E.M. Scherr

Thermal transitions and mechanical properties of films of chemically prepared polyaniline

The mechanical and thermal properties of the solution-cast films of chemically prepared polyaniline have been studied by means of dynamic mechanical analysis (d.m.a.), differential scanning calorimetry (d.s.c.) and thermogravimetric analysis (t.g.a.). The glass transition temperature (Tg) of the polyaniline films in emeraldine base form was determined and characterized for the first time to be in the range of ∼ 105–220°C for the films containing ∼ 16-0% of 1-methyl-2-pyrrolidinone (NMP) residual solvent, respectively, from a decrease in the storage modulus in d.m.a. and from d.s.c. studies. Depending on the content of NMP, the thin films of polyaniline have a storage modulus of ∼ 200 MPa-2 GPa at temperatures below Tg. Other thermal transitions and reactions in the temperature range of ∼ 25–500°C are also characterized by infra-red spectroscopy, X-ray diffraction and cyclic voltammetry and are discussed in relation to the mechanical properties of polyaniline.

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.

Towards optimization of electrical and mechanical properties of polyaniline: Is crosslinking between chains the key?

Abstract A distinction has been made experimentally between the effect on conductivity and tensile strength caused by 1-D mechanical alignment of parent polyaniline films and the effect produced by the combination of physical crosslinking by crystalline domains and associated 1-D nematic-type alignment of amorphous material. At least in the case of films, a small amount of alignment in amorphous regions results in surprisingly large increases in conductivity and tensile strength; however, extensive crosslinking by crystalline domains and associated 1-D nematic alignment in amorphous regions is necessary in order to optimize interchain electrical and mechanical properties.

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.

Polyaniline : dependency of selected properties on molecular weight

Abstract The conductivity and tensile strength of stretch-oriented, doped, crosslinked films of polyaniline are found to be considerably greater than those prepared from non-crosslinked films of the polymer. The conductivity of the former films show little dependence on molecular weight or degree of crosslinking whereas their tensile strength shows significant dependence on these variables.

Structural aspects of the polyaniline family of electronic polymers

Abstract Recent structural studies of the polyaniline family of electronic polymers in its base and salt forms are reviewed, including a description of their crystalline and amorphous structures. Implications of some relevant structural parameters for the control of physical properties of these materials are also 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.

The eletronic structure of emeraldine doped in situ from HCl in the gas phase as studied by photoelectron spectroscopy

Abstract The chemical and electronic structure of spin-coated films of polyaniline in the emeraldine state, treated in-situ with HCl in the gas phase, have been studied for the first time by means of X-ray Photoelectron Spectroscopy (XPS) and Ultra-violet Photoelectron Spectroscopy (UPS). Ultra thin films, of about several hundreds of Angstroms thickness, were spin-coated from a solution of chemically prepared emeraldine in NMP, onto substrates of aluminum or silicon. The salt forms were prepared both by (a) “wet” doping in 1M HCl and (b) the in-situ treatment of the films with HCl in the gas phase. With XPS three different types of chlorine have been observed, two ionic and one covalent. With UPS the valence band spectra of the doped and undoped state, are studied.