0000000000359023
AUTHOR
R. Steitz
Relationships between fatty acid monolayer structure on the subphase and on solid substrates
Abstract Docosanoic acid monolayers with known molecular packings on the water surface have been deposited on thin polymer films and then investigated using transmission electron diffraction at normal and tilted incidence. The diffraction patterns from monolayers deposited under all conditions investigated could be indexed as arising from the same conformationally disordered centred rectangular packing with molecules standing perpendicular to the substrate, although with a spread of unit cell parameters within and between each deposition condition significantly greater than the experimental error. This packing has been seen in monolayers on the water surface, but only under conditions compl…
An electron diffraction study of deposited docosanoic acid monolayers
Docosanoic acid monolayers deposited on thin polymer films under different water surface conditions have been investigated using transmission electron diffraction at normal and tilted incidence. Diffraction patterns obtained from the L2 and L2' phase are quite similar, but distinctly different to samples coated from the CS phase. The former were consistent with molecules perpendicular to the substrate, arranged in a texture of grains with unusual orthorhombic packing. There is evidence for a phase transition from a liquid crystalline phase on the water surface.
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 deposi…
An investigation of the spot profiles in transmission electron diffraction from Langmuir-Blodgett films of aliphatic chain compounds
The profiles of the transmission diffraction spots from a Langmuir-Blodgett film of aliphatic chain compound are derived from three plausible models of molecular organisation : a polycrystalline phase with long-range orientational order; a paracrystal possessing a density of point defects which do not interrupt the lattice rows ; and a Nelson and Halperin hexatic smectic phase in the «Debye-Huckel» limit of weakly-interacting dislocations. The three resulting predictions are distinctly different. Experimental results are presented for the room-temperature diffraction patterns from Langmuir-Blodgett films of a lipid, DMPE, and the cadmium soap of a fatty acid, 22-tricosenoic. Only the Nelson…
An Analysis of the Broadening Induced by Beam Damage in Transmission Electron Diffraction Spots from an Oriented Aliphatic Monolayer
We have analysed the progressive changes in diffraction spot shape during prolonged transmission electron diffraction observation of a soap monolayer supported on a thin polymer film. The material used to form the monolayer was cadmium eicosanoate (arachidate). The observed changes cannot be explained at all in terms of the chemical crosslinking which is known to occur as a result of beam damage, nor completely in terms of the strain fields caused by unbound dislocation defects of the crystalline lattice. The most plausible explanation involves the formation of linear dislocation aggregates which resemble grain boundaries but yet which are not linked into a continuous network. The evolution…