Rheological properties steady state rheology

Rheological Properties Measurements. The viscoelastic behavior of the UHMWPE gel-like systems was studied using the Rheometric Mechanical Spectrometer (RMS 705). A cone and plate fixture (radius 1.25 cm cone angle 9.85 x 10" radian) was used for the dynamic frequency sweep, and the steady state shear rate sweep measurements. In order to minimize the error caused by gap thickness change during the temperature sweep, the parallel plates fixture (radius 1.25 cm gap 1.5 mm) was used for the dynamic temperature sweep measurements. 

Bhat PG, Flanagan DR, Donovan MD. Drug diffusion through cystic fibrotic mucus steady-state permeation, rheologic properties, and glycoprotein morphology. J Pharm Sci 1996, 85, 624-630. 

A standard commercial film blowing LLDPE resin, LPX-30, was blended at different ratios with either other LLDPE s or a LDPE polymer. The characteristic properties of these materials are listed In Table II. The resins were generously donated to the project by Esso Chem., Canada. Prior to blending the polymers were thoroughly characterized by SEC, SEC/LALLS, solution viscosity, CNMR, Atomic Absorbance, and their rheological behavior was characterized In steady state and dynamic shear flow as well as In the uniaxial extenslonal deformation (44-46). 

The process of macroscopic gelation that is sensed as a change in the rheological properties (a rapid increase in the steady-state shear viscosity) then involves the aggregation and crosslinking between these preformed gel particles to form an infinite network. 

A review of rheo-optical techniques by Sherman et al. (1996) notes that there has been an increase in the use of rheo-optic set-ups both for FT-IR dichroism and for dynamic IR dichroism spectroscopies for polymer melts and polymer blends. Skytt et al. (1996) highlight the use of simultaneous measurement of the transient or steady-state rheological properties and IR dichroism to characterize orientation in polymer melts. However, there is little reference to dual spectroscopic-rheological techniques for reactive polymer systems in the literature. 

Buevich, Yu. A. and Shchelchkova, I. N., Rheological properties of homogeneous finely divided suspensions. Steady-state flows, J. Eng. Phys. Thermophys., Vol. 33, No. 5, 1977. 

The above references mainly describe rheological behavior of graphite fiber (length 0.5-16 cm) in poly-ether-ketone-ketone (PEKK) at 370°C. Anthors conclnde that the transient and steady-state rheological properties of these materials are different from the unfilled melt. 

The purpose of our study was a rheological evaluation of the effect of composition on the properties of ABS resins in the molten state. Steady-state viscosity was determined over a wide range of temperatures and shear rates. The shear modulus in the molten state was determined by measurement of the diameter of the extrudate. ABS resins in the molten state behaved as an amorphous homophase polymer. The effect of the elastomer phase on the viscoelastic properties which characterize the behavior of the continuous matrix, i.e. monomer friction coefficient and molecular weight between entanglements (Me), was calculated by the application of the molecular theories. The significance of these properties in heterophase systems is discussed. 

The steady-state recoverable compliance is an important rheological parameter because it is very sensitive to the high molecular tail of the molecular weight distribution, and thus can be correlated with elastic properties of a rubber. 

Chu, S. G., Venkatraman, S., Berry, G. C., and Einaga, Y., Rheological properties of rodlike polymers in solution 1. Linear and nonlinear steady-state behavior. Macromolecules, 14, 939-946(1981). 

The steady-state shear flow properties in the low shear rate region and the dynamic functions were measured using a rotational viscometer (cone-plate type, RGM151-S, Nippen Rheology Kiki Co., Ltd., Japan). The cone radius R was 21.5mm, the gap between the central area of the cone and plate H was kept at 175p.m, and the cone angle 0 was 4°. The measurements were carried out at 200°C Steady state shear properties (shear viscosity //, and the first normal stress difference Ni) as well as dynamic functions (storage and loss moduli G, G", respectively. 

Rheological properties under steady state and oscillatory shear flow of isotropic and nematic solutions of PpPTA, PBT and PBO were studied by Baird [70] and Berry et al. [46]. Baird observed shear thinning for a series of PpPTA solutions in sulfuric acid (4-15%). These results also suggest that at higher shear rates very little difference exists between the anisotropic and isotropic phases. Steady-state viscosities as a function of the temperature observed for solutions of PBO in methane sulfonic acid showed a sharp increase near T,, a behavior which has also been reported for PpPTA and PpBA solutions [46],... 

Low molecular weight PS was mixed vdth poly(methyl phenyl siloxane), PMPS, to form an immiscible blend with an upper critical solution temperature (UCST) [199]. The viscoelastic properties were studied by dynamic and steady-state shearing the neat polymers showed Newtonian behavior. Within the miscible region the blend viscosity followed the Mertsch and Wolf equation, Eq. (2.35), but with the parameter /fit = calculated from Bondi s tables. The phase separation created a rheolog-ically complex behavior. 

The various nonlinear rheological properties (e.g., viscosity ri and normal stress functions and N ) can then be correlated with P. This sort of argument and the basic assumptions of the model have been proven useful, as the model was previously found to fit steady-state data very well (3,4). 

We have successfully carried out the first phase of extending our original kinetic network model for calculating steady-state properties (3,4) to apply to transient experiments involving step changes in shear rate. The model is seen to possess the ability to describe these stress transients. In addition, a number of new rheological tests have been proposed as potential means to... 

Rheological measurements are used to investigate the bulk properties of suspension concentrates (see Chapter 7 for details). Three types of measurements can be applied (1) Steady-state shear stress-shear rate measurements that allow one to obtain the viscosity of the suspensions and its yield value. (2) Constant stress or creep measurements, which allow one to determine the residual or zero shear viscosity (which can predict sedimentation) and the critical stress above which the structure starts to break-down (the true yield stress). (3) Dynamic or oscillatory measurements that allow one to obtain the complex modulus, the storage modulus (the elastic component) and the loss modulus (the viscous component) as a function of applied strain amplitude and frequency. From a knowledge of the storage modulus and the critical strain above which the structure starts to break-down , one can obtain the cohesive energy density of the structure. 

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