Small-angle neutron scattering, electron paramagnetic resonance, electrophoretic NMR, and time-resolved fluorescence quenching studies of sodium dodecyl sulfate and tetra(ethylene oxide) dodecyl ether mixed surfactant micelles

• Small-angle neutron scattering (SANS), time-resolved fluorescence quenching (TRFQ), electrophoretic NMR (ENMR), and electron paramagnetic resonance (EPR) have been used to study mixed micelles formed from the two dodecyl tailed surfactants, sodium dodecyl sulfate (SDS) and tetra(ethylene oxide) dodecyl ether. By combining the TRFQ and EPR techniques, one is essentially able to calculate the SANS data, lending significant weight to the micelle characteristics thus obtained. EPR reports the degree of hydration of the surfactant headgroups; TRFQ, the micelle aggregation number and inter alia the volume of the hydrophobic core. Given the physical dimensions of the surfactant, i.e., alkyl chain length, headgroup volumes, etc., it is then possible to calculate the micelle ellipticity and shell thickness. The ENMR studies provide a rather different but complementary estimate of the ionic character of the micelle. With increasing nonionic content, the aggregation number increases, the micelle becomes more elliptical, and the headgroup region of the micelle becomes less hydrated and significantly more viscous. The degree of sodium counterion dissociation shows an initial small decrease with decreasing SDS micelle mole fraction but subsequently increases, reflecting the interplay between the electrostatic character of the micelle surface and the micelle curvature.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

nuclear-magnetic-resonance

glycol monododecyl ether

counterion binding

nonionic surfactant

ionic surfactants

solution behavior

sds micelles

spin-probe

systems

micellization

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