Polyelectrolyte solutions phase separation

Dormidontova EE, Erukhimovich IY, Khokhlov AR. Microphase separation in poor-solvent polyelectrolyte solutions phase diagram. Makromol Theory Simul 1994 3 661-675. 

We have recently initiated studies concerned with interactions between surfaces across solution containing both polyelectrolytes and oppositely charged surfactants. These studies are complicated by the fact that the solution phase separates into a polymer and surfactant rich phase and a phase depleted of these components. This renders the... 

An example of the use of conductance to estimate the complex stoichiometry is illustrated in Fig. 4.27 for poly(vinyl amine)/poly(acrylic acid) (PVAm/PAA). The minimum in conductance depends on the formation of the complex. In the forward curve, PAA was added at predetermined increments to a PVAm solution, followed by 60 s stirring and conductance measurements. The reverse curve involved PVAm addition to a PAA solution. The minimum in conductance depends on the path chosen to prepare the complexes, indicating that tmcom-plexed polymer maybe trapped during the polyelectrolyte complex phase separation process. As the minimum points are on both sides of the equimolar position, this complex appears to be equimolar. 

Overbeek, J.T.G., Voorn, M.J. (1957). Phase separation in polyelectrolyte solutions the theory of complex coacervation. Journal of Cellular and Comparative Physiology, 49,... 

In the case of a neutral gel, the values a and Q change smoothly as Qo increases, while in the case of a polyelectrolyte network the jumpwise collapse takes place. Note that the composition of the mixture in the swollen network practically coincides with Q0, whereas a significant difference between solvent compositions in the collapsed network and solution exists. The enrichment of the sample by good solvent can be very considerable. An analysis shows that this redistribution increases with the growth of interaction parameter Xab °f solvent components. The reason for this is the following with an increase of Xab. the tendency to phase separation becomes stronger and preferential solvation of... 

The theories of polymer solutions upon which steric-stability theories are based are usually formulated in terms of a portmanteau interaction parameter (for example Flory s X Parameter and the excluded volume integral) which does not preclude electrostatic interactions, particularly under conditions where these are short range. It is thus appropriate to consider whether polyelect-roly te-stabilisation can be understood in the same broad terms as stabilisation by non-ionic polymers. It was this together with the fact that polyelectrolyte solutions containing simple salts show phase-separation behaviour reminiscent of that of non-ionic... 

Nanostructures primarily result from polyelectrolyte or interpolyelectrolyte complexes (PEC). The PEC (also referred to as symplex [23]) is formed by the electrostatic interaction of oppositely charged polyelectrolytes (PE) in solution. The formation of PEC is governed by physical and chemical characteristics of the precursors, the environment where they react, and the technique used to introduce the reactants. Thus, the strength and location of ionic sites, polymer chain rigidity and precursor geometries, pH, temperature, solvent type, ionic strength, mixing intensity and other controllable factors will affect the PEC product. Three different types of PEC have been prepared in water [40] (1) soluble PEC (2) colloidal PEC systems, and (3) two-phase systems of supernatant liquid and phase-separated PEC. These three systems are respectively characterized as ... 

Perrau, M. B. Iliopoulos, I. Audebert, R., "Phase Separation of Polyelectrolyte/Nonionic Polymer Systems in Aqueous Solution Effects of Salt and Charge Density," Polymer, 30, 2112 (1989). 

Deposition of polyelectrolytes Lajimi et al. [56] explored the surface modification of nanofiltration cellulose acetate (CA) membranes by alternating layer-by-layer deposition of acidic chitosan (CHI) and sodium alginate (AEG) as the cationic and anionic polyelectrolyte, respectively. The supporting CA membranes were obtained by a phase separation process from acetone/formamide. The permeation rate of salted solutions was found to be higher than that of pure water. The rejection of monovalent salt was decreased, while that of divalent salt remained constant so that the retention ratio increased. Increasing the concentration of feed solutions enhanced this selectivity effect. 

Mixtures of oppositely charged polyelectrolytes dissolved in water can interact to form a variety of precipitates, gels, or phase-separated solutions. What is formed depends on the mixing conditions and the density of ionic charges carried by the polymer chains. Polyelectrolytes with high charge densities usually interact to form precipitates. As the charge density decreases, liquid-liquid phase separation, called complex coacervation, occurs. 

Complex coacervation is a phenomenon by which an aqueous solution of oppositely charged polyelectrolytes separates into two distinct phases. The more dense phase is called the complex coacervate or coacervate. It is a relatively concentrated polyelectrolyte solution. The second phase, a relatively dilute polyelectrolyte solution, is called the equiibrium liquid. The difference in concentration of the coacervate and equilibrium liquid phases is determined by the intensity of the coacervation interaction. The more intense this interaction is, the greater the concentration difference. ... 

Though the phase boundary is not necessarily observable, the remarkable salt concentration (Cs/mol/dm3) dependence of the ion binding equilibria in polyion systems implies the phase separation nature of the polyelectrolyte solutions. A straightforward proof for this property can be gained by the careful examination of the acid dissociation equilibria of weak acidic polyelectrolytes, (HA) , and the conjugate acids of weak basic polyelectrolytes, (BH+) , respectively, expressed as the repeated functionalities of HA and BH+ ... 

In the preceding section, the remarkable salt concentration effect on the acid dissociation equilibria of weak polyelectrolytes has been interpreted in a unified manner. In this treatment, the p/( ,pp values determined experimentally are believed to reflect directly the electrostatic and/or hydrophobic nature of polyelectrolyte solutions at a particular condition. It has been proposed that the nonideality term (Ap/Q corresponds to the activity ratio of H+ between the poly electrolyte phase and the bulk solution phase, and that the ion distribution equilibria between the two phases follow Donnan s law. In this section, the Gibbs-Donnan approach is extended to the equilibrium analysis of metal complexation of both weak acidic and weak basic polyelectrolytes, i.e., the ratio of the free metal ion activity or concentration in the vicinity of polyion molecules to that of bulk solution phase is expressed by the ApAT term. In Section III.A, a generalized analytical treatment of the equilibria based on the phase separation model is presented, which gives information on the intrinsic complexation equilibria at a molecular level. In Secs. B and C, which follow, two representative examples of the equilibrium analyses with weak acidic (PAA) and weak basic (PVIm) functionalities have been presented separately, in order to validate the present approach. The effect of polymer conformation on the apparent complexation equilibria has been described in Sec. III.D by exemplifying PMA. 

By the systematic work on the complexation equilibrium analyses of both weak acidic and weak basic polyelectrolytes, the Gibbs-Donnan approach is validated to provide deep insights into the complexation behaviors of linear polymer ligands. This concept does not need any adjustable parameter it only uses the logic of phase separation of polyelectrolyte aqueous solutions. The electrostatic nonideality (polyelectrolytic effect) observed in the acid dissociation equilibria of a polyion can directly be used to correct for the electrostatic nonideality for metal complexation. The potentiometric titration technique with concurrent measurements of pH and pM is most suit-... 

In solutions of normally encountered randomly coiled macromolecules the formation of spontaneously birefringent phases is not expected. (Phase separation does occur when the interaction between solute molecules is strong.) Here, we have investigated solutions of the polyelectrolyte sodium carboxymethylcellulose in water, which are rubberlike at high concentrations 12). (Materials that form such solutions are commonly called gums.)... 

Bilayer films of poly(ethyleneimme) (positively charged) and poly(ethylene-co-maleic acid) have been used for chemical sensing [49]. The technique of surface plasmon resonance was used to monitor, in-situ, the deposition of these films. Subsequent exposure to aqueous solutions of metal acetate (metal = copper, nickel) resulted in a shift in position of the SPR curve. Phase-separated polyelectrolyte multilayer films that undergo a reversible pH-induced swelling transition have also been exploited for erasable nanoporous antireflection coatings, opening up applications for biore-sponsive materials and membrane applications [50]. 

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