Demixing region

Fig. 20 reproduces the analytical results for some five isohydric series of mixtures of 2% gelatin and gum arabic sols. Of the 5 corresponding branches of the equilibrium liquids only two are drawn so as not to overload the figure. Here we already see that the demixing region is displaced on changing the pH. 

Whereas ordinary mixtures of low-molecular liquids in case of demixing usually exhibit binodals having a maximum (the so-called upper critical solution temperature, UCST), cloud-point curves of polymer solutions show in the rule minimum behavior (characterized by the so-called lower critical solution temperature, LCST). However, a number of polymer solutions possess even two demixing regions, one with UCST-behavior at moderate temperatures and one at higher temperatures with LCST-behavior (often at temperatures near the critical temperature of the solvent). At least, there are systems exhibiting closed miscibility gaps. 

BES Bessonov, Yu.S. and Eager, A.A., Ehermodynamic investigation of oligomeric polyoxypropylenediol-water system in the demixing region, Tr. Khim. Khim. 

Fig. 2. Phase equilibria of [Cnmim]NTf2-CHCl3 mixtures u>ii is weight fraction of IL. ( ) n = 5.000 (x) w = 4.337 ( ) n = 4.330 (o) n = 4.320 ( ) n = 4.300. The shaded areas depict the demixing regions for n = 4.330. Reprinted from reference which is downloaded from pubs.acs.org (Lachwa et al., 2005).

The quality of all model calculations with respect to solvent activities depends essentially on the careful determination and selection of the parameters of the pure solvents, and also of the pure polymers. Pure solvent parameter must allow for the quantitative calculation of pure solvent vapor pressures and molar volumes, especially when equation-of-state approaches are used. Pure polymer parameters strongly influence the calculation of gas solubilities, Henry s constants, and limiting solvent activities at infinite dilution of the solvent in the liquid/molten polymer. Additionally, the polymer parameters mainly determine the occurrence of a demixing region in such model calculations. Generally, the quantitative representation of liquid-liquid equilibria is a much more stringent test for any model, what was not discussed here. To calculate such equilibria it is often necessary to use some mixture properties to obtain pure-component polymer parameters. This is necessary because, at present, no single theory is able to describe correctly the properties of a poly-... 

Membrane structure has been observed to be affected by the choice of solvent. In a study preparing poly(vinylidene fluoride) (PVDF) membranes, eight solvents including V,V-dimethylacetamide (DMAc), A/,V-dimethylformamide (DMF), dimethylsulfoxide, V-methyl-2-pyrrolidone (NMP), hexamethylphosphoramide, tetramethylurea, triethyl phosphate (TEP), and trimethyl phosphate were employed and the resultant membranes were compared [25]. It was found that the membrane porosity and hence the water permeability of the membranes were dependent on the mutual diffusivity of solvent and nonsolvent (water). It was claimed that the formation path in the ternary phase diagram led to entry into the demixing region at a higher polymer concentration when the solvent-nonsolvent diffusivity was... 

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