An Insight into the Structure of Surfactants
The structure of inhomogeneous (core-shell) nanoparticles was studied with the SAXSpace system. The internal structure of Sodium Dodecyl Sulfate micelles in water was determined by calculating the radial electron density profile.
Surfactants and SAXS
Sodium Dodecyl Sulfate (SDS) is a highly effective anionic surfactant used in many hygiene and cleaning products or drug carrier systems. In aqueous solution, SDS molecules self-assemble and form micelles:
Small-angle X-ray scattering (SAXS) allows to obtain the shape and size of such nano-sized micelles and - due to its sensitivity to electron-density differences - to determine the internal (core-shell) structure.
This is of great importance for understanding and controlling the role of surfactants in different materials, e.g. the stability of emulsions or the release rate of the active ingredient in drug carrier systems.
Experimental and Results
A solution of SDS (1% in water) was measured with the SAXSpace system. Due to the weak scattering power this sample is ideally measured in line-collimation in order to obtain good data quality in short time. The scattering curve is shown in Fig. 1.
Fig. 1 Scattering curve of SDS with fit from GIFT
The Pair-Distance Distribution Function (PDDF) was calculated using program GIFT1 (see Fig. 2) indicating inhomogeneous spherical particles with a maximum diameter of 6.4 nm.
Fig. 2 Pair-distance distribution function
Furthermore, the internal structure of the SDS particles was evaluated with program DECON1. The PDDF is converted (“deconvoluted”) into the radial electron density profile showing the core-shell structure of the inhomogeneous micelles and the respective dimensions.
1 O. Glatter, J. Phys.: Condens. Matter 18 (2006) 2403