COMPARATIVE-STUDY ON STRUCTURE OF SOLUBILIZED WATER IN REVERSED MICELLES - 1 - FT-IR SPECTROSCOPIC EVIDENCE OF WATER AOT/N-HEPTANE AND WATER/NADEHP/N-HEPTANE SYSTEMS/

The interactions of water with the polar headgroups in the reversed mi celles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and sodium bis (3-ethylhexyl) phosphate (NaDEHP) have been studied by means of Fourie r transform infrared spectroscopy (FT-IR). O-H stretching bands of wat er in both systems varied with water content (W-0, the molar ratio of water to surfactant). When W-0 increased from 1 to 20, the O-H stretch ing frequency shifted from 3493 to 3416 cm(-1) in AOT formed reverse m icellar system and from 3385 to 3417 cm(-1) in NaDEHP system, approach ing the frequency of the bulk water. As a response to water solubiliza tion, frequency decreases of sulfonate and phosphate stretching mode i n AOT and NaDEHP reverse micellar solutions have also been observed, i ndicating hydrations of the two surfactants. Results showed that the w ater molecules encapsulated in reversed micelles are similar to that i n the bulk form when W-0 > 16 in AOT system and W-0 > 12 in NaDEHP sys tem. In addition, the splitted peaks of the asymmetric sulfonate stret ching band were found shifting to lower frequencies upon hydration, du e to the weakening of the sodium-sulfonate interaction after hydration and an associated increase in their spatial separation.