Langmuir-Blodgett Films of Chiral Perfluorinated Gelators: Effects of Chirality and Chain Length on Two-Dimensional Behavior

Abstract

Abstract Surface pressure versus molecular area (π-A) curves were measured on pure water as a subphase for a series of N,N′-diperfluoroalkanoyl-1,2(R,R)-diaminocyclohexanes. A molecule is denoted as RR-CFn, where n is the number of carbon atoms in a perfluoroalkanoyl chain (or n − 2 = the number of difluoromethylene units). The chain length was varied for n = 4, 5, 6, 8, 9, and 10. The results for n = 7 were reported previously. The effects of chain length and optical purity on film formation were investigated. The surface morphology of a film deposited onto a hydrophilic glass plate was observed using an atomic force microscope (AFM). For n = 4, 5, and 6, the floating films were already multilayered before compression and the deposited films were composed of rectangular or rod-like aggregates. For n = 7, 8, 9, and 10, monolayered films were formed and underwent structural transformation upon compression. From the AFM images, the films deposited after the transformation were composed of fiber-like aggregates. For a racemic mixture, no monolayer film was formed, and the film transfer was impossible irrespective of the chain length. p-Polarized infrared multiple angle incidence resolution spectrometry (pMAIRS) measurements were carried out on a film of RR-CF8 deposited onto a silicon wafer to determine the orientation of the composite molecules. The results were compared with the monolayer behavior reported for a compound having a single perfluoroalkyl chain. The relation to their gelation behavior is also discussed.