A square nano-array formed by surface aligned self-assembly of a bicontinuous lipid cubic phase

We present the formation of oriented thin lipid films belonging to the primitive (Q_II^P) bicontinuous cubic phase, as characterized by grazing-incidence small angle X-ray scattering and atomic force microscopy. The phase shows high out-of-plane orientation with the (100) plane parallel to the substrate; this is consistent across a number of different lipid and surfactant systems. We demonstrate that the adopted orientation can be predicted using a theoretical framework, based on the most favorable facet in terms of curvature energy whilst assuming a closed bilayer. Significantly, the Primitive bicontinuous cubic phase is unique in that it contains straight water channels, with the [100] orientation presenting a square array at the surface with the straight channels running directly parallel and perpendicular to the interface. Moreover, by tuning the composition we show that we can tune the periodic pore-to-pore spacing (lattice parameter) of the structure with control over nanostructure dimensions. We present structures with lattice parameters between 13 and 23 nm. These structural features are important for applications including delivery of bioactive agents, and patterning and templating of inorganic nanomaterials. These findings represent a route to square arrays of nanofeatures with 2 3 times smaller periodicity (4-9 times higher per-area density) than those reported from block copolymer lithographic template systems.