Some examples of extensional viscosity curves

The obvious difference between the two kinds of viscosity is most marked in those cases where the extensional viscosity increases with increasing extension rate, which even if the viscosity eventually begins in decrease at much higher extension rates, still results in the extensional viscosity being very much larger than the shear viscosity. 

The overall situation is summarised in figure 21, which shows that behaviour ranges from simple suspensions and emulsions, where the extensional viscosity is only a small multiple of the shear viscosity, to the cod-stretch situation of a possible thousand-fold difference. The behaviour at the highest (relative) extension rates is shown in figure 22, where a concentrated rod-hke pol)uner—say xanthan gum—is stretched very quickly, see [6]. Both shear and extensional viscosities flatten out as the polymer chains are completely untangled and aligned, and show and approximately forty-fold difference. 

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