Effect of Constrained Environment on the Interaction between the Surfactant and Different Polar Solvents Encapsulated Within AOT Reverse Micelles.

ANDRES DURANTINI; FALCONE R.D.; SILBER J.J.; CORREA N.M*

Chemphyschem

WILEY-V C H VERLAG GMBH

Año: 2009 vol. 10 p. 2034 - 2040

1439-4235

The present contribution reports the study of the different interactions between different non-aqueous polar solvents ethylene glycol (EG), propylene glycol (PG), glycerol (GY), dimethylformamide (DMF) and, dimethylacetamide (DMA) and the sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT) polar heads in non-aqueous AOT/n-heptane reverse micelles media, in order to gain insights on the unique reverse micelles microenvironment created upon these polar solvents encapsulation. For the first time the study was focused in which region of the AOT molecular structure are involved in the interactions with the polar solvents. To achieve this goal we use FT-IR, a noninvasive technique, to follow the changes in the AOT?s C=O, symmetric and asymmetric SO3- vibration modes with the increase in the polar solvents content in the micelles. The results show that GY interacts through H-bond with the SO3- group removing the Na+ counterions from the interface remaining in the polar core of the micelles. PG and EG interact through H-bond mainly with the AOT?s C=O group penetrating into the oil side of the interface. Thus, they interact weakly with the Na+ counterion which seems to be close to the AOT sulfonate group. Finally, DMF and DMA encapsulated inside the reverse micelles, interact neither with the C=O nor with the SO3- groups but their weakly bulk associated structure is broken because the interactions with Na+. We suggest that DMF and DMA can complex the Na+ ions through their carbonyl and nitrogen groups. Hence, our results give insights, not only in how the constrained environment affects the bulk properties of the polar solvents encapsulated inside the reverse micelles but, more important, in the elucidation of the tricky question about which region of the AOT moiety are involved in the polar solvents interactions. We believe that our results will show a clear picture of the interactions present at the non-aqueous reverse micelle interfaces which is important since these media are interesting nanoreactors for heterogeneous chemistry, templates for nanoparticles and models for membranes.