Rheological measurements elongational rheometer

The rheological behaviour of the two polymers was determined using classical techniques of rheometry, already described in Chapter II. 1 (rotational and capillary rheometers for shear viscosity and first normal stress difference measurements CogsweU method for the elongational viscosity). 

While dynamic mechanical and steady shear measurements are frequently used in rheology studies of surfactant systems, extensional viscosity measurements are lacking. This can be attributed to the difficulties associated with such measurements and the lack of commercial laboratory instrumentation since the discontinuance of the Rheometric Scientific RFX rheometer. For many detergent compositions, the relatively low viscosity further complicates such measurements. There appear to be very few data on extensional or elongation viscosity for detergent consumer products and actives in the technical literature at this time. 

A systematic study of the basic rheological properties for a wide variety of polypropylene melts has been made by Minoshima et al. [89]. These authors measured shear viscosities at low shear rates in a Rheomatrics mechanical spectrophotometer and at high rates in an Instron capillary rheometer. The principal normal stress difference, Ni, was measured in the mechanical spectrophotometer with a cone and plate device. The elongational viscosity, of special importance to fiber formation, was measured in an apparatus built by Ide and White [90],... 

Rheological properties of the same polymeric solution measured in shear and elongational flows can be very different as discussed in earlier section. However, a cursory examination of current textbooks on rheology (e.g., Bird et al. [2], Ferry [3], and Tanner [14]) shows that shear rheology dominates and research in extensional rheology is comparatively much more recent. The measurements of the shear properties of polymeric fluids are well established and a number of rheometers are available for both melts and dilute polymeric solutions. Lately, more efforts have been directed in measuring the extensional properties of fluids [8, 9,15-19]. 

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