Fixed ionic charges

Membranes Ion-exchange membranes are highly swollen gels containing polymers with a fixed ionic charge. In the interstices of the polymer are mobile counterions. A schematic diagram of a cation-exchange membrane is depicted in Fig. 22-57. 

Ionic compounds are named using the same guidelines used for naming binary molecules, except that the cation name aiways precedes the anion name. Thus, NH4 NO3 is ammonium nitrate, Na2 CO3 is sodium carbonate, and Ca3 (P04)2 is caicium phosphate. The subscripts are not specified in these names because the fixed ionic charges determine the cation-anion ratios unambiguously. Example 3-6 reinforces these guidelines by showing how to construct chemicai formulas from chemical names. 

In the last few years, MS has been used to detect cationic surfactants because the fixed ionic charge of these molecules makes them suitable for the analysis by atmospheric pressure ionisation (API) MS. Radke... 

The host structure must carry a fixed ionic charge, termed the fixed ion. 

The plasma frequency corresponds to an oscillation as a whole of the electronic charge density with respect to the fixed ionic charge. By analogy with the phonon excitation, the corresponding excitation is called plasmon and it can be considered as the quantization of classical plasma oscillation. The plasmon oscillation is longitudinal with respect to its propagation and is comparable to the TO phonon mode. The macroscopic electric field associated... 

Polymers with fixed ionic charges may be used for ion exchange. When formed into membranes, these materials essentially prevent the passage of ions of the same charge as those fixed to the polymer... 

Based on the cluster-network model, the dependence of current efficiency on the polymer structure was first developed by Gierke [34]. This postulates that clusters with diameters of 4 nm are distributed throughout the matrix and connected to each other by short narrow channels 1 nm in diameter—the cluster separation distance being 5 nm. It should be noted that this structure was developed based on experimental evidence [23]. High caustic current efficiency, according to this model, is a result of the repulsive electrostatic interaction between the OH ions and the fixed ionic charges on the surface... 

The governing criterion for equilibrium distribution of a solute between an ion exchange resin and an external solution is relation (3.3.8) when the solute is a weak electrolyte or a nonelectrolyte. The namre of the equilibrium is similar to that with nonionic adsorbents. When the solute is a strong electrolyte, criterion (3.3.29) has to be used due to the presence of fixed ionic charges and counterions in the resin. 

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