Rheology methods used

There are a number of other rheological methods used for characterizing viscoelastic fluids. A detailed discussion can be found in Chapter 4 or a rheology text such as Barnes et al. [12]. 

Compound processibiUty is a key factor in the optimiza tion of new polychloroprene types. As a result, commercial compounds can be mixed, shaped, and cured by virtually all the methods used in the mbber industry. A typical polychloroprene compound includes a variety of additives designed to improve compound rheology, cure rate, and vulcanizate properties. 

Rheological methods of measuring the interphase thickness have become very popular in science [50, 62-71]. Usually they use the viscosity versus concentration relationships in the form proposed by Einstein for the purpose [62-66], The factor K0 in Einstein s equation typical of particles of a given shape is evaluated from measurements of dispersion of the filler in question in a low-molecular liquid [61, 62], e.g., in transformer oil [61], Then the viscosity of a suspension of the same filler in a polymer melt or solution is determined, the value of Keff is obtained, and the adsorbed layer thickness is calculated by this formula [61,63,64] ... 

This formula may be useful as a rheological method for determining the thickness of adsorption layer, which is formed as a result of interaction between a dispersion medium and filler, by the results of measuring the t] versus q> dependence. Especially curious phenomena, connected with surface effects, arise when a mixture of fillers of different nature is used according to concentration of an active filler the introduction of the second (inert) filler can either increase or decrease the viscosity of a multicomponent system [35],... 

In the sol-gel procedure for the preparation of hybrids, polymeric acid catalysts such as poly (styrene sulfonic acid) were also used instead of hydrogen chloride [14]. The polymeric acid catalyst was effective for the preparation of hybrids at a similar level to that of hydrogen chloride catalyst. In some cases, the increased modulus was observed due to the higher extent of reaction. No difference was observed in morphologies between the hybrids prepared with polymeric and small molecule acid catalysts. The method using polymeric acid catalyst may depress the ion-conductive property, characteristic to the mobile acidic small molecules. Polymeric catalyst may also influence the rheology of the resulting hybrids. 

Fruit preprations for yoghurt are a typical example, how the influence of pectins in these preparations can be characterized with the help of rheological methods (Kratz and Dengler, 1995), using... 

Elagerstrom, El., Paulsson, M., and Edsman, K., Evaluation of mucoadhesion for two polyelectrolyte gels in simulated physiological conditions using a rheological method, Tinr. J. Pharm. Biopharm., 9 301—309 (2000). 

Note 3 The gel point is often detected using rheological methods. Different methods can give different gel points because viscosity is tending to infinity at the gel point and a unique value cannot be measured directly. 

Methods used to obtain conformational information and establish secondary, tertiary, and quaternary structures involve electron microscopy, x-ray diffraction, refractive index, nuclear magnetic resonance, infrared radiation, optical rotation, and anisotropy, as well as a variety of rheological procedures and molecular weight measurements. Extrapolation of solid state conformations to likely solution conformations has also helped. The general principles of macromolecules in solution has been reviewed by Morawetz (17), and investigative methods are discussed by Bovey (18). Several workers have recently reexamined the conformations of the backbone chain of xylans (19, 20, 21). Evidence seems to favor a left-handed chain chirality with the chains entwined perhaps in a two fold screw axis. Solution conformations are more disordered than those in crystallites (22). However, even with the disorder-... 

The solid-like properties may be measured by non-destructive dynamic rheology analysis or by destructive methods using a Penetrometer, Jelly Tester, Instron instruments, or other types of texture analyzers. The latter methods are the most useful due to their simplicity and speed. Texture analysis of whippable emulsion must always be compared with the amount of air incorporated into the foam, which is known as percentage overrun and is calculated as follows ... 

Irrespective of the method used, the quality of a syntactic foam depends substantially on the rheological properties of the initial mixture with the microspheres68 70). The investigation of the rheology of syntactic compositions by Petrilaenkova et al. 71)... 

Research on the impeller method using the helical ribbon impeller is well documented (7,8). The impeller method is often employed to measure the rheology of suspensions. Previous researchers assumed that the effective shear rate of such a device is related to the impeller speed by a fluid-independent constant, but this assumption may not be accurate for all impellers (8,9). It has been suggested that a properly designed helical ribbon impeller might be more appropriate for this technique. 

Fig. 4. Rheologic models used to fit shear stress vs shear rate data calculated from impeller method for 10 and 15% corn stover suspensions.

Methods used to Determine the Rheological Properties of Milk Fat... 

Most of the methods used to characterize the rheological behavior of butter are empirical and attempt to imitate certain sensory perceptions. They typically involve penetrometry, extrusion or sectility tests (Prentice, 1972). In these tests, the structure of the material is destroyed in order to probe its response to an applied stress or deformation. These methods mostly serve a quality control function. Their results provide an index of consistency to adjust milk-blending operations or to regulate a step in the butter-making process. While the results have practical significance, they often have no theoretical basis. Therefore, attempts have also been made to study the intrinsic properties of plastic fats. In many such cases, small deformation tests, in which the structure of the sample remains intact have been used to probe milk fat rheology. 

Several physicochemical methods of investigation, such as measurement of optical rotation (including optical rotation dispersion and circular dichroism) rheological methods, and X-ray analysis of fibers and films, have played a very important role for determination of conformations of galactan molecules and characterization of their supramolecular structures.8,19 As mentioned in Section I, only physicochemical methods used for determination of primary structures of polysaccharides are considered in this chapter. 

AFM can also be used to probe local mechanical properties of thin films of food biopolymers, which are difficult to measure using traditional rheological methods. Several mechanical models have been developed to analyze the Young s modulus of food systems. One of the simplest models, the Hertz model, assumes that only the elastic deformation exists in a surface with spherical contacts, and the adhesion force can be neglected (Hugel and Seitz 2001). Equation (8.2) describes the relationship between the loading force, F and the penetration depth, d, where a is the radius of contact area, R the curvature of the tip radius, Vi and the Poisson s ratios of the two contact materials that have Young s modulus, Ei and E2. ... 

Bremer et al. (1989) described a detailed experimental method used to measure the permeability fractal dimension of a fat crystal network. Similarly to the rheology fractal dimension, the permeability fractal dimension, Dp, could be obtained from the nonlinear regression between Q and O as shown in Figure 17.23 (Tang and Marangoni 2005). 

As their name implies, plastics are easily deformable and once molten they may be heated not only externally, but also internally, by dissipating friction or dielectric heat. Once the pyrolysis temperature is attained, the melt viscosity starts decreasing rapidly and rising pyrolysis vapour bubbles agitate the mix. Many properties of plastics can be derived using methods used and developed by Van Krevelen [13]. The pyrolyzing plastic s rheology is poorly-documented, however, since the evolution of molecular size and strucmre with time and the effects of extraneous matter are difficult to predict. 

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