Self-assembled behaviors of lecithin/inorganic salt in thin films
Date Issued
2016
Date
2016
Author(s)
Lin, Chen-Shin
Abstract
It has been known that amphiphilic molecules self-assembles into reverse spherical micelles in non-polar organic solvent and the addition of inorganic salts into lecithin organosol lead to the formation of reverse wormlike micelles. The cations of salt interact with phosphate group (PO2-) of lecithin, resulting in such a self-assembly behavior. In this work, instead of self-assembled structures in solutions, we focused on the bulk samples and thin films cast from phospholipid/salt mixtures in non-polar solvent, and studied how the salt affects the self-assembled structures of lipids without solvent. We investigated the effects of three inorganic salts on the formation of lipids, including calcium chloride (CaCl2), Magnesium chloride (MgCl2) and Lanthanum Chloride (LaCl3). With specific molar ratio of salt to different kinds of lipids, spherical, cylindrical, and lamellar domains can be observed by atomic force microscopy (AFM). For the lipids with one or two double bonds on each tail, the structure can be transformed from spherical to cylindrical microdomains as the fraction of the salts increases. The ability of the three inorganic salts to induce the structure transformation is in order of LaCl3 > CaCl2 > MgCl2. For the lipids with only one or no double bond, however, the structure is unaffected by the salts, remaining lamellar regardless of the type and the fraction of the salts. We also utilized small-angle X-ray scattering (SAXS and GISAXS) to analyze the structure and found the d-spacing of the ordered stuiructures in lecithin/salt mixtures is only 4 nm, which is much smaller than that of the phase-separated domains in typical block copolymer systems.
Subjects
phospholipid
self-assembly
wormlike micelles
thin film
sub-4 nm structure
Type
thesis
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