STRUCTURAL RELATIONSHIPS BETWEEN FLOATING AND DEPOSITED MONOLAYERS OF DOCOSANOIC ACID

Floating docosanoic acid (behenic acid) monolayers in the SmI and SmH phase were deposited with the Langmuir-Blodgett technique onto thin polymethylmethacrylate (PMMA) and Formvar substrates and investigated by electron diffraction. The molecular packing of the monolayers on the substrates vary from those on the water surface and are different for different substrates. On PMMA four phases (H, SmB, SmI, SmL) have been identified, depending on the deposition conditions. While SmB and SmI are known for docosanoic acid on the water surface, H and SmL have only been unequivocally observed in other substances or on other subphases. The monolayer structure on Formvar was identical under all deposition conditions and identified as the H-phase. The monolayer/substrate interaction was directly addressed by measurements of the work of adhesion. The work of adhesion between the monolayer and PMMA depends strongly on the surface pressure, indicative of interactions that vary with the molecular arrangement in the monolayer.