Rheological method

The turbidity methods are unsatisfactory for lar particles and/or high particle number concentrations when multiple scattering effects intrude. As shown by Hunter et al. (1975), rheological measurements can then be used to detect flcK ulation. Stable dispersions exhibit an Ostwald-type flow curve whereas flocculated systems behave in a pseudoplastic fashion. Bocculation is thus accompanied by a large increase in the Bingham yield value, t, of the dispersion (see Fig. 5.4). 

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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],... 

Rheological Methods to Characterize Pectins in Solutions and Gels... 

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... 

J. F. Steffe 1996, Rheological methods in food process engineering 2nd edn, Freeman Press, East Lansing, MI, USA. 

Hassan, E. E. and Gallo, J. M. A simple rheological method for the in vitro assessment of mucin-polymer hioadhesive bond shength. Pharmaceutical Research 1993, 7(5), 491-495. 

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. 

Ross-Murphy, S. B. (1984). Rheological methods. In H. W. -S. Chan (Ed.), Biophysical Methods in Food Research (pp. 138-199). Blackwell Publishers, New York. 

Steffe, J.F. 1996. Rheological Methods in Food Process Engineering, 2nd ed. Freeman Press. East Lansing. Mich. 

Ross-Murphy, S.B. 1994. Rheological methods. In Physical Techniques for the Study of Food Biopolymers (S.B. Ross-Murphy, ed.) pp. 343-392. Blackie Academic Professional, Glasgow, U.K. 

Experimental e"(t) curves exhibit an inflection point that corresponds to the maximum rate of change of conductivity, associated to the maximum decrease of mobility. For this reason this inflection point has been attributed to gelation (Wasylyshyn and Johari, 1997). In some cases good agreement between the inflection time and the gel time obtained by rheological methods was observed. A very complex explanation taking into account inter-molecular H bonds, protonic conduction, and a bond percolation law has been proposed to explain this mobility change (Johari and Wasylyshyn, 2000). 

J.F. Steffe Rheological Methods in Food Processing, 2nd edition, Freeman Press, 1996... 

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. 

The binding capacity of iodine by starch was studied by spectrophotomet-ric, potentiometric, amperometric, and rheological methods. A sharp increase in the viscosity of starch solutions occurred after the amylose helix... 

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. ... 

Tang, D., and Marangoni, A.G. (2005). Quantitative measurements of mierostrueture of fat crystal networks by microscopy and rheology methods. 96th AOCS Annual Conferenee Meeting, Salt Lake City. (Oral Presentation)... 

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