Lower critical solution temperature , for

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. 

Second, Schneider s article reviews recent work (notably by Rowlinson, Kohn and co-workers) on phase relations in binary liquid systems where one of the components is much more volatile than the other (D1, D2, E3, M8, R9). Such systems may have lower critical solution temperatures for these systems, an increase in temperature (and, indirectly, pressure) causes precipitation of the heavy component, thereby providing a possible separation technique, e.g., for the fractionation of polymers. 

The phase diagram of some oil-solubilizer-water must be measured as a function of temperature in order to test the above approach. For this purpose decane (DEC) was chosen as a typical oil and 2-bu-toxyethanol (BE) as the solubilizer. We thought BE would be a good model solubilizer since the lower critical solution temperature for the BE-H2O system is 49 C this gives a good workable temperature range for our investigation. 

There exists an upper and lower critical solution temperature for same CD solutions. 

Saraiva, A. et al.. Application of the van der Waals equation of state to polymers. IV. Correlation and prediction of lower critical solution temperatures for polymer solutions. Fluid Phase Equilibria, 115, 73-93, 1996. 

MIP Mi, P., Chu, L.-Y., Ju, X.-J., and Niu, C.H., A smart polymer with ion-induced negative shift of the lower critical solution temperature for phase transition,... 

FIGURE 8.4 Chain length dependence of the upper critical consolute solution temperature for (1) polystyrene in cyclohexane and (2) polyisobutylene in di-isobutyl ketone (data from Schultz, A.R. and Flory, P.J., J. Am. Chem. Soc., 74, 4760, 1952), and the lower critical solution temperature for (3) polyoctene-1 in w-pentane (data from Kinsinger, J.B. and Ballard, L.R, Polym. Lett., 2, 879, 1964). 

Saeki et al. (1973) measured a set of upper and lower critical solution temperatures for the polystyrene/methyleyelohexane system at various molecular weights. Demonstrate that the data listed as follows for both UCST and LCST behavior follow the expeeted trend with moleeular wdghL (Note that r should be taken as the ratio of the molar volumes of the polyma-and the solvent, and it can be assumed to be independent of the temperature.) What is the difference between the theta temperature for UCST and LCST ... 

Phase diagrams of IPNs have also been researched. Sophia and co-workers (30) found that the phase diagram of a semi-IPN indicates a lower critical solution temperature for these materials (Fig. 7), similar to that of polymer blends. Seemingly strange, these materials are more mutually soluble at lower temperatures than at higher temperatures, a consequence of their low entropy of mixing. 

These workers also found that the lower critical solution temperature for the material was at 265°C. 

COW Cowie, J.M.G., Horta, A., McEwen, I.J., and Prochazka, K., Upper and lower critical solution temperatures for star branched polystyrene in cyclohexane, Polym. Bull., 1, 329, 1979. 

VAR Varennes, S., Charlet, G., and Delmas, G., Use of the lower critical solution temperature for the characterization of polymer mixtures and the study of their compatibility. Application to polyethylene, polypropylene, and their copolymers, Polym. Eng. Sci., 24, 98, 1984. 

The cloud point, as defined in Chapter 1, is the temperature at which the solubility of the nonionic surfactant is not sufficient to provide the solubility necessary for effective surfactant action. In essence, it is a lower critical solution temperature for the low-molecular-weight POE chain. At the cloud point, a normally transparent solution of nonionic surfactant becomes cloudy and bulk-phase separation occurs. That is not to say that the material precipitates from solution rather, a second swollen phase containing a high fraction of the POE surfactant appears, and its domains are significantly larger than those of a normal micelle. 

Fig. 1. Phase diagram for mixtures (a) upper critical solution temperature (UCST) (b) lower critical solution temperature (LCST) (c) composition dependence of the free energy of the mixture (on an arbitrary scale) for temperatures above and below the critical value.

Reactive compatibilization can also be accomplished by co-vulcanization at the interface of the component particles resulting in obliteration of phase boundary. For example, when cA-polybutadiene is blended with SBR (23.5% styrene), the two glass transition temperatures merge into one after vulcanization. Co-vulcanization may take place in two steps, namely generation of a block or graft copolymer during vulcanization at the phase interface and compatibilization of the components by thickening of the interface. However, this can only happen if the temperature of co-vulcanization is above the order-disorder transition and is between the upper and lower critical solution temperature (LCST) of the blend [20]. 

The first elastomeric protein is elastin, this structural protein is one of the main components of the extracellular matrix, which provides stmctural integrity to the tissues and organs of the body. This highly crosslinked and therefore insoluble protein is the essential element of elastic fibers, which induce elasticity to tissue of lung, skin, and arteries. In these fibers, elastin forms the internal core, which is interspersed with microfibrils [1,2]. Not only this biopolymer but also its precursor material, tropoelastin, have inspired materials scientists for many years. The most interesting characteristic of the precursor is its ability to self-assemble under physiological conditions, thereby demonstrating a lower critical solution temperature (LCST) behavior. This specific property has led to the development of a new class of synthetic polypeptides that mimic elastin in its composition and are therefore also known as elastin-like polypeptides (ELPs). 

The phase transition temperatures (lower critical solution temperature, LCST) of the pol5miers were obtained from the change in the transmittance of their aqueous solutions (Figure 1). The aqueous solution of the obtained pol5uner was prepared and its transmittance at 500 nm was monitored with increase in the ambient temperature. Both of poly-NIPA and poly-NEA showed a sudden decrease in the transmittance at 37.5 and 69.2 °C, respectively. The result shown in Figure 1 clearly suggests the thermosensitivity of the pol5mers, and the obtained LCST values are close to those reported for poly-NIPA (34.8 °C) [8] and poly-NEA (72 °C) [9]. 

Figure 8 Schematic for the transition of lower critical solution temperature polymer. (From Ref. 29.)...

Adsorption behavior and the effect on colloid stability of water soluble polymers with a lower critical solution temperature(LCST) have been studied using polystyrene latices plus hydroxy propyl cellulose(HPC). Saturated adsorption(As) of HPC depended significantly on the adsorption temperature and the As obtained at the LCST was 1.5 times as large as the value at room temperature. The high As value obtained at the LCST remained for a long time at room temperature, and the dense adsorption layer formed on the latex particles showed strong protective action against salt and temperature. Furthermore, the dense adsorption layer of HPC on silica particles was very effective in the encapsulation process with polystyrene via emulsion polymerization in which the HPC-coated silica particles were used as seed. 

For the two-component, two-phase liquid system, the question arises as to how much of each of the pure liquid components dissolves in the other at equilibrium. Indeed, some pairs of liquids are so soluble in each other that they become completely miscible with each other when mixed at any proportions. Such pairs, for example, are water and 1-propanol or benzene and carbon tetrachloride. Other pairs of liquids are practically insoluble in each other, as, for example, water and carbon tetrachloride. Finally, there are pairs of liquids that are completely miscible at certain temperatures, but not at others. For example, water and triethylamine are miscible below 18°C, but not above. Such pairs of liquids are said to have a critical solution temperature, For some pairs of liquids, there is a lower (LOST), as in the water-tiiethylamine pair, but the more common behavior is for pairs of liquids to have an upper (UCST), (Fig. 2.2) and some may even have a closed mutual solubility loop [3]. Such instances are rare in solvent extraction practice, but have been exploited in some systems, where separations have been affected by changes in the temperature. 

Fig. 2.2 Liquid immiscibility. The guaiacol (A) + glycerol (B) system happens to have a closed miscibility loop. The (phase) coexistence curves are shown on the left-hand side (a) for lower temperatures, at which a lower critical solution temperature (LCST), = 40°C, is seen, and on the right-hand side (b) for higher temperatures, where a UCST, Tcs = 82°C, is seen. The compositions of the A-rich phases" and the B-rich phases are shown at 50°C and 70°C, respectively.

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