Rheology oscillatory testing

Ritman, E.L., Borah, B., Dufresne, T.E., Phipps, R.J., Sacha, J.P., Jorgensen, S.M., and Turner, R.T. 2002. 3-D Synchrotron pCT allows unique insight of changes in bone quality. The American Society for Bone and Mineral Research Annual Meeting, San Antonio TX, September 20-24. Ross, K.A., Pyrak-Nolte, L.J., and Campanella, O.H. 2004. The use of ultrasound and shear oscillatory tests to characterize the effect of mixing time on the rheological properties of dough. Food Res. Int. 37, 567-577. 

Davis SS, Khanderia MS. Rheological characterization of Plastibases and the effect of formulation variables on the consistency of these vehicles part 3 oscillatory testing. Int J Pharm Technol Prod Manuf 1981 2(Apr) 13-18. 

A biconical disk interfacial rheometer is available from Anton Paar, known as the Physica Interfacial Rheology System (IRS). A schematic of the rheometer tool is shown in Figure 4.22. Current specifications of the instrument include a torque range of 0.02 xNm to 150 mNm with temperature control from 5 to 70°C. All rheological test modes are available for the interfacial rheometer including oscillatory testing [59],... 

Concentrated suspensions commonly display viscoelatic behavior. The viscoelastic properties can be measured by oscillatory tests (26). Comparing with steady shear measurements, oscillatory measurements are made under small deformations, at which the suspension structure is only slightly perturbed. Hence, oscillatory measurements are suitable for correlating rheological behavior with structural data and interparticle potentials, even for strongly flocculated systems that show irreversible changes when subjected to large deformations. 

McKinley, G. H., and O. Hassager. 1999. The Considere condition and rapid stretching of linear and branched polymer melts. Journal of Rheology 43 1195-1212. Safari-Ardi, M., and N. Phan-Thien. 1998. Stress relaxation and oscillatory tests to distinguish between doughs prepared from wheat flours of different varietal origin. Cereal Chemistry 75 80-84. 

Dynamic mechanical analysis in polymeric multiphase systems in solid state, as part of rheology, is associated with oscillatory tests that are employed to investigate all kinds of viscoelastic material from the point of view of flow and deformation behavior. In particular, it evaluates the molecular mobility in polymers, the pattern of which may be an indication of phase-separated systems. Although there are certain preferred tools for visual examination of phenomena for these kinds of systems, dynamic mechanical analysis has the advantage of examination in dynamic conditions and of the prediction of properties. 

Frequently used single-point viscosity tests in the starch plant are orifice pipettes,56 orifice funnels,57 the Hot Scott viscometer, and various methods to determine alkaline fluidity.58 For absolute measurements of the rheological properties, rotating viscometers with coaxial cylinders are used.59 The paper industry uses mainly the Brookfield viscometer and the Hercules viscometer for determining shear-dependent viscosity, pseudoplasticity, and thixotropy. Oscillatory and capillary viscometers are used for more detailed viscosity characterization, such as yield value, elastic properties, and viscoelasticity.60... 

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. 

The relaxation times, t, and corresponding moduli, G, constitute what is called the distribution or spectrum of relaxation times. The relaxation spectrum given in Eq. (3-40) is a distinctive feature of the Rouse model that can be tested experimentally. A simple type of rheological experiment from which this spectrum can be obtained is small-amplitude oscillatory deformation, discussed in Section 1.3.1.4. In this test, at low frequencies, (o < /x, the Rouse model predicts the usual terminal relaxation behavior G — Gco rf, and G" = Gcnxi. More significantly, at higher frequencies, where co is in the range 1/t, oj < 1/tat, the Rouse model predicts a power-law frequency dependence of G and G" ... 

In the rheological structure of most food systems there is a viscous element present, and the deformation curves are often highly influenced by the rate of the imposed strain. This is due to the fact that the material relaxes (or flows) while tested under compression and the resultant deformation of this flow is dependent on the nature of the viscous element (Szczesniak, 1963 Peleg and Bagley, 1983). In the viscoelastic food systems, where during processing it is caused to oscillate sinusoidally, the strain curve may or may not be a sine wave. In cases when a periodic oscillatory strain is applied on a food system like fluid material, oscillating stress can be observed. The ideal elastic solid produces a shear stress wave in phase with... 

The rheological behavior of these materials is still far from being fully understood but relationships between their rheology and the degree of exfoliation of the nanoparticles have been reported [73]. An increase in the steady shear flow viscosity with the clay content has been reported for most systems [62, 74], while in some cases, viscosity decreases with low clay loading [46, 75]. Another important characteristic of exfoliated nanocomposites is the loss of the complex viscosity Newtonian plateau in oscillatory shear flow [76-80]. Transient experiments have also been used to study the rheological response of polymer nanocomposites. The degree of exfoliation is associated with the amplitude of stress overshoots in start-up experiment [81]. Two main modes of relaxation have been observed in the stress relaxation (step shear) test, namely, a fast mode associated with the polymer matrix and a slow mode associated with the polymer-clay network [60]. The presence of a clay-polymer network has also been evidenced by Cole-Cole plots [82]. 

Lee et al. [2007] studied the rheological behavior of poly(ethylene-co-vinyl acetate) (EVAc 40 wt% VAc) and its CPNC with < 10 wt% C30B the tests were conducted under steady-state and small oscillatory shear flow. The samples were prepared by melt compounding at 110 C for 25 min, which resulted in a high degree of dispersion. The flow behavior was quite regular, well described by the Carreau-Yasuda equation [Carreau, 1968,1972 Yasuda, 1979] ... 

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