Oscillatory shear flow stability

Section 5.5 describes two simple shear flows shear flow near a boundary and shear flow between two parallel plates. This leads on to a discussion of scaling properties, and it is pointed out in Section 5.5.5 that the apparent viscosity, defined by equation (5.146) below, scales differently from that of an isotropic fluid. Stability and instabiUty of oscillatory shear flow are discussed in Section 5.6 this Section contains what is perhaps the most advanced analysis in this Chapter. 

The structure of Immiscible blends Is seldom at equilibrium. In principle, the coarser the dispersion the less stable It Is. There are two aspects of stability Involved the coalescence In a static system and deformability due to flow. As discussed above the critical parameter for blend deformability Is the total strain In shear y = ty, or In extension, e = te. Provided t Is large enough In steady state the strains and deformations can be quite substantial one starts a test with one material and ends with another. This means that neither the steady state shearing nor elongatlonal flow can be used for characterization of materials with deformable structure. For these systems the only suitable method Is a low strain dynamic oscillatory test. The test Is simple and rapid, and a method of data evaluation leading to unambiguous determination of the state of miscibility is discussed in a later chapter. 

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