J.M. Ginder

Insulator-to-metal transition in polyaniline

Abstract A study of the magnetic susceptibility of the emeraldine form of polyaniline shows the presence of a Pauli susceptibility approximately linearly proportional to the degree of protonation in agreement with phase segregation into metallic and nonmetallic phases. A model based upon the transition upon protonation from isolated doubly charged protonated diimine groups to a polaronic metal is suggested, together with the role of localization of polarons at the surface of and within the disordered small metal particles formed.

Insulator-to-metal transition in polyaniline: Effect of protonation in emeraldine

Abstract The emeraldine base form of the polymer can be varied from insulating ( σ ∼ 10 −10 ohm −1 cm −1 ) to conducting ( σ ∼ 10 0 ohm −1 cm −1 ) states through protonation. Based upon extensive magnetic, optical and transport data, we demonstrate that the resulting emeraldine salt is metallic with a finite density of states at the Fermi energy. The roles of a novel bipolaron-to-polaron lattice transition and phase segregation into conducting and non-conducting regions are discussed.

Polyaniline: Oriented Films and Fibers

Abstract The dependency of the conductivity of polyaniline (emeraldine oxidation state) on its molecular weight has been determined. Uni- and biaxially oriented films and uniaxially oriented fibers of emeraldine base have been studied and the dependency of their degree of crystallinity, tensile strength, and conductivity (after doping) on draw ratio has been determined.

N-substituted derivatives of polyaniline

Fully N-methylated polyaniline was obtained analytically pure by the oxidative polymerization of C6H5N (CH3) (H) with (NH4)2S2O8 in 1.0M aqueous HCl. The resulting black-green polymer (σ ∼10−4 s/cm) was shown to have a similar backbone structure to parent polyaniline, and upon heating, lost HCl and H2O, yielding a black-brown solid, (σ < 10−8 s/cm) containing ∼14% oxidized groups. “Pseudo-protonic” acid doping of “emeraldine” base with neat (CH3)2SO4 yielded polymers whose extent of doping could be monitored continuously. The ∼50% methylated “emeraldine” base (σ = ∼10−2 s/cm) had a χPauli approximately half that of 50% proton doped “emeraldine” base, consistent with the symmetrically effect of the methyl groups.

Thermochromism in the insulating forms of polyaniline: Role of ring‐torsional conformation

The temperature‐dependent optical spectra of the major insulating forms of polyaniline—the fully reduced leucoemeraldine base, half‐oxidized emeraldine base (EB), and fully oxidized pernigraniline base (PNB)—and of two oligomeric model compounds for polyaniline are reported. All three forms of the polymer possess a ∼3.8 eV optical absorption assigned to a transition from the valence band to a narrow π* conduction band; in all cases this transition shifts to higher energy and weakens with increasing temperature, T. The oxidized forms also exhibit transitions at ∼2 eV; in EB, this absorption feature has previously been assigned to a ‘‘molecular exciton’’ and is found to increase in energy with increasing T. In PNB, the observed ∼2.3 eV transition is correlated with the expectation of a Peierls dimerization gap in this half‐filled band system; in contrast to the ∼2 eV transition in EB, this optical transition energy decreases with increasing T in PNB. These observations are for the most part understood by a ...

IR absorption, photoinduced IR absorption, and photoconductivity of polyaniline

Abstract The infrared spectra, photoinduced infrared spectra, and photoconductivity of polyaniline are reported. Oxidative doping of leucoemeraldine base yields changes that are consistent with breaking the symmetry of the polymer and an overlap of the vibrational modes with a continuum of states. Small photoinduced changes in the vibrational modes of emeraldine base also indicate this symmetry breaking and the creation of polarons. The absence of significant photoconductivity suggests that the photoexcited polarons have low mobility. Calculations based on the amplitude mode formalism give a very large polaron mass in emeraldine base, consistent with low polaron mobility.

Solution studies of the emeraldine oxidation state of polyaniline

Abstract Optical studies of emeraldine base in solutions show a red shift in both 2eV and 3.8eV absorption peaks compared with the optical absorption for emeraldine films and powders. As for solids, the 2.0eV peak is absent for the salt form. Unlike the salt film, the strong absorption peak is narrow without the free electron absorption tail, suggestive of strong localization of polarons in the solution form. Dilution studies show there is no shift in the absorption peaks with concentration in both emeraldine base and salt, indicating that optical absorption is an intrachain interaction. Temperature dependent UV-VIS spectra show the first thermochromatic effect in a system without side groups that suggests possible ring flipping. Photoinduced optical studies of emeraldine base polymer in solution shows photoinduced absorption peaks at 1.4eV and 3.0eV and photoinduced bleaching at 1.8eV. The photoinduced absorption peak observed at 0.9eV in film is no longer present. Its disappearance implies the importance of interchain interactions for the formation of the electronic state. In contrast, the 1.4eV absorption is from the interchain excitation of polarons.

Ring-rotational defects in polyaniline

Abstract The effects of electron-lattice coupling via ring rotation on the electronic structure of leucoemeraldine base (LB) and its charged defects are investigated. We suggest that in LB and other phenyl-ring-containing polymers the charged defect states, particularly hole polarons, are associated with localized distortions of the ground state ring torsion angles toward a planar conformation, in contrast with the bond-alternation defects present in conducting polymers. The relevance of these defects to recent photoinduced optical experiments is discussed.

Ring-torsional polarons in polyaniline and polyparaphenylene sulfide

Abstract The role of the dihedral angle of the backbone phenyl rings in determining the electronic structure and charge storage mechanism in polyaniline (PAN) and polyparaphenylene sulfide (PPS) is reviewed. The sensitivity of the average ring torsion angle to the effects of steric repulsion and electron delocalization is manifest in the effects of derivatization and temperature on the optical spectra of these materials. It is shown that charge is self-trapped into localized defect states in part via changes in ring angle, leading to novel ring-torsional polarons which induce only one defect level into the energy gap and possess a very large kinetic mass (50 – 500 m e ). Evidence for the existence of these defects in PAN and PPS is discussed.

Photoinduced Absorption and Erasable Optical Information Storage in Polyanilines

Abstract Photoinduced absorption spectroscopy has been used to study a variety of forms of polyaniline. Experiments on emeraldine base and leucoemeraldine base have led to a picture of the photoproduction and decay of massive, long-lived defect states that can be described in terms of conformational changes involving rotations of the C 6 H 4 rings. Photoexcitation spectra of other polyanilines, such as pernigraniline base and poly( o -toluidine), exhibit similar features including relatively weak photoinduced infrared vibrations and a relatively strong photoinduced absorption peak near 1.4–1.5 eV. In several of these materials, the photoinduced changes are very long-lived, leading to an investigation of the polyanilines as media for erasable optical information storage.