Rapid expansion of supercritical solution into liquid solvent

RESOLVE Rapid expansion of supercritical solutions into a liquid solvent chamber that can contain surfactant that act to impede particle growth... 

Rapid expansion of supercritical solution Rapid expansion of supercritical solution with a solid co-solvent Rapid expansion of supercritical solution into a liquid solvent Supercritical solvent impregnation... 

The supercritical fluid mefhod is a relafively new method, which can minimize the use of organic solvents and harsh manufacturing conditions taking advantage of two distinctive properties of supercritical fluids (i.e., high compressibility and liquid-like density). This method can be broadly divided into two parts rapid expansion of supercritical solutions (RESS), which utilizes the supercritical fluid (e.g., carbon dioxide) as a solvent for the polymer, " and supercritical antisolvent crystallization (SAS), using the fluid as an antisolvent that causes polymer precipitation. Recent reviews of the supercritical technology for particle production are available in the literature. ... 

In our laboratory, we have modified the supercritical fluid processing method known as RESS (Rapid Expansion of Supercritical Solution) (7 J-7S) by expanding the supercritical solution into a liquid solvent, or RESOLV (Rapid Expansion of a Supercritical Solution into a Liquid SOLVent), to produce nanoscale semiconductor and metal particles (7, 9, 19-22). For the solubility of metal salts, supercritical ammonia, THF, and acetone were used in the rapid expansion at relatively higher temperatures. The nanoparticles thus obtained were small (less than 10 nm), with relatively narrow size distributions. In an effort to replace the organic solvents with C02-based systems for RESOLV at ambient temperatures, we used a water-in-C02... 

Supercritical fluid transport involves dissolving the precursor(s) in a supercritical fluid and spraying this liquid into a CVD reactor.43-45 The rapid expansion of the supercritical fluid enhances evaporation of the solute and so aids transport of the precursor to the substrate. This method has the potential advantages of the other methods, but is more limited in the choice of solvent, e.g., C02. It should be noted that this method may not require the evaporation of the precursors and under these conditions would not be classified as a CVD method. 

SCF technologies deserve a special mention as they have been less commonly applied on a laboratory scale in the preparation of nanoparticles (73). Scheme 7 and Figures 8 and 9 summarize the approach used. A drug and polymer mixture is dissolved in an organic solvent or carbon dioxide. Under certain conditions of pressure and temperature, the liquid phase is transformed into the supercritical state as seen in Figure 8. Here the supercritical state is found at pressures >74 bar (atmospheric pressure = 1.013 bar) and at temperatures >31°C. The rapid expansion of this supercritical solution on exposure to atmospheric pressure causes the formation of microspheres or nanospheres Figure 9 on the other hand illustrates the use of a solvent, which can be formed into a... 

Nanocrystalline metal (silver and copper) and metal sulfide (silver sulfide, cadmium sulfide, and lead sulfide) particles were prepared via RESOLV (Rapid Expansion of a Supercritical Solution into a Liquid SOLVent) with water-in-carbon dioxide microemulsion as solvent for the rapid expansion. The nanoparticles were characterized using UV/vis absorption. X-ray powder diffraction, and transmission electron microscopy methods. The results of the different nanoparticles are compared and discussed in reference to those of the same nanoparticles produced via RESOLV with the use of conventional supercritical solvents. 

The basic RESS process has been further modified to produce nanoparticles with tight particle size control and minimal agglomeration. Rapid expansion of a supercritical solution into a liquid solvent (RESOLV Pathak et al. 2004) and rapid expansion from supercritical to aqueous solution (RESAS Young et al. 2004 Tozuka et al. 2010) are the most notable ones. In RESOLV, the supercritical solution is allowed... 

Gold Nanoparticles Han and coworkers [49] proved that the CO -continuous microemulsions with IL domains could solubilize HAuCl and prepared gold particles by a process of rapid expansion of a supercritical solution into a liquid solvent. Au nanoparticles were formed in the reverse micelles, when the weight ratio of HAuCl to 1,1,3,3-tetramethylguanidinium trifluoroacetate (TMGT) was 0.01. However, Au networks were obtained at a higher concentration of HAuCl. ... 

Besides the supercritical fluid extraction (SFE) for preparation of medicines and materials processing, supercritical fluid technology involves processes such as supercritical anti-solvent (SAS), rapid expansion supercritical solutions (RESS), rapid expansion of a supercritical solution into a liquid solvent (RESOLV), supercritical assisted atomization (SAA), impregnation and solution enhanced dispersion by supercritical CO2 (SEDS) that involves the supercritical fluid in drug processing to drug delivery systems. 

The second method is quite harsh but similar to RESS process as they both involve use of SFCO as a solvent rather than an anti-solvent. This process involves dissolving the SF in molten solute and the resulting supercritical solution fed via an orifice into a chamber to allow rapid expansion under ambient conditions [17], The dissolved gas decreases the viscosity of the molten compound and so the gas saturated liquid phase is expanded to generate particles from materials that are not necessarily soluble in SF. The presence of the CO allows the material to melt at temperature significantly lower than the normal melting or glass transition temperature. 

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