E. Gelade

Fluorescence quenching in micelles: A theoretical model for the intramicellar first order quenching rate constant

Considering the fact that in a micellar medium solubilized molecules are mostly present near the surface, a solution of Fick’s diffusion law on a spherical surface is obtained to calculate the rate of diffusion controlled reactions in a micelle. It is shown that transients are small. Corrections are applied for the radial distribution of probe and quencher. The model is extended to reactions slower than diffusion controlled.

Fluorimetric determination of the aggregation number of cetyltrimethylammonium chloride (CTAC)

Micellar aggregation numbers have already been determined by several methods: fight scattering (1-3), excimer formation (4), stationary fluorescence methods (5, 6), timeresolved fluorescence measurements (single photon counting) (7, 8), and stopped-flow technique (9). The kinetic expression for fluorescence quenching in micellar systems has been developed by Tachiya (10), Infelta et al. (11), and Dederen et al. (12). The time dependence of the fluorescence quenching is expressed in Eq. [1]:

A study of temperature dependence of the mean aggregation number and the kinetic parameters of quenching in CTAC and TTAC micelles

From the study of the fluorescence quenching of 1-methylpyrene by n-methyl-N-decylaniline and the iodide ion in the micellar systems cetyltrimethylammonium chloride CTAC and tetradecyltrimethylammonium chloride TTAC the aggregation numbers and quenching rate constants could be determined. The influence of the temperature on these values was investigated. Comparing the calculated activation energies of the quenching process for the different quenchers gives information on the location and the mobility of the quenchers in the micelles.

Fluorescence quenching in dodecylammonium propionate reversed micelles

Abstract Depending on the kind of quencher (capacity and concentration), multi-exponential decay curves are obtained which can be analysed by a four-parameter equation, on the assumption that ion exchange between micelles is possible. The occurrence of probe exchange by intermicellar collisions is also suggested.

Fluorescence Quenching in Micellar Systems

The use of the excited state properties and particularly of the fluorescence of an added probe in non homogeneous systems such as micelles, anionic as well as cationic, and inverse micelles has expanded tremendously over the past few years. Using the single photon counting technique and steady state fluorescence it is possible to determine a number of important parameters such as the aggregation number, the rate constants of exit and entrance of compounds and the quenching rate constants in these systems.

Fluorescence: A Method to Obtain Information About Reverse Micellar Systems

Using the fluorescence properties of several naphthalene derivatives in the presence and absence of quenchers, it was possible to characterize DAP- and AOT-micelles in cyclohexane. Based on simple fluorescence lifetime measurements, it is proposed that the aggregation mechanisms for both systems are identical. The meaning of the CMC is also discussed. The use of fluorescence quenching to obtain information on e.g. the mean aggregation number and on the solubilizate exchange between colliding micelles is discussed.

Spectroscopic Evidence for a Unified Mechanism of Aggregation of Surfactant Molecules in Apolar Media

The neutral l-naphthalene acetic acid and the ionic sodium l-pyrenesulfonate and l-naphthylmethy1ammonium chloride were used as probes in both fluorescence lifetime and U.V.-absorption measurements to obtain information on the aggregation mechanism of the anionic surfactant sodium bis-(2-ethylhexyl)-sulfosuccinate (AOT) and the cationic surfactants dodecylammonium propionate (DAP) and didodecyldimethylammonium chloride (DDAC) in dried cyclohexane. In contrast with results in literature, a unified aggregation mechanism is proposed: starting from linear aggregates, cyclic inverse micelles are formed by a structural reorganization in a small concentration range, indicated as the operational CMC. For the first time experimental evidence is given for such a cyclization process. A critical evaluation of the use of spectroscopic probes to determine the “CMC” is also presented.