Electrical conductivity of ion exchange membranes

Donnan adsorbed ions. For a 1 1 electrolyte the specific conductivity of the cation exchange membrane, ic (cm), is expressed as15 

However, because the flux is obtained from Eq. (2.3), the electric current (Eq. 2.10) is obtained using electro-neutralization (Eq. 2.9) as follows 

The specific conductivity of the ion exchange membrane is an important property that is usually expressed using the electrical resistance of the membrane (product of the reciprocal of the specific conductivity and the thickness of the membrane, Q cm). 

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Important Quantities Connected with Electro Dialysis 3.5.1. Electrical Conductivity of Ion-Exchange Membranes The specific electrical conductivity of an ion selective membrane is given by ... 

The electric conductivity of ion-exchange membranes increases as temperature rises. This change may be characterized with an equation similar to the Arrhenius equation for viscosity. 

R. Arnold, Structure of ion-exchange membranes from acid absorption data, Aust. J. Chem., 1968, 21, 521-525 R. Arnold and D.F.A. Koch, Electrical conductivity of cation-exchange membranes in the hydrogen ion form, Aust. J. Chem., 1966, 19, 1299-1313 R. Wodzki, A. Nar bska and J. Ceynowa, Nonuniform distribution of the ionogenic groups in permselective membranes, Angew. Makromol. Chem., 1979, 78, 145-155. 

By the time the next overview of electrical properties of polymers was published (Blythe 1979), besides a detailed treatment of dielectric properties it included a chapter on conduction, both ionic and electronic. To take ionic conduction first, ion-exchange membranes as separation tools for electrolytes go back a long way historically, to the beginning of the twentieth century a polymeric membrane semipermeable to ions was first used in 1950 for the desalination of water (Jusa and McRae 1950). This kind of membrane is surveyed in detail by Strathmann (1994). Much more recently, highly developed polymeric membranes began to be used as electrolytes for experimental rechargeable batteries and, with particular success, for fuel cells. This important use is further discussed in Chapter 11. 

Figure 3 shows the relation between electric conductivity and ion exchange capacity of membranes produced from the PVEX monomers with m = 0 and 1 which are indicated by formula (2). 

T. Sata, Properties of ion-exchange membranes combined anisotropically with conducting polymers. 2. Relation of electrical potential generation to preparation conditions of composite membranes, Chem. Mater. 1991, 3, 838-843. 

We wish only to remind readers that there are three main methods of electrochemical re-vealment conductivity, direct current (d.c.) amperometry, and integrated amperometry (pulsed amperometry is a form of integrated amperometry). In revealment by conductivity, the analytes, in ionic form, move under the effect of an electric field created inside the cell. The conductivity of the solution is proportional to the mobility of the ions in solution. Since the mobile phase is itself an electrolytical solution, in order to increase the signal/noise ratio and the response of the detector, it is very useful to have access to an ion suppressor before the revealment cell. By means of ionic exchange membranes, the suppressor replaces the counterions respectively with H+ or OH , allowing only an aqueous solution of the analytes under analysis to flow into the detector. 

A boundary layer with a gradient in caustic soda concentration also forms at the surface of the membrane facing the catholyte based on a similar principle, resulting in a caustic soda concentration on the membrane surface which is higher than that in the bulk phase. Since this tends to reduce the current efficiency and electric conductivity of the membrane, it is necessary to minimize the boundary layer thickness or reduce the caustic soda concentration in the bulk phase. It is also essential to purify the brine with ion-exchange resin of high selectivity, in order to prevent precipitation of metal ions as hydroxides in the membrane and the boundary layer (74). 

The structure and properties of perfluorocarbon cation exchange membranes have been actively studied using various analytical methods SAXS, SANS, NMR, ESR, electrical conductance and IR and Mossbauer spectroscopy.109 The phase separation of perfluorocarbon ion exchange membranes by transmission electron microscopy has also been shown in detail.110... 

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