Optical and Related Methods of Absorption

Optical reflection from a monomolecular film must be measured from the interface with a very small amount of material present. Therefore, in these methods, repeated interaction of the light beam with one or more identical films is generally employed. The simplest way to observe a light beam that has passed through several identical monolayers is to transfer portions of the layer to suitable transfer end plates, which are then stacked and examined in a conventional spectrophotometer. This method was used where monolayers of chlorophyll were deposited on glass slides by the LB method. Ferrodoxin and chlorophyll monolayers were investigated by measuring the spectra (550-750 nm) of these films at the interface. 

To examine monolayers on liquid surfaces in situ, multiple interactions by mounting mirrors above and below the surface have been used. X-ray reflectivity measurements have been used to study the counterion overlayers at the interface between electrolyte solutions and monolayers of carboxylic acids terminated alkanethiols self-assemblies on Au (Birdi, 1999). 

The Brewster angle microscope (BAM) has been used to investigate the mono-layers of polyamic acid at the air-water interface in situ and without the addition of probes. The morphology of the monolayer was observed as a function of surface 

Grazing incidence x-ray diffraction (GID) measurements have indicated that both precollapse and collapsed state monolayers at the air-water interface can be crystalline (Birdi, 1989). A general procedure was delineated that could provide near-atomic resolution of two-dimensional crystal structures of -triacontanoic acid (C29H59COOH). A monolayer composed of rod-like molecules would generally pack in such a way that each molecule has six nearest neighbors, that is, hexagonal cell. 

No direct method exists by which monolayer film structures on water can be studied. Therefore, the LB method has been used to study molecular structures in past decades. The most useful method for investigating the detailed LB-deposited film structure is the well-known electron diffraction technique (or the scanning probe microscope [Birdi, 2002a]). The molecular arrangements of deposited mono-and multilayer films of fatty acids and their salts, using this technique, have been reported. The analyses showed that the molecules were almost perpendicular to the solid surface in the first monolayer. It was also reported that Ba-stearate molecules have a more precise normal alignment compared to stearic-acid monolayers. In some investigations, the thermal stability of these films has been found to be remarkably stable up to 90°C. 

---