Are Aqueous Sodium Dodecyl Sulfate Micelles in the Presence of Added Salt Polydisperse? A Time-Resolved Fluorescence Quenching Study with Global Analysis

Abstract

Aggregation numbers of aqueous sodium dodecyl sulfate (SDS) in the presence of added salt were estimated using the time-resolved fluorescence quenching method. Tris (2,2′-bipyridyl)ruthenium(II) and 1-ethylpyrene were used as probes and 9-methylanthracene, 3,4-dimethylbenzophenone, and 1-dodecylpyridinium chloride were used as quenchers. It was found that aqueous SDS micelles are monodisperse even in the presence of high salt concentrations contrary to what has been reported. Similar studies were carried out using the nonionic surfactant hexaethylene glycol mono-n-dodecyl ether (HEGDE) in water. Aqueous 33.1% (w/w) HEGDE solutions were found to be polydisperse.

Identifiability of Models for Fluorescence Quenching in Aqueous Micellar Systems

“…However, the latter procedure, which further reduces the number of adjustable parameters, requires one to limit the experiments to the range of [S] where the aggregation number or micellar shape does not depend on [S]. [13,24,[39][40][41] and not for n. [30] Indeed, [M] is a global parameter which can be linked over fluorescence decays recorded as a function of [Q], whereas n is not linkable.…”

Aggregation Behavior of Sugar Surfactants in Aqueous Solutions: Effects of Temperature and the Addition of Nonionic Polymers

“…Note that the literature reports about micellar systems characterized by nearly monodisperse micelles with aggregation numbers well above that of the minimum spherical micelles. The most recent studies concern sodium dodecylsulfate micelles in the presence of NaCl (60) and micelles of C m E n surfactants (61). It may be argued that the polydispersity increases with the average value of N more slowly than theoretically expected and remains low, and thus not detected by TRFQ measurements, even when the average value of N is twice or more larger than for the minimum spherical micelle (60).…”

“…The most recent studies concern sodium dodecylsulfate micelles in the presence of NaCl (60) and micelles of C m E n surfactants (61). It may be argued that the polydispersity increases with the average value of N more slowly than theoretically expected and remains low, and thus not detected by TRFQ measurements, even when the average value of N is twice or more larger than for the minimum spherical micelle (60). Another possibility is a partial mixing of the alkyl chains and the sugar head groups.…”

Dye–Surfactant Interaction: Modulation of Photophysics of an Ionic Styryl Dye

“…4b). It is reported in literature that the size and hydration of SDS micelle increases significantly with the addition of salt (29,30). The addition of salt causes increased micellar aggregation number and the content of mechanically trapped water in the Stern layer (31,32) along with increase in micellar hydration layer.…”