FABRICATION OF MONOLAYERS CONTAINING INTERNAL MOLECULAR SCAFFOLDING -EFFECT OF SUBSTRATE PREPARATION

The nanoscale design and fabrication of monolayer assemblies is becomi ng increasingly important for research areas ranging from adhesion to chemical sensors. The formation of molecular scaffolding within a sing le molecular layer by linking adjacent molecules provides an important means for the nano- to microscale fabrication of such interfacial ass emblies. Unfortunately, key factors in the design and fabrication of t hese internally linked monolayers are often overlooked due to direct a nalogy with the often studied n-alkyl monolayer systems. In this inves tigation, the impact of substrate preparation on the resulting monolay er structure is compared for n-alkyl (C18) and internally linked polyd iacetylene monolayer assemblies formed on evaporated, sputtered, and c olloidal gold surfaces. Polydiacetylene monolayers are fabricated by t he spontaneous assembly of diacetylene-containing disulfides followed by photoinduced polymerization. The resulting polydiacetylene monolaye rs exhibit systematic variations in the degree of polymerization, alky l chain crystallinity, advancing contact angle, and electron-transfer inhibition with substrate preparation. By all these measures, both the short- and long-range order of these polymerized monolayers are obser ved to increase substantially on evaporated gold substrates. In contra st, the n-alkyl-based monolayers formed under identical conditions sho w minimal structural variation. Moreover, surface pretreatment is demo nstrated to have a significant impact on the long-range order for both the n-alkyl and polydiacetylene monolayers. These experimental observ ations implicate domain size as a significant parameter in the fabrica tion of polydiacetylene monolayers, while exhibiting little or no impa ct on the apparent structure of n-alkyl-based monolayer assemblies. Ul timately, the successful fabrication of monolayer structures containin g internal molecular scaffolding is made possible by the judicious cho ice of substrate preparation conditions.