Doping secondary

Occasionally, the term secondary dopant is used more loosely for a second redox treatment of a polymer chain that has already been subjected to a redox agent. Generally, the term is used, however, in the way as defined by MacDiarmid and Epstein and will therefore only be used in this more specific sense in this book. Also, the term conductivity enhancement agent is widely used as an alternative for the term secondary doping. 

In the case of polyaniline doped with d,Z-camphorsulfonate the secondary dopant m-cresol leads to conductivities as high as 400 S/cm. - This is due to a strong increase in crystallinity of the prepared films. Already in the dispersion an increase in viscosity was observed hinting at an increase in the hydrodynamic volume of the polymer chain. X-ray diffraction spectra of films clearly show the formation of crystals upon the addition of the secondary dopant. 

In the case of FEDOTrFSS, a range of different explanations can be found in the literature. The aim of the following section is first a summary of the observations found by various analytical techniques and followed by their discussion and interpretation resulting in a consistent model for the doping effect. 

Additives and Their Effect on the Conductivity of PEDOTPSS Pilms 

Substance Example Conductivity-Enhancement Factor (Maximum of Different Values) Reference 

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The bulk conductivity a depends on the concentration of charge carriers and on their mobility, either of which can be modulated by exposure to the gas. The first prerequisite of such an interaction is the penetration of the analyte to the interior of the layer. The second is the ability of the gas to form a charge-transfer complex with the selective layer. This process then constitutes secondary doping, which affects the overall conductivity. For a mixed semiconductor, the overall conductivity is determined by the combined contribution from the holes (p) and electrons (n), as given by the general conductivity equation. 

To enhance the response of the polypyrrole sensor towards DMMP, acid dopants were added to the polypyrrole structure. The rational for doping polypyrrole was to introduce secondary doping sites for DMMP in the structure. Secondary doping... 

Analyte Induced Secondary Doping, Counter Doping, and Carrier Trapping. 100... 

The nitrogen-containing conductive polymers, polypolypyrrole (PPY) and polyaniline (PAN) in particular, have been of great interest because of their controllable electrical conductivity, environmental stability and interesting redox properties associated with the chain heteroatoms, More importantly, the century-old [57,58] aniline family of polymers has been found to exhibit solution [59,60] and counter-ion induced [61-63] processability. Furthermore, the electrical properties of the aniline polymers can be substantially improved through secondary doping [64]. The aniline polymers have the general formula [(-B-NH—B—NH—), (-B—N=Q=N-)i.,.]v, in which B and Q denote the... 

EB-CSA powder could then be dissolved in appropriate solvent mixtures. For the data reviewed here, these powders were dissolved in m-cresol, chloroform, or mixtures of these solvents. The resulting properties were shown to vary dramatically depending on which solvent was used through the effects of secondary doping [76,83,137]. The alternative way to obtain solutions of doped PAN-CSA is to separately add the EB powder and the HCSA into a volume of solvent and then mix the two solutions. 

Conductivity is undoubtedly the most closely investigated physical parameter of EPs. It is heavily dependent on the level of the primary doping, i.e. on the concentration of the counterion. Addition of another type of electroactive molecule to the polymer can be viewed as a secondary doping and, as expected, it also affects the conductivity of the EP, albeit usually less than the primary doping. Nevertheless, this incremental change of conductivity is the basis for operation of conductimetric chemical sensors, better known as chemiresistors. 

A new wave of interest in PANI occurred in the mid-1990s when MacDiarmid and Epstein identified a process termed secondary doping in... 

A number of reviews exist describing the synthesis of PANI in many of its different oxidation states, as well as the direct synthesis of its doped ES form, and the various advantages and disadvantages of differing procedures. This chapter will focus on the experimental aspects of the polymerization of various forms of PANI and its derivatives, and will detail secondary doping techniques for enhancing the properties of PANI postsynthesis. 

Example 15 Secondary Doping of Camphorsulfonic Acid-Doped PANI with fft-Cresol... 

Example 16 Secondary Doping of PANI-PAAMPSA with Dichloroacetic Acid... 

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