Structure Supercritical” cluster

With such low concentrations of components available to form critical nuclei, hydrate formation seems unlikely in the bulk phases. However, at an interface where higher concentrations exist through adsorption (particularly at the vapor-liquid interface where both phases appear in abundance) cluster growth to a supercritical size is a more likely event. High mixing rates may cause interfacial gas + liquid + crystal structures to be dispersed within the liquid, giving the appearance of bulk nucleation from a surface effect. 

In supercritical fluids, the possibility of local composition enhancements of cosolvent about a solute suggests that we should see enhancement of anion fluorescence if the water cosolvent clusters effectively about the 2-naphthol solute. Although in liquids the water concentration must be >30% to see anion emission, the higher diffusivity and density fluctuations in SCFs could allow stabilization of the anion at much lower water concentrations provided that the water molecules provide sufficient structure. Therefore the purpose of these experiments was to investigate 2-naphthol fluorescence in supercritical CO 2 with water cosolvent in the highly compressible region of the mixture to probe the local environment about the solute. 

What is the structure and the dynamics of hydrated/solvated electron in hot/supercritical water In dispersed clusters of polar liquids in nonpolar liquids In microheterogeneous media (e.g. water clusters in zeolite cavities) In mixed and complex solvents of practical importance (e.g. Ref. 107) on surfaces ... 

The solvation structures which we have determined for the supercritical solutions of LJ molecules appear to be in agreement with the recent theoretical and experimental suggestions of solvent-solute clustering and solute-solute aggregation near the CP. Quantitative testing of theoretical models for solvation structure of supercritical solutions (such as that presented here) may become possible if recent efforts at simulation of supercritical solutions (elsewhere in this volume) prove successful. Clearly, the LJ model used in our theoretical studies to date does not provide an adequate representation of real molecular interactions. However, the method we have demonstrated is potentially capable of application with much more accurate (and complicated) potential functions, and meaningful quantitative interpretation of experiments may then become possible. 

The problems of properly characterizing the compounds from ammonia solutions caused a major hiatus in the exploration of the cluster anions. However, in 1970 Kummer and Diehl reported that liquid ammonia may be replaced by more easily handled and considerably more stable polyamines, most conveniently by tetraethy-lenediamine (en). Extraction of sodium-tin alloys in en and subsequent precipitation with THE or monoglyme yields the reasonably stable compound (Na+)4(Sn9 ) 6-8en. Kummer and Diehl pointed out the analogy between Sn9" and the previously characterized cluster cation Bi9 , and a partial structural characterization was reported for (Na+)4(Sn9 ) 7 en. However, in terms of the synthesis of well-defined, stable cluster compounds, the route pioneered by Kummer and Diehl left a lot to be desired. Nevertheless, supercritical amines have recently been found to be good reaction media for the synthesis of extended chal-cogenide structures. 

An original method of orgametallic compounds impregnation into the PS, PEHP, and PETE amorphous regions and polyacrylates with their subsequent structural modification and clustering is based on the usage of some liquids in a supercritical state (CO2, 8-25 MPa, 303-313 K), as was shown for cyman-threne (r -C5H5)Mn(CO)3) [118]. In another method the platinum dimethyl-... 

Beckman et al. observed an effect of the secondary microemulsion structure on the molecular weight and yield of the polymer. Under conditions where extensive micelle-micelle clustering occurred, at lower fluid density the molecular weight of the polymer was as much as two times higher. Thus, the density of the supercritical phase could be used to control the polymer morphology. Beckman and Smith also completed an extensive study [74] of the effect that acrylamide, surfactant, and water concentrations as well as the pressure and temperature had on the phase stability of the microemulsions. The phase behavior of these systems depends on the choice of operating parameters, and this behavior can be exploited to optimize the properties of the polymer. 

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