The effect of shear rate on the molecular weight determination of acrylamide polymers from intrinsic viscosity measurements
Chemical Engineering Department, McMaster University, Hamilton, Ontario, CanadaJournal of Applied Polymer Science (Impact Factor: 1.77). 06/1979; 23(11):3323 - 3339. DOI: 10.1002/app.1979.070231118
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.
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ABSTRACT: Experimental results on pressure losses of flows of dilute polymer solutions through porous media are summarized. The polymer products employed in this study consisted of partially hydrolyzed polyacrylamides (HPAM) with different degrees of hydrolysis. The effect of the hydrolysis on the pressure drop is investigated in a porous media test section designed to minimize polymer degradation. The investigations were carried out for various solvent conditions, and it is shown that the maximum increase in pressure drop is mainly dependent on the molecular weight of the polymers. The onset of the polymer action is measured for various fluid and solvent properties. Particular attention is given to measurements near θ-conditions. The results stress the importance of the solvent properties on the actions of the polymers and on the resultant pressure drop for porous media flows. The addition of salt ions to solutions of partially hydrolyzed polyacrylamides yields onset behavior previously observed for nonionic polymers. The differences measured between various solvent properties can be explained by the actual hydrodynamic molecule dimensions for a given molecular weight and polymer concentration. To quantify the influences of the solvent properties on the polymers, measurements were carried out in aqueous solutions for various pH values and therefore at various degrees of dissociation. The importance of separating polymer effects caused by their linear dimension in the solution from those that are introduced by and increase in solvent viscosity is shown. Measurements were performed to quantify the effects of solvent viscosity on the polymer action and to separate these effects from those due to changes in molecule dimensions. The implications of the present results are stressed in connection with applications of polymer solutions in tertiary oil recovery, and the positive features of the molecule actions on flow in such applications are described.Journal of Applied Polymer Science 09/1981; 26(9):3125 - 3149. DOI:10.1002/app.1981.070260926 · 1.77 Impact Factor
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ABSTRACT: For 62 days the aging behaviour of diluted solutions of an extremely pure, linear, noncharged polyacrylamide with Mw = 8400 000 g/mol in water was examined. The solutions were stored in a sterile surrounding at 298 K. The following quantities, all of which give information about the molecular weight or the dimension of the macromolecules, were measured: the intrinsic viscosity [η], the sedimentation cofficient s0, the translational diffusion coefficient (Dt)z, the molecular weight, Mw, and the radius of gyration, Rz. Within the accuracy of the measurements all these quantities remained constant. That means, in contrast to other authors, that we could not observe any aging effect in our solutions. It seems that polyacrylamide dissolved in water shows a behavior like a coil molecule in a thermodynamically good solution.Die Makromolekulare Chemie 10/1982; 183(10):2515 - 2525. DOI:10.1002/macp.1982.021831021
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ABSTRACT: In this report a survey is given on structure and properties of polyacrylamide homopolymers (PAAm) in solution. However the review is restricted to all those papers, where a molecular characterization of the polymers has been achieved as a basis to correlate this fundamental information with applicational properties. Different polymerization methods are summarised in brief, the preparation and solution structure of long chain branched polyacrylamides as well as chemical modification reactions of linear PAAm are also mentioned. A number of experimental characterization methods (GPC, ultracentrifugation, intrinsic viscosity, and light scattering measurements) are described with special emphasis on the difficulties of the different procedures including some proposals for properly designed experimental techniques. The state of solution is discussed in view of experimental data obtained with different solvents. Moreover viscosity constant ø is calculated for aqueous solution and the unperturbed dimensions are estimated. All available data on cross correlations (e.g. [η] - M, S0 - M, 1 2 - M) are collected with the intention to give a survey of established relations and, comparing the given relationships, to suggest the reliable ones of them. The phenomenon of long-term viscosity decrease of aqueous PAAm solutions has been investigated and discussed with regard to its molecular origin. The viscoelastic properties are discussed in dependence on molecular weight, concentration, solvent quality, and shear rate (≤106 · s-1). Based on these data a simple equation was developed oped for the η0-c-M relationship, which can be applied to other polymer systems as well. It is further described that the elastic nature (first normal stress difference) may overwhelm the viscous nature (shear stress) at relatively low shear rates. This high elasticity can cause deviation from laminar flow conditions. Moreover, it can be demonstrated - based on instationary measurements as well as the comparison of steady shear flow with dynamic rheology - that energetic interactions (H-bonds) strongly influence the rheological behaviour.Progress in Polymer Science 12/1982; 8(4):373-468. DOI:10.1016/0079-6700(82)90004-1 · 26.93 Impact Factor
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