Hydrophobically associating polymer concentration

Viscoelastic properties of hydrophobically associating polymers were significantly affected above the overlap concentration. Increased hydrophobe... 

As can be seen, there are many water-soluble polymers for potential use in oilfield applications. Partially hydrolyzed polyacrylamide and xanthan gum are the most commonly employed in EOR applications [40]. Therefore, this review will concentrate on these polymers in addition to hydrophobically associating polymers. 

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. 

A further complication in understanding the rheology of hydrophobically associating polymers is the unique response to shear rate and solvent quality (e.g. salt content). As shown in Fig. 3.8, the viscosity can be independent (Newtonian), decrease (pseudoplastic) or even increase (dilatant) with shear rate depending on the polymer concentration and shear rate. As the hydrophobe level and polymer concentration increase beyond a critical value, a shear rate region in... 

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. 

Low charge density, hydrophobically modified polybetaines were shown to interact and comicellize with nonionic, anionic, cationic, and amphoteric surfactants [181-183] and many ionic organic dyes [264,265]. The association mechanism of hydrophobically modified polymers and surfactants in dependence on the concentration of interacting components can be modeled by two pathways (Scheme 21) [183]. 

Hydrophobically modified polymers can associate in aqueous media to form micelle-like structures above their critical association concentrations (CACs). The nanosized self-aggregates were prepared using modified natural polysaccharides such as pullulan, curdlan, and glycol chitosan. The modified polysaccharides provide excellent biocompatibility, biodegradability, low immunogenicity, and biological activities. 

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