Dielectric Analysis for the Spherical and Rodlike
Micelle Aggregates Formed from a Gemini Surfactant: Driving Forces
of Micellization and Stability of Micelles
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Abstract
The
self-aggregation behavior of Gemini surfactant 12-2-12 (ethanediyl-1,2-bis(dimethyldodecylammonium
bromide)) in water was investigated by dielectric relaxation spectroscopy
(DRS) over a frequency range from 40 Hz to 110 MHz. Dielectric determination
shows that well-defined spherical micelles formed when the concentration
of the surfactant was above a critical micelle concentration CMC<sub>1</sub> of 3 mM and rodlike micelles formed above CMC<sub>2</sub>, 16 mM. The formation mechanism of the spherical micelles and their
transition mechanism to clubbed micelles were proposed by calculating
the degree of counterion binding of the micelles. The interactions
between the head groups and the hydrophobic chains of the surfactant
led to the formation of the micelles, whereas the transition is mainly
attributed to the interaction among the hydrophobic chains. By analyzing
the dielectric relaxation observed at about 10<sup>7</sup> Hz based
on the interface polarization theory, the permittivity and conductivity
of micelle aggregates (spherical and clubbed) and volume fraction
of micelles were calculated theoretically as well as the electrical
properties of the solution medium. Furthermore, we also calculated
the electrokinetic parameters of the micelle particle surface, surface
conductivity, surface charge density, and zeta potential, using the
relaxation parameters and phase parameters. On the basis of these
results, the balance of forces controlling morphological transitions,
interfacial electrokinetic properties, and the stability of the micelle
aggregates was discussed