Viscosity of associating polymers

PART IV RHEOLOGY OF ASSOCIATING POLYMERS, 650 Viscosity of Associating Polymers in the Dilute Regime, 652 Viscosity of Associating Polymers in the Semi-Dilute Regime, 656... 

Viscosity of Associating Polymers in the Semi-Dilute Regime... 

Surfactant concentration (varied after polymerization) greatly affects the viscosity of associating polymer systems. Iliopoulos et al. studied the interactions between sodium dodecyl sulfate (SDS) and hydrophobically modified polyfsodium acrylate) with 1 or 3 mole percent of octadecyl side groups [85]. A viscosity maximum occurred at a surfactant concentration close to or lower than the critical micelle concentration (CMC). Viscosity increases of up to 5 orders of magnitude were observed. Glass et al. observed similar behavior with hydrophobically modified HEC polymers. [100] The low-shear viscosity of hydrophobically modified HEC showed a maximum at the CMC of sodium oleate. HEUR thickeners showed the same type of behavior with both anionic (SDS) and nonionic surfactants. At the critical micelle concentration, the micelles can effectively cross-link the associating polymer if more than one hydrophobe from different polymer chains is incorporated into a micelle. Above the CMC, the number of micelles per polymer-bound hydrophobe increases, and the micelles can no longer effectively cross-link the polymer. As a result, viscosity diminishes. 

The rheological properties of all HMHEC polymers are profoundly affected by the hydrophobe molar substitution (MS) and the hydrophobe chain length. For any given hydrophobic moiety, there is a threshold hydrophobe MS below which there are no significant associative interactions. The most common phenomenological evidence for associative behavior is a dramatic increase in the solution viscosity of HMHEC polymers as a function of hydrophobe MS. The solution viscosity of HMHEC polymers continues to increase as a function of hydrophobe MS until the maximum limit of solubility is reached, as which point the HMHEC polymer becomes insoluble in water.33... 

Viscosity of dissolved polymers drops irreversibly under acoustic treatment65 A8). The depolymerization process us rather fast during the first minutes of the treatment and then it becomes slow and ceases completely when the equilibrium molecular mass (MM) M is reached. The higher the polymer s initial molecular mass N0, the higher the rate of destruction. The majority of authors associate polymer destruction in solution with cavitation effects occurring under acoustic treatment. 

Both RAMEB and SDS are called rheology modifiers, since they greatly increase and decrease viscosity. Since their discovery, CD-based rheology modifiers have been found for a great variety of associative polymers, such as a-CD for dodecylamido-polyacrylic acid [194], HP- 3-CD for hexadecyl modified hydroxyethyl-cellulose [195], and RAMEB for adamantane modified polyacrylamide [196],... 

In summary, these solution studies of sodium salts of lightly sulfonated polystyrene In tetrahydrofuran verify the presence of associating polymer behavior In lonomer solutions with nonionizing solvents. The results provide a molecular basis for the understanding of solution viscosity behavior. Individual lonomer colls are observed to retain constant dimensions while associating... 

Another issue was the applicability of this approach to characterize the dilute-solution properties of associating polymers. Reduced viscosity is a linear function of the polymer concentration at low concentrations for the systems in this study, so the use of a Huggins-type relationship is justified. 

Rheological Properties. Incorporation of ions into a polymer invariably causes an increase in the melt viscosity of the polymer. This is mainly due to the strong association between the ionic segments (which lead to the so called bluster formation in some cases ) which can best be described as time - dependent crosslinks. Such crosslinks are regarded as extra entanglements or as decreasing the segmental mobility which can be described by free volume considerations. 

The intrinsic viscosity, [t ], and Huggins constant, k, can be used to determine the molecular weight of the polymer and to assess the degree of hydrophobic interactions [89], Therefore, it is useful to discuss these two parameters before examining the rheological properties of associating polymers. 

The introduction of hydrophobic groups will affect the intrinsic viscosity and the Huggins constant. Bock et al. prepared copolymers of N-octylacrylamide and acrylamide using micellar copolymerization [89]. The prepared copolymers were nonionic, had a molecular weight of 3 x 10 g/mole, and contained a hydrophobe content of 0, 0.75 and 1 mol%, respectively. The intrinsic viscosity of these polymers decreased as the hydrophobe content was increased. This is mainly due to intramolecular association that leads to the contraction of the polymer chain. On the other hand, Huggins constant increased with the hydrophobe content such that... 

The most important aspect of Figure 38 is that there is a minimum hydrophobe content below which the amount of association will not be sufficient to increase viscosity. Also, hydrophobic association significantly increases the viscosity of the polymer solutions. 

This chapter is devoted to the molecular rheology of transient networks made up of associating polymers in which the network junctions break and recombine. After an introduction to theoretical description of the model networks, the linear response of the network to oscillatory deformations is studied in detail. The analysis is then developed to the nonlinear regime. Stationary nonhnear viscosity, and first and second normal stresses, are calculated and compared with the experiments. The criterion for thickening and thinning of the flows is presented in terms of the molecular parameters. Transient flows such as nonhnear relaxation, start-up flow, etc., are studied within the same theoretical framework. Macroscopic properties such as strain hardening and stress overshoot are related to the tension-elongation curve of the constituent network polymers. 

Chapter 9 presents the transient network theory of associating polymer solutions, which is the other one of the two major theories treated in this book. It studies the dynamic and rheological flow properties of structured solutions from a molecular point of view. Thus, linear complex modulus, nonlinear stationary viscosity, start-up flows, and stress relaxation in reversible polymer networks are studied in detail. 

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