Dielectric relaxation of microemulsions

Infrared and Dielectric Study of Ca(AOT)2Reverse Micelles

“…25 Furthermore, the Debye extension of the Clausius-Mossotti equation 12,14 has been used to estimate the apparent dipole moment µ app of a single AOT group within the Ca(AOT) 2 micelle (W ) 1). We obtain for µ app a value of approximately 0.7 D; this value is found to be consistent with the corresponding one for AOT group 14,26 in a NaAOT micellar aggregate, and it is lower than that of the same isolated group for at least a factor of 10. 26 This result supports the idea of almost spherical-shaped Ca(AOT) 2 micelles.…”

Effect of Counterion Substitution on AOT-Based Micellar Systems: Dielectric Study of Cu(AOT)2Reverse Micelles in CCl4

“…The ability to change the nature of the counterion in an AOT reverse micelle is a useful and flexible tool for understanding the structural properties of these aggregates, i.e., shape and size. We expect that the variation of electrical properties of the micellar interface can also influence the hydration properties of the micellar system and, as previously found [5][6][7][8][9] for NaAOT and Ca(AOT) 2 , their intrinsic dynamical properties. In fact, dielectric spectroscopy in the 0.02-3 GHz region on Ca(AOT) 2 and Na(AOT) micelles revealed the presence of a relaxation phenomenon whose characteristics strongly depend on the hydration degree of the micelle and that it is connected, at the highest hydration values, to the motion of single AOT headgroups.…”

“…A very similar behavior is found both for Na(AOT)/H 2 O/CCl 4 and for Ca(AOT) 2 /H 2 O/CCl 4 micellar systems. [5][6][7][8][9] Two distinct relaxation phenomena are present in all dielectric spectra for these samples, and the frequency dependence of dielectric function *(ω) ) ′(ω)i ′′(ω) can be well described in terms of a sum of a Cole-Cole and a Debye-type relaxation function, according to the equation where ∞ is the high-frequency (unrelaxed) dielectric constant, ω the angular frequency of the applied field, ∆ 1 and ∆ 2 the low-and high-frequency dielectric increments, respectively, τ 1 The best-fit curves of the experimental spectra are reported in Figure 2 (solid lines) together with the Cole-Cole and the Debye type contributions to the best fit of ′′(ω) (dashed lines). The Debye dispersion is located at higher frequencies in the region of relaxation of bulk water; in our frequency range it makes only a small contribution that increases with water content in the sample, as previously found for NaAOT and Ca(AOT) 2 .…”

“…In the whole range of W, the dielectric data for Cu(AOT) 2 system have been analyzed with the model previously reported [5][6][7][8][9] for Ca(AOT) 2 and NaAOT reverse micelles. In this model, one supposes that at the lowest water content the almost dehydrated reverse micelles exhibit a nearly rigid structure, and the experimental relaxation time can be described according to the reorientation of the whole micellar aggregate in the applied electric field.…”

Aggregate Structure and Dynamic Percolation in Microemulsions

“…A so called Maxwell-Wagner relaxation caused by the differences in conductivity of water and oil can be observed which is often referred to as core relaxation [59,72,73]. Furthermore a high frequency relaxation [54] in the GHz regime is reported which is attributed to the AOT shell and the associated hydration process, accordingly called shell relaxation [7,51,52,54,[74][75][76][77][78][79][80]. In particular this relaxation is strongly influenced by the percolation transition.…”