Interactions between lecithin and inorganic salts in oil and their effects on the reverse micellization

• Main Authors: Shih-Ting Lin, 林詩婷
• Other Authors: Shih-Huang Tung
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/64855875137581691373

碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 103 === Biological surfactants play an important role in human bodies, one of the common type of biological surfactants in human body is lecithin, which is main component of cell membranes. Although the content of inorganic salts existing in our body is not much, inorganic salts have a vital impact on our physiological mechanisms. Because the interaction between lecithin and inorganic salts in the aqueous solution is difficult to analyze due to the interference of water molecules, we explore the influence of inorganic salts on the self-assembly behavior of lecithin in a non-polar solvent to clarify the interactions, and we find different results from previous studies. Lecithin can self-assemble into reverse spherical micelles in non-polar organic solvent. Previous study has shown that the addition of inorganic salts with specific divalent and trivalent cations into lecithin organosols can form reverse wormlike micelles in low polar solvents. The long chain of micelles which are similar to polymer chains entangle in the solution to cause the viscosity to substantially increase, and give rise to a viscoelastic solution or a quasi-permanent gel-like network. This study further investigates the effects of the interactions between lecithin and monovalent cation inorganic salts, including lithium, sodium, potassium with different halides (chloride, bromide, iodide) on the self-assembly structure. We utilized rheology and small-angle X-ray scattering techniques to analyze the rheological properties and the structure of the reverse micelles and we find that all the lithium salts in lecithin organosols can induce the transformation of the original reverse spherical micelles into reverse wormlike micelles to form viscoelastic or even gel-like fluid. In sodium salts, only sodium iodide can induce change of structure, while there is no significant change for all potassium salts. Therefore, the ability to induce the formation of reverse wormlike micelles from high to low is in order of Li+ > Na+ > K+. Furthermore, the ability of the cations to interact with phosphate group of lecithin is indirectly affected by the anions, in order from high to low I− > Br− > Cl−. The interactions between lecithin and inorganic salts are the key responsible for the different self-assembly behaviors. We used Fourier transform infrared spectroscopy (FTIR) to investigate the interactions and show that among the monovalent cations, lithium ion interacts most strongly with the negatively charged phosphate group (PO2-) of lecithin, and in the presence of large anions, such as iodide, the interaction between cations and phosphate is strengthened. The strong attraction between cation and phosphate forces lecithin molecules to pack more closely and thus changes the effective molecular geometry, which in turn leads to the formation of cylindrical micelles that cause the solutions to be viscoelastic or gel-like.