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摘要
The aggregation behavior and the interaction of four mixed systems for a cationic fluorocarbon surfactant, diethanolheptadecafluoro-2-undecanolmethylammonium chloride (DEFUMACI), mixing with cationic hydrocarbon surfactants, alkyltrimethylammonium chloride, C(n)TACI (n = 12, 14, 16, and 18; where n = 12 is DTACI, n = 14 is TTACI, n = 16 is CTACI, and n = 18 is OTACI), were studied by (1)H and (19)F NMR in more detail. The results of (19)F NMR measurements strongly indicate that in the three mixed systems of DEFUMACI/DTACI, DEFUMACI/TTACI, and DEFUMACI/CTACI at different molar fractions of fluorocarbon surfactant (alpha(F) = (c(DEFUMACI)/c(DEFUMACI) + cC(nTACI))), with an increase of the total concentration of fluorocarbon and hydrocarbon surfactants (c(T) = c(F) + CH), the mixed micelles at the first break point and the individual DEFUMACI micelles at the second break point form. However, three different types of micelles were determined in DEFUMACI/OTACI mixtures by (19)F NMR measurements, OTACI-rich and DEFUMACI-rich mixed micelles and individual DEFUMACI micelles, respectively. The chemical shifts of proton Delta delta ((1)H) for -CH(3) in the mixed systems of DEFUMACI/C(n)TACI (n = 12, 14, 16, and 18) have different variation trends from the (19)F NMR measurements. For the two systems of DEFUACI/DTACI and DEFUMACI/TTACI, the mixed micelles form at the first break point. At the second break point, for lower alpha(F) values the DTACI-rich and TTACI-rich mixed micelles form with a strong downfield shift and for higher alpha(F) values DEFUMACI-rich mixed micelles form with a strong upfield. For the other two systems of DEFUMACI/CTACI and DEFUMAC/OTACI, the chemical shifts of proton Delta delta ((1)H) of -CH3 increase with an increase of the total concentration of DEFUMACI/CTACI or OTACI, and mixed CH- and CF-surfactant micelles form. At higher total concentration, the greater effect of fluorinated chains of DEFUMACI on CH-chains was obvious, resulting in the strong upfield chemical shifts. In cationic fluorocarbon and hydrocarbon surfactant mixtures, the different kinds of micelles observed by (19)F and (1)H NMR measurements could be caused by the increase in alkyl chain length of hydrocarbon surfactants with different critical micelle concentrations. Combining two theoretical models for mixing, for the four different chain-length hydrocarbon surfactants studied, one can conclude that the two components of mixtures interact with each other and form mixed micelles in two completely different ways according to their molecular properties and cmc values in a certain range of total concentrations. One is close to an ideal mixing case with the formation of one type of mixed micelles, such as the DEFUMACI/DTACI and DEFUMACI/TTACI systems. The other is a demixing case with the formation of two types of micelles, i.e., fluorocarbon-rich and hydrocarbon-rich mixed micelles, such as DEFUMACI/CTACI and DEFUMACI/OTACI systems. However, as the total concentrations of the mixed systems are high enough, the four systems tend to demix and to form individual micelles of corresponding components due to the initial respective interaction between fluorocarbon and hydrocarbon chains. That is to say, at high total concentration, the individual DEFUMACI micelles in all four systems could form. These results may be primarily directed toward acquiring an understanding o the mechanism of CF-CH mixtures in aqueous solution and secondarily directed toward providing more detailed information on nonideal mixing.
- 出版日期2008-8-7
- 单位山东大学
