Electrolytes Polyelectrolytes

Figure 3.1a shows a membrane that is permeable to water and K+ and Cl - ions but impermeable to colloidal electrolytes (polyelectrolytes such as charged proteins). Let a denote the interior of the cell and (3 the extracellular region. In the absence of the poly electrolyte, water, K + and Cl" partition themselves into the two sides such that the chemical potentials of each species are the same inside as well as outside, as thermodynamics would demand. Moreover, the requirement of electroneutrality in both ot and (3 demands that the concentrations of each species K + and CP be the same on either side of the partition. 

This chapter shows that a unified explanation can be given of the adsorption from dilute aqueous solutions of different organic solutes, from nonelectrolytes to electrolytes, polyelectrolytes, and bacteria. Thus, the adsorption process is a complex interplay between electrostatic and nonelectrostatic interactions. Electrostatic interactions depend on the solution pH and ionic strength. The former controls the charge on the carbon surface and on the adsorptive... 

Catalysis by High Molecular Weight Electrolytes (Polyelectrolytes)... 

Description of electrolyte transport using the MSA for simple electrolytes, polyelectrolytes and micelles... 

The formation and growth of polyelectrolyte multilayers is the result of an intricate balance of interactions [103], among their components polyelectrolyte— poly-electrolyte, polyelectrolyte—solvent, polyelectrolyte—surface, etc. The different interactions involved are governed by the complex interplay between electrostatic and entropic contributions, as well as solvent quality. 

The thermodynamic properties of aqueous electrolyte-polyelectrolyte mixtures are quite unusual, and therefore, a subject of interest because apparently they can be described empirically as a superposition of the individual properties of the pure components [2-6]. For example, the osmotic pressure, exerted by a mixture is equal to the sum of the osmotic pressure of the salt-free polyelectrolyte solution, Up, and of the polyelectrolyte-free salt solution, tt, each at the same concentration as when it was present in the mixture ... 

Thus, far few experimental tests have been conducted on the scope and limitations of the Additivity Rule. The approximate character of relation (B) for counter-ion activities has been demonstrated by Lyons and Kotin [9]. Departures from (B), defined Ja+ =a+ —a+ — +, were greatest when the contributions from each component in the electrolyte-polyelectrolyte mixture were equal, and Aa+ approached zero when either component was present in excess. The deviation also was significant for large concentrations, but decreased and vanished with increasing dilution. Alexandrowicz [6] has performed an extensive series of measurements of the osmotic pressure of electrolyte-polyelectrolyte mixtures in an attempt to establish the general validity of strict additivity as expressed in (A). An analysis of his data shows, however, that when the electrolyte and polyelectrolyte are present in approximately equal amounts and the osmolality of the mixture exceeded 0.5, the difference from additivity was as much as ten percent. Additivity was obeyed, however, whenever salt or polyelectrolyte was present in large excess. 

In Equations (6) and F c are the activity coefficients of the salt or of the polyelectrolyte, respectively, in their own pure solutions (i.e., two-component) at molalities Mb and Me in isopiestic equilibrium with the mixed electrolyte-polyelectrolyte (i.e., three-component) solutions. The required values of Fg are tabulated [12] but those for F c must be estimated from the measurements on the pure polyelectrolyte solution as will be shown below. The quantities Rb and Rc are isopiestic ratios defined by ... 

The dependence of A (p for the electrolyte-polyelectrolyte mixtures on yc is of the same type as with electrolyte mixtures, namely, A(l)=yBycPo- value of Pq for the NaCl+NaPSS mixture, for example, was 0.0409 at m= 1.0 compared with 0.0042 for a NaCl-NaBr mixture at m = 2.9. The excess free energy of mixing, AG, may be estimated with Equation (14) if it is assumed that Pq is a linear function of the concentration ... 

Interaction coefficients for aqueous electrolyte-polyelectrolyte mixtures at 25°... 

These results show more clearly than Fq. (8.126)-of which they are special cases-the effect of charge and indifferent electrolyte concentration on the osmotic pressure of the solution. In terms of the determination of molecular weight of a polyelectrolyte by osmometry. ... 

Polyelectrolyte complex membranes are phase-inversion membranes where polymeric anions and cations react during the gelation. The reaction is suppressed before gelation by incorporating low molecular weight electrolytes or counterions in the solvent system. Both neutral and charged membranes are formed in this manner (14,15). These membranes have not been exploited commercially because of then lack of resistance to chemicals. 

Monovalent cations are good deflocculants for clay—water sHps and produce deflocculation by a cation exchange process, eg, Na" for Ca ". Low molecular weight polymer electrolytes and polyelectrolytes such as ammonium salts (see Ammonium compounds) are also good deflocculants for polar Hquids. Acids and bases can be used to control pH, surface charge, and the interparticle forces in most oxide ceramic—water suspensions. 

Significant variations in the properties of polypyrrole [30604-81-0] ate controlled by the electrolyte used in the polymerization. Monoanionic, multianionic, and polyelectrolyte dopants have been studied extensively (61—67). Properties can also be controlled by polymerization of substituted pyrrole monomers, with substitution being at either the 3 position (5) (68—71) or on the nitrogen (6) (72—75). An interesting approach has been to substitute the monomer with a group terminated by an ion, which can then act as the dopant in the oxidized form of the polymer forming a so-called self-doped system such as the one shown in (7) (76—80). 

Usually the acid-base properties of poly electrolyte are studied by potentiometric titrations. However it is well known, that understanding of polyelectrolyte properties in solution is based on the knowledge of the thermodynamic properties. Up to now, there is only a small number of microcalorimetry titrations of polyelectrolyte solutions published. Therefore we carried out potentiometric and microcalorimetric titrations of hydrochloric form of the linear and branched polyamines at 25°C and 65°C, to study the influence of the stmcture on the acid-base properties. 

A membrane ionomer, in particular a polyelectrolyte with an inert backbone such as Nation . They require a plasticizer (typically water) to achieve good conductivity levels and are associated primarily, in their protonconducting form, with solid polymer-electrolyte fuel cells. 

The polyelectrolyte catalysis of chemical reactions involving ionic species has been the subject of extensive investigations since the pioneering studies of Morawetz et al. [12] and Ise et al. [13-17]. The catalytic effect or the ability of poly-electrolytes to enhance or retard reaction rates is mainly due to concentration or exclusion of either or both of the ionic reactants by the polyions added to the reaction systems. For example, the chemical reaction between ionic species carrying the same charge is enhanced in the presence of polyions carrying the opposite charge. This enhancement can be attributed to an increase in the local concentration... 

Chemically active plastics such as the polyelectrolytes have been used to make artificial muscle materials. This is an unusual type of mechanical power device that creates motion by the lengthening and shortening of fibers made from a chemically active plastic by changing the composition of the surrounding liquid medium, either directly or by the use of electrolytic chemical action. Obviously this form of mechanical power generation is no competitor to thermal energy sources, but it is potentially valuable in detector equipment that would be sensitive to the changing... 

For poly electrolyte solutions with added salt, prior experimental studies found that the intrinsic viscosity decreases with increasing salt concentration. This can be explained by the tertiary electroviscous effect. As more salts are added, the intrachain electrostatic repulsion is weakened by the stronger screening effect of small ions. As a result, the polyelectrolytes are more compact and flexible, leading to a smaller resistance to fluid flow and thus a lower viscosity. For a wormlike-chain model by incorporating the tertiary effect on the chain... 

Surface force profiles between these polyelectrolyte brush layers have consisted of a long-range electrostatic repulsion and a short-range steric repulsion, as described earlier. Short-range steric repulsion has been analyzed quantitatively to provide the compressibility modulus per unit area (T) of the poly electrolyte brushes as a function of chain density (F) (Fig. 12a). The modulus F decreases linearly with a decrease in the chain density F, and suddenly increases beyond the critical density. The maximum value lies at F = 0.13 chain/nm. When we have decreased the chain density further, the modulus again linearly decreased relative to the chain density, which is natural for chains in the same state. The linear dependence of Y on F in both the low- and the high-density regions indicates that the jump in the compressibility modulus should be correlated with a kind of transition between the two different states. 

The density-dependent jump in the properties of poly electrolyte brushes has also been fonnd in the transfer ratio and the snrface potential of the brnshes [38], establishing the existence of the density (interchain distancej-dependent transition of polyelectrolytes in solntions. 

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