Molecular Behaviors of n-Fatty Acids in Liquid State.

Dynamic Molecular Behavior of Semi-Fluorinated Oleic, Elaidic and Stearic Acids in the Liquid State

“…This is probably because the long methylene chain existing between a double bond and a carboxylic group reduces the effect of the perfluorooctyl group on the hydrogen bonding ability of the carboxylic group. As reported in the previous paper 7,8 , the degree of a dis- sociation of fatty acid dimer into monomers is extremely low in the liquid state: for example, the degree of dissociation of the fatty acid dimer is almost zero at room temperature and 2 even at 353 K. Thus, in spite of the slight up-field shift in 1 H-NMR signals arising from increasing temperatures, both SF-and H-acids are estimated to exist almost as their dimers. Consequently, the dimers of SF-acid are also the units of molecular movements in the liquid state.…”

“…Namely, in the pure liquid of fatty acids, the free rotational end-over-end as well as the transverse motion of the linear long molecule would be severely restricted due to the entanglements of the molecules: only a longitudinal translation is allowed. This is supported by the fact that the apparent hydrodynamic radius Stokes-Einstein radius , a, was almost constant regardless of the length of their hydrocarbon chains 8,30,31 ; the hydrodynamic radius was calculated from self-diffusion coefficient D and viscosity η of linear molecules such as alcohol, alkane, and fatty acid homologues by using the Stokes-Einstein formula a kT/4πη D under a slip-boundary condition. Namely, linear long molecules can move only longitudi- Fig.…”

Dynamical dimer structure and liquid structure of fatty acids in their binary liquid mixture: dodecanoic and 3-phenylpropionic acids system

“…In the region above liquidus line, a liquid of mixture of LA and PPA is existing. In the liquid, LA and PPA should exist mostly as dimers (Pauling, 1960;Leiserowitz, 1976;Iwahashi et al, 1995Iwahashi et al, , 2002.…”

“…By the way, near infrared spectroscopic (NIR) results indicated that ca. 2% dimeric carboxylic groups rupture at 80 • C (Iwahashi et al, 1995;Iwahashi et al, 2002). As the NIR spectroscopy can detect the rupture and/or the re-bonding of the dimeric carboxylic groups, which occur in a very short period, the latter case (2) would highly occur.…”

“…Through the measurements of near infrared spectroscopy and vapor pressure osmosis it has been revealed that cis-9-octadecenoic acid (Iwahashi et al, 1995) and n-fatty acids (C 8 -C 11 ) (Iwahashi et al, 2002) in their liquid states exist as dimers even at 80 • C. That is to say, the dimers are the units in intraor intermolecular movements. Through the measurements of ESR, NMR, viscosity, DSC, fluorescence polarization, and X-ray diffraction for cis-9-octadecenoic acid in its liquid state, it has become apparent that the dimers aggregate to make clusters possessing the structure of a quasi-smectic liquid crystal (Iwahashi et al, 1991).…”