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Molecular theory of critical phenomena in aliphatic carboxylic acid monolayers
Author(s) -
Dunne Lawrence J.,
Bell George M.,
Combs Leon L.
Publication year - 1984
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560250504
Subject(s) - monolayer , chemistry , intermolecular force , dimer , carboxylic acid , molecule , perpendicular , monomer , computational chemistry , chemical physics , organic chemistry , polymer , geometry , biochemistry , mathematics
A statistical mechanical theory is presented for the behavior of monolayers of aliphatic carboxylic acids at the air/water interface. A lattice fluid model is introduced with monomer states to represent molecules in the all‐ trans conformation directed perpendicular to the interface, dimer states to represent rotational isomers, and vacant sites or “holes.” Using a Flory–Huggins‐type approximation, the temperature and chain length dependences of the monolayer behavior are satisfactorily reproduced for a certain range of parameters. These parameters are compared with those intermolecular energies calculated using the methods of computational quantum chemistry. The agreement thus obtained is fairly satisfactory indicating that the higher‐order nature of fatty acid monolayer transitions is due to the onset of the rotational ordering of pairs of chains about their longitudinal axes, while the sensitive temperature dependence is attributed to the flexible nature of fatty acid molecules. Some possible effects due to the presence of the substrate are discussed.