Self-assembled Behavior And Properties Of Catanionic Surfactant Systems In High-Salinty Solution And Catanionic Surfactant Systems Containing Lecithin

The study on the self-assembly, structural transition and properties of surfactants in aqueous solutions is the focus of colloid and interface science. In most cases, the mixed systems of surfactants usually have more excellent performance than the single surfactant solutions. The cationic and anionic surfactants mixture system, called catanionic systems, is a typical example, which has unique characteristics. The catanionic systems display a large diversity of phases. An outstanding property of theses systems is their ability to spontaneously form catanionic vesicles which can remain stable for years. The addition of salts can affect the properties of surfactant solution. Lecithin is the best known of all natural surfactants. It is widely distributed in living nature, being a basic structural component of the lipid matrix of biological membranes and membranous organelles. And it widely uses in food industries, cosmetics, pharmacology, and biotechnology as an effective dispersive and emulsifying agent. All this explains the keen interest of investigators from different fields of science in s lecithin. The research on interaction between lecithin and the catanionic surfactant systems can provide fundamental knowledge for the nano materials, biotechnology and pharmaceutical technology.In this thesis we investigated that the phase transition of surfactant aggregates in salt solution and the catanionic surfactant systems with lecithin. The outline and contents of this doctoral thesis are as follows:Chapter Ⅰ is a brief introduction of basic knowledge of the research background, in which surfactant science are reviewed, especially we conferred about the general features concerning the catanionic systems. The object and scientific significance of this thesis are also discussed at the end of this chapter.In Chapter Ⅱ, we determined the solubility of three commercially available inorganic salts, NaBr, NaCl, and KBr in cationic tetradecyltrimethylammonium bromide (TTABr) and anionic sodium dodecyl sulfate (SDS) solutions from298.15K to353.15K, respectively. The data show that the solubility of three salts in SDS and TTABr solution increase progressively with temperature increasing, which is similar to those in water. The solubility of NaBr, NaCl and KBr in surfactant aqueous solutions with concentration below the critical micelle concentration (cmc) of TTABr or SDS is higher than those with concentrations above TTABr or SDS cmc. The solubility of NaCl and NaBr in SDS are much lower than those in water and increase slowly along with the temperature increasing. For the case of KBr and NaBr in TTABr, it becomes more complicated. When temperature is below T=312.15K, the solubility of KBr and NaBr are much lower than those in water. But the solubility become higher when temperature is above T=340.15K. And the data are similar to those in water between312.15K and340.15K. The solubility of inorganic salts in surfactant aqueous solutions is very important parameter in scientific research and industry. The data and the results of inorganic salts in surfactant aqueous solutions should provide the basic data and make for understanding for inorganic and surfactant industries.In Chapter Ⅲ, the phase behavior induced by adding NaBr in two systems of cationic and anionic (catanionic) mixtures with same surfactant components but salt-free and saline in water, i.e.,(ⅰ) an excellent extractant of rare-earth metal ions, di-(2-ethylhexyl) phosphate (HDEHP, commercial name:P204), mixing with a cationic trimethyltetradecylammonium hydroxide (TTAOH) and (ⅱ) the sodium salt of HDEHP, NaDEHP (HDEHP+NaOH→NaDEHP+H2O), mixing with tetradecyltrimethylammonium bromide (TTABr), were studied. With adding NaBr, the salt-free system was transferred from an original two-phase Lα/L1to single Lα phase consisting of vesicles, the saline system from a two-phase Lα/L1to single Lα phase of vesicles, too. A very interesting finding is that the both finally single Lα phases of the two systems contain vesicles having different hyperfine structures which could be induced by much higher ionic strength because of the addition of NaBr. For the salt-free system, the densely deformed and packed vesicles are transferred to smooth and spherical ones with the addition of NaBr. However, for the saline system, the spherical vesicles with a high spontaneous curvature are changed to be largely, densely, and remarkably deformed ones. The hyperfine vesicle evolvement was demonstrated by polarization observations, rheology measurements, deuterium and phosphorus nuclear magnetic resonance spectra (2H and31P NMR), and cryogenic transmission electron microscopy (cryo-TEM) images. The theoretical considerations of vesicle evolvement in the two systems were discussed from energy and packing parameter. This control over aggregate shape with salt concentration may provide an understanding of transmutation of surfactant aggregates originating from different surfactant systems.In Chapter Ⅳ the phase behavior, structures, and properties of lecithin/tetradecyltrimethylammonium hydroxide (TTAOH)/water systems were investigated by cryo-TEM, polarization optical microscope,1H and31P NMR spectra, surface tension and rheological measurements. With the variation of mixing molar ratio and concentration of lecithin and TTAOH, the system exhibits the phase transition from micelles (L1phase) to vesicles (La Phase) through a phase separation region. The rod-like micelles, uni-and multilamellar vesicles were determined by means of cryo-TEM observations. The surface tension and rheological measurements were performed to follow the phase transition. The samples of L1phases behave as Newton fluids at a low concentration of lecithin. With increasing of the lecithin concentration, a shear-thinning L1phase at the shear rate80s-1was found. The samples of La phases show viscoelastic properties of typical vesicles. The interactions between lecithin and TTAOH were monitored by]H and31P NMR spectra. These results could contribute towards the understanding of the basic function of lecithin in biological membranes and membranous organelles.In Chapter V, the phase equilibria in mixtures of lecithin and the salt-free catanionic system TTAOH/MA (Myristic acid)/H2O were studied with particular emphasis on the behavior of the lamellar and hexagonal liquid crystal. The solvent corner of this system features an extensive lamellar and hexagonal phase and which we have characterized by means of polarization optical microscope, small-angle X-ray scattering and rheology. The findings from X-ray scattering determine the structural parameters of lamellar and hexagonal phase, which indicate the arrangement of surfactant molecules in lamellar and hexagonal phase.