Nanostructured smectic networks towards integrated nano membranes

Localized photopolymerization of smectic liquid crystalline monomers lock in structures on three different length scales (1,2). The first length scale is set by the resolution of lithographic mask that is being used and can go down into the sub-micrometer region with the minimum size being restricted only by the diffraction limits. The second length scale is set by the periodicity of the smectic layers and can be equivalent to the length of the monomers, or smaller in case of interdigitation, but is typically of the order of a few nanometers. And the third length scale is the intermolecular distance between the molecules packed in the smectic layers, which is usually around 0.4 nm. By modifying the smectic molecules partly with non-covalent hydrogen bridges (H-bridges) the smectic periodicity can break-up into separated layers with a well-defined space, often also in the nanometer range. This principle is shown schematically in Figure 1. The nanopores form by breaking the hydrogen bridges in the polymer at elevated temperatures or by contact with an alkaline solution. The integrity of the film is maintained by the presence of fully covalent smectic monomers. The process of pore formation and the properties of the films formed are elaborated further in this paper.