Temperature-induced phase separation

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... 

A common technique for separating the water and the oil in a microemulsion is a temperature-induced phase separation, yielding an excess water phase (increasing the temperature) or an excess oil phase (decreasing the temperature). It is the simplest way to separate the oil and the water. Nevertheless this method is quite time consuming and often not complete. In case of enzymatic reaction, a change in temperature can lead to a loss of enzyme stabiUty. 

Phase inversion is a process in which a polymer is transformed from a liquid to a solid state. There are a number of methods to achieve phase inversion. Among others, the dry-wet phase inversion technique and the temperature induced phase separation (TIPS) are most commonly used in the industrial membrane manufacturing. The dry-wet phase inversion technique was applied by Loeb and Sourirajan in their development... 

In some cases, temperature-induced phase separation does not result in the required quantitative separation of all components or damages temperature sensitive catalysts. This is especially true for catalytic reactions with expensive noble metal catalysts. Such reactions often require more than 99% recovery of the catalyst in order to avoid severe economic losses due to the extremely high costs of such catalysts. Here, ultrafiltration is a suitable tool for quantitative catalyst recovery under mild conditions. In general the same conditions for reaction and ultrafiltration should be chosen in order to recycle the catalyst in its active form. 

Temperature induced phase separation, proposed by Galaev and Mattiasson [86] and studied extensively by Tjerneld and coworkers [87-90] enables the recovery and recycling of the polymers so the economics have improved to a large extent. It also improves the yield, degree of selectivity, etc. Methods for faster demixing of the phases were developed by employing electric fields [91, 92] and by acoustic fields [93]. In the near future ATPE is expected to enjoy further commercial adaptation. 

MOD Modlin, R.F., Aired, P. A., and Tjemeld, F., Utihzation of temperature-induced phase separation for the purification of ecdysone and 20-hydroxyecdysone from spinach, J. Chromatogr. A, 668, 229, 1994. 

Figure 1. Schematic representation of the influence of various factors on the miscibility and phase separation. The shaded areas represent the two-phase regions. The arrows show the paths for phase separation, while the reverse directions would be the paths for miscibility. From left-to-right Temperature-induced phase separation solvent-induced phase separation reaction (i.e. polymerization) -induced phase separation (the two-phase regions are entered with increasing degree of polymerization (DP)) and pressure-induced phase separation. < ) = polymer concentration, S2 and SI solvent and nonsolvent PI andP2 = polymer 1 and polymer 2.

Phase separation techniques include emulsion freeze-drying or temperature-induced phase separation, where an immiscible solvent is mixed with the polymer solution in order to form an emulsion or where temperature is lowered... 

DIA Diab, C., Akiyama, Y., Kataoka, K., and Winnik, F.M., Microealorimetric study of the temperature-induced phase separation in aqueous solutions of poly(2-isopropyl-2-oxazolines), Macromolecules, 37, 2556, 2004. 

KOU Koirrilova, H., Stastrra, J., Hanykova, L., Sedlakova, Z., and Spevacek, J., H NMR study of temperature-induced phase separation in solutions of poly(A/-isopropyl-methacrylamide-co-acrylamide) copolymers, Eur. Polym. J., 46, 1299, 2010. 

Shibayama, M. and Osaka, N., Pressure- and temperature-induced phase separation transition in homopolymer, block copolymer, and protein in water, Macromol. Symp., 291-292, 115,2010. 

Temperature-induced phase separation of Triton X-114 Temperature-induced phase separatipmof Triton X-114 was carried out as described (9,10) with minor modifications. I-chloroplast fructose-1,6-bisphosphatase was incubated in 50 mM Tris-HCl buffer (pH 7.9) (final volume 0.2 ml). After 30 minutes at 24°C, 0.02 ml of 50% Triton X-114 was injected and the solution was vortexed. The enzyme solution was incubated for 30 minutes at 0°C, and subsequently layered over a cushion of 0.75 M sucrose. Tubes were kept for 10 minutes at 30 °C, and centrifuged for 5 minutes at room temperature. The amount of radioactivity was estimated in the detergent-rich phase formed at the bottom of the tube. 

A method developed from temperature induced phase separation was completed to obtain PLA/bacterial cellulose composites [174]. In this work, bacterial cellulose was added to 1,4-dioxane and homogenized before PLA was added and dissolved before the mixture was added dropwise into a liquid nitrogen bath. The precipitate was collected and freeze-dried to produce composite microspheres, which were then fed into a twin-screw extruder and were mixed at 180°C, extruded, pelletized and hot press compression moulded into films. PLA films containing bacterial cellulose showed an increase in tensile modulus, with composites containing bacterial cellulose, and chemically modified bacterial cellulose shown to have improvements over PLA alone [174]. 

Rarkas, T., Stalbrand, H., Tjemeld, R. (1996). Partitioning of beta-mannanase and alpha-galactosidase from Aspergillus niger in ucon/reppal aqueous two-phase systems and using temperature-induced phase separation. Bioseparation, 6, 147-157. 

Of course, the temperature-responsive behavior of poly(acrylamide)s and poly(vinyl amide)s is not limited to the exact structures of PNIPAM and PVCL, and also analogous polymer structures have been reported to undergo temperature-induced phase separation upon heating in aqueous solution, such as poly(A-cyclopropylacrylamide) (Kuramoto and Shishido, 1998), poly(A( A-diethylacrylamide) (Lessard et al, 2001), poly(A-vinyl pip-eridone) (leong et al, 2011) and various substituted poly(A-vinyl pyrroli-done)s (Yan et al, 2010). 

Figure 3 (a) Temperature-induced phase separation (b) Nonsolvent-induced phase separation. 

Solvent selection was also proven to affect the resulting structure in temperature-induced phase separation (TIPS) (Lloyd et al. 1990 Gu et al. 2006 Lu and Li 2009). Diluents such as phthalates promote the formation of irregular fuzzy structures (Lloyd et al. 1990). PVDF membranes prepared from dimethyl phthalate (DMP) as a solvent showed larger spherulite structures compared to that of membranes prepared from DBP, or mixtures of DMP with dioctyl sebacate and dioctyl adipate. It can be ascribed from these differences that the degree of polymer-solvents interactions influences the extent of PVDF crystallization (Lloyd et al. 1990 Gu et al. 2006). Using different types of solvents, the crystallization temperature of PVDF during TIPS can also be changed. A more complex mechanism is indeed expected for a combined solvent system. For instance, in the PVDF/DMAc/TEP system, TEP (weaker solvent) acts as a latent solvent in the immersion precipitation process (Liu et al. 2012). 

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