Incompatible components

Several studies have been performed to investigate the compatibalizing effect of blockcopolymers [67,158, 188,196-200], It is generally shown that the diblock copolymer concentration is enhanced at the interface between incompatible components when suitable materials are chosen. Micell formation and extremely slow kinetics make these studies difficult and specific non-equilibrium starting situations are sometimes used. Diblock copolymers are tethered to the interface and this aspect is reviewed in another article in this book [14]. 

Multiblock copolymers, as shown in Fig. 5.8 e), with incompatible components form similar structures to those found in diblocks and triblocks. 

A large volume (11.25 m3) of mixed fatty acids was to be bleached by treatment with successive portions of 50 wt% hydrogen peroxide. 2-Propanol (450 1) was added to the acids (to improve the mutual solubility of the reactants). The first 20 1 portion of peroxide (at 51°C) was added, followed after 1 min by a second portion. Shortly afterwards an explosion occurred, which was attributed to spontaneous ignition of a 2-propanol vapour-oxygen mixture formed above the surface of the liquid. Oxygen is almost invariably evolved from hydrogen peroxide reactions, and volatile flammable solvents are therefore incompatible components in peroxide systems. 

A compound that has two immiscible hydrophilic and hydrophobic parts within the same molecule is called an amphiphilic molecule (as mentioned earlier). Many amphiphilic molecules show lyotropic liquid-crystalline phase sequences, depending on the volume balances between the hydrophilic part and the hydrophobic part. These structures are formed through the microphase segregation of two incompatible components on a nanometer scale. Hand soap is an everyday example of a lyotropic liquid crystal (80% soap + 20% water). 

If such a powder blend is fused on a hot plate after suction and drying, a turbid two-phase melt is formed with incompatible components (e.g., PS/PMMA), whereas a clear mixed melt is formed from compatible components (PS/PPE or SAN/PMMA). 

To overcome the fact that a single solvent rarely completely extracts all the potentially available components from a herb, multi-solvent extracts have been developed. In this process, initial extraction of the herb using a non-polar solvent is followed by extraction using a more polar solvent. The two extracts are then concentrated to remove the solvents. Finally, they are combined using a suitable emulsifier system to hold the two incompatible components together without separating. This will render the extract water soluble (or at the least miscible) without settling-out in the final product. 

In general the diffusion of a solute like Xe is not driven by the concentration gradients but by the chemical potential. In polymer blends with incompatible components, as we investigate here, in the equilibrium situation it may occur that different domains have different concentrations of Xe. Then the usual Fick laws do not hold. 

Thermodynamic compatibility of the partners of a complex is another condition which must be accounted for in complex formation. Thermodynamically incompatible components separate into two phases. Tolstoguzov et a/.984 studied complexes of starch with gelatin in aqueous solutions and showed that complexation requires adjustment of the solution acidity and... 

Polymers are not usually mutually miscible. Even polymer mixtures with other substances (fillers, dyes, stabilizers, softeners, etc.) are not always stable. At the same time, materials are often required to have the properties of a mixture of two or more components. Mutually insoluble, incompatible components can be held together by the addition of a compound exhibiting affinity to all components. Block and graft copolymers often possess the required property to affect the van der Waals force distribution at phase boundaries. 

In addition, many peridotites bear the obvious signatures of metasomatism, which re-enriches the rock in incompatible components subsequent to depletion by melt extraction. Where this is obvious (e.g., in reaction zones adjacent to later dikes) it may be avoided easily but often the metasomatism is cryptic, in that it has enriched the peridotite in incompatible trace elements without significantly affecting major-element chemistry (Frey and Green, 1974). Peridotites thus have very variable contents of highly incompatible trace... 

Granules, pellets, and tablets can be filled into capsules using automatic-filling machines. Products are prepared in these forms to modify the release rates of active ingredients, separate incompatible components, or densify a product to achieve the fill weight in a specific size of capsule. 

The effect of the presence of compatibilized incompatible components is apparent in PVC plastisols. Monomeric and polymeric esters are good plasticizers for PVC because they have suitable solubility parameters. A good plasticizer is one which, in sufficient quantity, would almost be a solvent for the polymer. However, a good plasticizer, i.e. solvent, in a plastisol results in a high viscosity composition. This may be unsuitable for slush molding or other applications when low viscosity is desirable. The latter is obtained by adding a secondary plasticizer such as a hydrocarbon oil. In reality, the latter is not a plasticizer but actually a non-solvent which converts the good solvent plasticizer to a poor solvent mixture with resultant decrease in plastisol vis-... 

A key paper involving the experimental interfacial aspects of polymer blends discussed the blends of more than two components wherein a polymeric constituent will concentrate at the interface between two of the blend constituents [Hobbs et al., 1988]. Employing the concepts of interfacial relationships, it was shown that a ternary component can concentrate at the interface between the other constituents and allow for compatibilization of dissimilar and incompatible components. As an example, it was shown that in the ternary blend of PMMA/PC/PBT, PC encapsulates PMMA as a dispersed phase in a matrix of PBT. PC, which exhibits partial miscibility with PMMA and PBT thus compatibil-izes PMMA/PBT blends. 

There are four types of the polymer blends (i) Additive blends whose melt viscosity follows Equation 18.3, (ii) Blends with a positive deviation of from Equation 18.3. These include blends with strong interphase interactions, (iii) Blends with a negative deviation from the logarithmic additivity, which is typical of incompatible components with weak interphase interactions, (iv) Blends that show both positive and negative deviations of py from the additive values (such a relationship is typical of materials in which structural changes take place during flowing). 

Coatings can shield formulation components from heat, oxygen, moisture, or other incompatible components. 

Fig. 13.9 Application of the lever rule to a mixture of two incompatible components A and B.

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