Phase Transitions of Branched Fatty‐Acid Calcium Salt/Water Systems

Abstract

Calcium (Ca) salts of fatty acids are powder materials, which exhibit lubricant, hydrophobic, and bactericidal properties. These physical and biological properties depend on the chemical structure of the alkyl chain of the fatty acids. In this study, the phase behavior of iso‐stearic acid Ca salt/water binary systems was studied, and the effect of the branched structure in the alkyl chain was analyzed. Herein, calcium chloride is added to the iso‐stearic acid aqueous solution. The state of the binary systems changed with the molar ratio (R) of [Ca2+]/[iso‐stearic acid]. Precipitation occurred when R was more than 0.05, whereas the mixture changed from a micelle phase (Wm) to an oil phase (O) through a liquid crystalline phase (LC) when R was less than 0.01. The polarized microscopy images and small‐angle X‐ray scattering profiles showed that the LC is in a lamellar liquid crystalline state. In addition, we evaluated the crystal structure of the precipitated material. These results showed that the iso‐stearic acid Ca salt was in the amorphous state. In contrast, the n‐stearic acid Ca salt formed only the Wm and gel phases. These findings suggest that the branched structure of fatty acids induces loose intermolecular packing of liquid crystalline structures.

Review of the use of NMR spectroscopy to investigate structure, reactivity, and dynamics of lead soap formation in paintings

“…It is known that, in the presence of water, salts of fatty acids can form liquid crystalline structures, as has been reported for calcium salts of stearic acid and water. 57 The structural state of a phase can be addressed by computational methods and/or diffraction methods, but ssNMR methods may also provide structural and crystallographic information on samples as varied as reasonably large proteins and pharmaceutical compounds. 58 Low solubilities of the metal carboxylates make it extremely difficult, if not impossible, to grow single crystals of these compounds sufficient to obtain X-ray diffraction structures.…”

Adsorption and Lubrication of Glutamic Acid-Based Surfactant with Calcium Ions

“…The excellent lubricity results from (i) the cleavage of lamellar layers of the powdered aggregates, (ii) the disintegration of the aggregates, and (iii) the low surface energy of the calcium salts, leading to increased hydrophobicity of solid surfaces 6−9) . The authors also demonstrated the phase transitions of the calcium salt of a branched fatty acid (2,2,4,8,10,10-hexamethylundecane-5-carboxylic acid, generally called iso-stearic acid ) with water 10) . The key finding of this study was that the calcium salt yields a liquid crystal phase at low Ca 2＋ mole ratios, despite the calcium salt of octadecanoic acid (n-stearic acid) exhibiting a gel phase under the corresponding conditions.…”