High-Pressure Studies on Aggregation Number of Surfactant Micelles Using the Fluorescence Quenching Method

Abstract

The aggregation number of a nonionic surfactant micelle, Triton X 100 (TX100), in aqueous solution was determined as a function of pressure by using the method of steady-state fluorescence quenching. The method of this work uses the fluorescence quenching of a probe (pyrene) by a quencher (coumarin 153), which are solubilized within a micelle. With increasing pressure, the aggregation number of TX100 takes a minimum. Namely, it decreases from 250 at atmospheric pressure down to 80 at around 100−150 MPa and then increases up to 230 at 500 MPa, the highest pressure studied. This behavior is closely related to the turnover phenomenon of critical micelle concentration (cmc) against pressure. By taking the pressure effect on the micellar concentration into account, it is demonstrated that in addition to the equilibrium between dispersed state and micellar state, there are equilibria among different-sized micelles.

Origins of Pressure-Induced Protein Transitions

“…The latter can be scrutinized against the published data on the pressure dependences of the critical micelle concentrations of ionic and nonionic surfactants, including sodium alkylsulfates, alkyltrimethylammonium bromides, and n-alkyl polyoxyethylene ethers. [49][50][51][52][53][54][55] The critical micelle concentration of these surfactants exhibits an initial increase with pressure followed by a decrease with a maximum at around 1 kbar. This behavior is in satisfactory agreement with the pressure dependence of the free energy change we have calculated for the transfer of methylene groups from water to a micelle, which shows a maximum of ΔG at around 0.6 kbar.…”

Laboratory and pilot scale soil washing of PAH and arsenic from a wood preservation site: Changes in concentration and toxicity

“…The lower effect of the WTC treatment could also be explained by changes in the physical characteristics of surfactants as a consequence of the elevated pressure utilized for the introduction of the soil washing solution into the soil. In a surfactant solution exposed to elevated pressure, the CMC increases up to pressures around 150 MPa [43,44]. A higher CMC demands a higher concentration of surfactant before micelles start to form, resulting in a lower solubilization of hydrophobic contaminants.…”

Fluorescence behavior of intramolecular charge transfer probe in anionic, cationic, and nonionic micelles

“…Among the various methods employed, fluorescence has turned out to be one of the most powerful techniques due to its excellent sensitivity [6][7][8]. By comparing fluorescence spectral data obtained in the micellar medium with the calibration curve constructed using various homogeneous systems, mean micellar properties like effective polarity, apparent micellar viscosity, aggregation numbers, and electrostatic mean field potentials at interfaces have been successfully determined [9][10][11][12]. However, the large variation in the values of the mean micellar properties was criticized by several authors [13].…”