Polymorphism of Natural Fatty Acid Liquid Crystalline Phases

Abstract

We study the phase behavior in water of a mixture of natural long chain fatty acids (FAM) in association with ethylenediamine (EDA) and report a rich polymorphism depending on the composition. At a fixed EDA/FAM molar ratio, we observe upon dilution a succession of organized phases going from a lamellar phase to a hexagonal phase and, finally, to cylindrical micelles. The phase structure is established using polarizing microscopy, SAXS, and SANS. Interestingly, in the lamellar phase domain, we observe the presence of defects upon dilution, which SAXS shows to correspond to intrabilayer correlations. NMR and FF-TEM techniques suggest that these defects are related to an increase in the spontaneous curvature of the molecule monolayers in the lamellae. ATR-FTIR spectroscopy was also used to investigate the degree of ionization within these assemblies. The successive morphological transitions are discussed with regards to possible molecular mechanisms, in which the interaction between the acid surfactant and the amine counterion plays the leading role.

Water sub-diffusion in membranes for fuel cells

“…This is a universal mechanism controlling, for instance, the lamellar-to-hexagonal transition observed in surfactants at intermediate water contents. [57,58] The morphology and swelling of PFSAs have been shown indeed to resemble that of ionic surfactants, [23] assigning to side-chains and acidic functions the predominant effect in controlling size, shape and organization of the ionic domains.…”

A Thermally Stable Polyamine/Unsaturated Fatty Acid System: Gelation Behaviors and Application

“…At pH = 10.12, diamine and protonated diamine (DETA + ) coexist with nearly the same concentration, which can explain the existence of N–H stretching of DETA in the gel at 3286 cm −1 (El‐Hendawy, ). Normally, DETA + and OLA − can strongly associate via Coulombic attraction (Fay et al, ), whereas the amino groups and OLA − may associate through NH…O hydrogen bonding (Taylor and Kennard, ).…”

“…However, the characteristic peaks of –NH 2 and –NH 3 + are not isolated from other signals, and the state of the primary amino groups cannot be convincingly analyzed. The FTIR results are further analyzed according to the calculation based on pK a using a deduction method (Fay et al, ). DETA has three pK a values, 4.4, 9.1, and 10.1 (Zhou et al, ).…”

Measuring Temperature Induced Phase Change Kinetics in Subcutaneous Adipose Tissues Using Near Infrared Spectroscopy, MR Imaging and Spectroscopy and OCT

“…This hysteresis was observed during multiple heating/cooling cycles in several samples. This could be due to formation of different polymorphs 13 of the fat crystals between cooling and heating cycles 19 .…”

“…It has also been shown that the exposure time affect the crystallization process for example, samples exposed to 8 °C for 25 min have larger crystal size compared to the samples exposed for 10 min 12 . The variation in amount of unsaturated fat between patients and the fact that mono and poly saturated fatty acids have different liquid-to-gel transition points 13 , 14 suggest that each patient experiences different crystallization kinetics during cryo-procedures. Thus, monitoring the kinetic of these changes in each individual patient can help enhancing the treatment outcome.…”