Determination of the Composition of Mixed Hydrogenated and Fluorinated Micelles by Small Angle Neutron Scattering

Abstract

The compositions of mixed micelles formed in aqueous solutions of sodium dodecanoate and sodium perfluorooctanoate at different total surfactant concentrations and at three (0.33, 0.53, and 0.73) sodium perfluorooctanoate mole fractions were determined by the small angle neutron scattering technique coupled with the external contrast method. At each concentration, measurements were performed as functions of the solvent H2O/D2O composition in order to determine the micellar neutron scattering densities. The method described has allowed, at least for the cases under study, a direct determination of the micellar compositions, which, in the past, had been particularly difficult and the object of considerable debate. At all concentrations considered and within the experimental error, one kind of mixed micelle was always observed; these micelles were always richer in the component present in solution in greater proportion. An overall qualitative agreement between the present results and literature predictions based on regular solution theory was found, although a significant difference was noticeable at large sodium perfluorooctanoate concentrations, suggesting that further tests of the theory are required in order to include subtle interaction effects due to differences in the chemical nature of the surfactants.

Ion-dipole induced interaction between cationic gemini/TTAB and nonionic (Tween) surfactants: interfacial and microstructural phenomena

“…In the present study, we have used c = 45mNm 21 . Similarly, eqn ( 11)- (13) give the strength and nature of interaction among the components at the interface as well as the activity coefficients of the two components…”

“…Different combinations of surfactant systems, like cationic/cationic, cationic/anionic, cationic/nonionic, anionic/anionic, anionic/nonionic and nonionic/nonionic have been studied using a wide array of different experimental techniques, like electron spin resonance, fluorescence quenching, Guoy interferometry, surface tensiometry, neutron X-ray scattering, PGSE-NMR, static/ dynamic light scattering, etc. [10][11][12][13][14][15][16][17][18] Among these, ionic/nonionic systems are more important as they exhibit highly nonideal behaviour.…”

Mixed micellar aggregates of cationic and nonionic surfactants with short hydrophobic tails. An intradiffusion studyElectronic supplementary information (ESI) available: Micelle intradifusion data. See http://www.rsc.org/suppdata/cp/b2/b202731c/

“…2 This is due to the difficulty in finding experimental methods able to discriminate between the contributions of the different surfactants to the observed property, and, at the same time, to elaborate theoretical treatments representative of the mixed aggregation process. Various papers have been published reporting and discussing experimental studies on surfactant mixtures, using electron spin resonance, 3 static and dynamic light scattering, 4 neutron scattering, 5,6 fluorescence quenching, 7 Gouy interferometry, 8 and surface tension. [9][10][11] The pulsed gradient spin echo (PGSE)-NMR technique, which was firstly applied to this kind of system by Carlfors and Stilbs, 12 was found to be one of the most informative.…”

Volumes and heat capacities of the aqueous sodium dodecanoate/sodium perfluorooctanoate mixtures in the presence of β-cyclodextrin

“…Thermodynamic 7 and structural 20 studies proved that NaL and NaPFO are miscible with each other leading to the formation of mixed micelles the composition of which is a function of m t and X NaPFO . In particular, small angle neutron scattering measurements 20 demonstrated that the micellar composition monotonically increases and decreases with m t for X NaPFO ¼ 0.33 and 0.73, respectively, tending to the stoichiometric value at high concentration whereas it is independent of m t for X NaPFO ¼ 0.53. On this basis, one expects contributions to the apparent molar properties for the change of the micellar composition specific of the NaL/NaPFO ratio.…”