Langmuir-Blodgett films electron diffraction

Transmission electron microscopy (TEM) can resolve features down to about 1 nm and allows the use of electron diffraction to characterize the structure. Since electrons must pass through the sample however, the technique is limited to thin films. One cryoelectron microscopic study of fatty-acid Langmuir films on vitrified water [13] showed faceted crystals. The application of TEM to Langmuir-Blodgett films is discussed in Chapter XV. 

Despite their potential importance, there are few spectroscopic studies of polymerizable surfactants. The only well-characterized polymerized surfactants are the polydiacetylenic fatty acids. The polymerization mechanism (1,4 addition) was only recently discovered as a result of studies on crystals of non-surfactant monomers which become brightly colored on polymerization [1], indicating the formation of polymer concurrent with a solid-solid phase transition. Several groups, particularly that of Ringsdorf, have pioneered the study of polydiacetylenic fatty acids [2-5]. A significant amount of spectroscopic work has been done on non-surfactant polydiacetylenes [6-9]. In addition, Lando and co-workers have used electron diffraction from mono- and bilayers of fatty acids to establish the conformation of the diacetylene backbone chains in this ordered surfactant system [10,11], and others have performed Raman spectroscopy on Langmuir-Blodgett films of similar surfactants [12]. This provides one with a powerful "basis set" of information from which to study other polydiacetylenic systems. 

FIGURE 11.1 Electron diffraction patterns of the linear chain carbon films (a-c), the distribution of electron diffraction intensity, its atomic arrangement (g), the Langmuir-Blodgett multi-layered film diffraction patterns (d,e). 

We have applied high-precision diffraction analysis to monomers, oligomers, and polymers based on thiophene residues, in the form of single crystals, of powders, of cast thick films, and even as thin films prepared using the Langmuir-Blodgett technique. Preliminary results encourage us to perform further detailed studies on diffraction techniques suitable for well-ordered thin films, which are of interest for non-linear optics and for electronic applications. 

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