Issue 21, 1997

Analysis and modelling of positron lifetime spectroscopy data for the characterisation of water-in-oil microemulsion systems stabilised by Aerosol OT Effect of changing the counter-ion

Abstract

In previous work using positron lifetime spectroscopy, a model was proposed leading to the satisfactory description of both positronium (Ps) formation and decay in sodium AOT–water–isooctane reverse micelles. The shorter lifetime found for the Ps triplet state in the aqueous core of the micelles, compared to that found in pure water, was attributed to Ps outdiffusion from these cores, enabling the quantification of this lifetime with two fitting parameters: r0, the aqueous core radius, and h, a factor which describes the ease of passage of Ps at the water/isooctane interface. To assess the validity of the model, the experiments have been extended to the study of the Ca(AOT)2 and 2:1 mole ratio Na(AOT):Ca(AOT)2–water–isooctane systems, to examine the effect of the counter-ion on r0 as a function of the water/AOT ratio, w0 and (for Ca2+) of temperature. Using, for all systems, the value of h previously found for the Na(AOT) microemulsions, the presence of the Ca2+ counter-ion appears to result in the formation of larger reverse micelle aggregates, compared to with Na(AOT), with radii in agreement with published data. With the Ps yields, the model implies a semi-empirical parameter, Atrap, related to the probability that the energetic positrons end up in the aqueous subphase before forming Ps. As expected and experimentally verified, Atrap is proportional to r02. Unexpectedly however, with the above value for h, the variation of Atrap with r02 is found to depend on the counter-ion. Therefore, the possible variation of h was considered. Using different values of h for each system, it is possible to obtain a unique variation of Atrap with r02, independent of the counter-ion. In this case, however, the radii for the microemulsions containing Ca2+ are significantly lower than those found in previous work.

Article information

Article type
Paper

J. Chem. Soc., Faraday Trans., 1997,93, 3827-3831

Analysis and modelling of positron lifetime spectroscopy data for the characterisation of water-in-oil microemulsion systems stabilised by Aerosol OT Effect of changing the counter-ion

M. F. Ferreira Marques, H. D. Burrows, M. da Graça Miguel, A. P. de Lima, C. Lopes Gil and G. Duplâtre, J. Chem. Soc., Faraday Trans., 1997, 93, 3827 DOI: 10.1039/A703029K

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Spotlight

Advertisements