Formation of Vesicles and Micelles in Aqueous Systems of Tetrameric Acids as Determined by Dynamic Light Scattering

Abstract

A comprehensive dynamic light scattering (DLS) study on the system BP10Na₄/water is presented. BP 10Na₄ is a tetrameric fatty acid in sodium form. In order to change molecular packing conditions both electrolyte (NaCl) and alcohol (1-butanol, 1-pentanol) are added to the surfactant system. Phase diagrams of the systems reveal not only an extensive micellization, but also the occurrence of a lamellar liquid crystalline D phase. The DLS study shows an existence of vesicles at very dilute BP10Na₄ concentrations ( ≪cmc) and also a co-existence of micelles and vesicles at higher BP10Na₄ concentrations. Cryo-TEM pictures verify the existence of the vesicles. Based on the DLS and SLS experiments the weight-average molar mass of the micelles are estimated to be 13500 g/mol at 100 mM NaCl and 22700 g/mol at 600 mM. The corresponding aggregation numbers are 13 and 22, respectively.

Keywords:

• Light scattering
• micelles
• tetraacids
• vesicles

Acknowledgements

This work was supported by the Natural Sciences and Engineering Research Council (NSERC) Industrial Research Chair in Oil Sands Engineering. Canada Foundation for Innovation (CFI) is also acknowledged for the facility of DLS. The authors acknowledge the members of the consortium JIP 2:3 (Akzo Nobel, BP, Champion Technologies, Clariant Oil Services, ConocoPhillips, Statoil ASA, Talisman Energy, and TOTAL). The Research Council of Norway is thanked for financial support through the PETROMAKS program.

Notes

^a Diameters are obtained by extrapolation to C → 0.

^b M_W is the molecular weight of BP10 micelles. Determined by assuming dn/dC = 0.150 mL · g⁻¹.