EFFECT OF ALCOHOLS IN AOT REVERSE MICELLES - A HEAT-CAPACITY AND LIGHT-SCATTERING STUDY

Apparent molar heat capacities at 25 degrees C of a series of 1-alcoho ls 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 measure ments were done for different p values as a function of alcohol concen tration. For all the other alcohols p = 5. Heat capacities for the bin ary (AOT + nC(10)) and the ternary (AOT + W + nC(10)) mixtures, as wel l as for 1-hexanol in a 5 wt % solution of dioctyl succinate, were als o measured at 25 degrees C. For all alcohols + AOT + n-decane, kinemat ic viscosities and dynamic light scattering (DLS) were measured at 25 degrees C for R = 10 and p = 13 as a function of alcohol concentration . DLS was also measured for the ternary mixture AOT + W + nC(10) with R = 10 at 25 degrees C. A reasonable molecular picture of the alcohol- AOT interactions in the presence and absence of reverse micelles emerg es from the experimental DLS and heat capacity results, the latter hav ing been analyzed within the Treszczanowicz-Kehiaian model framework. In the absence of reverse micelles, ail alcohols form complexes with t he free AOT molecules in the solution, a process that competes with th e alcohol self-association. The alcohol-AOT complex is most probably f ormed via an interaction between the hydroxyl group of the alcohol and the ionic head of AOT. When reverse micelles are present, two behavio rs were found: (i) Methanol and ethanol are located in the micelle wat er pool; at low AOT concentration these alcohols only interact with wa ter, but at higher AOT concentration they also form a complex with AOT molecules at the micellar interface. (ii) For butanol, longer I-alcoh ols, and the three branched alcohols studied here two different proces ses occur: AOT molecules are withdrawn from the micelles to be complex ed with alcohol molecules in the bulk of the solution, and alcohol mol ecules penetrate the micellar shell, where they also form a complex wi th AOT.