The effect of shear rate on the molecular weight determination of acrylamide polymers from intrinsic viscosity measurements
ABSTRACT The rheological response of dilute solutions of high molecular weight polyacrylamides at low shear rates has been measured using a capillary viscometer that provided for a fivefold variation in shear rate at each concentration. The non-Newtonian effects were found to be significant for polyacrylamides with number-average molecular weights exceeding 106. The molecular weight average–intrinsic viscosity relationship most widely used in the literature, [η] = 6.80 × 10−4M, was found to be valid when [η] was measured at high shear rates where the polymer solutions approached Newtonian behavior. A new relationship was developed relating Mn to the intrinsic viscosity extrapolated to zero shear rate.
SourceAvailable from: Meysam Nourani[Show abstract] [Hide abstract]
ABSTRACT: The intrinsic viscosity of high molecular weight-partially hydrolyzed poly(acrylamide) which is mainly used in enhanced oil recovery (EOR) processes has been investigated in reservoir conditions. Since, the EOR efficiency of hydrolyzed poly(acrylamide) is very sensitive to the temperature and salinity of petroleum reservoirs, investigations have been carried out at different possible reservoir temperatures using high saline polymer solutions. Non-linear relationships between reduced viscosities and polymer concentrations were observed at low polymer concentrations. Plotting the relative viscosity variation versus polymer concentration in semi-logarithmic scale was used to calculate the intrinsic viscosity. Furthermore, the critical concentration was calculated which could be helpful in determination of the optimized polymer concentration to introduce into the reservoir. Moreover, the effects of temperature and salt concentration are studied on the Mark-Houwink-Sakurada parameters and hydrodynamic molecular diameter. Zero-specific-viscosity which is the specific viscosity at zero polymer concentration is introduced, to find out whether a zero value is obtained at zero polymer concentration. However, experimental observations show that the specific viscosity is not zero at zero polymer concentration for high molecular weight-partially hydrolyzed poly(acrylamide). In this work, an empirical correlation is developed to relate zero-specific-viscosity and the hydrodynamic diameter of polymer molecule.Iranian Polymer Journal 01/2010; 19(2):105-113. · 1.47 Impact Factor
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ABSTRACT: Carefully prepared aqueous solutions of drag-reducing polymers have been characterized by means of steady viscometric and molecular weight measurements. Solutions of anionic polyacrylamide (Cyanatrol-750), 0.5-50 ppm, and nonionic poly (ethylene oxide) (Polyox WSR-303), 100-1000 ppm, were investigated. Steady shear viscosity measurements, with a Rheometrics Stress Rheometer and a Contraves LS30 rheometer, reveal substantial shear thinning for Cyanatrol solutions above 2 ppm and Polyox solutions above 500 ppm, for the shear-rate range investigated. Zero-shear viscosity was accurately determined for all solutions. Intrinsic viscosity, hydrodynamic radius of gyration, and overlap concentration were also estimated. The Carreau and Carreau-Yasuda models successfully fit all shear viscosity data, and allow estimates of elasticity. Reduced variables were used for generalizing the shear viscosity data. Aging tests show that both polymers are stable. The molecular weight and polydispersity of Cyanatrol were measured using the technique of band sedimentation/low angle laser light scattering. The drag-reducing capability of these polymers has been confirmed by pipe flow experiments.Journal of Rheology 09/1994; 38(5):1427-1446. DOI:10.1122/1.550605 · 3.28 Impact Factor