Issue 28, 2022

SANS characterization of time dependent, slow molecular exchange in an SDS micellar system

Abstract

We have investigated the molecular exchange of sodium dodecyl sulfate (SDS) micelles in aqueous solution by time-resolved small angle neutron scattering (TR-SANS) measurements as a function of the surfactant and salt concentration. Starting with deuterated (d-SDS) and protonated (h-SDS) SDS micelles, surfactant exchange across the micelles leads to a randomized distribution of d-SDS and h-SDS within each micelle. By employing the contrast matching technique, we have studied this randomization process which is a direct measure of the molecular exchange of this system. Our results show that the randomization of the pure h-SDS and d-SDS micelles occurs in two steps: first, an almost instantaneous drop in the scattering intensity is observed where ∼80% of the micelles are randomized (contrast matched). After this, micelle randomization progresses slowly spanning over ∼100 hours. Importantly, we show that the kinetics in the second step are dominated by the formation of domains rich in either h-SDS, d-SDS and randomized (50 : 50 h-SDS : d-SDS). The slow exchange step is modeled via a phenomenological approach by drawing analogy to the Langmuir adsorption theory. Finally, the effects of the surfactant and salt concentrations on the instantaneous, and the time dependent randomization of SDS micelles are discussed.

Graphical abstract: SANS characterization of time dependent, slow molecular exchange in an SDS micellar system

Supplementary files

Article information

Article type
Paper
Submitted
24 Feb 2022
Accepted
10 May 2022
First published
13 May 2022

Phys. Chem. Chem. Phys., 2022,24, 16988-16996

SANS characterization of time dependent, slow molecular exchange in an SDS micellar system

T. Shoaib, J. Ha, Y. Han, W. Chen and C. Do, Phys. Chem. Chem. Phys., 2022, 24, 16988 DOI: 10.1039/D2CP00930G

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