General Ideas and Stability of Blend Phase Morphology

General Ideas and Stability of Blend Phase Morphology 

Polymer melt blends maybe miscible or immiscible. Miscible blends form solutions and there is no phase morphology to be of concern. Immiscible blends are characterized by two or more phases that are separated by interfaces. Most polymer blend systems are immiscible because of the low entropies of mixing associated with mixing chain-like molecules to produce homogeneous solution. 

The interface between two phases in a liquid system is characterized by an interfacial tension (k), which seeks to control the interface shape and coalesce with other dispersed phase. The interfacial tension is generally resisted by the melt viscosity, which slows the changes the interfacial tension seeks to achieve. 

Notably, interfacial tension in two-phase low viscosity systems has been recognized and studied since the nineteenth century. Indeed Clerk Maxwell [138] discussed it in an 1879 Encydopedia Britannica review. Various researchers developed methods and made measurements of the interfacial tension in the nineteenth century and early twentieth century. Measurements for combinations of polymer melts, however, date back only to the 1960s [139-142] and generally accepted values were available by the 1990s [143-146]. We summarize data for various binary systems in Table 1.1. 

When the interfadal tension goes to zero, the blend becomes miscible. Large interfadal tensions lead to unstable interfaces, especially when the viscosity is low. 

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