Phase diagram polymer-salt

Aqueous two-phase systems can be formed by combining either two "incompatible" polymers or a polymer and a salt in water above a certain critical concentration. Many systems have been tested by Albertsson and their phase diagrams determined (2). Comprehensive reviews have been compiled by Walter (1) and Kula (3). Most current commercial applications of ATPS are based on polymer-salt systems. These systems are attractive because of their low-cost and rapid phase disengagement. Polymer-salt... 

The basis for the separation is that when two polymers, or a polymer and certain salts, are mixed together in water, they are incompatible, leading to the formation of two immiscible but predominantly aqueous phases, each rich in only one of the two components [Albertsson, op. cit. Kula, in Cooney and Humphrey (eds.), op. cit., pp. 451 71]. A phase diagram for a polyethylene glycol (PEG)-Dextran, two-phase system is shown in Fig. 22-85. Proteins are known to distribute unevenly between these phases. This uneven distribution can be used for the selective concentration and partial purification of the products. Partitioning between the two phases is controlled by the polymer molecular weight and concentration, protein net charge and... 

Diphasic liquid systems used in CCC may have a wide variety of polarities. The most polar systems are the ATPS made by two aqueous-liquid phases, one containing a polymer, for example, polyethylene glycol (PEG), the other one being a salt solution, for example, sodium hydrogen phosphate. The less polar systems do not contain water there can be two-solvent systems, such as heptane/acetonitrile or dimethylsulfoxide/hexane systems or mixtures of three or more solvents. Intermediate polarity systems are countless since any proportion of three or more solvents can be mixed. Ternary phase diagrams are used when three solvents are mixed together. 

Both phases of an aqueous polymer biphasic system contain not less than 70 to 80% (w/w) of water. Separation into two phases occurs only above certain concentrations of the phase polymers and the curve relating these concentrations in a phase diagram is called the binodial90). The position of the binodial depends on the chemical nature of the phase polymers and on their molecular weights as well as on the nature and concentration of inorganic salts present in the system 93,94). 

As discussed in the sections on individual polymers, PEO is a semicrystalline polymer with about 60% of the bulk being crystalline at room temperature with the rest being present in an amorphous phase. In spite of the difficulties involved in obtaining phase diagrams with polymer electrolytes such as the slow kinetics of crystallization and randomness and therefore to determine exact boundaries between the various phases involved, phase diagram studies on PEO system suggests 3-4 repeat units of PEO per metal salt (vide supra) [53-56]. 

Phase diagrams for these polymers with (NH4)2S04 are presented in Fig. 4 [41]. The three PEG systems show the anticipated behavior with the binodals shifted to lower salt concentrations as polymer molecular mass increases. [It takes less (NH )2SO to salt out PEG-12000 than PEG-3400.] The binodal for PVP-K15, which has an average molecular mass of... 

Increasing the temperature of an ABS results in an increase in phase incompatibility [32], as shown in the phase diagrams in Sec. II, where the binodal for PEG-2000/(NH4)2S04 moves toward lower salt and polymer concentrations. As predicted from the preceding discussion, Dtc increases with increasing temperature (Fig. 6). 

Fig. 7. Phase diagram of CCM-water-salt system as a function of the polymer concentration, Cp=0.05 (1), 0.1 (2) and 0.5 wt% (3)...

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