The aggregation behaviors of a series of symmetric and dissymmetric cationic Gemini surfactants, [CmH2m+1(CH3)2N-(CH2)2-N(CH3)2CnH2n+1]Br2, designated as m-2-n (m = n with m = 10, 12, 14; or m ? n with a ?xed m + n = 24, m = 16, 14, 12) have been investigated in three protic ionic liquids, ethyl-, propyl- and butyl-ammonium nitrates (EAN, PAN and BAN). Surface tension, polarized optical microscopy (POM), small-angle X-ray scattering (SAXS), and rheological measurements were adopted to investigate the micellization and lyotropic liquid crystal (LLC) formation. Compared to LLCs formed in aqueous environment, the normal hexagonal (H?) and lamellar (La) phases are found to disappear with a new reverse hexagonal (HII) phase instead in EAN. The structure dissymmetry plays an important role in aggregation process of m-2-n. With increasing degree of dissymmetry, the critical micellization concentration, the maximum reduction of solvent surface tension, and the minimum area occupied per surfactant molecule at the air/EAN interface all become smaller. The thermostability of formed LLCs is therefore improved because of the more compact molecules. These characteristics can be explained by the enhancement of solvophobic e?ect due to the increased structure dissymmetry of Gemini surfactants. In PAN and BAN, however, their better hydrocarbon solubility due to longer chain length and penetration capability into the space between surfactants will induce the formation of aggregates with lower critical packing parameter, H? and the biscontinuous cubic phase (V?) in 12-2-12/PAN, H?, V? and La in 12-2-12/BAN systems.References: X. D. Wang, X. Chen, et al.,Langmuir, 2012 ,28, 2476.X. D. Wang, Q. T. Li, X. Chen, et al., Langmuir, 2012 , 28, 16547.Acknowledgements: The financial supports from the National Natural Science Foundation of China (20973104, 21033005 and 21373127) are acknowledged.

Aggregation behaviors of Gemini cationic surfactants in alkylammonium nitrate protic ionic liquids

247th National Meeting (2014)

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