| Summary: | 博士 === 國立成功大學 === 化學工程學系 === 104 === The effects of two organic salts, tetraalkylammonium bromides (TAABs, alkyl chain from methyl to butyl) and imidazolium-based ionic liquids (1-ethyl-3-methylimidazolium tetrafluoroborate, EmimBF4 and 1-butyl-3-methylimidazolium tetrafluoroborate, BmimBF4) on the micellization of sodium dodecylsulfate (SDS) and the association behavior of SDS with polyvinylpyrrolidone (PVP) in aqueous solution both have been investigated by using pyrene solubilization experiment and several nuclear magnetic resonance (NMR) techniques. Firstly, for the SDS micellization behavior, the results of pyrene solubilization indicate that adding organic salts to the SDS solution can not only promote the formation of SDS micelle but also modify the micelle properties. The spatial arrangements and compositions of organic cations bound on the SDS micelles are respectively investigated by two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY) and pulse field gradient (PFG) NMR experiments. The TAA+ and Rmim+ organic cations are confirmed to firmly attach to the micelle surface or even reside at the hydrophobic micelle core, forming the mixed micelle structure. The compositions of the mixed micelle, which are calculated by measuring the self-diffusion of SDS, TAA+ and Rmim+ cations, were found to strongly relate to the concentration of SDS. When the number of SDS micelle increases with increasing the [SDS], the organic cations in the SDS solution at constant [salt] are mostly bound with the SDS micelles, but the number of micelle-bound ions on each SDS becomes less. Corresponding to the microstructure of mixed micelle, the micelle-bound organic ions could further remove water from the hydration shell of SDS micelle. The degree of hydration on the SDS micelle surface bound with various organic cations can be compared by determining the chemical shift change of SDS α-CH2 protons. When the SDS micelles bound with organic cations having longer chain, a more obvious upfield shift of SDS α-CH2 protons is observed, indicating that the surface of mixed micelle is dehydrated more pronounced. Moreover, in terms of 1H T1 relaxation, the insertion of Rmim+ ions into the SDS micelle are found to greatly restrict the fast motion of SDS -CH2 and -CH2 segments, whereas the central carbons and the terminal CH3 group of SDS are only slightly affected.
Two distinct complexation behaviors of SDS with PVP are found in the PVP/SDS solution containing the short-chain (EmimBF4, Me4NBr and Et4NBr) and long-chain (BmimBF4, Pr4NBr and Bu4NBr) organic salts. The formation of PVP-SDS complex promoted by the presence of short-chain organic salts is similar to that caused by inorganic salts. By means of 2D NOESY experiment, these short-chain organic cations are found to be incorporated into the PVP-bound SDS aggregates, making the distance between PVP and SDS in the ternary complex become longer. However, the PVP-SDS interaction in the presence of long-chain organic salts does not occur until the [SDS]/[salt] ratio 〉 a specific value (for BmimBF4, 0.45; for Pr4NBr, 0.6 and for Bu4NBr, 1.1). For example, as the [SDS]/[Bu4NBr] ratio 〈 1.1, only Bu4N+-SDS mixed micelles form in the PVP/Bu4NBr/SDS solution, and the mixed micelles do not interact with PVP even though the [SDS] 〉 2.0 mM (the regular CAC). Since the [SDS]/[Bu4NBr] ratio for the occurrence of PVP-SDS interaction is the highest, Bu4N+ ion is considered to have the highest ability to restrict the formation of PVP-SDS complex. When the [SDS]/[Bu4NBr] ratio 〉 1.1, the PVP-induced SDS aggregate is detected along with the mixed micellization between SDS and Bu4NBr. Moreover, the Bu4N+ cations binding with the ternary PVP-(Bu4N+-SDS) complex had been observed by measuring their self-diffusion coefficient using PFG NME experiment. Note that, the PVP segments in the ternary PVP-(Bu4N+-SDS) complex is apart from the bound Bu4N+ cations, and the complex microstructure is thus changed. Unlike the penetration of PVP into the SDS aggregates in the pure PVP/SDS solution, the PVP chains can only thread through the surface of PVP-(Bu4N+-SDS) complex. Based on the complexation behavior of SDS with PVP in the presence of organic salts, we not only proposed an interaction model for the role of organic cations on the associating behavior between PVP and SDS but also suggested some necessary driving forces for the occurrence of polymer-surfactant interaction.
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