Abstract:

Subzero temp. DSC was applied to a model nonionic microemulsion system (water/pentanol/dodecane/C12(EO)8) to det. the relative concns. of bound and free H2O. Conclusions are drawn concerning the low-temp. behavior of the system, the surfactant hydration, and the role of pentanol. The surfactant becomes satd. with H2O at a ratio of 3 mols. of "interphase" H2O per ethylene oxide group. Free H2O can only be detected by DSC at higher water/surfactant ratios. Apparently nonfreezing H2O is not formed in the model system (at least not before the inversion from W/O to O/W microemulsion has occurred). The thickness of the bound H2O layer in the nonionic model system evaluated by several methods is ∼ 5 \AA (i.e., 2 monolayers of interphase H2O are closely assocd. with the surfactant). Although pentanol enhances H2O solubilization and is present at the interface, its interaction with H2O or surfactant is not revealed by DSC. [on SciFinder(R)]