“Standing, Lying, and Sitting: Phospholipid Striped Phases as Templates for Nanomaterials at Interfaces”
A surprisingly broad array of problems in modern materials chemistry relate to creating interfaces with two distinct, well-structured chemical environments at near-molecular scales. For instance, positioning nm-wide metal and semiconductor features with a pitch of 5-7 nm in a structured matrix represents a central requirement for next-generation electronic devices. In biological environments, phospholipids comprised of a polar headgroup and two nonpolar alkyl tails create chemical environments of exquisite precision in the cell membrane periphery, based on standing-phase bilayers that expose only the polar headgroups. However, on certain surfaces, they can also be assembled into striped phases that orient the molecules horizontally, exposing both polar headgroups and nonpolar tails. This non-biological orientation creates 1-nm-wide functional patterns of headgroups alternating with ~5 nm stripes of exposed alkyl tails. Using these functional patterns to direct further assembly at the interface, we find that striped phases of phospholipids create interfaces with very different properties than simple diynoic acids or diyne amines. In part, this difference appears to arise from strong, orientable headgroup dipoles found in phospholipid headgroups, which confer function based on collective interactions similar to those in the cell membrane periphery. We will discuss the relationship between structure and function at striped phospholipid interfaces, and useful material properties that emerge from the unusual surface chemistry; these include assembly of inorganic nanocrystals and assembly of functional organic molecules.