SELF-AGGREGATED 2-DIMENSIONAL CRYSTAL-STRUCTURE OF THE MIXED MONOLAYER OF TRIACONTANOIC ACID AND NONACOSYLAMINE - EVIDENCE IN FAVOR OF AN ORDERED ARRANGEMENT OF IONIZED HEAD GROUPS

Grazing incidence synchrotron X-ray diffraction measurements were made on an uncompressed monolayer of 1:1 triacontanoic acid (C29H59COOH) a nd nonacosylamine (C29H59NH2), spread on pure water and on aqueous ZnC l2 solution. The measured diffraction data of the mixed monolayer on w ater provides clear evidence of a complete mixing of the acid and amin e molecules into a two-dimensional crystal where the hydrocarbon chain s pack in a herringbone motif. A model has been proposed in which the ionized acid and amine moieties are ordered and form a continuous hydr ogen-bonded array.