SELF-ASSEMBLED LANGMUIR MONOLAYERS AND TRILAYERS AT THE AIR FORMAMIDEINTERFACE

The spontaneous formation of highly crystalline two-dimensional films of uncompressed long chain amide and carboxylic acid amphiphiles sprea d on formamide has been demonstrated by grazing incidence X-ray diffra ction. These results were compared to those found for the same amphiph iles on water. The observed diffraction data Of C29H59CONH2 over both water and formamide and those Of C29H59CO2H over formamide are strikin gly similar, while those Of C29H59CO2H over water are different. Arach idamide (CH19H39CONH2) over water subphase forms a unimolecular layer with the molecules tilted by 18-degrees. Over formamide, the crystalli tes are made up, at least in part, of three molecular layers, with the molecules standing vertically. This was confirmed by X-ray specular r eflectivity. These results are analogous to the well known, but as yet unexplained, influence which solvent may have on the growth of polymo rphic modifications of three-dimensional crystals.