Stability and Phase Separation

V. J. Klenin, Stability and Phase Separation (Elsevier, Amsterdam, 1999)... 

Santore, M.M., Han, C.C., and McKenna, G.B. (1992) A comparison of the thermodynamic stability and phase separation kinetics of polymer blends containing cyclic chains of high molecular weight. Macrorrwlecules,... 

Phase Separation. An approximate estimation of phase separation may be obtained visually. In general, creaming, flocculation, and coalescence have occurred before phase separation is visible, thus sometimes making quantitative evaluations more difficult. Accelerating the separation by centrifugation followed by appropriate analysis of the specimens may be useful to quantitatively determine the phase separation. Details on mechanisms of creaming and phase separation as well as some advances in the monitoring techniques of emulsion stability have been reviewed by Robins [146]. 

The adsorption of block and random copolymers of styrene and methyl methacrylate on to silica from their solutions in carbon tetrachloride/n-heptane, and the resulting dispersion stability, has been investigated. Theta-conditions for the homopolymers and analogous critical non-solvent volume fractions for random copolymers were determined by cloud-point titration. The adsorption of block copolymers varied steadily with the non-solvent content, whilst that of the random copolymers became progressively more dependent on solvent quality only as theta-conditions and phase separation were approached. 

There is, however, another statement of the necessary and sufficient condition of thermodynamic stability of the multicomponent system in relation to mutual diffusion and phase separation that is less stringent than equation (3.20) because it may be fulfilled not for every component of the multicomponent system. For example, in the case of the ternary system biopolymeri + biopolymer2 + solvent, it appears enough to fulfil only two of the inequalities (Prigogine and Defay, 1954)... 

The complexities of the polymer-mediated forces evident from the above discussions make it difficult to formulate theories of coagulation and phase separation for such interactions. Nevertheless, it is instructive to consider in detail an example of how the effects of polymer chains are incorporated in quantitative prediction of dispersion stability. In the following section we discuss such an example, although we restrict ourselves to a discussion of a thermodynamic analysis of stability. 

Liquid emulsions are inherently unstable to a varying degree. It is important to understand, therefore, the mechanisms that contribute to emulsion stability. Before the solidification step, instability of an emulsion can arise due to either phase separation or phase inversion (Mulder and Walstra, 1974). It is evident that the likelihood of phase inversion will increase as the fraction of dispersed phase increases. The vast majority of literature references are concerned with the stability to phase separation as coalescence or creaming in oil-in-water emulsions (Hailing, 1981 Jaynes, 1983). In addition, a method for determining the stability of water-in-oil emulsions to inversion has not been reported. It is usually assumed that certain aspects of oil-in-water emulsion theory apply in reverse to water-in-oil emulsions. 

Blends of poly(ether sulfone) 300 with the poly(hydroxyether) of bisphenol A proved to be quite homogenous and had better thermal stability, though phase separations occurred at higher temperatures <2003PLM867>. As a... 

Stability is the most important property of a bubble-containing product once the desired characteristics for the product have been achieved, the structure must be kept at least until product consumption. Destabilization processes can combine in various ways and at various rates between foam formation and phase separation thus the reference to foam stability must be accompanied by the specific mechanism under observation (Hailing 1981). In general, the following phenomena can be distinguished when a liquid foam is allowed to stand (Prins 1986) ... 

Solvents are important ingredients of emulsifiable concentrates and of solution formulations. When the formulation is to be used on crops, it is critical that the solvent be nonphytotoxic. The solvent must have a high level of solvent power if an EC is being formulated. Because most toxicants are insoluble in water, the solvent must also be water insoluble. Otherwise, when the EC is added to water in the spray tank, the solvent will mix with the water and leave the toxicant behind as a crystalline precipitate. The carrying power of the solvent, i.e., the amount of pesticide it will hold in solution, is important in the storage stability of formulations. If near its saturation point at ordinary temperatures, it may exceed this at low temperature with the result that solvent and pesticide may separate, causing crystal formation and phase separation (Terriere, 1982). 

Emulsions have been widely used as vehicles for oral, topical, and parenteral delivery of medications. Although the product attributes of an emulsion dosage form are dependent on the route of administration, a common concern is the physical stability of the system, in particular the coalescence of its dispersed phase and the consequent alteration in its particle-size distribution and phase separation. The stabilization mechanism(s) for an emulsion is mainly dependent on the chemical composition of the surfactant used. Electrostatic stabilization as described by DLVO theory plays an important role in emulsions (0/W) containing ionic surfactants. For 0/W emulsions with low electrolyte content in the aqueous phase, a zeta potential of 30 mV is found to be sufficient to establish an energy maximum (energy barrier) to ensure emulsion stability. For emulsions containing... 

In this work, we have analyzed the phase behavior of various freeze-dried mixtures of DPPE, DPPC, and cholesterol and have examined the effects of trehalose addition to these liposomes. Generally, dehydration leads to increase in transition temperature of the phospholipids and also to phase separation. Addition of trehalose, however, can prevent the increase in transition temperature and phase separation freeze-dried DPPC-cholesterol liposomes exhibit only one transition and their retention capability increases by more than 40%. Further studies on the phase separation and stability of multicomponent model membranes will be required to understand better its relation to the survival of cells to freeze-drying procedures. 

ATRP polymerization (Mn=5750) was chain extended with St to yield a block copolymer with Mn=21,400 and an Mw/Mn=1.15, after 24 h and 78% monomer conversion, as shown in Fig. 29 [121], Although the authors showed that both statistical and block copolymers could be prepared in the water-borne system, the latex stability was often low and phase separation was observed. Success in these polymerizations depends strongly on the nature of the additives present (i. e., surfactant, macroinitiator, etc.) [121,212]. 

U.S. 4801395 (1989) [62] Chazard et al. (Colgate-Palmolive) Clay thickener and long-chain fatty acids Improved stability against phase separation increased viscosity lower clay levels needed... 

Styrene, DVB, and surfactants A1,A2,A1/A2 1 2-2 1 Extrusion DMPA, UV lamp or pulsed laser Hollow polymer spheres and phase separated structures Cryo TEM, QELS, CPC, stability tests Jung et al. (2000) [15]... 

Depending on the aggregate state of dispersion medium, isothermal mass transfer, coagulation and coalescence may play different roles in the loss of stability of disperse systems towards aggregation. Coagulation, coalescence, and phase separation during sedimentation are typical in systems with liquid... 

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