Composition and Size of Reverse Micelles of Tergitol NP-4 and Tergitol NP-4 + AOT in N-Decane during Evaporation Crystallization of KNO3

We have determined the solubilization and crystallization fields of KNO3 for simple (Tergitol NP-4 and AOT) and mixed (Tergitol NP-4 + AOT) microemulsions at 35 degrees C, depending on water content and concentration of KNO3. An increase in the content of AOT in mixed microemulsions leads to widening of the solubilization field, but the crystallization field narrows up to complete disappearance (in simple microemulsions of AOT). Fourier transform-infrared spectroscopy, photon-correlation spectroscopy, and flame photometry were used to determine the rate of water evaporation (2.6-7.4 mu L/min), hydrodynamic diameter of micelles (4.3-10 nm), and the content of water and K+ and Na+ ions in the studied microemulsions at different stages of evaporation crystallization of KNO3. In simple microemulsions of Tergitol NP-4 crystallization begins well before that in mixed microemulsions; in mixed microemulsions the beginning of crystallization requires higher supersaturation (up to 13 M) compared to simple microemulsions (similar to 4 M at initial solubilization capacity of 0.5 vol %). In accordance with the Gibbs Thomson (Kelvin) theory, high supersaturations suggest that in mixed micelles cores of smaller sizes are formed. During crystallization, micelles with KNO3 solution coexist with KNO3 crystals. The function of micelles is to supply "building material" for their growth. Numerical simulation with the help of direct optimization showed that in mixed micelles at low water contents, Na+ ions are stronger bound with AOT(-), owing to which Na+ ions occur only as impurities in powders.