Viscosity surfactant-polymer systems

Polymer-surfactant interactions are the basis for the rheological behavior of MHAPs. Other surfactant-polymer systems have previously been investigated. One example is the interaction of surfactants with polymers such as poly(ethylene oxide), which results in greater solution viscosities than with the polymer alone (e.g., ref. 25 and references therein). The interaction of surfactants or latexes with hydrophobically modified water-soluble polymers has also been shown to produce unique rheology (2, 5, 26, 27). In these systems, the latex particles or the surfactant micelles serve as reversible cross-link points with a hydrophobic region of a polymer molecule in dynamic association with a latex particle or surfactant micelle (27). 

With respect to the rheological parameters fliey come to the conclusion that surface elasticity effects are superior to surface viscosity effects. This, however, apphes to pure surfactant layers and may be different for pure protein or mixed surfactant/protein adsorption layers. It has been stressed also by Langevin (26), in her review on foams and emulsions, fliat studies on the dynamics of adsorption and dilational rheology studies for mixed systems, in particular surfactant-polymer systems, are desirable in order to understand these most common stabilizing systems. 

It was observed that the formulations consisting of ethoxylated sulfonates and petroleum sulfonates are relatively insensitive to divalent cations. The results show that a minimum in coalescence rate, interfacial tension, surfactant loss, apparent viscosity and a maximum in oil recovery are observed at the optimal salinity of the system. The flattening rate of an oil drop in a surfactant formulation increases strikingly in the presence of alcohol. It appears that the addition of alcohol promotes the mass transfer of surfactant from the aqueous phase to the interface. The addition of alcohol also promotes the coalescence of oil drops, presumably due to a decrease in the interfacial viscosity. Some novel concepts such as surfactant-polymer incompatibility, injection of an oil bank and demulsification to promote oil recovery have been discussed for surfactant flooding processes. 

Whereas in simple aqueous solutions the carbomers and the cross-polymers show a significandy better efficiency, Table 5.2 shows that in surfactant-based systems this no longer holds true. The use levels indicated in the table are the quantities of polymer required to obtain a given apparent Brookfield LV-60 viscosity of about 3000 mPa s, and in all the anionic surfactants the results are more equitable for the different classes of polymer compared with the situation in water. In the case of the nonionic surfactant, the difference is still maintained, however. 

The presence of polymers at the interface between oil and water makes for excellent stabilization of emulsions (1,4). Figure 13 shows the interfacial shear viscosity of the interfacial film between a model oil and NaOH solution or polymer solution at 45°C. The model oil consisted of 20% Daqing crade oil injet fuel. The contents ofNaOH, ORS41, and a biological surfactant in the NaOH solution were 1.2, 0.5, and 0.15%, respectively. The concentration ofpolymer hydrolyzed polyacrylamide (HPAM) in the solution was 150mg/L. It can be seen that the interfacial shear viscosity of the system with the polymer is three times higher than... 

There also exists a need to avoid surfactant aggregate structures such as lamellar liquid crystals which exhibit high viscosity (29-32). System parameters should be such that mixing between the fluids in the surfactant, oil and polymer slugs does not occur. A dispersion of surfactant and oil would form an undesired emulsion, while a dispersion of surfactant and polymer, if incompatible, could lead to phase separation, which would decrease the effectiveness of the process. Other points to take into account are (i) the mass transfer of surfactant to the oil bank can change the interfacial tension, and (ii) surfactant-polymer incompatibility leads to a phase separation, which would reduce the efficiency of the process (30, 31). 

One additional polymer system which will not be detailed in this report is a surfactant-like polymer which in aqueous solution has little viscosity and forms independent micelles ... 

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. 

These different enhanced oil recovery methods become even more involved when the combination of two or more different techniques is used, for example, when CO2 injection is combined with surfactant-polymer flooding. A simple schematic correlation has been found between the EOR method and the depth of the reservoir and oil viscosity (Figure 12.4). Obviously, in such a complex system no simple correlation can be absolutely valid, but it can be a useful guideline. Field operations have provided evidence for a good relation as depicted in Figure 12.4. 

Correlation of photophysical data with rheological data was possible with the surfactant polymerized system. Plots of Ie/Im reduced viscosity as a function of log polymer concentration indicated interpolymer associations. 

Interactions between polymers and surfactants have been widely investigated in the recent decades. The interaction may lead to a polymer-surfactant complex formation, which may have a significant influence on the system properties e.g. emulsification, colloidal stability, viscosity enhancement, gel formation, solubilization, and phase separation [Goddard 1993a Goddard 2002]. The properties and structure of surfactant-polymer complexes depend on the molecular characteristics of both the polymer and surfactant [Lindman Thalberg,... 

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