title: From two-dimensional to three-dimensional at the air/water interface: the self-aggregation of the acridine dye in mixed monolayers.
abstract: The formation of well-defined supramolecular structures on the nanoscopic scale is a fundamental step in nanotechnology. The fine control of the layer-by-layer growth of the supramolecular assemblies at interfaces is most desirable. The collapse of a mixed monolayer composed of two surfactants in an equimolar ratio (the organic dye N-10-dodecyl acridine (DAO) and stearic acid (SA)) is analyzed herein. The collapse process of the DAO/SA mixed monolayer has been monitored using surface pressure-molecular area (π-A) and surface potential isotherms, UV-visible reflection spectroscopy, polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS), Brewster angle microscopy (BAM), and synchrotron-based in situ X-ray reflectivity (XRR) measurements. The collapse of the DAO/SA mixed monolayer leads to an ordered trilayer. The growth of anisotropic 2D domains of micrometric size is observed during the formation of the trilayer, related to the ordering of the acridine polar headgroups. The trilayer is organized with the first and third monolayers displaying the polar headgroups pointing to the aqueous subphase, whereas the intermediate layer displays the polar headgroups pointing to the air. The trilayer is stabilized by the strong self-aggregation acridine dye group of the DAO molecule. The controlled transition from a monolayer to a trilayer described herein is proposed as a model for further interfacial supramolecular structures of tunable thickness comprising organic dyes.
authors.affiliation: Department of Physical Chemistry and Applied Thermodynamics, University of Córdoba, Campus de Rabanales, Edificio Marie Curie, Córdoba, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Rubia-Payá
authors.forename: Eugenio
authors.initials: E
authors.lastname: Jimenez-Millán
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Giner-Casares
authors.forename: Gerald
authors.initials: G
authors.lastname: Brezesinski
authors.forename: María T
authors.initials: MT
authors.lastname: Martín-Romero
authors.forename: Luis
authors.initials: L
authors.lastname: Camacho
mesh_terms: D000165:Acridine Orange / Q000737:chemistry*; D000388:Air; D004396:Coloring Agents / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D010316:Particle Size; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D004396:Coloring Agents; D013501:Surface-Active Agents; D014867:Water; D000165:Acridine Orange