Doping compensating counterions

These copolymers are described as self-doped because the charge-compensating counterion is covalently bonded to the main chain of the polymer. Because ion mobility is restricted to the cationic species, the polymer can be visualized as an ion-specific membrane. 

As repeatedly stressed, the doping processes imply the diffusion of electrolyte counterions to compensate for the electric charge assumed by the polymeric chain and thus polymers are expected to experience changes of mass upon doping. Consequently, by monitoring these changes it is possible to control the nature and the extent of the doping processes. 

Using chemical or protonic doping, the electric charges on the polymer chains are compensated by counterion injection. In the case of protonic doping (essentially in polyaniline), the addition of protons does not change the overall number of electrons in the chain skeleton. But one of the two electrons of the nitrogen doublet become caught in the N—H bond, and then the effective number of electrons available for the tt system is modified. 

Employing a polyelectrolyte to bind to and preferentially align the aniline monomers before polymerization (e.g., by S2082-) has shown promise in facilitating the desired head-to-tail coupling of the aniline substrates. During polymerization, the anionic polyelectrolytes such as poly(styrenesulfonate) and poly(acrylate)86-88 also provide the required counterions for charge compensation in the doped PAn products. This can lead to water-soluble or water-dispersed ES products. 

Elemental analysis and X-ray fluorescence measurements of films electrochemically oxidized in aqueous KCIO4 solutions, at pH values below the pK of the carboxylic acid indicate the absence of perchlorate counterions in the films [25]. This shows that the oxidized polymer backbone is charge compensated by covalently bound carboxylate anions and confirms the self-doping mechanism of poly( -(3-thienyl)octanoic acid). In contrast to films oxidized in aqueous solutions,... 

A dispersion of compensated (neutral) PAni in DMSO (0.5 PAni) can be filtered through the 20 nm sieve (pressure filter) without discoloration. Using membranes of different sizes, the membrane with 5 nm pores does not allow the dispersion to pass colored, whereas the 10 nm pore membrane does. This indicates that this is also a dispersion, with a particle size between 5 and 10 nm. PAni-HCl is dissolved, when filtered through 5 nm pores, and stays completely colored through a 20 nm filter. Using 10 nm, partial decoloration occurs, which shows that "doped PAni occurs in somewhat bigger particles around 10 nm. These could be primary particles, which are bigger than the neutral particles because of the counterions. For many dispersions of various other ICPs prepared by our method, we found a particle size between 20 and 100 nm. 

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