Electrical Behavior of LB Films

No direct method exists by which one can study the monolayer film molecular structures on water (i.e., in situ). Therefore, one has been using the LB method to study the molecular structures in the past decades. This procedure has been found to provide the most useful information for monolayers. LB deposited film structure is the well-known electron diffraction technique (or scanning probe microscopes (SPMs) [Birdi, 2003b]). The molecular arrangement of deposited mono-layer and multilayer films of fatty acids and their salts using this technique has been reported. These 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 than in the case of stearic acid monolayers. In some investigations, thermal stability of these films has been found to be remarkably stable up to 90°C. 

Based on these structural analyses obtained by electron diffraction technique, these deposited films are known to be mono-crystalline in nature thus, they can be regarded as a special case of a layer-by-layer mechanical growth forming almost two-dimensional crystals. There is, however, evidence that Ba-behenate multilayers do in fact show an absence of crystallization which has been demonstrated by electron micrographic studies. Nevertheless, it would be an over-simplification to regard the film transferred at n high as perfectly uniform, coherent, and defect free. The unidirectional surface conductance of monolayers of stearic acid deposited on a glass support was 

Cc is the capacity e denotes the dielectric constant N is the number of layers d is the layer thickness 

On the other hand, the values of the resistance per layer showed a definite increase with the thickness of the film. The specific resistance of the films thus determined from their values of the resistance per layer was ca. 10 fl. This was based on the results of capacity measuranents on some 75 samples. The capacitance measurements thus performed on stearate films (1-10 layers) led to e values between 2.1 and 4.2, with a bulk value of 2.5. 

The dielectric anisotropy of long-chain fatty acid monolayers was analyzed. These fatty acids were considered as being oriented in a cylinder cavity with length [L] diameter [D]. Considering each bond in these molecules as a polarization ellipsoid with axial symmetry about the -C-C- bonds, the mean polarizability of the bonds was calculated. 

---