Viscosity hydrophobically associating polymer

This shear reversibihty is very beneficial in enhanced oil recovery field applications. It improves the well injectivity because of the shear thinning effect at the perforation and near the wellbore. Far away from the wellbore, flow velocity is reduced and viscosity is restored. For the hydrophobically associating polymers, both shear thickening and shear thinning were observed by Bock et al. (1988). It has also been reported that the viscosity after shearing was stopped was higher than that before shearing (McCormick et al., 1988). 

A further complication to understanding the rheology of hydrophobically associating polymers is their unique response to shear rate and solvent quality (e.g., salt content). As shown in Figures 5 and 6, the viscosity can be independent (Newtonian), decrease (pseudoplastic), or even increase (dilatant)... 

Previously, wel had shown that hydrophobically associating polymers can be isoviscous in salt solutions of increasing brine level. We [13,14] and others [15,16] has also shown that aqueous poly zwitterions are antipolyelectrolytes i.e. their solubility and viscosity increases with increasing salt content. 

The effect of hydrophobic association on viscosity in the semi-dilute regime is different from that observed at low polymer concentrations. Figure 40, from Bock et al. [89], shows the variation of the reduced viscosity with polymer concentration for polyacrylamide and N-octylacrylamide copolymers having hydrophobe contents of 0.75 and 1 mol%. At a hydrophobe content of 0.75 mol%, the viscosity significantly increased because of intermolecular association. Increasing hydrophobe content further to 1 mol% resulted in higher viscosities. 

Rheological studies also indicated differences in behavior as a function of concentration for these two polymers. The plots of relative and reduced viscosities for the copolymer prepared in surfactant were similar to the profile in Fig. 2.1, indicating that it behaved as a hydrophobically associating polymer in deionized water and 2% NaCl. The solution polymer, in contrast, was shown to behave as a polymeric microsuspension in these solvents. 

By covalently attaching reactive groups to a polyelectrolyte main chain the uncertainty as to the location of the associated reactive groups can be eliminated. The location at which the reactive groups experience the macromolecular environment critically controls the reaction rate. If a reactive group is covalently bonded to a macromolecular surface, its reactivity would be markedly influenced by interfacial effects at the boundary between the polymer skeleton and the water phase. Those effects may vary with such factors as local electrostatic potential, local polarity, local hydrophobicity, and local viscosity. The values of these local parameters should be different from those in the bulk phase. 

There have been many studies of hydrophobic crosslinking. For example, Flynn40 produced a series of poly (acrylamides) (PAM) and recorded the low shear rate viscosity as a function of the chain overlap parameter. This was performed for a range of molecular weights and concentrations. This procedure was then repeated with the same polymer backbone but with the addition of differing concentrations of alkyl side chains which give rise to hydrophobic association (HPAM). A comparison between hydrophobe and non-hydrophobe polymers is shown in Figure 5.30. 

The conversion of dextran with 1,2-epoxy-3-phenoxypropane, epoxyoctane or epoxydodecane may be exploited for the preparation of amphiphilic dextran derivatives. Polymeric surfactants prepared by hydrophobic modification of polysaccharides have been widely studied, starting with the pioneering work of Landoll [261]. Neutral water-soluble polymeric surfactants can be obtained by reaction of dextran with 1,2-epoxy-3-phenoxypropane in 1 M aqueous NaOH at ambient temperature (Fig. 35, [229,233]). The number n of hydrophobic groups per 100 Glcp units varies between 7 and 22 depending on the reaction conditions. 2-Hydroxy-3-phenoxy propyl dextran ethers (DexP) behave like classical associative polymers in aqueous solution. In dilute solution, the intrinsic viscosity decreases significantly whereas... 

As the hydrophobe content of the HMHEC increases, the viscosity first increases, reaches a maximum, and then decreases rapidly. The viscosity finally approaches that of the solvent as the polymer becomes insoluble. A minimum hydrophobe level (discussed in detail later) is necessary to achieve an observable increase in viscosity as compared to that of the unmodified HEC. Above this threshold, viscosity increases rapidly with increase in the hydrophobe content. After reaching the peak viscosity at an appropriate hydrophobe level, the viscosity decreases upon further increase in hydrophobe level. This decrease is not caused by a diminution in the degree of hydrophobic association, but by the incomplete solubility of the sample. That is, a given HMHEC sample has a distribution of polymer chains with different hydrophobe levels. The proportion of insoluble species increases as the overall hydrophobe content of the sample increases. The hydrophobe... 

Because of their chemical similarity, the polymer-bound hydrophobes have a tendency to interact with the hydrophobic part of the surfactant molecule. If the surfactant concentration in the system is high enough, micelles are formed. If there are enough micelles in the system, then all the hydrophobes will get bound to micelles (Figure 14). As a result, there will be no intermolecular hydrophobic association (Figure 2) and no viscosity... 

Semidilute Viscometrics. Solution viscometrics at concentrations above the overlap concentration (C ) indicated dramatic effects caused by the associative nature of the hydrophobic groups in the polymer. As shown by the reduced viscosity-concentration profiles of Figure 3, the introduction of only 1.0 mol % N-n-octylacrylamide to polyacrylamide can increase the viscosification efficiency dramatically. Increasing the hydrophobe level to 1.25 mol % further increased solution viscosity. At 2000 ppm, the presence of the hydrophobe caused a greater that 10-fold increase in viscosity. This result was in contrast to the behavior of these polymers in dilute solution see the box in Figure 3). The presence of hydrophobic functionality on the polymer resulted in a decrease in the reduced viscosity at concentrations below C. In dilute solution, intramolecular hydrophobic associations decreased the hydrodynamic radii of the polymer coils and thus reduced the... 

Hydrophobic associations can dominate polymer conformation in solution and solution rheological properties. Intrinsic viscosity and Huggins interaction coefficients provided information on the conformation and intramolecular aggregation behavior of these polymers in dilute solution. The presence of hydrophobic associations caused a decrease in the intrinsic viscosity and an increase in the Huggins constant. These effects could be counterbalanced by increasing the ionic charge on the polymer through hydrolysis or by copolymerization with sodium acrylate. 

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