Rheological measuring techniques

To avoid the apparent complications with absolute rheologic measurement techniques, a number of investigators (4,5). have used relative measurement systems to make rheologic measurements. The major difference between the relative and absolute measurement techniques is that the fluid mechanics in the relative systems are complex. The constitutive equations needed to find the fundamental rheologic variables cannot be readily solved. Relative measurement systems require the use of Newtonian and non-Newtonian calibrations fluids with known properties to relate torque and rotational speed to the shear rate and shear stress (6). 

For Newtonian lipid-based food systems, it is sufficient to measure the ratio of shearing stress to the rate of shear, from which the viscosity can be calculated. Such a simple shear flow forms the basis for many rheological measurement techniques. The rheological properties resulting from steady shear flow for variety of food systems have been studied by many laboratories (Charm, 1960 Holdsworth, 1971 Middleman, 1975 Elson, 1977 Harris, 1977 Birkett, 1983 Princen, 1983 Shoemaker and Figoni, 1984 Hermansson, 1994 Kokini et al., 1994, 1995 Morrison, 1994 Pinthus and Saguy, 1994 and Meissner, 1997). 

Miinstedt, H., Auhl, D. Rheological measuring techniques and their relevance for the molecular characterization of polymers. J. Non-newton. Fluid Mech. 128, 62-69 (2005)... 

For the purposes of constant consideration the most significant is the circumstance that all these data on the whole give the information which is equivalent or close to that obtained during measurements of rheological properties under the conditions of shear flow. Therefore a method of investigation here is determined by the taste of the experimenter and measuring technique available. 

Rheological measurements, 21 702-758 techniques in, 21 739-747 viscometers, 21 725-739 Rheological oscillation experiments,... 

There are a number of techniques that are used to measure polymer viscosity. For extrusion processes, capillary rheometers and cone and plate rheometers are the most commonly used devices. Both devices allow the rheologist to simultaneously measure the shear rate and the shear stress so that the viscosity may he calculated. These instruments and the analysis of the data are presented in the next sections. Only the minimum necessary mathematical development will he presented. The mathematical derivations are provided in Appendix A3. A more complete development of all pertinent rheological measurement functions for these rheometers are found elsewhere [9]. 

A. A. Collyer, ed., Techniques in Rheological Measurement, Chapman and Hall, New York, 1993. 

Barnes, H. A., Hutton, J. F., and Walters, K., An Introduction to Rheology, Elsevier, Amsterdam, Netherlands, 1989. (Undergraduate and graduate levels. A practical introduction to the rheology of suspensions and polymer solutions. Chapter 2 presents introductory concepts and measurement techniques at the undergraduate level. Effects of colloidal interactions are not described.)... 

The study of mechanical properties encompassing rheology and fracture mechanics is a vast, dynamic and an exciting area and can scarcely be reviewed in one chapter. In this review, the focus is to define the material functions of foods and to discuss the current measurement techniques for the material properties that are of growing interest in the industry. The discussion centers on measurement techniques for the following three topics ... 

D.F. James and K. Walters, A Critical Appraisal of Available Methods for the Measurement of Extensional Properties of Mobile Systems, in "Techniques in Rheological Measurement", A.A. Collyer (ed.), Chapman and Hall, London, 1993, pp. 33-53. 

There are a number of types of rheological measurement, some are appropriate for Newtonian fluids only, while others may be used for Newtonian or non-Newtonian fluids. Some of the principal types are listed in Table 6.4. Some very useful descriptions of experimental techniques have been given by Whorlow [355] and others [215,352,353,356,357]. The principal methods are discussed in the next several sections. 

Te Nijenhuis K, "Survey of Measurement Techniques for the Determination of the Dynamic Moduli", in Astarita G, Marrucci G and Nicolais L (Eds) "Rheology", Plenum Publishing Company, New York, Vol. 1,1980. 

Collyer AA, "Techniques in Rheological Measurement", Chapman Hall, London, 1993. 

James DF and Walters K, "A Critical Appraisal of Available Methods for the Measurement ofExtensional Properties of Mobile Systems" in Collyer AA (Ed), "Techniques in Rheological Measurement", Chapman Hall, London, 1993. Janeschitz-Kriegl H, "Flow Birefringence of Elastico-Viscous Polymer Systems", Adv Polym Sci 6 (1969) 170-318. 

As will be seen in the second section, computer techniques are very useful in this optimization process. Rheological measurements are used to predict physical stability, and accelerated and longterm storage tests are used to confirm physical stability. There are four papers in this section which deal with these topics. The papers by Knowles et al. and Warrington et al. deal with novel... 

The application of low shear rheological measurements were the outcome of a joint research project between ICI Plant protection Division (Th. F. Tadros) and Bristol University (Prof. R. H. Ottewill, Dr G J Goodwin and Dr R Buscall). The authors are grateful to the Bristol group for establishing these techniques and their application to model suspensions. 

Another well documented, but less widely used method for formulation development is the measurement of electrokinetic properties [14]. These tests require more disdnc-tive/elaborate sample preparation and are mosdy restricted to use during development. Also widely used and relied on are rheological measurements. The scope of rheological measurements ranges from viscosity measurements to the determination of yield points or oscillatory properties, such as the G and G -modules [15]. Since suspoemulsions are not ideal viscous but mostly viscoelastic or dilatant, a wide range of characterization techniques exists. Instrumentation required for this are simple rotary viscosimeters (Brookfield) or more sophisticated stress or shear controlled rotational viscosimeters. 

Appraisal of the technological properties of aminoplasts involves a large-scale application of diverse rheological and physico-chemical measurement techniques. 

How reliable are the data Are the data reproducible Are the measurement techniques reliable Are the test samples reproducible, reliable, and suitable for rheological measurements ... 

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