Liquid-solid phase separation

Fig. 5. (a) Schematic of the scaffold design showing the inner and outer scaffolds, (b and c) Inner scaffolds seeded with NSCs. (Scale bars 200 pm and 50 tm, respectively.) The outer section of the scaffold was created by means of a solid-liquid phase separation technique that produced long, axially oriented pores for axonal guidance as well as radial pores to allow fluid transport and inhibit the ingrowth of scar tissue (d scale bar, 100 pm), (e) Schematic of surgical insertion of the implant into the spinal cord. [Reproduced with permission from Teng et al. (2002).]... 

New Protocols Based upon Temperature-Dependent Solubilities of Fluorous Compounds and Solid/Liquid Phase Separations... 

Fig.1 Schematic of tide processes strategies for the recovery of lluorous catalysts via solid/liquid phase separation...

Fig. 3 Recycling of thermomorphic fluorous phosphine catalysts 5a,b via solid/liquid phase separations (Starting concentration of 2, 1.25 M cycle time, 8 h for 5a and 1 h for 5b)...

Fig. 10 Additional thermomorphic fluorous catalysts that have been recovered by solid/ liquid phase separations...

Gladysz JA, Tesevic V (2008) Temperature-Controlled Catalyst Recycling New Protocols Based upon Temperature-Dependent Solubilities of Fluorous Compounds and Solid/Liquid Phase Separations. 23 67-89... 

Liquid-liquid and solid-liquid phase separations are achieved that produce sludges that are more easily filtered compared to chemical flocculent addition. This technology enhances the filtration and dewatering rates of solids removed from an effluent. The vendor states that this technology is commercially available however, the technology has not been demonstrated at full scale for Superfund site remediation. 

An example of a solid-liquid phase separation - often referred to as a mechanical separation - is filtration. Filters are also used in gas-sohd separation. Filtration may be used to recover liquid or sohd or both. Also, it can be used in waste-treatment processes. Walas [6] describes many solid-hquid separators, but we will only consider the rotary-drum filter. Reliable sizing of rotary-drum filters requires bench and pilot-scale testing with the slurry. Nevertheless, a model of the filtering process will show some of the physical factors that influence filtration and will give a preliminary estimate of the filter size in those cases where data are available. 

Solid-liquid phase separations at elevated temperatures are unit operations that we have not investigated. The efficiency of this type of separation, the design and material requirements, and the reliability of the phase separation must be studied. 

The solubility of Zr(OH)4 was measured over a wide pH range (0 to 15). The ionic media was 1.0 M (H,Na)C104 except for the solutions at pH > 14. The solubility tests were done very carefully carbon dioxide free glove box, use of carbonate free NaOH for tests under alkaline conditions, solid/liquid phase separation by centrifugation at 14000g, provision for avoiding errors due to Zr sorption at reaction vessel walls and sampling equipment. The exact hydroxide concentrations in the solutions were determined at the end of each experiment by titration. XRD measurement has shown that the phase was amorphous prior to, and after, the solubility tests. The solid phase was a commercial hydrated production of uncertain stoichiometry and hydration. It was not fully characterised by the authors. 

In the vast majority of chemical destabilisation/bioinactivation processes, water acts either as a catalyst or it participates as a reactant and/or product. It therefore seems logical to conclude that the removal of water should eliminate many causes of chemical instability. The situation is not quite so clear however in the case of physical instability. Processes of concern that can take place in the solid state include polymorphic solid/ solid transitions and the compaction of powders. Even low levels of water vapour sorption may lead to other undesirable changes, e.g. solid/ liquid phase separations, recrystallisation in the solid state or polymorphic transitions. Since all these processes occur only in the solid state, it follows that they cannot necessarily be eliminated by drying. The important factors in physical and mechanical stabilisation are the actual state of the solid produced by drying, the level of residual water and the temperature and pressure employed during processing and storage. 

One way to conceptualize this phenomenon is to view the ponytails as short pieces of Teflon, which does not dissolve in any common solvent. As the ponytails become longer, some physical properties of the molecule approach those of Teflon. However, just as the miscibilities of fluorous liquid phases and organic liquid phases are highly temperature dependent, so are the solubilities of fluorous solids in fluorous or non-fluorous liquid phases. Hence, much higher solubilities can be achieved at elevated temperatures. This phenomenon can be used to conduct homogeneous reactions at elevated temperatures, with catalyst or reagent recovery by solid/liquid phase separation at lower temperatures. ... 

In both of the processes just described, a crystallizer produces a solid and, following a solid-liquid phase separation, a dryer removes the moisture. In some cases, all three of these operations can be carried out in a single piece of equipment, a spray dryer or a drum dryer, but at the expense of increased utility cost because all of the solvent is evaporated. Such dryers are used extensively to produce dried milk and detergents. For these products, spray dryers are particularly desirable, because the drying process produces porous particles that are readily dissolved in water. Spray dryers can also handle slurries and pastes. 

Until a few years ago, most of the recognized examples of miscible pol3nner blend pairs involved only amorphous components. However, recently numerous blend systems have been identified in which one or both components are crystallizable. The systems of interest here are miscible in the melt state, but upon cooling one or more of the components separates from the mixture as a pure crystalline phase. This form of solid-liquid phase separation represents a different situation than a liquid-liquid miscibility gap since complete miscibility may still exist in the remaining amorphous phase. The objective of this paper is to review some of the pertinent fundamental issues and recent results for miscible blends where crystallization is possible. 

Some authors have named the polymeric matrices fabricated via conventional freeze-drying by the term cryogels. Certainly, freezing of polymeric solutions or colloidal dispersions causes solid-liquid phase separation, and the subsequent sublimation of the solidified solvent crystals fixes the system thus structured [17, 18], but no gelation occurs during these consecutive steps. Therefore, it is more correct to call such freeze-dried polymeric matrices cryostructurates or cryotexturates rather than cryogels. ... 

Fractionation by crystallizability takes place by either decreasing or increasing the temperature, similarly to what is done in the methods of fractional precipitation or coacervate extraction for molecular weight fractionation. However, differently from those, solid-liquid phase separation occurs during fractionation by crystallizability. We will call Crystaf-mode the fractionation that takes place upon cooling the polymer solution, and TREF-mode the fractionation that takes place by dissolving previously precipitated polymer crystallites. This nomenclature is consistent with the continuous analysis techniques of Ciystaf and TREF, which will be described later in this article, and is more adequate for fractionation by crystallizability. 

Fig. 8. SEM micrographs of polymer scaffolds fabricated using solid-liquid phase separation (a) PLLA scaffold fabricated from 5% PLLA/dioxane solution (with local regular pore structure), (b) PLLA scaffold fabricated from 2.5% PLLA/dioxane solution (with less regular structure), (c) PLLA/HAP (hydroxyapatite) composite scaffold (PLLA/HAP 50/50) fabricated from a 2.5% PLLA/dioxane solution. Reprinted from Refs. 5 and 109. 2001, by permission of John Wiley Sons. 

Liquid—Liquid Phase Separation, in contrast to solid-liquid phase separation, lowering temperature can induce liquid-liquid phase separation of a polymer solution with an upper critical solution temperature and when the crystallization temperature of the solvent is sufficiently lower than the phase separation temperature. In an equilibrium phase diagram of a polymer solution, the spin-odal curve divides the liquid-liquid phase separation region into two regions a thermodynamically metastable region (between the binodal and spinodal) and a thermodynamically unstable region (enclosed by the spinodal) (Fig. 11). Above the... 

The excess method is a universally applicable and widely used technique. The only limitations are too small amounts of sample that make solid—liquid phase separation and analysis difficult. It involves the following steps ... 

Solid-liquid phase separation (preferably isothermally at measurement temperature). 

Lloyd, D.R., Kinzer, K.E., Tseng, H.S. 1990. Microporous membrane formation via thermally induced phase-separation. 1. Solid liquid-phase separation. J. Membr. Sci. 52 239-261. 

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