SUBZERO TEMPERATURE BEHAVIOR OF WATER IN NONIONIC MICROEMULSIONS

Sub-zero temperature DSC measurements were conducted to evaluate the b ehavior of water in non-ionic microemulsions. Two surfactant systems w ere studied. The first, based on ethoxylated fatty alcohol, octaethyle ne glycol mono n-dodecylether [hereafter referred to as C-12(EO)(8)] a nd also containing water, pentanol and dodecane at a fixed weight rati o of 1:1. The second system, based on oligomeric ethoxylated siloxanes , water and dodecanol as oil phase. In both systems it was found that in up to 30 wt.% of the total water content, all water molecules solub ilize in the amphiphilic phase and are bound to the ethylene oxide (he reafter referred to as EO) head-groups. No free water exists in the su rfactant aggregates' core. Up to three molecules of water are bound to each EO group. In the first system, the behavior changes significantl y upon adding more water. The added pentanol allows further swelling a nd the water penetrates into the amphiphile structures and forms a res ervoir of free water. Structures are deformed and grow from elongated channels (up to 15-20 wt.% water), via illdefined (one-dimensional gro wth) local lamellar structures (up to ca. 60 wt.% water) to spherical normal, O/W micelles (at greater than or equal to 85 wt.% water). In c ontrast, the oligomeric systems, due to geometrical restrictions of th e amphiphiles and the nature of their curvature that prevents inversio n, cannot further solubilize water in the surfactant aggregates' core, causing phase separation to occur.