This paper shows that it is possible to construct well-defined 2D structures at the air-water interface in which the lateral organization is controlled by means of the preparation of mixed films, and selecting the components so that there are attractive interactions between them. The goal here is to establish the lateral connection between components through self-aggregation of the dye. This can be achieved by selecting a suitable balance between the sizes of the hydrophobic and polar groups. In such a way, the domain structure depends on the ability of the tilt dye to fill the available area. Thus, the molecular organization and the domain morphology of mixed films containing dimyristoyl-phosphatidic acid (DMPA) and the hemicyanine dye, 4-[4-(dimethylamino)styryl]-1-docosylpyridinium bromide (SP), have been studied by using Grazing Incidence X-ray Diffraction (GIXD), Brewster angle microscopy (BAM), and reflection spectroscopy at the air-water interface. For this mixed system, the formation of circular domains with bright horizontal regions and dark vertical regions was observed. Furthermore, depending on the temperature, it is observed as branches grow from circular domains, whose brightness depends on the growth direction. Thus, BAM images allow us to observe some branches that, as their growth direction changes, their brightness also changes simultaneously. The GIXD experiment permits us to relate the circular domains with an orthorhombic phase and the branches grown from the circles with an Overbeck phase. In both cases, the formed structures are induced by the hemicyanine aggregation. Circular BAM domain textures have been simulated by using the Fresnel equations for biaxial anisotropic materials.

The molecular organization and the domain morphology of an anionic matrix dimyristoyl−phosphatidic acid (DMPA) as influenced by the presence of a cationic water-soluble methylene blue (MB) have been studied by using Brewster angle microscopy and reflection spectroscopy at the air−water interface. Mixed monolayers of DMPA:MB, molar ratios 5:1 and 1:1, were formed by the cospreading method. BAM images show particular domain morphologies as a function of the MB density in the mixed film: circular domains for DMPA:MB = 5:1, and domains with hexagonal shape for DMPA:MB = 1:1. The reflection measurements during the compression process of the mixed films reveal a blue shift of the visible band with respect to that of the MB monomer. This blue shift is larger for the DMPA:MB = 5:1 in comparison with that for the 1:1 monolayer, despite lower MB density. By using the extended dipole model, we demonstrate that such blue shift is due to the formation of a 2D hexagonal network of MB molecules underneath the DMPA monolayer in the mixed 1:1 film, while it is due to infinite linear aggregates in the 5:1 monolayer. BAM domain textures have been simulated by using the Fresnel equations for biaxial anisotropic materials. The results fit correctly the predictions of the extended dipole model.

The electrochemical behavior of mixed monolayers of N-tetradecyl-N′-methyl viologen (TMV) and L-Rdimyristoylphosphatidic acid (DMPA) has been studied. Mixed monolayers of TMV/DMPA ) 1:2 have been obtained at the air-water interface and transferred by the Langmuir-Blodgett (LB) method at π ) 40 mN m -1 onto In and Sn oxide (ITO) electrodes. These LB films were used as the working electrode in a conventional electrochemical cell and immersed in aqueous solutions with different electrolytes. The influence of the type and the electrolyte concentration on the voltammetric peaks related to the two one-electron processes of TMV has been studied. The formation of an insoluble salt of viologen perchlorate on the surface of the electrode is observed when concentrations of perchlorate higher than 0.3 M are used. Due to this, a reorientation of the polar group of the viologen in the transferred mixed monolayer from a flat to a perpendicular position is postulated.

Infrared transmission and reflection-absorption spectroscopies were used to determine the orientation of Langmuir-Blodgett (LB) mixed films consisting of a phospholipid (DMPA) and a viologen (TMV) in a ratio of TMV:DMPA ) 1:2. For comparison, the orientation of a DMPA monolayer was also studied. No important changes were observed for the organization of the DMPA monolayer when the TMV molecules were incorporated. The alkyl chains of both compounds adopted a hexagonal configuration where these alkyl tails were fully extended with all-trans conformation and an average tilt angle with respect to the support close to 20°. Further information about the hydrated CO groups and the orientation of the phospholipid headgroups was obtained from the CO stretching vibration mode and from the 1300-1000 cm -1 spectrum region, respectively. Finally, the average tilt angle for the plane of the bipyridyl group with respect to the substrate surface was estimated close to 10°from UV-visible absorption spectroscopy with plane polarized light (s and p) under different angles of incidence. Moreover, the bipyridyl group was located encapsulated between the headgroups of the phospholipid and the solid surface.

The particular behavior of a p-tert-butyl calix[8]arene derivative (C8A) has been studied at the air-water interface using surface pressure-area isotherms, surface potential-area isotherms, film relaxation measurements, Brewster angle microscopy (BAM), and infrared spectroscopy for Langmuir-Blodgett films. Thus, it is observed that the properties of the film, for example, isotherms, domain formation, and FTIR spectra, recorded during the first compression cycle differ appreciably from those during the second compression and following cycles. The results obtained are interpreted on the basis of the conformational changes of the C8A molecules by surface pressure, allowing us to inquire into the inter- and intramolecular interactions (hydrogen bonds) of those molecules. Thus, the compression induces changes in the kind of hydrogen bonds from intra- and intermolecular with other C8A molecules to hydrogen bonds with water molecules.