The Properties Of Self-assemble Structures Formed By Long Chain Imidazolium Ionic Liquids

The long chain imidazolium ionic liquids（ILs）, as a new class of amphiphilic molecules,have many unique micellization behavior and surface properties, which have drawn considerable interest. The long chain imidazolium ILs can self-assemble in aqueous to form micelles, vesicles, lyotropic liquid crystals and gels, etc, and the structure of aggregates can be tailored by additives, temperature or solvent. The self-assembly of amphiphilic ILs plays an important role in the applications of many chemical and biotechnological processes. Thus,it is important to research the properties of self-assemble structures formed by long chain imidazolium ILs. In this thesis, the micellization behavior and adsorption properties of CnmimBF₄（n=12, 14, 16） was studied firstly. The effects of temperature, inorganic salt and organic alcohols on the cmc of CnmimBF₄（n=12, 14, 16） were also investigated, and the micellization thermodynamic parameters were calculated. Then, the micellization of conventional anionic surfactants sodium dodecyl sulfate（SDS）/CnmimBF₄, sodium dodecylbenzenesulfonate（SDBS）/CnmimBF₄, and sodium dodecanoate（SL）/CnmimBF₄ mixed systems were investigated, and discussed the effect of head-groups in anionic surfactants molecules on micellization. The aggregate behavior and structure of C₁₆mimBF₄ and C₁₆mimBF₄/SL were studied by¹H NMR and 2D NOESY. Additional, the rheological properties of wormlike micelles formed by C₁₆ mim BF₄ were also studied by rheometer. This thesis is divided into four parts:（1） The micellization behavior of CnmimBF₄（n=12, 14, 16）.The micellization behavior and surface activity of CnmimBF₄ with different alkyl chain were studied. It is found that CnmimBF₄（n=12, 14, 16） can form micelles in water, and with the increase of the hydrocarbon chain, the hydrophobicity strengthens, which is beneficial to the micelle formation, critical micelle concentration（cmc） decreases. Compared withCnmimBr, CnmimCl, CnmimBF₄ have superior micellization behavior and surface activity, and the cmc and γcmc increased in the sequence CnmimBF₄<CnmimBr<CnmimCl. The effects of inorganic salt and organic alcohols on micellization behavior of CnmimBF₄（n=12, 14, 16）were also investigated. The results showed that the cmc values decrease remarkable with the presence of inorganic salt caused by the counterion effect. For alcohol-water system, the cmc values increase with the presence of ethanol, 1-propanol, but decrease or invariable with1-butanol, 1-pentanol. The thermodynamic parameters of micellization process were calculated through cmc and β at different temperatures, the results showed that the micelle formation process of C12mimBF₄ is entropy-driven, and the micellization behavior of C14mimBF₄ and C₁₆ mim BF₄ is enthalpy-driven process.（2） The micellization behavior of C₁₆mimBF₄/SDS, C₁₆mimBF₄/SDBS and C₁₆mimBF₄/SL mixed systems.The micellization behavior of mixed systems were investigated by surface tension,steady-state fluorescence and DLS. The results showed that surface activity and micellization behaviors of the three mixed systems were superior to that of individual surfactant solutions,and the micellization properties reached the strongest when the molar ratio of cationic/anionic surfactants was about 1:1. Both electrostatic interaction and hydrophobic interaction can contribute to the formation of aggregation. Due to the different of head-groups for SDS,SDBS and SL, the electrostatic interaction and steric effect are different during the micellization process, thus, the mixed effect increased in the order C₁₆mimBF₄/SDBS<C₁₆mimBF₄/SDS<C₁₆mimBF₄/SL.（3） NMR study of cmc and micellar structure for C₁₆mimBF₄ and C₁₆mimBF₄/SL.A detailed analysis of ¹H NMR and 2D NOESY was used to investigate the micelle formation mechanism. The cmc of C₁₆mimBF₄ was determined by¹H chemical shifts, and the formation of aggregations was verified by 2D NOESY technology. The mixed micelles of C₁₆mimBF₄/SL system were studied by the¹H chemical shifts, and the microscopic aggregation structures were SL molecules insert into the micellar internal formed by C₁₆mimBF₄ molecules. 2D NOESY further confirmed the interactions of alkyl chain between SL and C₁₆mimBF₄, and formed the mixed micelles.（4） The rheological properties of salt-induced wormlike micelles of C₁₆mimBF₄.The micellar structure can further growth from spherical to wormlike micelles or network structures in C₁₆mimBF₄ solution with the presence of an organic salt sodium salicylate（NaSal）. According to steady-shear viscosity curves, with the increase of NaSal concentration,the zero-shear viscosity η0 firstly showed a increase, meaning that there was wormlike micelles in solutions, then η0 showed a sharply decrease, which indicated the wormlike micelles were destroyed. NaSal exist an optimal concentration, which induce the best properties of wormlike micelles. The frequency sweep rheological measurements showed that the wormlike micellar solutions of C₁₆mimBF₄ have high viscoelasticity, and storage modulus was higher than the loss modulus, the elastic properties was prominent.