Spatially-resolved magnetic resonance study of the dissolution interface between soaps and water

E. Ciampi, U. Goerke, P. J. McDonald, J. G. Chambers, B. Newling

Research output: Contribution to journalArticle

2 Scopus citations

Abstract

The developing interfacial region between a soap bar and water has been studied using a suite of spatially resolved NMR techniques. Stray field imaging (STRAFI) allowed the dynamics of water ingress into a shop-bought, commercial soap to be followed. A simplistic analysis of the data shows the ingress to be a Fickian process (αt1/2) in the first 4 h. The T2 contrast employed in the STRAFI method is not sufficient to resolve detail of the mesophase formation at the interface. However, double quantum filtered 2H spectroscopy at different positions in the interracial region allowed water concentration (and mesophase distribution) to be mapped over the first 120 h of dissolution. A simple model shows good agreement with the water concentration data. In the isotropic soap solution above the interracial region, J-cyclic cross polarization was used to selectively interrogate the CH2 1H of the soap alkyl chains and, in combination with a pulsed field gradient measurement of self-diffusion, suggests a micellar solution in which the hydrodynamic radius of the micelles is ∼5 nm.

Original languageEnglish (US)
Article number325
Pages (from-to)1271-1281
Number of pages11
JournalJournal of Physics D: Applied Physics
Volume35
Issue number11
DOIs
StatePublished - Jun 7 2002

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