High Zero-shear viscosity

These essentially comprise a mixture of a skin-forming component, which comprises two distinct phases blended together, a high zero-shear viscosity material and a low zero-shear viscosity material, and a foam core-foaming component, which includes a blowing agent, physically dry blended together. The three materials are preferably selected from suitable homopolymers and copolymers of ethylene. CANADA... 

The most common procedure for eliminating creaming or sedimentation is to use a thickener in the continuous phase, e.g. a high molecular weight polymers such as hydroxyethyl cellulose or xanthan gum. These thickeners produce a gel in the continuous phase that has a yield value (> 0.1 Pa) and a high zero shear viscosity (>1000 Pa s), thus preventing any creaming or sedimentation. 

The above-mentioned viscoelastic polymer solutions reduce (or eliminate) creaming or sedimentation of the emulsion, providing they produce an elastic network in the continuous phase that is sufficient to overcome the stresses exerted by the creaming or sedimenting droplets. Such viscoelastic solutions produce a very high zero shear viscosity that is sufficient to eliminate creaming or sedimentation. 

Polymer solutions are often characterized by their high viscosities compared to solutions of nonpolymeric solutes at similar mass concentrations. This is due to the mechanical entanglements formed between polymer chains. In fact, where entanglements dominate flow, the (zero-shear) viscosity of polymer melts and solutions varies with the 3.4 power of weight-average molecular weight. 

Since pc 1/2, we observe that Me 2Mg, as commonly observed. Mg is determined from the onset of the rubbery plateau by dynamic mechanical spectroscopy and Me is determined at the onset of the highly entangled zero-shear viscosity law, T) M. This provides a new interpretation of the critical entanglement molecular weight Mg, as the molecular weight at which entanglement percolation occurs while the dynamics changes from Rouse to reptation. It also represents the... 

Polymers in solution or as melts exhibit a shear rate dependent viscosity above a critical shear rate, ycrit. The region in which the viscosity is a decreasing function of shear rate is called the non-Newtonian or power-law region. As the concentration increases, for constant molar mass, the value of ycrit is shifted to lower shear rates. Below ycrit the solution viscosity is independent of shear rate and is called the zero-shear viscosity, q0. Flow curves (plots of log q vs. log y) for a very high molar mass polystyrene in toluene at various concentrations are presented in Fig. 9. The transition from the shear-rate independent to the shear-rate dependent viscosity occurs over a relatively small region due to the narrow molar mass distribution of the PS sample. 

The zero-shear viscosity and the dynamic viscosity (at low frequencies) diverge at high concentration, while they are constant at low concentration [99,100,102-105],... 

Linear phosphonitrilic chlorides (LPNCs), silicone fluids and, 22 573 Linear photodiode arrays, 19 153 Linear polyesters, 14 116 Linear polyethylene fibers, 20 398 Linear polyimides, synthesis of, 20 273 Linear polymers, 20 391 25 455 high molecular weight, 23 733 zero-shear viscosity of, 19 839 Linear poly(thioarylene)s, 23 705 Linear PPS, 23 704. See also... 

The limiting low shear or zero-shear viscosity r 0 of the molten polymer can be related to its weight-average molecular weight, M 9 by the same relations noted for concentrated solutions rj0 = KMW for low molecular weight and rj0 = Kfor high molecular weight. 

Measurements of the zero shear viscosity (20 °C) were made with a Bohlin VOR rheometer in the viscometry mode. If a Newtonian region was not found at the lowest measurable shear rates, the samples were characterized with a Bohlin-CS constant stress rheometer, with which it was possible to obtain extremely low shear rates. This approach was especially needed for highly viscous samples exhibiting pseudoplastic behavior on the VOR rheometer. Newtonian regions were found for each sample in this manner, yielding the zero shear viscosities reported. 

It contains the free parameters zero shear viscosity r]0l a critical shear rate yc, at which shear thinning starts, and the gradient m at high shear rates. The reciprocal value of the critical shear rate Yc gives a time constant . At high shear rates, Eq. 3.7 can be approximated by Eq. 3.5 with a constant gradient of m= 1-n. 

Surfactant solutions with rod-like micelles can have notable viscosities up to six times higher than the water viscosity [37]. This can be explained by the presence of entangled rodlike micelles (often also called worm-like micelles or thread-like micelles) which arrange themselves in a supramolecular transient network [38-41 ]. Such solutions often have elastic properties but they do not show a yield stress. This means that even high viscous solutions flow under the influence of very small shear stress. In this situation they show a zero shear viscosity which is given by ... 

In most pseudoplastic liquids, Newtonian flow behavior is observed at sufficiently low and at high shear rates y, see Fig. 18. Viscosity approaching a constant value with low shear rates is called the zero-shear viscosity, p0> and its constant value at very high shear rates is called the infinite shear viscosity, p°°. 

Figure 7 shows that for four different SBS polymers with styrene content 27% and 40%, a delineation of log / against log [(170/T) y /] is in fact a master curve f (40% styrene) — 0.196, f (27% styrene) = 0.164. The zero shear viscosities for the SBS samples in Figure 7 are given in Table II. The fact that the SBS master curve deviates from the PS master curve at high values of (170/T )y f may be caused by non-isothermal conditions in the capillary. 

The increase in gel strength with increase in bentonite concentration above the gel point is consistent with the increase in yield value and modulus. On the other hand, the limited creep measurements carried out on the present suspension showed a high residual viscosity Oq of the order of 9000 Nm s when the bentonite concentration was 45g dm. As recently pointed out by Buscall et al (27) the settling rate in concentrated suspensions depends on 0. With a model system of polystyrene latex (of radius 1.55 vim and density 1.05 g cm ) which was thickened with ethyl hydroxy ethyl cellulose, a zero shear viscosity of lONm was considered to be sufficient to reduce settling of the suspension with = 0.05. The present pesticide system thickened with bentonite gave values that are fairly high and therefore no settling was observed. 

Following the initial discovery [27] that rj0 depends on just arm molecular weight for star polymers with sufficiently high levels of branching, this type of dependence was confirmed by others both theoretically [32] and experimentally [33]. Pearson and Helfand [32] predicted that the zero shear viscosity of star polymers should scale with arm molecular weight (Afa) as... 

Due to difficulties in measuring the zero-shear viscosity of such high molecular weight polymers, and thus deducing the monomeric friction coefficient from Graessley s uncorrelated drag model [43], the following equation adapted from the modified Rouse theory has been applied [8]. 

In a large range of concentrations (< )S0.05) where the high component is assumed to behave as an entangled melt, the variations of the terminal relaxation time (Oni in the iso-free volume state (Fig. 29) confirms relation (6-8). As the steady-state compUance J l scales as ( )" (Fig. 30), the zero-shear viscosity tiol varies as expected and the plateau modulus Gn which reveals the entanglement network is proportional to 0 . ... 

Figure 2-3 Plot of Shear Rate versus Apparent Viscosity for Shear Thinning Foods Identifying Three Separate Regions A Zero-Shear Viscosity at Low Shear Rates, a Power Law Region at Intermediate Shear Rates, and an Infinite-Shear Viscosity at High Shear Rates. Often, only data in the power law region are obtained.

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