SANS Study of the Structure of Sodium Alkyl Sulfate Micellar Solutions in Terms of the One-Component Macrofluid Model

Abstract

A SANS study of 0.073 c micellar solutions of sodium alkyl sulfates with chain length from n C = 9 to 16 was carried out. Micelles were assumed to be ellipsoids which may grow only in the direction of their axis of symmetry. The structure factor was calculated in terms of the one-component macrofluid model by assuming DLVO potential. The contact radius and the strength of the interaction potential were handled as free fitting parameters; the electrostatic potential and the apparent micellar charge on the contact surface were derived from the latter. The assumptions imposed on the conformation of the micellar cores are sustained by the best-fit parameters of the form-factor. For n C = 9−13 the mean aggregation numbers are in good, or at least, in acceptable agreement with the predictions of a recent thermodynamic theory of micellization. The difference found between the mean core and contact radii suggests that an unknown repulsive interaction may be present which prevents the micelles from astructurally possiblecloser approach. Although the surface potential indicates that the outgoing conditions for deriving the DLVO potential are violated, the agreement of the electric charge derived partly from the DLVO potential, partly from the nonlinearized Gouy−Chapman model supports the practical applicability of the well-known DLVO potential formula to interpreting SAS results.

Self-assembly of amphiphilic polyoxometalates for the preparation of mesoporous polyoxometalate-titania catalysts

“…UV-vis absorbance spectra (ESI Fig. 4 †), showed a bathochromic shift in the absorption edge upon attachment of the two hydrocarbon chains, so that the POM-2C 12 [66][67][68][69][70] where a surfactant with longer hydrophobic tail/tails has a lower CMC compared to the one with the same headgroup but shorter hydrophobic part.…”

“…7, POM-2C 12 and POM-2C 14 both form ellipsoid micelles in aqueous solutions, however, the ellipticity of POM-2C 14 (around 2) is less than half of that of POM-2C 12 (around 4.5), 3 and 4 † using the information provided by references). 64,67 For the POM-C n surfactants, the theoretical packing parameters, calculated for different tail lengths but assuming the same equilibrium area per molecule (the cross-sectional area of the headgroup estimated according to the size of the headgroup, 78 124.3 Å 2 ), lies close to the 1/3 limit between spherical and rod-like micelles, without any clear trend explaining the experimental data. This suggests that the equilibrium area per molecule may be different between them due to the difference in the repulsion between the surfactant headgroups.…”

“…From the SANS fitting, an increase in the radius of the micelles (comparing R min for ellipsoids and R for spheres) was observed with increasing hydrophobicity of the surfactant, in agreement with observations made for commercial C n TAB surfactants and sodium alkyl sulfates. 64,67 Moreover, the tail length strongly influences the shape of the micelles, with an obvious change from an ellipsoid to a sphere as the hydrocarbon tail of the surfactants becomes longer. As illustrated in Fig.…”

Monitoring the Transition from Spherical to Polymer‐like Surfactant Micelles Using Small‐Angle X‐Ray Scattering

“…The study of SDS and other classical surfactant systems is well‐established 5. 6, 8 The structure and phase behavior of SDS upon changing various conditions, such as salt, co‐solvents, temperature, and pressure, are well‐known 9–12. Recent advances in computer power and algorithms have also allowed simulations13 with atomic resolution that can reproduce very detailed aspects of the micelles including shape and critical micelle concentrations 14.…”

Investigation of nanoscale structures by small-angle X-ray scattering in a radiochromic dosimeter

“…This is in good agreement with previous scattering studies of SDS micelles. [28][29][30] The length of the cylindrical micelles in the dosimeter formulations with gelatin is shown in Fig. 3c.…”