Oscillatory shear rheology

Plutchok, G. J. and Kokini, J. L. 1986. Predicting steady and oscillatory shear rheological properties of CMC and guar gum blends from concentration and molecular weight data. J. Food Sci. 515 1284-1288. 

This problem of comparing of the dynamic exponents ji and n seems to be not settled at all and is still a controversial issue. It must be emphasized that in several studies (Takeda et al. 2000 Norisuye et al. 1999, 2000) the power law exponent in DLS was discussed in the inconsistent context to the viscoelastic exponent n, while no rheological experiments were performed. To demonstrate this we carried out oscillatory shear rheology experiments. In Figure 21 the frequency-dependent storage and loss moduli for three selected temperatures are shown. The power law behaviour regarding Eq. (12) (G (co) oc ftj° G"(co) oc ftj° ) can be observed at 25°C with an averaged exponent of 0.7. 

Oscillatory shear rheology and DLS studies have been performed on gelatin and several other gelling systems (Richter 2007). The occurrence of a power law behaviour observed with both methods was mostly assigned to the gel point. The physical meaning of p and, as a consequence, the physical origin of the power law behaviour in DLS seems to be not completely understood in detail and is therefore... 

Cross-over frequency at which G and G" are equal in oscillatory shear rheology... 

Oscillatory shear rheology of EPDM plasticized with resol was used to determine an equilibrium shear modulus Ge), relaxation in compression and strain recovery. Ge was analysed with consideration of crosslink density and permanent entanglements, including evaluation of plasticizer and soluble polymer fraction. Relaxation data were modelled with the empirical Chasset-Thirion equation and it was proposed that longer relaxation times were associated with chains pendant from the network. Relaxation times increased with crosslink density. When the crosslink density was low and pendant chains were longer and more numerous, relaxation times were increased and elastic recovery diminished. ... 

The second part of this section deals with a brief introduction of the most typical tests used to get materials functions in structured materials. Both continuous and oscillatory shear rheological techniques are briefly described. 

Oscillatory shear experiments are the preferred method to study the rheological behavior due to particle interactions because they directly probe these interactions without the influence of the external flow field as encountered in steady shear experiments. However, phenomena that arise due to the external flow, such as shear thickening, can only be investigated in steady shear experiments. Additionally, the analysis is complicated by the different response of the material to shear and extensional flow. For example, very strong deviations from Trouton s ratio (extensional viscosity is three times the shear viscosity) were found for suspensions [113]. 

Rheological observations of the UHMWPE pseudo-gels of different concentrations under oscillatory shear conditions at different temperatures showed that these systems exhibit considerable drawability at temperatures above ambient. The deformation of the crystalline phase of the gel-like system is not reversible and, as shown in the sequence of photographs Figure 2, for a pseudo-gel of 4% concentration, it was greater when the sample was sheared under the same oscillatory conditions at higher temperatures. The displaced crystals of the UHMWPE pseudo-gel showed remarkable dimensional stability after shear cessation and removal of any compression load in the optical rotary stage. 

The rheological properties, during the sol-gel transition, are investigated with a Weissenberg rheogoniometer in oscillatory shear (linear behaviour). 

Experimentally, the dynamic shear moduli are usually measured by applying sinusoidal oscillatory shear in constant stress or constant strain rheometers. This can be in parallel plate, cone-and-plate or concentric cylinder (Couette) geometries. An excellent monograph on rheology, including its application to polymers, is provided by Macosko (1994). 

The correlation between rheology and thermodynamics is likely to prove a fruitful area for investigation in the future. Very little is as yet known about the detailed mechanisms of non-linear viscoelastic flows, such as those involved in large-amplitude oscillatory shear. Mesoscopic modelling will no doubt throw light on the role of defects in such flows. This is likely to involve both analytical models, and mesoscopic simulation techniques such as Lattice... 

MSI) that uses the same time-dependent Ginzburg Landau kinetic equation as CDS, but starts from (arbitrary) bead models for polymer chains. The methods have been summarized elsewhere. Examples of recent applications include LB simulations of viscoelastic effects in complex fluids under oscillatory shear,DPD simulations of microphase separation in block copoly-mers ° and mesophase formation in amphiphiles, and cell dynamics simulations applied to block copolymers under shear. - DPD is able to reproduce many features of analytical mean field theory but in addition it is possible to study effects such as hydrodynamic interactions. The use of cell dynamics simulations to model non-linear rheology (especially the effect of large amplitude oscillatory shear) in block copolymer miscrostructures is currently being investigated. ... 

Uppuluri, S. Morrison, E.A. Dvornic, P.R. Rheology of dendrimers. 2. Bulk polyamidoamine dendrimers under steady shear, creep, and dynamic oscillatory shear. Macromolecules 2000, 33, 2551-2560. 

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