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The impact of N,N-dimethyldodecylamine N-oxide (DDAO) concentration on the crystallisation of sodium dodecyl sulfate (SDS) systems and the resulting changes to viscosity, crystal structure, shape and the kinetics of crystal growth

DOI: 10.1016/j.jcis.2018.05.058 DOI Help

Authors: Emily Summerton (University of Birmingham) , Martin J. Hollamby (University of Keele) , Georgina Zimbitas (University of Birmingham) , Tim Snow (Diamond Light Source) , Andrew J. Smith (Diamond Light Source) , Jens Sommertune (RISE Research Institutes of Sweden) , Jeanluc Bettiol (Procter and Gamble Brussels Innovation Center) , Christopher Jones (Procter and Gamble Brussels Innovation Center) , Melanie Britton (University of Birmingham) , Serafim Bakalis (University of Birmingham; University of Nottingham)
Co-authored by industrial partner: Yes

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

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

Abstract: Hypothesis: At low temperatures stability issues arise in commercial detergent products when surfactant crystallisation occurs, a process which is not currently well-understood. An understanding of the phase transition can be obtained using a simple binary SDS (sodium dodecyl sulfate) + DDAO (N,N-dimethyldodecylamine N-oxide) aqueous system. It expected that the crystallisation temperature of an SDS system can be lowered with addition of DDAO, thus providing a route to improve detergent stability. Experiments: Detergent systems are typically comprised of anionic surfactants, non-ionic surfactants and water. This study explores the crystallisation of a three component system consisting of sodium dodecyl sulfate (SDS), N,N–dimethyldodecylamine N-oxide (DDAO), and water using wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC) and confocal Raman microscopy. Findings: The presence of DDAO lowered the crystallisation temperature of a 20 wt. % SDS system. For all aqueous mixtures of SDS + DDAO at low temperatures, SDS hydrated crystals, SDS.1/2H2O or SDS.H2O, formed. SDS hydrates comprising of layers of SDS separated by water layers. DDAO tended to reside in the vicinity of these SDS crystals. In the absence of DDAO an additional intermediary hydrate structure, SDS.1/8H2O, formed whereas for mixed SDS + DDAO systems no such structure was detected during crystallisation.

Journal Keywords: sodium dodecyl sulfate; N,N-dimethyldodecylamine N-oxide; low temperature; crystallization; X-ray scattering; detergent stability

Subject Areas: Chemistry

Instruments: I22-Small angle scattering & Diffraction