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

Abstract

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 °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 μL/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 (∼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.

Ion-Exchange Processes between Surface Layer and Core of Reverse Micelles of NaAOT+Tergitol NP-4 during Evaporation Crystallization of KNO3

“…The water content is very low and the testing microdrops of pure water simply begin to be solubilized by the microemulsion. Therefore, for the analysis we will also use the results described in our previous work . These clearly established facts allowed us to calculate the compositions of cores and surface layers of micelles in the crystallization process of KNO 3 (Figure ).…”

“…The presence of carbon in the powder evidences the presence of sodium, most likely, in the form of NaAOT rather than NaNO 3 . The evidence in favor of the absence of crystallization of NaNO 3 is also the constant concentration of sodium in the microemulsion throughout the crystallization process . Let us explain this fact from the viewpoint of ionic exchange.…”

“…Study of crystallization mechanism for producing ultradisperse powders in the restricted volumes of various nanoreactors and templates is a topical problem. − In our previous work − we carried out the detailed study of the evaporation microemulsion crystallization of KNO 3 in simple (NaAOT, Tergitol NP-4) and mixed (NaAOT+Tergitol NP-4) micelles. We managed to reduce the dispersity of powders only in mixed micelles.…”

Synthesis and Concentration of Organosols of Silver Nanoparticles Stabilized by AOT: Emulsion Versus Microemulsion

“…In both cases, the synthesized organosols were dehydrated by stirring in an open beaker for 3 h. 24 A specified quantity of water in them was solubilized before electrophoresis.…”

Structural Properties of Span 80/Tween 80 Reverse Micelles by Molecular Dynamics Simulations

“…RMs attract attention due to their wide applications for various practical purposes. RMs are used as the template for the preparation of metallic nanoparticles, , polymeric materials, ultra-dispersed inorganic salt powders, , and drug nanocrystals . RMs are also applied in drug-delivery and extraction processes .…”