Determination of Micellar Aggregation Numbers in Dilute Surfactant Systems with the Fluorescence Quenching Method.

Abstract

This work addresses the problem of determining micellar aggregation numbers for dilute ionic surfactant systems by means of the time-resolved fluorescence quenching method. We argue that the use of quenchers that are themselves surfactants gives us two advantages. First, the altering of the micelles caused by the solubilization of quencher molecules is minimized. Second, the distribution of the quencher between the micelles and the aqueous subphase can be obtained. The latter point is particularly important for the case of dilute micellar systems and when the micelles are adsorbed at interfaces or associated with polymers. We describe a method to obtain the partitioning of the quencher for various surfactant/quencher combinations. The method is based on a detailed thermodynamic model of mixed micelles supported by Poisson−Boltzmann cell model calculations. It is shown that ideal mixing of surfactant and quencher in the micelles simplifies the analysis of effects related to polydispersity and probe distribution among the micelles. The method is applied to quaternary ammonium surfactants, both mono- and divalent, with various chain lengths, using the corresponding alkyl pyridinium ions as quenchers. Aggregation numbers at concentrations close to the critical micelle concentration (cmc) are presented and discussed.

Predicting the Critical Micelle Concentrations of Aqueous Solutions of Ionic Liquids and Other Ionic Surfactants

“…1 [N 1,1,1,16 ]Cl 1.3 [4] 1.46 [4] 1. 5 [N 1,1,1,16 ]Br 0.9 [23] 1. 1 [N 1,1,1,18 ]Cl 0.35 [26] 0.38…”

Aggregation of Non Ionic Surfactant Igepal in Aqueous Solution: Fluorescence and Light Scattering Studies

“…Extensive insight has been provided into the environment within micelles using steady state fluorescence quenching technique [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. The property of the surfactants to self-aggregate into micelles in solvents is the most fascinating aspect of these molecules and micelles remain one of the central topics of study within surface and colloid chemistry.…”

Predicting proton titration in cationic micelle and bilayer environments

“…17,27 This size was chosen as it is approximately the aggregation number of DTA micelles, 28 and the surfactant to fatty acid ratio was about 60-1 in the experiment that determined the pK a shift of lauric acid in DTA micelles. 29 The system was solvated in an octahedral box, with at least 10 Å between surfactant atoms and the box edge.…”