Dielectric Relaxation Spectroscopy Shows a Sparingly Hydrated Interface and Low Counterion Mobility in Triflate Micelles

Autor(es)

Lima, Filipe S. ^[1] ; Chaimovich, Hernan ^[1] ; Cuccovia, Iolanda M. ^[1] ; Buchner, Richard ^[2]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Quim, Sao Paulo - Brazil

^[2] Univ Regensburg, Inst Phys & Theoret Chem, D-93053 Regensburg - Germany

• Tipo de documento: Artigo Científico
• Fonte: Langmuir; v. 29, n. 32, p. 10037-10046, AUG 13 2013.
• Citações Web of Science: 13

Resumo

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 solutions, transitions apparently related to micellar hydration and counterion binding at the micellar interface. Thus, determining 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 organic anions as counterions. Interestingly, however, phase separation also occurs for dodecyltrimethylammonium triflate (DTATO micelles in the presence of sodium triflate (NaTf). Specific ion effects for micellar solutions of dodecyltrimethylammonium chloride (DTAC), bromide (DTAB), methanesulfonate (DTAMs), and triflate (DTATO were studied with dielectric relaxation spectroscopy (DRS), a technique capable of monitoring hydration and counterion dynamics of micellar aggregates. In comparison to DTAB, DTAC, and DTAMs, DTATf micelles were found to be 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 observed 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. (AU)

• Processo FAPESP: 07/50970-5 - Reatividade química e biológica em interfaces
• Beneficiário: Hernan Chaimovich Guralnik
• Modalidade de apoio: Auxílio à Pesquisa - Temático
• Processo FAPESP: 08/50041-7 - Trifluorometilsulfonato como contra íon de micelas catiônicas
• Beneficiário: Filipe da Silva Lima
• Modalidade de apoio: Bolsas no Brasil - Doutorado Direto