Thermal phase-separation process

Figure 4. Representation of the Thermal Phase-Separation Process Diagram...

The exploration of the thermal phase-separation process has added a new dimension to the science of microporous membranes. New and useful products can be made from a large spectrum of polymers ranging from hydrophobic polymers, like polypropylene or PVDF, to hydrophilic ones, like nylon which we have not touched upon in this article. 

The Accurel system has a microporous polymer sponge (e.g., of PP, LDPE, HDPE, polyamide) used as carrier for incorporating liquid additives into a thermoplastic melt. The earner is produced by a thermal phase separation process. A microcellular structure with cells of microns connected by pores of 0.5 microns and internal surface 90m /g, absorb up to 2.5 times its own weight of liquid. The key to this solution is the miscibility of a polymer with... 

Although there are many types of membranes employed in various gas separation and water purification processes, similar membrane formation processes are often employed. The phase inversion process promoted by nonsolvent addition and the thermal phase separation process based on the fundamentals discussed above are the most prevalent processes to produce membranes. In addition to References 20-22,References 25-31 " also discuss these processes, and therein applications are covered in more detail than will be attempted in this chapter. 

A major breakthrough in separation of products from catalyst, in particular heat sensitive products, came with the discovery of the NAPS or Non-Aqueous Phase Separation technology. NAPS provides the opportunity to separate less volatile and/or thermally labile products. It is amenable to the separation of both polar [14] and non-polar [15] products, and it offers the opportunity to use a very much wider array of ligands and separation solvents than prior-art phase separation processes. The phase distribution characteristics of the ligand can be tuned for the process. Two immiscible solvents are... 

The behavior of chemical phase-separated blends in the bulk after thermal quenching into the unstable region of the phase diagram is variable. In the bulk, the concentration fluctuations that govern the phase-separation process are random. As a result, the final morphology consists of mutually interconnected domain structures rich in a given blend component that coarsen slowly with time. 

Recently in the field of physics of semiconductors and materials science a great attention has been paid to formation and optical properties of semiconductor nanocrystals (quantum dots, QDs) dispersed in inorganic matrixes. An interest to glassy materials with QDs is associated with their unique physical properties and possibility to create elements of optoelectronic devices. Phase separation processes followed by crystallization are the basic in production of such materials. They result in formation of semiconductor nanocrystals stabilized within a glass matrix. The materials are advanced for various applications because of optical and thermal stability and possibility to control optical features through the technology of glass preparation and post-synthesis thermal treatment. 

The products of the thermal phase-separation membranes form a wide range of styles and configurations. Three pore sizes are currently In commercial production In polypropylene flat stock, rated at 0.45, 0.2, and 0.1 micrometers, having maximum pore sizes of about 1.0, 0.55, and 0.3 micrometers, respectively. The last two are particularly attractive for depyrogenatlon work which has been described by J. R. Robinson, et al W. A similar membrane-manufacturing process Is also used for making hollow fibers and tubes which are especially useful in cross-flow applications (10) and plasmapheresis ( ). 

Monji N, Hoffman AS. A novel immunoassay system and bioseparation process based on thermal phase separating polymers. Appl Biochem Biotechnol 1987 14 107-120. 

J.-L. Shi, L.-F. Fang, FI. Zhang, Z.-Y. Liang, B.-K. Zhu, L.-P. Zhu, Effects of the extractant on the hydrophilicity and performance of high-density polyethylene/polyethylene-b-poly (ethylene glycol) blend membranes prepared via a thermally induced phase separation process. J. Appl. Polym. Sci. 130, 3816-3824 (2013)... 

Asymmetric membrane structures have been created from these materials using the diffusion induced phase separation process (DIPS) as well as a thermally induced phase separation process (TIPS) [23] that relies on temperature gradients to produce a gradient in phase separated domain size. Moreover, membranes formed by either process can be further modified by stretching or drawing to alter pore size and porosity. 

The role of the thermal noise implemented as a Brownian force in DPD model is especially important factor in modeling of phase-separation process. 

Phase separation process takes place in a number of ways. It may be thermally induced, reaction induced, crystallization induced, etc. Thermally induced phase... 

All these results clearly show that PES-C-PEO blends are miscible and exhibit an LCST behavior. However, as shown above, different thermal behaviors are shown by the miscible blends of PES-C and PEO, depending on the blend composition. Blends with different compositions display different changes in thermal properties when phase separation occurs. Therefore, the investigation of phase separation should be performed in the light of the blend compositions. The studies of phase separation process are discussed in detail as below. 

Figures 3-4, 3-5, and 3-6 show the individual phases and the interface magnified 20,000, 30,000, and 50,000 times. The glass phase (Fig. 3-4) exhibits phase-separation processes in the form of droplet phases less than 200 nm in size. This phase separation creates the opal effect of the glass-ceramic. Although the crystals of the leucite type (Fig. 3-5) in the coastal areas (marked 2 in Fig. 3-3) measure only approximately 1 pm, they produce a highly translucent effect in the glass-ceramic. The crystals provide the material with a very high coefficient of thermal expansion. The crystal-glass interface is shown in Fig. 3-6. Clearly, crystal growth was interrupted at a specific st e of growth once a crystal front of some micrometer thickness had formed.

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