INDUCED PHASE SEPARATION

Gast A P, Flail C K and Russel W B 1983 Polymer-induced phase separations in nonaqueous colloidal suspensions J. Colloid Interface Sol. 96 251 -67... 

Post-heat treatment of glass induces phase separation and crystalliza tion A very precise secondary heat treatment is necessary to develop and control photochromic properties. Glass-ceramics receive a thermal ceramming process that induces crystallization... 

Supercritical fluids can be used to induce phase separation. Addition of a light SCF to a polymer solvent solution was found to decrease the lower critical solution temperature for phase separation, in some cases by mote than 100°C (1,94). The potential to fractionate polyethylene (95) or accomplish a fractional crystallization (21), both induced by the addition of a supercritical antisolvent, has been proposed. In the latter technique, existence of a pressure eutectic ridge was described, similar to a temperature eutectic trough in a temperature-cooled crystallization. 

Lipids in model systems are often found in asymmetric clusters (see Figure 9.8). Such behavior is referred to as a phase separation, which arises either spontaneously or as the result of some extraneous influence. Phase separations can be induced in model membranes by divalent cations, which interact with negatively charged moieties on the surface of the bilayer. For example, Ca induces phase separations in membranes formed from phosphatidylserine (PS)... 

Human osteoblast-like MG63 cells were cultured on the macroporous chitosan scaffolds reinforced with hydroxyapatite or calcium phosphate invert glass were fabricated using a thermally induced phase separation technique. 

Wood Hill (1991b) induced phase-separation in the clear glasses by heating them at temperatures above their transition temperatures. They found evidence for amorphous phase-separation (APS) prior to the formation of crystallites. Below the first exotherm, APS appeared to take place by spinodal decomposition so that the glass had an intercoimected structure (Cahn, 1961). At higher temperatures the microstructure consisted of distinct droplets in a matrix phase. 

Kiefer, Hedrick/. L and HibomJ. G. Macroporous Thermosets by Chemically Induced Phase Separation. Vol. 147, pp. 161-247. 

Williams, R. /. Rozenberg, B. A., Pascault, J.-P.. Reaction Induced Phase Separation in Modi-... 

It is now well known that the addition of Ca2+ in aqueous solutions of these copolymers induces phase separation with precipitation of a phase constituted by a polymer-Ca complex. From turbidity measurements, it is possible to define a critical concentration ca above which this phenomenon occurs(23-25). 

PVCL is one of several nonionic water-soluble polymers that undergo heat-induced phase separation in water (Fig. 13). It has a repeating unit consisting of a cyclic amide, where the amide nitrogen is connected directly to the hydrophobic polymer backbone. 

A slight increase in the turbidity upon heating of aqueous solutions of the s-fractions of the NVCl/NVIAz-copolymers obtained from the feeds with initial comonomer molar ratios of 75 25 (Tcp 65 °C) and 80 20 (Tcp 66 °C) could be due to the micellization phenomena, although the absence of DSC peaks over the same temperature range testified to the non-cooperative character of the process. This could indicate that the chains of these s-type copolymers had, nevertheless, a certain amount of oligoNVCl blocks non-buried by the hydrophilic microenvironment sufficiently well and thus capable of participating in the hydrophobically-induced associative intermolecular processes at elevated temperatures. At the same time, the sequence of monomer units in the s-copolymers obtained from the feeds with the initial comonomer ratios of 85 15 and 90 10 (mole/mole) corresponded to the block-copolymers of another type. The basis for such a conclusion is the lack of macroscopic heat-induced phase separation at elevated temperatures (Fig. 3 a and b) and, simultaneously, the transi-... 

The crucial question is at what value of <)> is the attraction high enough to induce phase separation De Hek and Vrij (6) assume that the critical flocculation concentration is equivalent to the phase separation condition defined by the spinodal point. From the pair potential between two hard spheres in a polymer solution they calculate the second virial coefficient B2 for the particles, and derive from the spinodal condition that if B2 = 1/2 (where is the volume fraction of particles in the dispersion) phase separation occurs. For a system in thermodynamic equilibrium, two phases coexist if the chemical potential of the hard spheres is the same in the dispersion and in the floe phase (i.e., the binodal condition). 

Figure 2.4. Induced Phase Separation Flow Diagram...

Whereas ligand selection for the biphasic water-organic and the induced phase separation system are somewhat limited, there is very wide array of organophosphorus... 

Induced Phase Separation would work technically, but would be uneconomic relative to Liquid Recycle because of additional unit processes and increased energy requirements. 

Induced Phase Separation is also a good choice for octene hydroformylation. Octene can easily dissolve in the organic based catalyst solution, and with addition of small amounts of water, nonanal and its condensation products will readily separate from the sodium salt of a monosulfonated phosphine. To choose between Liquid Recycle and Induced Phase Separation would require a detailed technical and economic study that is outside the scope of this chapter. 

NAPS is also a possibility for octene hydroformylation, but again a detailed technical and economic comparison would be required in order to chose among it, Liquid Recycle and Induced Phase Separation. 

Aqueous-phase catalysts are unsuitable since the vinyl naphthalene would have limited solubility in the phase containing the catalyst. Induced Phase Separation is also a questionable choice since at this time, suitable enantioselective ligands have not been identified. 

Sanchez-Ferrer A, Bru R and Garcia-Carmona F. 1989. Novel procedure for extraction of a latent grape polyphenoloxidase using temperature-induced phase separation in Triton X-114. Plant Physiol... 

Knight, D. P., Knight, M. M., and Vollrath, F. (2000). Beta transition and stress-induced phase separation in the spinning of spider dragline silk. Int. J. Biol. Macromol. 27, 205-210. 

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