Polymer Plus Two Low Molecular Weight Liquids

This formulation has been considered by Hildebrand and Scott [4] for various ternary systems. Experiments notably by Jakowkin [6] and later authors have studied the partition of compositions between various systems including water and carbon disulfide with bromoform and carbon tetrachloride. 

This three component system may exist in the same range of arrangements as the lowmolecu-lar weight liquids of the previous section. The three materials maybe completely irruniscible and exist as three separate phases. An example might be molten polyamide-6 with mercury and an aliphatic hydrocarbon. On the other hand, one might have complete miscibility and a single phase. This would be the case with polystyrene plus benzene and toluene. 

Of more interest are intermediate cases. Low molecular weight compounds have easier miscibility than polymers to form solutions than various polymers have to form miscible blends. This is associated with the reduced entropy of mixing in polymer solutions as modeled in the theories of Meyer [7], Huggins [8] and Flory [9,10] (as described in Chapter 3). Thus, benzene is soluble in propyl alcohol, while polystyrene is soluble in benzene but not in alcohol where the endothermic heat of mixing and low entropy of mixing is too unfavorable. If we consider such a ternary system, it often leads to the situation where we have two phases, which are solutions immiscible with each other. The polymer is distributed between the two phases. The polymer in the system cited above, polystyrene, would primarily be in the benzene-rich phase. 

The situation described above is well known, as are its implications and appHcation. If the second liquid with limited miscibility for the polymer is added to a solution of the polymer in the good solvent, one finds that when a certain volume fraction is reached, phase separation begins. One phase largely consists of a mixture of the two low molecular weight liquids and the other of the polymer (in a solution primarily of the good solvent). The polymer is thus precipitated out by the second liquid. 

6 Ternary Systems Polymer Blends plus Liquid Additives 

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