| The surfactants containing the sterol rings have attracted much attention, for their large and rigid hydrophobic parts. Aggregates formed based by surfactants contain with sterol ethoxylate could show the rigidity characteristic. Among them, the phytosterol ethoxylate surfactants (BPS-n) have received increasing attention due to their good biocompatibility and low toxicity. The researches on their aggregation behaviors have been mainly concentrated on solvents like water and ionic liquids. However, the organic solvents have great value in the daily life and production. Specifically, the alcohols solvents that favor the aggregation of surfactants have wide applications in the fields of food, cosmetics and medicine. Therefore, the study on the aggregation behavior of sterol surfactants in alcohols solvent has great theoretical and practical significance in understanding the self-assembly process of phytosterolethoxylate surfactants.This dissertation focuses on the aggregation behavior of phytosterol ethoxylate surfactants in alcohol solvents with the help of several modern characterization methods, such as surface tension, polarizing microscope (POM), small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), infrared spectroscopy (FT-IR) and rheology measurements. Moreover, theoretical calculation was applied to research the structure and properties of aggregates in alcohol solvents. The influences of the hydroxyl number and its relative position on aggregation behavior of phytosterol ethoxylate surfactants were investigated. The main contents and outline of the dissertation are listed as follows:The first part is a comprehensive introduction of the background. The basic knowledge of the surfactants has been introduced in detail, including the structure and properties of surfactants and their weak interaction in solution. The structure, properties and formation regularity of aggregates formed by sterol surfactant in solution were emphatically summarized. The researches of surfactants containing sterol rings in water, ionic liquids and organic solvents systems have been analyzed and summarized, which provide the technical and theoretical support for the researches of this dissertatioa At the end of this part, the scientific significance and the aim of the doctoral dissertation are also pointed outThe second part focuses on the aggregation behavior of phytosterol surfactants with the short EO chains (BPS-5 and BPS-10) in glycerol. Compared with the reported phase behaviors in water and ionic liquid system, the aggregation behavior performed specially in this unusual solvent The results are as follows:(1) The micelle phase has been formed by both BPS-5 and BPS-10 in glycerol solvent The critical micellization concentration (CMC) values in both systems are between those in water and ionic liquids, indicating stronger aggregation ability in glycerol than that in ionic liquid. This is mainly attributed to the molecular structure characteristics of glycerol which can form the hydrogen bond network structure similar to water and EAN.(2) Lamellar phase (La) has been obtained with increase ing surfactant concentratba Compared with the water and ionic liquid systems, only La phase was formed in glycerol. It was noteworthy that there were two different lamellar structures formed at 70%surfactant concentration, which can be attributed to the different interactions between solvent molecules and hydrophilic EO chains.In conclusion, the aggregation behaviors of phytosterol ethoxylate surfactants in alcohol solvent were studied. La phase has been obtained in glycerol, moreover, the concentration range where the LLCs formed has enlarged compared to water and ionic liquid system. This is mainly because the glycerol molecule has stronger hydrogen bonding network structure and a long lifetime of hydrogen bond.The third part of the research content is to further investigate the influence of solvent molecular structure on the aggregation behavior of phytosterol surfactants. Considering the hydroxyl number and its relative position should have effect on aggregation behaviours, propylene glycol, normal propyl alcohol and isopropyl alcohol have been chosen as solvents to study the influence of solvent molecular structure on the aggregation behavior of phytosterol ethoxylate surfactants with short EO chains. Main conclusions are as follows:(1) The micelle, vesicle and lytropic liquid crystals can be formed by sterol ethoxylate surfactants in propylene glycol. The smaller Gordon parameter of propylene glycol than glycerolcan lead to reducing the orderness of molecular, which is against the formation of aggregate. Accordingly, the CMC value has increased obviously in propylene glycol. In addition, the aggregate with larger curvature is easier to be formed in BPS-5/PG system due to its minimum occupied area per molecule at the interface was bigger. Thus the vesicles could be obtained which cannot be formed in glycerol. Besides, there are also two different lamellar structures forming in propylene glycol similar to that in glycerol.(2) The.weak hydrogen bond network inpropyl alcohol solvent leads to the weak interaction between solvent molecules. The normal propyl alcohol and isopropyl alcohol tend to penetrate into the palisade layer of the aggregates, resulting destruction of aggregates. Thus there were no micelle formed in normal propyl alcohol and isopropyl alcohol. A single lamellar phase was formed under high concentrations of surfactant, which was similar to the propylene alcohol and glycerol system. The reason is that the main driving force is the hydrophobic interaction between sterol rings from be gaining to end process of aggregating.(3) As the number of hydroxyl groups decreases, the concentration range where LLCs formed decreased. It can be attributeed to that the reduced ability of hydrogen bonding network weaken the aggregation ability of BPS-n. The strength of the hydrogen bonds between BPS-n and alcohol solvents has been calculated by theoretical simulation. The results shown that the order of the hydrogen bonds strength could be obtained as follows:glycerol> propylene glycol> normal propyl alcohol> isopropyl alcohol, which was in accordance with the experimental results.Such an investigation will not only provide a useful reference to better understand the influence of hydroxyl number and its relative position on the aggregation process, but also be a great supplement to the aggregation behavior of phytosterol ethoxylate surfactants in alcohol solvents.In the fourth section, ethylene glycol with the cohesive energy density and stable hydrogen bonding network structure has been chosen as the solvent to expand the aggregation behavior of phytosterol ethoxylate surfactants. The differences between ethylene glycol and propyl alcohol solvents with three or two hydroxyls were investigated. Following results can be obtained:(1) Micelle phase has been obtained in glycerol, propylene glycol and ethylene glycol system. The CMC value in ethylene glycol was higher than that in glycerol and lower than that in propylene glycol, due to the Gordon parameter of ethylene glycol is smaller than glycerol and lager than propylene glycol. Accordding to the calculation of thermodynamic parameters of micelle phase formation, the micelle formation was confirmed to be enthalpy-driven process in glycerol and propylene glycol, which was the same at high temperature, but was entropy-driven at low temperature in ethylene glycol system. This can be explained by the special structural characteristics of ethylene glycol, resulting stronger interaction between EO chains and solvents at low temperature, which was verified by theoretical calculation.(2) The vesicle phase was obtained in ethylene glycol and propylene glycol, while only La phase was obtained in glycerol at the low concentration of BPS-n. This can be attributed to the different stength and network structures of hydrogen bonds in the three alcohol solvents resulting different occupied area per molecule adsorbed at the interface, thus aggregates with different curvatures have been formed.(3) Lamellar phase was obtained at the high concentrations of BPS-n in three different alcohols solvents. This was because the main driving force to form aggregate under high concentrations was the hydrophobic interaction between steroid rings, so the aggregate structure would not change with the solventThis section mainly researched the aggregation behavior of BPS-n in ethylene glycol, and got different aggregates. We can conclude that the aggregation behavior in ethylene glycol was similar with that in propylene glycol under low concentrations and that in glycerol under high concentration.The work not only enriches the aggregation behavior of phytosterol ethoxylate surfactants in alcohol solvents, but also provides a valuable reference for the aggregation behavior of nonionic surfactants containing polyoxyethykne chain in organic solution. |
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