Two-dimensional order in mercury-supported langmuir films of fatty diacids.
The structure of mercury-supported Langmuir films of dicarboxylic acid molecules with 13 ≤ n ≤ 22 carbons is studied by X-ray methods and surface tensiometry. The molecules lie surface-parallel, forming mono-, bi-, or trilayers, depending on coverage. All films exhibit a full 2D order of the same single-molecule oblique unit cell. In particular, the distinct odd-even structure difference of 3D crystals of the same molecules is not observed. The unit cell's width and angle show a small systematic decrease with n, while the length increases commensurately with the molecular length. These results show the films to consist of closely packed, extended, polymer-like chains of diacid molecules, bound by their carboxyl end groups. Evidence is presented for the inclusion of a single mercury atom in the carboxyl-carboxyl bond. The possible conformation of this bond and implications of the parity-independent structure are discussed.
Physics Department, Bar-Ilan University, Ramat-Gan, Israel.
Lilach
L
Tamam
Benjamin M
BM
Ocko
Moshe
M
Deutsch
D003998:Dicarboxylic Acids / Q000737:chemistry*; D008628:Mercury / Q000737:chemistry*; D013499:Surface Properties
D003998:Dicarboxylic Acids; D008628:Mercury