Aggregation of double-tail sulfonate surfactants probed by /sup 23/Na NMR

Journal Article · Wed Apr 11 23:00:00 EST 1984 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j150652a042· OSTI ID:6765708

Kilpatrick, P K; Miller, W G

Analysis of sodium-23 NMR chemical shift and line-width data on sodium 4-(1-heptylnonyl)benzenesulfonate (SHBS) in water at 47/sup 0/C indicates the surfactant continuously aggregates in an anti- or weakly cooperative manner up to the surfactant solubility limit, a point beyond which a hydrated lamellar phase is in equilibrium with the surfactant-saturated isotropic solution. By contrast, sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT) shows little if any aggregation up to the point of a highly cooperative micellization. Both chemical shift and line-width data indicate the presence of an isotropic solution-liquid crystal phase boundary; the line shape of a biphasic mixture of isotropic solution and lamellar liquid crystal is not motionally averaged, in contrast to a micellar solution, and thus differentiation between micelle formation and solubility boundary is possible. A multiple equilibrium treatment of stepwise amphiphile aggregate formation is used to model both highly cooperative surfactant association, i.e., micellization, and anti- or noncooperative association. The sodium counterion binding to surfactant aggregates was modelled by assuming the oligomers are spherical and have a constant surface charge density with all anionic head groups residing at the surface of the sphere. It was then assumed that the sodium ion exists in one of two environments: free or bound, each having a characteristic chemical shift and transverse relaxation rate. On the basis of a comparison of the model with experimental data, it was concluded that SHBS aggregate concentration decreases with increasing aggregate size; i.e., the aggregation is non- or weakly anticooperative, while Aerosol OT associates very cooperatively, the large degree of cooperativity being an indication of micelle formation.

• Research Organization: Univ. of Minnesota, Minneapolis
• OSTI ID: 6765708
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 88:8; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
AGGLOMERATION
ALKALI METAL ISOTOPES
DATA
EXPERIMENTAL DATA
INFORMATION
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
MICELLAR SYSTEMS
NUCLEAR MAGNETIC RESONANCE
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
RESONANCE
SODIUM 23
SODIUM ISOTOPES
STABLE ISOTOPES
STRUCTURAL MODELS
SULFONATES
SURFACTANTS