Polarity of AOT micellar interfaces: use of the preferential solvation concepts in the evaluation of the effective dielectric constants

Abstract

Fluorescence lifetimes (rF) of 2-[p-(dimethylamino)phenyl]-3,3-dimethyl-3//-indole (1) have been extensively studied in a two-component mixture of p-dioxane/water and also in a three-component mixture of n-heptane/AOT (sodium bis(2-ethylhexyl) sulfosuccinate)/water. We have applied the concept of "dielectric enrichment" to solute/mixed solvents systems in order to evaluate the effective dielectric constants at the AOT interfaces in «-heptane. We have shown that the effective dielectric constant (D) at the interface increases from 2.3 (water molar ratio W = 0) to approximately 9.0 before reaching a plateau at W = 12. This was explained by the solvation of the polar head groups of the surfactant. Equations have been given for the variation of D vs W and for the variation of D vs [AOT] at various AOT and water concentrations, respectively. The validity of these results has been discussed by taking into account the role played by the probe molecule in the stabilization of the solvation energy (dielectric enrichment effect).

Transport in Proton Conductors for Fuel‐Cell Applications: Simulations, Elementary Reactions, and Phenomenology

“…Both experimental [119][120][121][122] and MD simulations [123][124][125][126] have revealed that water confined in systems such as reverse micelles and biological pores possesses a decreased polarity and rate of relaxation, and an increased degree of spatial and orientational order, when compared to bulk water. As such, assumptions of a constant dielectric constant for the water in the pore of a PEM (either that of bulk water or some other values) is clearly incorrect.…”

Intramolecular Charge Transfer near a Hydrophobic Surface. 2,6-p-Toluidinonaphthalene Sulfonate in a Reverse Micelle

“…Such dramatic differences of λ em max and φ f of TNS in the water pool of the microemulsions compared to ordinary bulk water indicates that the microenvironment of the TNS in the water pool is significantly different from bulk water. On further addition of water as the water pool swells in size and its polarity increases [26][27][28] the φ f decreases gradually to 0.063 at w 0 =32 and λ em max exhibits a red shift to 450 nm. However it should be noted that even at w 0 =32 emission properties of TNS is markedly different from those in bulk water.…”

“…Firstly, the dielectric relaxation time (τ D ) indicates a bimodal behavior with one component of 10 ps which is similar to ordinary water and another of 10 ns which is thousand times slower compared to bulk water. [11][12][13][14] Secondly, comparing the position of the steady state absorption or emission maxima of many probe molecules in the water pools with those in different solvents [26][27][28] (or comparing present data on TNS with ref. 19) the static dielectric constant (ε 0 ) of the water pool of the microemulsions seems to be close to that of alcohol (i.e.…”

“…sodium dioctyl sulfosuccinate, AOT) form so called reverse micelles with average aggregation number 20 and radius 15 Å, in which the polar headgroups point inwards. 4,[7][8][9][21][22][23][24][25][26][27][28] On addition of water to a solution of AOT in a hydrocarbon solvent a microemulsion is formed which consists of nanometer sized water droplets ("water pool") surrounded by a layer of the surfactant molecule. In heptane the radius (r w ) of such a water pool is about 2w 0 (in Å) where w 0 is the number ratio of the water to the surfactant molecules.…”

Demonstration of bicontinuous structures in microemulsions using automatic‐mode NMR (self‐)diffusion measurements

“…From the NMR (self-)diffusion measurements it is concluded that bicontinuous structures exist in microemulsions of the surfactant p(7-4-C 14) in benzene and water. On increasing the concentration of p (7-4-C,,), the interactions between microemulsion droplets in benzene change from strongly interacting droplets to non-interacting, hard spheres.…”