Structural studies of Langmuir and Langmuir-Blodgett films of functionalized surfactants

Structural studies of Langmuir and Langmuir-Blodgett films of functionalized surfactants show that the organization of surfactants is strongly dependent on cross-sectional match between the functionalized headgroup and the film-forming alkyl chain parts of the molecules. The organization of a particular functionalized surfactant with a slight cross-sectional mismatch between head and tail has been investigated by synchrotron radiation in floating monolayers and by atomic force microscopy (AFM) in Langmuir-Blodgett films. The transfer process was accompanied by an increase of the oblique unit cell area by 17% and by an increase of the average diameter of perfectly ordered domains from 3 nm to approximately 10 nm. We have calculated a number of likely packing patterns of alkyl chains and the lattice parameters of the Langmuir-Blodgett films are found to be consistent with one of these packings. For comparison, the results of preliminary studies on a functionalized surfactant with a severe cross-sectional mismatch between head and tail are presented, indicating that the tail is bent around the head group thereby preventing efficient packing of the alkyl chains.