Mixed micellar systems of geminal alkylammonium surfactants and long-chain amines

Abstract

Numerical characteristics of the aggregation behavior of geminal alkylammonium surfac tants in aqueous solutions (the size of micelles, the packing of surfactant molecules, the surface potential, the extent of counterion binding) were determined. The formation of mixed micelles geminal surfactant/decylamine resulted in substantial decrease in amine pK a ; this is the crucial factor determining the strong catalytic effect of the system in ester bond cleavage processes.The most important feature of aqueous micellar solu tions of surfactants is the capability of solubilization of reactive substances possessing different hydrophilic lipo philic properties; this substantially extends the possibility of their use as reaction media. 1-4 Transfer of the reactants from the bulk of solvent to the micellar pseudophase is accompanied by changes in their microenvironment, which in turn leads to changes in the reactivity, acid base properties, spectral, and other physicochemical parame ters. The most pronounced changes are observed for am phiphilic reagents (long chain aliphatic amines, alkylphe nols), 5-7 which can form mixed micelles with surfactants, containing functional groups sensitive to variation of pH values of the media and the component ratio.In the last decade, interest in the geminal (dimeric) surfactants and highly organized systems based on them increased sharply. Geminal surfactants contain two hy drophobic radicals and two head (usually, charged) groups linked by spacers with different rigidity. These compounds differ from their amphiphilic analogs containing only one head group and one hydrocarbon chain by lower values of the critical micelle concentration (CMC), high surface activity, and solubilizing action; they are also character ized by unusual morphological behavior. 8-11 A series of papers devoted to the study of the aggregation behaviour and the structural properties of geminal surfactants were published. 12-14 A number of studies 15-18 on the catalytic effect of micellar solutions of these compounds in the nucleophilic substitution reactions were reported.The present work is dedicated to elucidation of the possibility of using aqueous solutions of geminal cationic surfactants as media for reactions involving hydrophobic alkylamines. Taking n decylamine as an example, data on the solubilizing effect, aggregation properties, and cata lytic activity in ester bonds cleavage of two geminal alkyl ammonium surfactants with different length of hydropho bic fragments six methylene unit spacers [C 12 H 25 (CH 3 ) 2 N(CH 2 ) 6 N(CH 3 ) 2 C 12 H 25 ] 2+ •2Br -(Gem 12), [C 16 H 33 (CH 3 ) 2 N(CH 2 ) 6 N(CH 3 ) 2 C 16 H 33 ] 2+ •2Br - (Gem 16) were obtained.A comparative analysis of their properties and those of analogous monomeric cationic surfactants, dodecyltri methylammonium bromide (DdTAB) and cetyltrimethyl ammonium bromide (CTAB), was carried out. ExperimentalCommercially available CTAB and DdTAB (Sigma), n de cylamine, n octylamine, and also p nitrophenyl acetate (PNPA) (Fluka) with 99% purity were us...

Photoresponsive amphiphiles based on azobenzene-dendritic glycerol conjugates show switchable transport behavior

“…Taking into account the resulting mixture of cis and trans isomers which form at the pss, the higher aggregation number suggests a formation of ill-defined, mixed micelles. 16 The change in geometry during the switching process should also affect micelle stability and, accordingly, the critical micelle concentration (cmc), which was determined by the pendant drop method. The cmc for G2azoC11 was doubled to 8 Â 10 À5 M upon irradiation with UV light.…”

Influence of Carbon Nanotubes on Surfactants Supramolecular Structures

“…Были взяты образцы растворенного ЦТАБ с концентрацией 100 мМ. Дисперсии ЦТАБ характеризуются высокой температурой мицелло-образования (примерно 25 °С) и низкой критической концентрацией мицеллообразования, близкой к 0,9 мМ, а также некоторыми другими параметрами, приведенными, например, в работах [12,13]. Для приготовления растворов использова-лась вода, очищенная с помощью установки MilliQ.…”

Micellar growth of m-2-m type gemini surfactants (m=10, 12, 14) with higher chain length alcohols/amines (C6–C8) in the absence and presence of organic salts (sodium salicylate, sodium tosylate)

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