Polyelectrolytes, linear conductance

Linear arrays of protonatable or hydrogen bonded sites may allow the directed long range transfer of protons, thus functioning as proton-conducting channel, i.e., as proton wire. Relevant systems would be linear polyamines or polyphenolic condensed aromatic units [8.218], self-assembled hydrogen bonded heterocyclic ribbons such as 116 (see Section 9.4.4) or polyelectrolyte membranes [8.219] in which collective proton motion may take place and lead to proton conductivity. 

Plotting A vs. the ratio of the polyelectrolyte to the salt concentration, cp/cs, the largest change of the slope is located in the cp/cs region between 1 and 3. An example is given in Fig. 20 for the lowest molar mass and holds for all ionic strengths and molar masses that have been investigated. This implies that a linear increase of the equivalent conductivity below the overlap concentration will only be found if the polyelectrolyte concentration exceeds the concentration of monovalent low molecular electrolyte by a factor of two to three. 

In summary, the light-scattering investigations support the results obtained by conductivity measurements that the effective charge density of cylindrical polyelectrolyte brushes is much smaller than for linear flexible polyions. 

Among the early examples of the successful use of electric fields to probe ionic structures and electrical and optical anisotropies are the linear polyelectrolytes. Basic information about macromolecular dimensions, size, and shape have been derived from the relaxation of field-induced changes in optical properties and in electrical parameters of the electrically and optically anisotropic systems. The analysis of electric conductivity measurements has demonstrated that linear polyelectrolytes are electrically anisotropic. It was established that the extremely large dipole moments, which the electric field produces by displacement of the counterion atmosphere parallel to the long axis of the polyions, are responsible for their orientations in the direction of the external field. 

It is well established that the second Wien effect is particularly large in linear polyelectrolytes/ Compared to simple electrolytes the linear range of the conductivity increase with increasing electric fields starts already at relatively low field strengths (5-10 kV cm" ). Because of the rather extended linear region Onsager s equation for the dissociation field effect has been used as the basis for a qualitative discussion of the second Wien effect in polyelectrolytes. 

The analysis of electric conductivity relaxations of the linear polyelectrolyte poly(riboadenylate, K" ") according to Eq. (2.22) at 293 K yields a formal effective charge of about —6 for the interaction of a ion with the inner counterion atmosphere of this polyanion. ... 

It is, however, remarked that in electrically anisotropic systems like the linear polyelectrolytes the measured conductivity relaxation may not be determined by the rate of the chemical reaction (x = but may rather be rate controlled by orientational processes, i.e., t =... 

In addition to measuring solid samples by the methods just described, the orientation of dyes in suspension has been investigated using electric dichroism (199-205). Electric linear dichroism (ELD) measures the change in the absorption of incident light linearly polarized parallel and perpendicular to the applied electric field direction, as schematically shown in Figure 19. This technique has been applied extensively for dye-polyelectrolyte solutions. For cationic dye-clay systems, the roll and tilt angles of dyes at the surface of clays have been derived by detailed analysis of the ELD. It should be noted that electric dichroism can be performed only in solution of low ionic conductivity. IntCTcalation compounds... 

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