ATOMIC-FORCE MICROSCOPE OBSERVATION OF MONOLAYERS OF ARACHIDIC ACID, OCTADECYLDIMETHYLAMINE OXIDE, AND THEIR MIXTURES

Monolayers of arachidic acid, octadecyldimethylamine oxide (C(18)DAO), and their mixtures were prepared at a surface pressure of 25 mN m(-1) on a mica substrate by the Langmuir-Blodgett method and were observed by use of an atomic force microscope (AFM). Arachidic acid molecules in monolayer arranged with molecular axes vertical to the mica substra te. In contrast to it, C(18)DAO molecules in monolayer folded on the s ubstrate. For the equimolar mixture of arachidic acid and C(18)DAO, mo lecules were vertical in a part of the monolayer and folded in the oth er part. When the C(18)DAO monolayer was aged at 25 mN m(-1), molecule s were rearranged with vertical molecular axes. Molecular ordering in arachidic acid and aged C(18)DAO monolayers was compared at a nanomete r scale. Arachidic acid molecules ordered with a monoclinic unit latti ce, whereas AFM could not detect a regular arrangement of C(18)DAO mol ecules.