Elastic Nanocomposite Structures Formed by Polyacetylene-Hemicyanine Mixed Films at the Air-Water Interface

A mixed film of 10,12-pentacosadiynoic acid (DA) and an amphiphilic cationic hemicyanine (SP) in the ratio 1:1 has been fabricated. This mixed film has been proved to be completely homogeneous due to the good compatibility between both molecules, i.e., hydrophobic regions sized and polar regions of opposite charge. This adequate balance between the vertical sections of the hydrophobic and hydrophilic groups allows the formation of an ion pair between them. In this mixed film, DA molecules organize in monolayer instead of trilayer as occurs for pure DA film. Surface pressure measurements (isotherms and compression-expansion cycles), Brewster angle microscopy, reflection spectroscopy, and PM-IRRAS prove this structure. Using BAM to reveal the structure of this mixed film, circular domains with internal anisotropy because the ordered alignment of hemicyanine groups (strong self-aggregation) are observed. Under UV irradiation a new polyacetylene (PDA) form was fabricated in a homogeneous mixed monolayer despite of the distance measured between the DA molecules by the presence of SP dye. The polymerization takes place only in the circular domains. Under expansion the domains forming during compression and after UV irradiation form a nanocomposite stable material with partially elastic outer region.