Effect of Micelle Size on the Dielectric Relaxation and Dynamic Behavior of Reverse Micelles Using the Open-Ended Coaxial Line Technique

Abstract

A model system was used to study the molecular dynamics and transport of macromolecules, which are very often characterized by their confined state. This complex model consisted of a ternary mixture (reverse micelles) composed of the surfactant sodium bis (2-ethylhexyl) sulfosuccinate (AOT), H₂O and isooctane (C₈H₁₈) as the apolar, oil phase. The dielectric parameters of this system were investigated using the open ended coaxial line method. The high frequency response of the AOT reverse micelles was characterized over a frequency scale from 10 MHz to 20 GHz, as a function of the water-to-surfactant ratio (${\mathrm{W}}_0$) and the surfactant-to-oil ratio (${\mathrm{\Phi }}_{\mathrm{m}}$) at room temperature, 298 K. Measurements of the complex permittivity of this AOT/C₈H₁₈/H₂O system are reported. The experimental values of the real part of the complex permittivity of the AOT reverse micelles were fitted by the Havriliak-Negami function emphasizing the reverse micelles size effect; these measurements were sufficient to give us important information about the dynamic behavior of the AOT reverse micelles dispersed in isooctane. In the frequency range studied three different motions were identified as functions of the reverse micelle size (${\mathrm{R}}_{\mathrm{w}}$).

Keywords:

• Reverse micelles
• AOT:sodium bis (2-ethylhexyl) sulfosuccinate
• open-ended coaxial line method
• dielectric relaxation
• dynamic behavior
• rotational diffusion