Observing Diffusive Exchange between Surfactant and Aqueous Domains in Detergents

Abstract

Nuclear magnetic resonance (NMR) two-dimensional relaxation correlation experiments have been used to study an industrially relevant formulation of surfactant multilamellar vesicles (MLVs) in an aqueous solution. By correlating transverse T2 relaxation measurements before and after a storage interval, diffusive exchange of water molecules between domains can be observed. Two average exchange times of 0.04 and 0.83 s were determined by solving the one-dimensional Fredholm integral form of a model for region-to-region exchange. Diffusion coefficients for the restricted and free water fractions within the mixture determined via chemically selective pulsed field gradient (PFG) NMR measurements allowed exchange distances of 6.2 and 81 microm to be determined from the exchange times. These exchange distances are associated with the average MLV diameter and speculatively with the size of MLV clusters, respectively.

Structure of the two-dimensional relaxation spectra seen within the eigenmode perturbation theory and the two-site exchange model

“…when both (i-1, j) and (i, j À 1) are 'filled', then not only m iÀ1,j (t n ), but also m i,jÀ1 (t n ) have to be replaced by the fictitious statesm iÀ1;j ðt n Þ andm i;jÀ1 ðt n Þ in Eq. (52). Mention should be made, though, that such corners are most often a pure product of the present numerical method, in which smooth boundaries of the system are fragmented into parts parallel to either the axisĩ or the axisj the orthogonal Cartesian 6.…”

“…Thus, for the reasons inherent in the algorithms, the locations of the cross-peaks in T 2 -T 2 spectra were found shifted with respect to the corresponding diagonal peaks [52] and each of the broad components split into several narrower components by so-called 'pearling effect' [37]. Furthermore, unlike the 1D algorithms [53], the 2D one provides no mean to estimate the error for the spectra calculated from noise-impaired experimental data.…”

Spatially-resolved 1H NMR relaxation-exchange measurements in heterogeneous media

“…Inverse Laplace Transform (ILT) by Venkataramanan, Song and Hürlimann [37] and Hürlimann and Venkataramanan [38], pseudo-3D experiments for the study of diffusive exchange, like , represent undoubtedly the most complex and detail-rich approaches [14,[39][40][41][42]. The pulse sequence consists of two CPMG loops separated by a longitudinal storage period called mixing time ( ), during which diffusive coupling and/or chemical exchange may take place [43][44][45].…”

“…To obtain information about mass transfer and molecular exchange kinetics, the build-up of the cross-peak intensities upon increasing may be analysed. Therefore, various exact and numerical approaches to the analysis of multi-site exchange processes inspired by chemical exchange studies [46,47] have been discussed extensively by previous workers [42,43,[48][49][50]. A factor that complicates data analysis is that, in analogy to 1D diffusion or relaxation measurements, under intermediate-or fast-exchange regimes [51] the "apparent" peak positions and relative intensities can be tangibly different from their "true" values in the absence of exchange [48,52].…”

Rapid and Simple Identification and Quantification of Components in Detergent Formulations by Nuclear Magnetic Resonance Spectroscopy

“…However, there are very few reports on the application of NMR for studying commercial detergent formulations. In research dating 30–40 years back, a few references describe the application of 13 C NMR for identification of surfactants (Carminati et al, ; Kalinoski and Jensen, ; Kosugi et al, ), whereas more recent publications seem to focus on diffusion and behavior of surfactants and micelles (Griffith et al, ; Hologne et al, ; McLachlan et al, ; Nicolle et al, ; Soderman et al, ). In addition, Visser et al described the specific analysis of polycarboxylate polymers in detergents using liquid extraction, followed by size‐exclusion chromatography ‐ nuclear magnetic resonance (Visser et al, ), and Fournial et al have reported the NMR‐based characterization of commercial nonionic surfactants (Fournial et al, ).…”