Temperature Effect on the Nanostructure of SDS Micelles in Water

• Published in: Journal of research of the National Institute of Standards and Technology Vol. 118; no. 2; pp. 151 - 167
• Main Author: Hammouda, Boualem
• Format: Journal Article
• Language: English
• Published: United States National Institute of Standards and Technology 01.03.2013; Superintendent of Documents; [Gaithersburg, MD] : U.S. Dept. of Commerce, National Institute of Standards and Technology
• Subjects: Agreements; Aqueous solutions; Chemical properties; Composition; Crystals; Deuteration; Dissolution; Identification and classification; Material balance; Mathematical analysis; Micelles; Nanostructure; Neutrons; Salt; Scattering; Sodium dodecyl sulfate; Studies; Styrene acrylonitrile resins; Sulfates; Surfactants; Thermal properties; Volume fraction; Water chemistry; United States; material balance equations; critical micelle temperature; SDS; SANS; small-angle neutron scattering; sodium dodecyl sulfate; ellipsoidal particles; micelle structure; aggregation number; surfactant
• ISSN: 1044-677X; 2165-7254
• DOI: 10.6028/jres.118.008

Sodium dodecyl sulfate (SDS) surfactants form micelles when dissolved in water. These are formed of a hydrocarbon core and hydrophilic ionic surface. The small-angle neutron scattering (SANS) technique was used with deuterated water (D2O) in order to characterize the micelle structure. Micelles were found to be slightly compressed (oblate ellipsoids) and their sizes shrink with increasing temperature. Fits of SANS data to the Mean Spherical Approximation (MSA) model yielded a calculated micelle volume fraction which was lower than the SDS surfactant (sample mixing) volume fraction; this suggests that part of the SDS molecules do not participate in micelle formation and remain homogeneously mixed in the solvent. A set of material balance equations allowed the estimation of the SDS fraction in the micelles. This fraction was found to be high (close to one) except for samples around 1 % SDS fraction. The micelle aggregation number was found to decrease with increasing temperature and/or decreasing SDS fraction.