Properties Study Of Imidazoliumionic Liquid Surfactants With Different Counterion

Three imidazolium ionic liquid surfactants with different counterion(1-dodecyl-3-methyl imidazolium proline, 1-dodecyl-3-methyl imidazolium alanine, 1-dodecyl-3-methyl imidazolium benzoic acid) were synthesized on the basis of the ionic liquid surfactant 1-dodecyl-3-methyl imidazolium bromide through strongly basic anion exchange resin and for the neutralization reaction with proline, alanine and benzoic acid, then they were characterized by nuclear magnetic resonance(NMR).The critical micelle concentration of the three surfactants aqueous solution has been measured in the temperature range from 20 ℃to 40 ℃by the measurements of conductivity. The critical micelle concentration also obtained by surface tension and fluorescence measurements at 25℃. It can be seen the results were reliable. With the larger molecule and the stronger hydrophobic of the counter ions, the critical micelle concentration decreased. And with the temperature increased the critical micelle concentration increased. The degree of counterion association of micelle( β) can be determined by the slopes of the pre-micellar and post-micellar processes in the conductance plots. The degree of counterion association of micelle decreased with the temperature increased and it can be strongly influenced by hydration radius and polarity of the counter ions. Combining the critical micelle concentration, the degree of counterion association of micelle and the equations of the phase separation model, it can be obtained these thermodynamic parameters(ΔGo, ΔHo and ΔSo). It is founded by analyzing the thermodynamic parameters that the micellization process was spontaneous process. As the enthalpy and the entropy were in a linear way, the enthalpy-entropy compensation effect can be observed in the process. And the entropy(ΔHo) was the dominant factor responsible for the micellization in the investigated temperature range, it is an entropy-driven process.The lyotropic liquid crystal system composed of the synthesized three surfactants and water were investigated by using polarized microscopy(POM), small angle X-ray diffractometry(SAXS) and 2H NMR spectroscopy. It can be found that the concentration range of the liquid crystal formation and the structure of liquid crystal were connected with the molecule structures of the counter ions and the concentration of the surfactants in water. And it was inaccuracy to determine the structure of the liquid crystal by only using the measurement of POM. The quantitative analysis of SAXS and 2H NMR study on the microscopic characterization were indispensable in determination of liquid crystal structures.Sodium salicylate has been selected to study the influence on the aggregation behavior of ionic liquid surfactant 1-dodecyl-3-methyl imidazolium bromide in water. By using surface tension and conductivity measurement, the critical micelle concentration of [C12min][Br]/C7H5O3 Na solution with different mole ratio greatly reduced when the mole ratio increased. And the critical micelle concentration was much less than the single surfactant. It can be found that the variation trend of the micellization process with the thermodynamic parameters was mostly similar to the single surfactant. The variation trend of two components concentrations in two phases of the mixture system with the temperature changing has been investigated by using UV-VIS spectrophotometer. With the temperature decreased, the two components concentrations of the lower solution increased while the upper solution concentrations remained mostly unchanged. From the dynamic light scattering, it can be seen that with the mole ratio and solution concentration increased, the mean sizes of the mixture solutions increased firstly and then decreased. The results revealed that the concentration of solution and different mole ratio had strong influence on the aggregate morphology of the surfactant and sodium salicylate interacting strongly in water.