Adsorption density soluble polymers

Consider the complexity involved in modeling steric stabilization with a diblock copolymer. The reservoir bulk solution of copolymer is usually dilute (<1 wt % polymer) and the copolymer and solvent equilibrate between the bulk and surface regions. However, as solvent quality is decreased to the LCST phase boundary, the bulk solution will also separate into polymer-rich and polymer-lean phases. In addition, many diblock copolymers form self-assembled aggregates such as micelles and lamellae, if the concentration is above the critical micelle concentration. Thus, stabilizer can partition among up to four phases as solvent quality or polymer concentration is changed. The unique density dependence of supercritical fluids adds another dimension to the complex phase behavior possible. In the theoretical studies discussed below, surfactant adsorption energy, solubility, and concentration are chosen carefully to avoid micelle formation or bulk phase separation, in order to focus primarily on adsorption and colloid stability. 

Another interesting system is based on the adsorption of so-called complex coacervate core micelles (also called polyion complex micelles) [28,29]. These micelles are formed in aqueous solution when two oppositely charged polyelectrolytes are mixed, with at least one of these polyelectrolytes being connected to an uncharged and water-soluble polymer. The complexed polyelectrolytes then form the complex coacervate core of the micelles, while the neutral chain forms the corona. These micelles have been shown to adsorb to surfaces with very different properties, such as silica and polystyrene. Although formed brushes are of low density, good antifouling properties have been observed [28,30]. 

For PAA and PVS, the principle factor influencing adsorption under these conditions is the degree of ionization of the polymers. Figure 2 shows the percent ionization of PAA (pKa = 4.5) and PVS (pKa <2) across a wide range of pH. As shown in the figure, PAA is only 24% ionized at pH = 4, while PVS is essentially 1(X)% ionized. Therefore, the charge density on PVS is much greater than that on PAA at pH = 4. This difference has several ramifications in terms of electrostatic interactions and polyelectrolyte solubility. 

Oil displacement experiments were performed under different salinity conditions (1) constant salinity of pol3nner solution at 1.5% NaCl (i.e. optimal salinity of the soluble oil formulation), and variable connate water salinity (2) constant salinity of connate water at 1.5% NaCl and variable salinity of pol3mier solution and (3) the salinity of polymer solution equals the salinity of connate water, both varied simultaneously. Sand packs were chosen as the model porous media in order to avoid the effects of porous media heterogeneity, clays and surfactant adsorption loss. The compositions of aqueous formulation and soluble oils are specified in Figures 1 and 2. The difference between their compositions reflects the density difference between water and dodecane whereas the surfactant and alcohol concentrations (w/v) are the same in both types of formulations. The polymer solution used was 1000 ppm PUSHER-700 in brine. For polymer solution in distilled water, the polymer concentration was reduced to 250 ppm to avoid excessive viscosity. Several experiments were repeated and the reproducibility was established to be within 2% in tertiary oil recovery. 

Fig. 13 Left Density profiles of carlxMi dioxide and hexadeeane across the two interfaces in a box of linear dimension L = 98.88(Tpp. Densities are quoted in LI units (p = pffpp). The dotted ellipses highlight the interfacial adsorption of CO2 at the polymer-C02 vapor interface. Right The snapshots show Lx Lx. 5a slices where the positions of the CO2 molecules (lower image) and the polymer (upper image) are shown separately. Note that a few hexadeeane molecules are dissolved in the vapor phase as well (this finite solubility in the gas decreases rapidly with increasing polymer chain length)...

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