Apparent viscosity polymer

Wreath, D.G., Pope, G.A., Sepehrnoori, K.S., 1990. Dependence of polymer apparent viscosity on the permeable media and flow conditions. In Situ 14 (3), 263-284. 

Hydrophobically Associating Copolymers. Hydrophobically modified cellulose derivatives (28) and N-alkylacrylamido copolymers (24, 25, 27) were among the first nonionic associative thickeners reported in the patent literature. The concentration of hydrophobic units allowed for dissolution in aqueous solution is usually less than 1-2 mol %. Like conventional polymers, apparent viscosity is proportional to molecular weight and concentration. However, with associative copolymers, a very dramatic increase in apparent viscosity occurs at a critical concentration, C, which clearly is related to a phenomenon other than simple entanglement. Viscosity dependence on hydrophobe concentration, size, and distribution suggests mi-croheterogeneous phase formation. Surfactants enhance viscosity behavior in some instances (24), yet clearly reduce viscosity in others (i). 

Darcy flow in porous media and polymer apparent viscosity... 

Fiv. 9. A polymers apparent viscosity as a function of concentration and salinity (Aluhwal and Kalifa 2008). 

Polymers display pseudoplasticity, with apparent viscosity decreasing as 7 increases [Eq. (2.30) and Fig. 2.2]. 

Polymer melts are frequendy non-Newtonian. In this case the earlier expression given for the shear rate at the capillary wall does not hold. A correction factor (3n + 1)/4n, called the Rabinowitsch correction, must be appHed in such a way that equation 21 appHes, where 7 is the tme shear rate at the wall and nis 2l power law factor (eq. 22) determined from the slope of a log—log plot of the tme shear stress at the wad, T, vs 7. For a Newtonian hquid, n = 1. A tme apparent viscosity, Tj, can be calculated from equation 23. 

Variation of apparent viscosity with the blend ratio for both preblends and preheated blends is shown in Fig. 1. Comparing preblends and preheated, the viscosity of preheated 50 50(NBR-Hypalon) blends becomes maximum, whereas the prebends show a continuous decrease in viscosity from 100% Hypalon to 100% NBR in all shear rates studied. This decrease is explained by the difference in viscosity between two virgin polymers. Preheating of the blends may result in interchain cross-linking and it seems to be maximum at a 50 50 ratio. 

Liquids of complex structure, such a polymer solutions and melts, and pseudo-homogeneous suspensions of fine particles, will generally exhibit non-Newtonian behaviour, with their apparent viscosities depending on the rate at which they are sheared, and the time for which they have been subjected to shear. They may also exhibit significant elastic... 

A Newtonian liquid of viscosity 0.1 N s/m2 is flowing through a pipe of 25 mm diameter and 20 m in lenglh, and the pressure drop is 105 N/m2. As a result of a process change a small quantity of polymer is added to the liquid and this causes the liquid to exhibit non-Newtonian characteristics its rheology is described adequately by the power-law model and the flow index is 0.33. The apparent viscosity of the modified fluid is equal to ihc viscosity of the original liquid at a shear rate of 1000 s L... 

Utilization of a microfabricated rf coil and gradient set for viscosity measurements has recently been demonstrated [49]. Shown in Figure 4.7.9 is the apparent viscosity of aqueous CMC (carboxymethyl cellulose, sodium salt) solutions with different concentrations and polymer molecular weights as a function of shear rate. These viscosity measurements were made using a microfabricated rf coil and a tube with id = 1.02 mm. The shear stress gradient, established with the flow rate of 1.99 0.03 pL s-1 was sufficient to observe shear thinning behavior of the fluids. 

When dissolved in more saline waters, xanthan gum produces a higher apparent viscosity than the same concentration of polyacrylamide (292). Prehydration of xanthan in fresh water followed by dilution in the saline injection water has been reported to provide higher viscosity than direct polymer dissolution in the same injection water. Optical rotation and intrinsic viscosity dependence on temperature indicate xanthan exists in a more ordered conformation in brine than in fresh water (293). 

Variation of apparent viscosity with shear rate for a polymer... 

Because most shear-thinning fluids, particularly polymer solutions and flocculated suspensions, have high apparent viscosities, even relatively coarse particles may have velocities in the creeping-flow of Stokes law regime. Chhabra(35,36) has proposed that both theoretical and experimental results for the drag force F on an isolated spherical particle of diameter d moving at a velocity u may be expressed as a modified form of Stokes law ... 

Reduction in the apparent bulk viscosity due to a change in polymer rheology. It is well known that ultrasound can lead, via degradation, to a reduction in polymer solution viscosity. Although Fairbrother did not investigate whether degradation of the polymer, and subsequent reduction in R.M.M. and hence viscosity had occurred, it seems reasonable to assume that the polymer melt with an initial viscosity of 30000-100000 poise would certainly have resisted cavitation and thus degradation. 

Semisolid Dosage Forms The nature of the base (vehicle) used for the fabrication of semisolid dosage forms affects their hydrolytic stability. Increased degradation of benzylpenicillin sodium in hydrogels of various natural and semisynthetic polymers has been reported [14]. Also at pH 6 in Carbopol hydrogels, the percentage of undecomposed pilocarpine at equilibrium is a function of the apparent viscosity of the medium [15]. 

The effects of broth viscosity on k a in aerated stirred tanks and bubble columns is apparent from Equations 7.37 and 7.41, respectively. These equations can be applied to ordinary non-Newtonian liquids with the use of apparent viscosity as defined by Equation 2.6. Although liquid-phase diffusivity generally decreases with increasing viscosity, it should be noted that at equal temperatures, the gas diffusivities in aqueous polymer solutions are almost equal to those in water. 

Bueche,F. Influence of rate of shear on the apparent viscosity of a -dilute polymer solutions and b-bulk polymers. J. Chem. Phys. 22,1570-1576 (1954)... 

---