Rheological behaviour dynamic

Alvarez, M. D., Fernandez, C., Canet, W. (2004). Rheological behaviour of fresh and frozen potato puree in steady and dynamic shear at different temperatures. Fur. Food Res. Techrwl, 218, 544-553. 

Figure 3a-b illustrate the LCB effect on the melt rheological properties. The response of the rheological behaviour to the copolymerisation ability and vinyl end group selectivity of the siloxy-substituted metallocenes has been investigated from their dynamic modulus curves. The frequency dependency of the dynamic modulus of the polyethenes produced with catalysts 2 is demonstrated in Fig. 3a. For comparison dynamic modulus for a linear polyethene, prepared by the catalyst -BuCp2ZrCl2, is shown in Fig. 3b. 

Transient shear flows involve examining the shear stress and viscosity response to a time-dependent shear. The stress build up at the start of steady flow (<7+) and at the cessation of steady flow (a ) and the stress decay (ff(0) after a dynamic instantaneous impulse of deformation strain (y) can be used to characterize transient rheological behaviour. 

In the present work the effect of temperature on the rheological behaviour of wheat gluten in D20 is compared to that in water. The viscoelastic response was studied in shear by combining dynamical measurements and creep and recovery tests, in order to encompass a large timescale. 

In general one can say that the thermodynamic description of an adsorption layer at a liquid interface provides the basis for the dynamic and mechanical understanding. As it is the final state of a process, it controls also the mechanism of its formation, the adsorption kinetics (sf. Fig. 1). The response to small or large deformations of a hquid interface is governed by the adsorption mechanism and hence the thermodynamic characteristics. After a compression, the surface concentration F reaches values larger than the respective equihbrium adsorption Fq and a desorption process sets in. Both, adsorption and desorption induced by interfacial perturbations are processes governed by the thermodynamic and kinetic characteristics. Thus, the surface rheological behaviour seems to be most sensitive to the specificity of adsorbed surfactants. 

The interest in the phase behaviour of block copolymer melts stems from microphase separation of polymers that leads to nanoscale ordered morphologies. This subject has been reviewed extensively [1 ]. The identification of the structure of bicontinuous phases has only recently been confirmed, and this together with major advances in the theoretical understanding of block copolymers, means that the most up-to-date reviews should be consulted [1,3]. The dynamics of block copolymer melts, in particular rheological behaviour and studies of chain diffusion via light scattering and NMR techniques have also been the focus of several reviews [1,5,6]. 

Using a Rheometrics mechanical spectrometer and powdered polymer samples, the authors compared the rheological behaviour of two polymers with similar chemical compositions but different structures. The rheological profiles of polymers 21 and 22 were determined between 140 and 400°C by increasing the temperature at 10°C min from 140 to 190°C and from 300 to 400°C. In the predominant region of isoimide-imide conversion (190-300°C), the temperatme was raised by 2 or 5°C increments, the dynamic viscosity rj being measured at each temperature step. At 190°C, the viscosity of poly(isoimide) 21 was approximately 5 X 10 Pas and decreased to a minimum value of 10 Pas at 243°C as the polymer softened and melted. Thermal conversion to polyimide 22 concurrently... 

Oommen et al. had studied melt rheological behaviour of the blends between NR and poly(methyl methacrylate) based on the effect of blend ratio, processing conditions and graft copolymer concentration as a function of shear stress and temperature. It was clarified that the viscosity of the blends increased with the increase of the amount of NR. On the other hand, the flow behaviour of the blends was found to be influenced by dynamic vulcanization of the rubber phase. 

Rheological behaviour of the TPVs that were prepared from dynamic vulcanization of NR-g-PMMA and PMMA blends using various vulcanization systems including conventional vulcanization (CV) and efficient sulphur vulcanization (EV) systems were studied by Nakason et al The ingredient formulas of each vulcanization systems are summarized in Table 18.6. 

As mentioned above, interfacial films exhibit non-Newtonian flow, which can be treated in the same manner as for dispersions and polymer solutions. The steady-state flow can be described using Bingham plastic models. Viscoelastic behaviour can be treated using stress relaxation or strain relaxation (creep) models as well as dynamic (oscillatory) models. The Bingham-fluid model of interfacial rheological behaviour [54] assumes the presence of a surface yield stress, as, i.e. 

Cowman et al. [43] investigated the effect of temperature in the range of 25-65 °C on the dynamic rheological behaviour of salt-containing aqueous solution of hyaluronan, Hylan A (cross-linked HA) and a mixture of hylans (known under the trade name Synvisc ). The increase in temperature substantially reduces the modulus and complex viscosity for all three samples. 

The rheological behaviour of the lamellar phases is again determined by the structure and the dynamic properties... 

Van der Linden and co-workers have developed a theory for the rheological behaviour of multilamellar vesicles on the basis of their bending and dynamic properties, which could be suitable for an understanding of the phase transitions of lamellar phases under shear. These authors calculated the energy required for the deformation of the vesicles, which is determined both by the bending energy of the bilayer and by the interactions between such layers. With this model, they could obtain relaxation times and elastic frequencies for the different modes of deformation of the multilamellar vesicles that were of the same order of magnitude, like the shear rates at which the transformation of the lamellar phases into monodisperse multilamellar vesicles takes place. 

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