Acetone critical point

For SEM investigations, specimens were stained with 2% osmium tetroxide, dehydrated in ethanol and acetone, critical-point dried and sputter-coated with gold, and studied at 20 kV with a Hitachi S-4000 scanning electron microscope. The liquid-fixed material and the permanent slides of serial microtome sections are deposited at the Institute of Systematic Botany of the University of Zurich (Z). 

Pressure-temperature diagrams offer a useful way to depict the phase behaviour of multicomponent systems in a very condensed form. Here, they will be used to classify the phase behaviour of systems carbon dioxide-water-polar solvent, when the solvent is completely miscible with water. Unfortunately, pressure-temperature data on ternary critical points of these systems are scarcely published. Efremova and Shvarts [6,7] reported on results for such systems with methanol and ethanol as polar solvent, Wendland et al. [2,3] investigated such systems with acetone and isopropanol and Adrian et al. [4] measured critical points and phase equilibria of carbon dioxide-water-propionic acid. In addition, this work reports on the system with 1-propanol. The results can be classified into two groups. In systems behaving as described by pattern I, no four-phase equilibria are observed, whereas systems showing four-phase equilibria are designated by pattern II (cf. Figure 3). 

For the separation of the polyesters with respect to functionality, LC-CC was used the critical point of adsorption of the polymer chain corresponding to an eluent composition of acetone/hexane 51 49 (v/v) on silica gel. The critical chromatogram of a polyester sample together with the functionality fraction assignment is given in Fig. 22 and Table 4. The ether peaks are obtained due to the formation of ether structures in the polyester samples. 

In the following year, Houk provided three alternate mechanisms for the aldol reaction in water, computing the critical points at B3LYP/6-311++G(3d,3p) //B3LYP/6-31G(d) with the CPCM solvation model. Honk noted that the proposed mechanism. Reaction 6.30, begins not with acetone but with its enol, produced... 

Because of its extensive hydrogen bonding, the boiling point, melting point and critical points of water are much higher than those of acetone, ethanol and... 

The tunability of solvency with temperature and pressure as illustrated in Figs. 1 and 2 is a key advantage of cleaning with supercritical fluids. This allows optimization of conditions to extract a particular material from a part and then selection of other conditions in the recycle reactor to separate it from the SCF. As an example, hexane has a solubility much like CO2 near the critical conditions. At higher pressures, carbon dioxide acts like acetone, a more polar solvent. A good rule of thumb is that if low molecular weight materials are soluble in hexane, they are soluble in CO2 at pressures just above the critical point. As pointed out by DeSimone,t °l however, polymers exhibit a different behavior. 

The mole fraction of acetone in the liquid phase is not a strong function of intermolecular interactions for pressures less than approximately 80 bar. For the immiscible systems, the shape of the mole fraction versus pressure curve is characteristic of solubility curves of solids in supercritical solvents Q4), with a minimum around the pure solvent critical point. The effect of changing the intermolecular interactions is in the expected direction the solubility of acetone in the fluid phase is lower (by a factor of 5) for the system with - 0.70 relative to the one with - 0.80. Again, a few percent change in the magnitude of the unlike-pair interactions has a greatly amplified effect on the solubility. 

Figure 5.12. Composition trajectory in the region of the critical point in the system glycerol (1), water (2), acetone (3). Source of data Krishna et al. 1985).

Figure 3. B oundary of limiting superheats of water and solutions of acetone with water 1 — water, 2 - water + 5 % acetone, 3 — water + 15 % acetone. Solid line — line of liquid-vapor phase equilibrium, C - critical point, dashed line — calculation by homogeneous nucleation...

Figure 4. Boundary of limiting superheats of acetone and water solutions in acetone 1 - acetone, 2 - acetone + 10 % water, 3 - acetone + 30 % water. Solid line - line of liquid-acetone vapor phase equilibrium, C - critical point, dashed line - calculation by homogeneous nucleation theory for J = 10 s m (acetone). ...

Some of the particles were studied after supercritical point drying. The particles were dispersed in acetone by several centrifugation steps (45,000 X g). In a critical point dryer (Balzers Union, CPD 020), the carbon-coated grids and the dispersion in acetone were placed. Under pressure, the acetone was exchanged against liquid CO2 after increasing the temperature and passing the critical point, the particles adsorbed on the film were supercritically dried. 

The unmodified and chemically activated specimens were sputtered with platinum without any other treatments. The cell-covered specimen (cantilevers and PTFE) were fixed with 2.5% glutaraldehyde-phosphate-buffered saline solution (Sorensen/Arnold pH 7.4) for 2 h and, after extensive washing, drained in an ascending ethanol column (30, 50, 70, 80, 90, 96, and 100%). After this procedure, the specimens were transported in water-free acetone to remove alcohol, subjected to critical point drying, and sputtered with platinum. All specimens were investigated under vacuum conditions (10 -10 atm). 

Supercritical drying can be performed at high temperature, the lower limit being the critical point of the filling solvent (i.e. methanol Pc=80.9bar, Tc=512.6K, ethanol Pc=61-4bar, Tc=513.9K, acetone Pe=47.0bar, 7 =508.1 K) or at low... 

Fig. 21. Chromatograms of triblock copolymers of THF and l,3,6-trioxocane(TO) at the critical point of poly-THF stationary phase RP-18 mobile phase acetone-hexane 95 5 v/v. (From [42] with permission)...

Flower material was fixed in FAA and stored in 70% ethanol. Flowers were prepared and dried in an ethanol (70%, 95%, 100%) and acetone 100% series before being critical-point dried in COj using an Emitech K850. Finally, the material was coated with platinum and observed with a LEO Supra 55VP Scanning Electron Microscope at the Royal Botanic Garden, Edinburgh. 

Poly(methyl methacrylate) and polytetrahydrofuran polymers were studied at the critical point of adsorption. This critical point of adsorption occurs where the retention of a given polymer is governed strictly hy the number and types of functional groups on the polymer [858]. The authors show plots of log MW vs. retention time for various mobile phase compositions on a given column. The critical point is reached when the retention time becomes independent of the molecular weight of the polymer. For poly(methyl methacrylate) that point was reached on a silica column (RI detector) with a 73/27 methyl ethyl ketone/cyclohexane mobile phase. For polytetrahydrofuran, the silica column and a 95/5 acetone/hexane mobile phase created the critical conditions. This approach has enabled the individual blocks within the co-polymer to be studied (i.e., the portion of the polymer that can make contact with the support surface). 

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