Adsorption polymer concentration effect

Figure 5.49 shows the polymer concentration effect on the permeability reduction factor, F, predicted from Eq. 5.36. This figure shows that F is a weak function of polymer concentration, and it increases shghtly within a low concentration range. Concentration quickly reaches a plateau. This effect is consistent with the polymer adsorption shown in Figure 5.43. 

Among the various branches in colloid and interface science, polymer adsorption and its effect on the colloid stability is one of the most crucial problems. Polymer molecules are increasingly used as stabilizers in many industrial preparations, where stability is needed at a high dispersed phase volume fraction, at a high electrolyte concentration, as well as under extreme temperature and flow velocity conditions. 

The rheological properties of a fluid interface may be characterized by four parameters surface shear viscosity and elasticity, and surface dilational viscosity and elasticity. When polymer monolayers are present at such interfaces, viscoelastic behavior has been observed (1,2), but theoretical progress has been slow. The adsorption of amphiphilic polymers at the interface in liquid emulsions stabilizes the particles mainly through osmotic pressure developed upon close approach. This has become known as steric stabilization (3,4.5). In this paper, the dynamic behavior of amphiphilic, hydrophobically modified hydroxyethyl celluloses (HM-HEC), was studied. In previous studies HM-HEC s were found to greatly reduce liquid/liquid interfacial tensions even at very low polymer concentrations, and were extremely effective emulsifiers for organic liquids in water (6). 

The principle of depletion is illustrated in Figure 1. If a surface is in contact with a polymer solution of volume fraction , there is a depletion zone near the surface where the segment concentration is lower than in the bulk of the solution due to conformational entropy restrictions that are, for nonadsorbing polymers, not compensated by an adsorption energy. The effective thickness of the depletion layer is A. Below we will give a more precise definition for A. 

Polymer Concentration. The effect of polymer dosage on additional flocculation responses was measured together with adsorption... 

Figure 3. Adsorption. Experimental and theoretical polymer concentration vs. time, solid lines. Theoretical effective surface coverage of singlets, 9, vs. time, dashed line. Initial dose in OFC units beside curves. Molecular weight 1x10, charge density 95%. Shear rate 1800 s 1.

In most cases, polymer adsorption is considered irreversible that is, it does not decrease as polymer concentration decreases (Szabo, 1979 Lakatos et al., 1979 Gramain and Myard, 1981). The irreversible effect is caused by polymer adsorption on rock. However, this is not exactly true because small amounts of polymer can be removed from porous rock using prolonged exposure to water or brine injection. Usually, however, the rate of release is so small that it is not possible to measure the concentrations accurately. It is thus more accurate to state that the rate of polymer retention is much greater than the rate of polymer removal. Retention also may occur when flow rates are suddenly increased. This process is called hydrodynamic retention, which is reversible (Green and Willhite, 1998). 

As we know, adding alkali in a polymer solution will reduce the polymer solution s viscosity. We may take advantage of this fact in low-injectivity wells. Initially, the polymer solution with alkali has a low viscosity. As the alkah is consumed by reacting with formation water and rocks, the polymer solution s viscosity will become higher than the initial value. Thus, initially the injectivity and later the sweep efficiency will be improved. Note that the polymer concentration will also be reduced by adsorption. The final effect is determined by the balance between the two effects of the reduced alkaline and polymer concentrations. 

Addition of a surfactant can further enhance the flocculation at the ultralow polymer dosage regime. As shown in Figure 7.37, the addition of anionic surfactant (SDS) significantly improves the flocculation at very low polymer concentrations. At higher polymer levels, the surfactant addition has no effect on flocculation. This is probably due to a significant fraction of adsorption sites already occupied by polymer, making them unavailable for adsorption of the surfactant molecules. 

For all cellulose derivatives tested, a reduction of the zeta potential of the suspensions with increased polymer concentration is observed (Table 20). The effect of the molecular mass differs depending on the derivative concerned. For HEC and HPC, the amount adsorbed and the area per molecule decreased as the molecular mass increased, indicating a flatter adsorption conformation. For HPMC, the adsorption increased as the macromolecular chains became longer. Adsorption was maximum for the more hydrophobic HPC. 

Macromolecular colloid solutions also play an important role in ensuring the stability of disperse systems (e.g. suspensions, emulsions). In the case of emulsions the polymer decreases the rate of separation by increasing viscosity on the one hand, and it has an enthalpy stabilizing effect by adsorption on the surface of the droplets on the other hand [3, 4, 7]. Depending on the concentration of the polymer, a protecting and flocculating effect can be observed during the interaction between suspensions and polymers. If the polymer concentration is low, the polymer adsorbed on the surface of the particles connects the particles into loose floccules. Thereby, the rate of... 

The formation of floes due to bridging flocculation has a dramatic effect on sedimentation rates, sediment volumes and on the ease of filtration. Effective flocculation may occur over a narrow range of polymer concentration because too little polymer will not permit floe formation, while too much polymer adsorption will eliminate the fraction of free particle surface needed for the bridging action (i.e. the polymer molecules will adsorb onto single particles in preference to bridging several particles). It has been proposed that the optimum degree of bridging flocculation may occur when particle surfaces are half covered with adsorbed polymer. 

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