Abstract
The properties of ionic micelles are affected by the nature of the counterion. Specific ion effects can be dramatic, inducing even shape and phase changes in micellar solns., transitions apparently related to micellar hydration and counterion binding at the micellar interface. Thus, detg. the hydration and dynamics of ions in micellar systems capable of undergoing such transitions is a crucial ...
Abstract
The properties of ionic micelles are affected by the nature of the counterion. Specific ion effects can be dramatic, inducing even shape and phase changes in micellar solns., transitions apparently related to micellar hydration and counterion binding at the micellar interface. Thus, detg. the hydration and dynamics of ions in micellar systems capable of undergoing such transitions is a crucial step in understanding shape and phase changes. For cationic micelles, such transitions are common with large org. anions as counterions. However, phase sepn. also occurs for dodecyltrimethylammonium triflate (DTATf) micelles in the presence of Na triflate (NaTf). Specific ion effects for micellar solns. of dodecyltrimethylammonium chloride (DTAC), bromide (DTAB), methanesulfonate (DTAMs), and triflate (DTATf) were studied with dielec. relaxation spectroscopy (DRS), a technique capable of monitoring hydration and counterion dynamics of micellar aggregates. In comparison to DTAB, DTAC, and DTAMs, DTATf micelles are considerably less hydrated and showed reduced counterion mobility at the micellar interface. The obtained DTATf and DTAMs data support the reported central role of the anion's -CF3 moiety with respect to the properties of DTATf micelles. The reduced hydration obsd. for DTATf micelles was rationalized in terms of the higher packing of this surfactant compared to that of other DTA-based systems. The decreased mobility of Tf- anions condensed at the DTATf interface strongly suggests the insertion of Tf- in the micellar interface, which is apparently driven by the strong hydrophobicity of -CF3.
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