Effect of Alcohols in AOT Reverse Micelles. A Heat Capacity and Light Scattering Study

Abstract

Apparent molar heat capacities at 25 °C of a series of 1-alcohols and three branched alcohols were determined in mixtures of the type alcohol + (p wt % AOT + n-decane) at R = 0 and 10, R being the water−surfactant molar ratio [W]/[S]. For methanol and 1-hexanol, the measurements were done for different p values as a function of alcohol concentration. For all the other alcohols p = 5. Heat capacities for the binary (AOT + nC10) and the ternary (AOT + W + nC10) mixtures, as well as for 1-hexanol in a 5 wt % solution of dioctyl succinate, were also measured at 25 °C. For all alcohols + AOT + n-decane, kinematic viscosities and dynamic light scattering (DLS) were measured at 25 °C for R = 10 and p = 13 as a function of alcohol concentration. DLS was also measured for the ternary mixture AOT + W + nC10 with R = 10 at 25 °C. A reasonable molecular picture of the alcohol−AOT interactions in the presence and absence of reverse micelles emerges from the experimental DLS and heat capacity results, the latter having been analyzed within the Treszczanowicz−Kehiaian model framework. In the absence of reverse micelles, all alcohols form complexes with the free AOT molecules in the solution, a process that competes with the alcohol self-association. The alcohol−AOT complex is most probably formed via an interaction between the hydroxyl group of the alcohol and the ionic head of AOT. When reverse micelles are present, two behaviors were found: (i) Methanol and ethanol are located in the micelle water pool; at low AOT concentration these alcohols only interact with water, but at higher AOT concentration they also form a complex with AOT molecules at the micellar interface. (ii) For butanol, longer 1-alcohols, and the three branched alcohols studied here two different processes occur: AOT molecules are withdrawn from the micelles to be complexed with alcohol molecules in the bulk of the solution, and alcohol molecules penetrate the micellar shell, where they also form a complex with AOT.

Binding of Nitrodiphenylamines to Reverse Micelles of AOT inn-Hexane and Carbon Tetrachloride: Solvent and Substituent Effects

“…This reinforces the conclusions that Kb may be affected by the spatial restriction of the bigger molecules. Very similar effects have been observed when comparing the hydrogen binding constants of alkanols with AOT in the micellar interface (41).…”

“…Similar behavior was found for some phenols in AOT/isooctane/ water (37) and naphthols in AOT/cyclohexane/water (40). Very recently, the effect of the addition of a series of linear and branched alcohols to AOT/n-decane/water reversed micelles has been studied (41). The formation of hydrogen bond complexes between the polar heads of AOT in the micellar interface and the alcohols has been proposed.…”

Distribution of amines in water/AOT/n-hexane reverse micelles: influence of the amine chemical structure

“…They had concluded that the main driving force is the existence of the hydrophilic group, while the presence of a long alkyl chain becomes practically irrelevant. Perez-Casas et al [42] have also found that the interaction of the OH group with the polar head of AOT is dominant once alcohols have penetrated the micelle.…”

Physicochemical characteristics of reverse micelles of polyoxyethylene nonyl phenol in different organic solvents

“…The radius of the water pool and size of the reverse micelles are characterized by ω, which is the watersurfactant molar ratio. The aggregates [4,5] formed in solution when a small amount of water is present (ω < 15) are called reverse micelles and when a large amount of water is present are called microemulsions. Reverse micelles can solvate a wide range of hydrophilic compounds.…”