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

Journal Article · Thu Apr 12 00:00:00 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), Vol. 88:8
• Country of Publication: United States
• Language: English

Related Subjects

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