Upper critical solution density

A variety of organic colloids including emulsions and polymer latexes have been dispersed in carbon dioxide in the presence of surfactants (3,13). In most cases, owing to the lower interfacial tension of the former as explained shortly it is easier to form organic-in-C02 emulsions than water-in-C02, emulsions. Sterically stabilized colloids are stable above the critical flocculation density (CFD) and precipitate below this density. In some cases the CFD occurs at the upper critical solution density of the steric stabilizer, that is, the density at which the stabilizer phase separates from CO2, as has been shown by theory (14,15) and experiment (16). So-called ambidextrous surfactants have been designed to allow polymer latexes produced in CO2 to be transferred to an aqueous solution to form a dispersion (17,18). 

Figure 7. (a) Schematic illustrating the increase in concentration and expulsion of solvent as surfaces are compressed in the simulations, (b) Pressure-polymer concentration phase diagram. Flocculation of surfaces occurs at the upper critical solution density when the concentration between the surfaces reaches an unstable value (the critical concentration). 

Parallel to C02-philic homopolymers and their upper critical solution density, the existence of both CMT and CMP transitions is actually indicative of a CMD. This concept was introduced by Buhler et al. [31], performing static and dynamic light-scattering studies on a poly(l,l-dihydroperfluorooctyl acrylate)-/>-poly(vinyl acetate) (PTAN-/>-PVAc) block copolymer (see Figure 13.22). The respective molecular weights of the blocks were 43,100 and 4400 g/mol. Through the examination of aggregation numbers this copolymer was found insoluble at densities lower... 

Stability, systems are intrinsically stable as one homogeneous phase when the temperature is greater than rcnticai- Hence, rcnticai is consistent with the definition of an upper critical solution temperature. Since Sp/SV)t, w, = 0 at rcriacai. small changes in pressure produce enormous changes in density near the critical point. This phenomenon is exploited by physical chemists, who perform lightscattering studies near Tcriticai-... 

From eq 10.59, we see that the relationship of the mole fraction x with the scaling densities tpi and (pi is independent of either or b. Hence, the theoretical expressions for the temperature dependence of the mole fraction along the two phase boundaries, developed in the previous section, remain equally valid for weakly compressible liquid mixtures. This is the physical reason why eq 10.65 yields an excellent representation of the behaviour of the mole fraction x for liquid-liquid equilibria. As an example we show in Figure 10.5 closed solubility loops in 2-butanol + waterAs we explained earlier, closed solubility loops can be represented by the expansion of eq 10.65 provided that Ar is replaced by IATulI in accordance with eq 10.66. The closed solubility loops collapse into a double critical point at P = 85.6 MPa and T = 340 K. The implications of the theory for the behaviour near such a double critical point have been elucidated by Wang et Both near the upper critical solution temperature Ju and near the lower critical solution temperature Tl, Axcxc varies as A7 il in accordance with eq 10.65a. Near the double critical point both 7 j and 7 approach the temperature I d of the double critical point. Hence, near the double critical point... 

Interestingly, CH4 modifies the MDPE stracture but is easily removed from the modified polymer. Since the upper critical solution pressure of the MDPE-CH4 system is rather high (>250 MPa [57]), CH4 can be a plasticizer of MDPE up to elevated pressures. Experimentally, an MDPE sample (density 938 kg m degree of... 

Figure 5.15 Phase diagram of a binary mixture of methanol and n-hexane with an upper critical solution temperature of 34.5 °C. Methanol (M) has a higher density than hexane (H) and will therefore form the bottom phase.

What is the value of m, the ratio of the molar volume of polymer to the molar volume of solvent, for polystyrene of 250,000 molecular weight dissolved in toluene Thus, determine %c lii polymer volume fraction corresponding to the upper critical solution temperature. Assume that the density of polystyrene is 1.1 g/cm and that of toluene is 0.86 g/cm. ... 

It has been proposed to define a reduced temperature Tr for a solution of a single electrolyte as the ratio of kgT to the work required to separate a contact +- ion pair, and the reduced density pr as the fraction of the space occupied by the ions. (M+ ) The principal feature on the Tr,pr corresponding states diagram is a coexistence curve for two phases, with an upper critical point as for the liquid-vapor equilibrium of a simple fluid, but with a markedly lower reduced temperature at the critical point than for a simple fluid (with the corresponding definition of the reduced temperature, i.e. the ratio of kjjT to the work required to separate a van der Waals pair.) In the case of a plasma, an ionic fluid without a solvent, the coexistence curve is for the liquid-vapor equilibrium, while for solutions it corresponds to two solution phases of different concentrations in equilibrium. Some non-aqueous solutions are known which do unmix to form two liquid phases of slightly different concentrations. While no examples in aqueous solution are known, the corresponding... 

Systems with No Critical Solution Temperature. A large number of liquid pairs form systems without upper or lower critical points. In these cases, a solid phase forms before the appearance of a lower C.S.T. on cooling, and on heating, a vapor-liquid critical condition (vapor phase of the same composition and density as one of the liquid phases) occurs. Ether... 

System Upper Critical Density of Stabilizerin Bulk Solution (P/Pc) Critical Flocculation Density (P/Pc)... 

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