Solution processability, polyaniline

P.C. Ramamurthy, W.R. Harrell, R.V. Gregory, and A.M. Rao, Integration and distribution of carbon nanotubes in solution-processed polyaniline/carbon nanotube composites, J. Electrochem. Soc., 154, H495-H498 (2007). 

S. Cho, K.-H. Shin, J. Jang, Enhanced Electrochemical Performance of Highly Porous Supercapacitor Electrodes Based on Solution Processed Polyaniline Thin Films. ACS Appl. Mater. Interfaces 2013,5,9186-9193. 

Two nitrogen-containing electroactive polymers, polypyrrole (PPY) [21] and polyaniline (PAN) [22], have been of particular interest because of their environmental stability, high electrical conductivity and interesting redox properties associated with the chain heteroatoms. More importantly, PAN has been found to exhibit solution processability [23, 24] and partial crystallinity [25,26]. 

Polyaniline (137) is one of the most promising conductive polymers and the conductivity could be reversibly controlled by oxidation or protonic doping mechanisms228,229. In addition, polyaniline displays good environmental and thermal stability, and its undoped form is solution processable from both organic and aqueous acid solutions. The polymerization of aniline is usually carried out by a chemical or electrochemical oxidation reaction230,231. However, photochemical methods toward the preparation of poly aniline have recently been reported232-240. 

Very few CPs are produced in bulk quantities. Polyphenylene sulfide, a member of the third generation of polymers, was produced in bulk quantities many years before CPs were established and its dopability was elucidated. Polyethylenedioxythiophene is commercially available as a water-based colloidal dispersion (Baytron P water dispersion), and presumably as dispersible powders. The powders with a conductivity of 5-10 S/cm can be dispersed in thermoplastic polymers and in organic solvents such as xylene. Polyaniline doped with dodecylbenzene sulfonic acid and complexed with zinc dodecylbenzene sulfonate is commercially available as a powder, which can be dispersed in polyolefins. The same polymer doped with p-toluenesulfonic acid is also available as a dispersible powder, Ormecon, and in a predispersed form for solution processing in polar and nonpolar media. Based on Ormecon PANi, there are many commercial products marketed for many different applications. 

Polyaniline is less tolerant of preparation conditions than polypyrrole, and the list of anion dopants used in the preparation is more limited. However, subsequent replacement of the anion used in preparation by a dodecylben-zene sulfonate makes polyaniline become soluble in solvents such as Af-methyl pyrrolidone (NMP), or zn-cresol, and it can be spin-coated or otherwise solution-processed. In a similar way derivatives of aniline, such as... 

Polyaniline (PAn) is most amenable to solution processing. The emeraldine base (EB) form of PAn is soluble in selected solvents such as methyl pyrrolidinone1 or strong acids.2 3 More recently, it has been discovered that solubility of the doped form can be induced by the use of appropriate surfactant-like molecules as dopants.4 Camphorsulfonic acid (HCSA) and dodecylbenzenesulfonic acid have proved particularly useful in this regard. Once solubilized, these PAn s can be cast into sheets or blended with other conventional polymer structures. For example, the pres-... 

Electrospinning [29] is a facUe method to make almost any polymer into nano- and micro-fibers if the polymer can be solution-processed or melt-processed (Figure 7.4). However, due to the low solubility of polyaniline, it is very difficult to make polyaniline fibers thinner than 100 nm. To solve this problem, polyaniline is usually blended with a more soluble polymer to increase the weight percentage of polymer in solution. As a result, the obtained nanofibers are a polymer blend [29—33] this significantly reduces the conductivity of the polymer. Additionally, when the size of the fiber decreases, phase separation may occur, yielding a mixture of nanofibers of polyaniline and other polymers [33]. 

Yang, C.Y., Y. Cao, P. Smith, and A.J. Heeger. 1993. Morphology of conductive, solution-processed blends of polyaniline and poly(methyl methacrylate). Synth Met 53 (3) 293-301. 

In contrast to the base-processed polyaniline fibers described earlier, it was not possible to use water as a coagulant due to the slow precipitation kinetics of the dope solution. It has been generally found that... 

Although we have been able to electrospin polyaniline into nanofibers, polypyrrole is unable to be processed into homogenous textile fibers since this ICP is insoluble in common organic solvents and infusible, thus making thermal or solution processing difficult. To overcome this limitation. 

The largest aetuation strains in ICPs have been obtained from polypyrroles (PPy) and these polymers are the most studied. Both polyaniline (PANi) and polythiophene (PTh) ICPs have also been investigated and the solution-processability of these polymers offers some advantages in fabricating actuators. For example, continuous fibres of doped PANi that can be readily bundled to give large force actuators have been prepared [22] (Figure 10.4). 

In this technique, the intractable doped polyaniline is dispersed in the solution or melt of a non-conductive processable matrix. The resulting processable dispersion is ready for use without further modification. Key advantages of dispersion techniques for processing polyaniline are ... 

Electronic conductivity can be as high as 10 S/m (10 S/cm) in stretch-aligned polypyrrole and polyaniline, as well as in solution-processable PEDOT. Typical values of conductivity seen in actuators are in the range of 10 -10" S/m, 2-3 orders of magnitude lower than is achieved in metals. As the neutral doping state is approached, conductivity drops markedly and can be lower than 100 S/m (Warren and Madden 2006a). 

Solution Processing of Conductive Polymers Fibers and Gels from Emeraldine Base Polyaniline... 

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