Formation and research of Langmuir monolayers based on an asymmetrically substituted porphyrin derivatives and arachidic acid
V.N. Mironyuk Education and Research Institute of Nanostructures and Biosystems, Saratov State University.
N.N. Begletsova Education and Research Institute of Nanostructures and Biosystems, Saratov State University.
A.J. Al-Alwani Faculty of Nano- and Biomedical Technologies, Saratov State University.
A.I. Smirnova Research Institute of Nanomaterials, Ivanovo State University.
N.V. Usoltseva Research Institute of Nanomaterials, Ivanovo State University.
E.G. Glukhovskoy Education and Research Institute of Nanostructures and Biosystems, Saratov State University.
Abstract
Langmuir monolayers of mixtures with different component ratios have been investigated. Arachidic acid (AA) and an asymmetrically substituted porphyrin (PR) derivative (type A3B) was selected as a component of the mixture. The parameters of monolayers (ranges of formation of phases state with close packing of molecules, specific areas, compression modulus and compressibility) were calculated from compression isotherms. In addition, the specific area occupied by a single molecule was calculated from molecular models. We compared the value of the theoretical and experimental areas and found that the area per molecule was about 2 times less than expected. Such of mismatch can be explained by a change in the orientation of the head parts of the molecules (deviation from the horizontal) or the combination of molecules into aggregates. We also found that the compact packing of molecules is the most dense when the fraction of arachidic acid does not exceed 20% and pressures reaches 40-55 mN/m.
The diagrams obtained by plotting the mean area per molecule as a function of molar fraction of porphyrin showed positive deviations from ideal conditions at mole fraction PR:AA 0.43:0.56 and showed ideal miscible behavior at mole fraction PR:AA 0.20:0.79 and 0.69:0.30. The occupied area of mixed monolayers increases with a decrease in the mole fraction of arachidic acid. The isotherm at a mole fraction of 0.69:0.30 showed two collapses (the transition of a monolayer to a multi-dimensional phase, by which floating material is forced out of the monolayer at high compression to form multilayer or bulk structures).
This work was supported by the Russian Foundation for Basic Research Grant No. 19-03-00763-a.
Speaker
Mironyuk V.N.
Education and Research Institute of Nanostructures and Biosystems, Saratov State University
Russia
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