Comparative study on the structure of reverse micelles.: 2.: FT-IR, 1H NMR, and electrical conductance of H2O/AOT/NaDEHP/n-heptane systems

The microstructure of mixed reverse micelles stabilized with surfactants of sodium bis(2-ethylhexyl)sulfosuccinate (aerosol OT, or AOT) and/or sodium bis(2-ethylhexyl)phosphate (NaDEHP) has been studied by means of Fourier transform infrared spectroscopy (FT-LR), proton nuclear magnetic resonance (H-1 NMR), and electrical conductometry. The O-H stretching band in IR and the chemical shift in H-1 NMR of water solubilized in the reverse micelles change concomitantly with both water content (W-0, the number of solubilized water molecules per amphipathic molecule) and relative content of surfactants (AOT and NaDEHP). As in the reverse micelles stabilized with AOT and AOT + NaDEHP (50:50), the maxima of conductivity were observed in respective conductivity vs water content (kappa-W-0) curves below the percolation threshold, while the conductivity of.NaDEHP-formed reverse micelles changed proportionally with water content. The striking point is that, at a certain water content, the conductivity of the H2O/AOT/NaDEHP/n-heptane system decreases with increasing temperature from 0 to 55 degrees C, a rare phenomenon in solution. The changes are attributed to the hydration of surfactant ions plus the morphology change of surfactant aggregates in respective systems.