembly nanosystems, the lipid bilayer can not be infinite. Hence, the lipid cubic phase structure should have a bounding surface somewhere in space. This causes the closure of one of its nanochannel networks and opening of the other to the external aqueous environment. Upon application of thermal or chemical hydration stimulus, the kinetics of hydration or dehydration of the two kinds of water channel systems could not be identical because of the enhanced surface area of the cubic assembly. This structural asymmetry was established to cause spontaneous domain orientation under given experimental conditions. We employed small-angle neutron (SANS) and X-ray scattering (SAXS) to study these effects. Temperature stimuli as well as the hydration-enhancing guest component octyl glucoside were acting as hydration modulators on model cubic membranes of monoolein. The experimental results indeed revealed the nucleation and growth of large spontaneously oriented domains of single crystal cubic nature. These findings could have potential application in the field of cubosome delivery of therapeutic molecules.

B.A. is funded by BMBF (BMBF-Projekt „Strukturbildende Copolymere zur Primären und Sekundären Ausrüstung von Oberflächen mit funktionalen und schaltbaren Eigenschaften“, 03X0019)