Sulfuric acid doping

As mentioned in the introduction, the electrical conductivity upon doping is one of the most important physical properties of conjugated polymers. The conductivity ranges from lOOOOOS/cm for iodine-doped polyacetylene [41], 1000 S/cm for doped and stretched polypyrrole [42], to 500 S/cm for doped PPP [43], 150 S/cm for hydrochloric acid doped and stretched polyaniline [44], and 100 S/cm for sulfuric acid doped PPV [45] to 50 S/cm for iodine-doped poly thiophene [46]. The above listed conductivities refer to the unsubstituted polymers other substitution patterns can lead to different film morphologies and thus to a different electrical conductivity for the same class of conjugated polymer in the doped state. 

By proper combination of acld-ester/para-meta monomer ratios, a variety of oxadiazole/N-methyl hydrazide copolymers could be prepared and evaluated in fiber form. High molecular weight polymers were easily prepared with inherent viscosities of 3-6. The sulfuric acid dopes were spun to fiber by dry-jet or wet-jet solution spinning into dilute sulfuric acid at ambient temperature in a conventional solution spinning process including a fiber neutralization step as well as a hot-drawing operation 350-400°C. Representative fiber properties are given in Table I. 

Aromatic polyamide fibers are produced by spinning liquid crystalline polymer solutions of PPTA-sulfuric acid dopes into a water coagulation bath [414], resulting in the formation of a crystalline fiber with a surface skin. Variations in the structure produced by annealing at elevated temperature are known to increase the fiber modulus due to a more perfect alignment of the molecules [472]. The chemistry and physics of the aromatic polyamide fibers have been reviewed [419]. 

GlipaX, Bonnet B, Mula B et al (1999) Investigation of the conduction properties of phosphoric and sulfuric acid doped polybenzimidazole. J Mater Chem 9 3045-3049... 

Aromatic polyamide fibers are produced by spinning liquid crystalline polymer solutions of PPTA-sulfuric acid dopes into a water coagulation bath [337], resulting in the formation of a crystalline fiber with an exterior surface skin. 

The use of other dopants also leads to relatively high selectivities [54]. For example, a 36% sulfuric acid-doped sample had an O2/N2 selectivity of 13.4, while a 36% paratoluenesulfonate-doped sample had an O2/N2 selectivity of 14.9. A thin film composite doped with 38% nitric acid had an O2/N2 selectivity of 14.8. 

The transport of water through supported polyaniline membranes grown electrochemically was investigated by Schmidt et al. [71]. A 25-30% increase in water permeation was observed for sulfuric acid-doped polyaniline compared to the undoped polymer. The doped polymer was believed to have a more open structure, accounting for the enhanced water permeation. However, a simpler explanation is the increased hydrophil-icity of doped polyaniline. Analogous increases in methanol transport through both polyaniline and polypyrrole were found [72,73]. 

The electrospinning of conductive polymers mainly focuses on PANi and its blends. Highly conductive sulfuric acid-doped electrospun PANi fibres can be prepared using a mixture of PANi and different conventional polymers such as PEG, PS, PAN, etc. [273, 279]. 

Polyaniline (PANI) can be formed by electrochemical oxidation of aniline in aqueous acid, or by polymerization of aniline using an aqueous solution of ammonium thiosulfate and hydrochloric acid. This polymer is finding increasing use as a "transparent electrode" in semiconducting devices. To improve processibiHty, a large number of substituted polyanilines have been prepared. The sulfonated form of PANI is water soluble, and can be prepared by treatment of PANI with fuming sulfuric acid (31). A variety of other soluble substituted AJ-alkylsulfonic acid self-doped derivatives have been synthesized that possess moderate conductivity and allow facile preparation of spincoated thin films (32). 

Cellulose acetate [9004-35-7], prepared by reaction of cellulose with acetic anhydride, acetic acid, and sulfuric acid, is spun into acetate rayon fibers by dissolving it in acetone and spinning the solution into a column of warm air that evaporates the acetone. Cellulose acetate is also shaped into a variety of plastic products, and its solutions are used as coating dopes. Cellulose acetate butyrate [9004-36-8], made from cellulose, acetic anhydride, and butyric anhydride in the presence of sulfuric acid, is a shock-resistant plastic. 

The performance of many metal-ion catalysts can be enhanced by doping with cesium compounds. This is a result both of the low ionization potential of cesium and its abiUty to stabilize high oxidation states of transition-metal oxo anions (50). Catalyst doping is one of the principal commercial uses of cesium. Cesium is a more powerflil oxidant than potassium, which it can replace. The amount of replacement is often a matter of economic benefit. Cesium-doped catalysts are used for the production of styrene monomer from ethyl benzene at metal oxide contacts or from toluene and methanol as Cs-exchanged zeofltes ethylene oxide ammonoxidation, acrolein (methacrolein) acryflc acid (methacrylic acid) methyl methacrylate monomer methanol phthahc anhydride anthraquinone various olefins chlorinations in low pressure ammonia synthesis and in the conversion of SO2 to SO in sulfuric acid production. 

To determine of Ce(IV) in acid soluble single crystals, a simple and sensitive method is proposed. The method is based on the reaction of tropeoline 00 oxidation by cerium(IV) in sulfuric acid solution with subsequent measurement of the light absorption decrease of the solution. The influence of the reagent concentration on the analysis precision is studied. The procedure for Ce(IV) determination in ammonium dihydrophosphate doped by cerium is elaborated. The minimal determined concentration of cerium equal to 0.04 p.g/ml is lower than that of analogous methods by a factor of several dozens. The relative standard deviation does not exceed 0.1. 

Poly(2-methoxy, 5-(2 -ethylhexyloxy)-1,4-phenylene vinylene) MEH-PPV Emission peak = 605 nm p-type doping by sulfuric acid (H2SO4) -type doping by sodium (electron donor) Iodine (I2) = electron acceptor = > oxidizing agent... 

Ellis A process for making isopropyl alcohol from light olefin mixtures by treatment with concentrated sulfuric acid. Operated in World War I by the Melco Chemical Company, as an intermediate for the production of acetone for airplane dope. ... 

Treatment of PVDF by dehydrofluorination and doping with sulfuric acid prior to blending have been shown to improve the hydrophilicity of a Nafion/PVDF blend. Such blends were demonstrated to show comparable conductivity and FC performance to unmodified Nation and significantly improved over blends in which the PVDF had not been treated. MeOH crossover rates, however, were not reported. PEMs composed of "sandwiches" of Nation plus Nafion/PVDF blends have also been used as PEMs in order to reduce MeOH crossover and improve DMFC performance. - Other non-ionic polymers that have been blended with Nation include PPCF and polypyrrole. 21... 

Continuous Sampling and Determination. There are no truly continuous techniques for the direct determination of sulfuric acid or other strong acid species in atmospheric aerosols. The closest candidate method is a further modification of the sensitivity-enhanced, flame photometric detector, in which two detectors are used, one with a room-temperature de-nuder and one with a denuder tube heated to about 120 °C. Sulfuric acid is potentially determined as the difference between the two channels. In fact, a device based on this approach did not perform well in ambient air sampling (Tanner and Springston, unpublished data, 1990). Even with the SF6-doped H.2 fuel gas for enhanced sensitivity, the limit of detection is unsuitably high (5 xg/m3 or greater) because of the difficulty in calibrating the two separate FPD channels with aerosol sulfates. 

The polymer coated electrode may be doped with an electroactive species by exposing it to a dilute solution of the chosen material. A good example is [Ru(bipy)3]2+ (bipy = 2,2 -bipyridyl), which can be exchanged from a solution of die ruthenium complex in sulfuric acid. It is observed that the value of E° for the [Ru(bipy)3]%+ couple is the same as the aqueous solution value. Also the loading of the polymer can be such that the local surface concentration of the electroactive complex is greater than that in the solution from which it is exchanged thus larger currents are observed than with the bare electrode under the same conditions. 

Fig. 2.10 Evolution of COD and ICE inset) with the specific electrical charge passed during the oxidation of 4-chlorophenol (4-CP) on a boron-doped diamond anode. Electrolyte sulfuric acid 1M 7 = 30°C i = 30mA cm-2 initial 4-CP concentration open square) 3.9mM cross) 7.8 mM filled circle) 15.6 mM (Rodrigo et al. 2001)...

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