Reverse Micelle Based Growth of Zincophosphate Sodalite:  Examination of Crystal Growth

Abstract

Formation of zincophosphates from zinc and phosphate containing reverse micelles (water droplets in hexane) has been examined. The frameworks formed resemble those made by conventional hydrothermal synthesis. Dynamics of crystal growth are however quite different and form the main focus of this study. In particular, the formation of zincophosphate with the sodalite framework was examined in detail. The intramicellar pH was found to have a strong influence on crystal growth. Crystals with a cubic morphology were formed directly from the micelles, without an apparent intermediate amorphous phase over a period of 4 days by a layer-by-layer growth at the intramicellar pH of 7.6. At a pH of 6.8, an amorphous precipitate rapidly sediments in hours. Sodalite was eventually formed from this settled phase via surface diffusion and reconstruction within 4 days. With a rotating cell, it was possible to minimize sedimentation and crystals were found to grow epitaxially from the spherical, amorphous particles. Intermediate pH's of 7.2 led to formation of aggregated sodalite crystals prior to settling, again without any indication of an intermediate amorphous phase. These diverse pathways were possible due to changes in intramicellar supersaturation conditions by minor changes in pH. In contrast, conventional syntheses in this pH range all proceeded by similar crystallization pathways through an amorphous gel. This study establishes that synthesis of microporous frameworks is not only possible in reverse micellar systems, but they also allow examination of possible crystallization pathways.

Reverse Micelle Based Formation of BaCO3 Nanowires

“…On aging, pairs of wires may be coupled through their c -axes, leading to the increase in the wire length. Although such a proposed mechanism remains to be confirmed by more detailed investigation, it is evidenced that the BaCO 3 nanowires of single crystals are formed by an aggregation growth rather than the layer-by-layer growth proposed for the zincophosphate sodalite with a cubic morphology in AOT reverse micelles . It seems that the C 12 E 4 reverse micelles provide significant control over the directional nucleation and aggregation growth of the BaCO 3 nanowires.…”

“…For instance, bicontinuous reverse microemulsions have been used as preorganized systems for the fabrication of crystalline calcium phosphate materials with extended reticulated microstructures . On the other hand, microporous zincophosphate sodalite with a cubic morphology has been synthesized in reverse micelles, indicating that the reverse micelle based approach can provide a means of controlling the morphology as well as the size of growing crystals. , …”

Surfactant‐facilitated crystallization of dihydrate carbamazepine during dissolution of anhydrous polymorph

“…Surfactant assemblies can promote crystallization by acting as templates for the nucleation and growth of crystals14,20 and/or by solubilizing, and thus concentrating solute molecules in micelles 17. The former mechanism explains the increase in the transformation rates of CBZ(A) to CBZ(D) in the presence of STC because there is a small increase in the solubilization of CBZ, whereas both templating and solubilization may be effective in the presence of SLS.…”

“…in aqueous solution, could have a profound effect on crystallization in addition to their effects on dissolution. Surfactants have been shown to promote or inhibit crystallization steps (nucleation, crystal growth) in organic and inorganic crystals13–18 and direct the crystallization of solid phases that otherwise are not formed 19,20…”

An electron spin resonance study of the soy bean phosphatidylcholine-based reversed micelles

“…This enables one to carry out organic enzymatic reactions [6] and also grow nanosize metal particles in the core of droplets [7]. This raises various problems requiring knowledge of dynamic structure of w/o microemulsions on different structural levels.…”