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Nuclear magnetic resonance and small-angle X-ray scattering studies of mixed sodium dodecyl sulfate and N,N-dimethyldodecylamine N-oxide aqueous systems performed at low temperatures

DOI: 10.1016/j.jcis.2018.09.053 DOI Help

Authors: Emily Summerton (University of Birmingham) , Martin J. Hollamby (University of Keele) , C├ęcile S. Le Duff (University of Birmingham) , Emma S. Thompson (University of Birmingham) , Tim Snow (Diamond Light Source) , Andrew Smith (Diamond Light Source) , Christopher Jones (Procter & Gamble Brussels Innovation Centre) , Jeanluc Bettiol (Procter & Gamble Brussels Innovation Centre) , Serafim Bakalis (University of Birmingham) , Melanie M. Britton (University of Birmingham)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Journal Of Colloid And Interface Science

State: Published (Approved)
Published: September 2018
Diamond Proposal Number(s): 16560

Abstract: Surfactant crystallisation is important in many applications in the food, consumer product and medical sectors. However, these processes are not well understood. In particular, surfactant crystallisation can be detrimental to the stability of detergent formulations, such as dish liquid products, resulting in a turbid solution that fails appearance criteria. With the rising global demand for detergent products, understanding the factors that influence formulation stability is of increasing importance. To enable industry to build more robust formulations, it is important to understand the underlying chemistry of the crystallisation process. Here, a model system containing anionic (sodium dodecyl sulfate, SDS) and amphoteric (N,N-dimethyldodecylamine N-oxide, DDAO) surfactants, at concentrations typical of dish liquid products, is studied. Variable temperature 1H nuclear magnetic resonance (NMR) spectroscopy and small-angle X-ray scattering (SAXS) is used to probe the compositional and structural properties of this system, as a function of pH. On cooling, at pH 9, a mixture of hydrated crystals, predominately composed of SDS, and micelles containing both surfactants, have been observed prior to complete freezing. At pH 2, both surfactants appear to undergo a simultaneous phase transition, resulting in the removal of micelles and the formation of hydrated crystals of mixed composition.

Journal Keywords: Sodium dodecyl sulfate; N,N-dimethyldodecylamine N-oxide; Low temperature; Crystallization; Nuclear magnetic resonance; X-ray scattering

Subject Areas: Chemistry

Instruments: I22-Small angle scattering & Diffraction