THERMAL-PROCESS FOR ORIENTATION OF POLYANILINE FILMS

It is demonstrated that films of the emeraldine base form of polyaniline can be processed through simultaneous heat treatment and application of stress to produce oriented, partially crystalline polyaniline films. The emeraldine base films were produced by casting emeraldine base polymer dissolved in NMP (N-methylpyrrolidinone) onto smooth glass substrates. The resulting films contained up to 20% by weight NMP. Heating the samples at an elevated temperature (T greater-than-or-similar-to 110-degrees-C) while under stress leads to an elongation of the polymer film with l/l0 up to 4.5. The resulting material has enhanced mechanical properties with tensile strengths of the emeraldine base films increasing from an average of 54 MPa for unstretched films to an average of 124 MPa for 4-fold uniaxially stretched films. A 2x biaxially stretched polyaniline film has a tensile strength similar to that of a 4x uniaxially stretched film. The X-ray diffraction studies show a directional enhancement of the Debye-Scherrer rings, indicating a spreading angle of approximately 7-degrees, reflecting significant orientation of the polymer chains. Similarly, infrared and UV visible spectroscopy reveal anisotropic optical constants. Detailed analysis of the infrared spectra gives a measure of the angle between the phenyl rings and the plane defined by the nitrogens of the polyaniline backbone. Temperature-dependent audio-frequency conductivity studies of oriented emeraldine base show anisotropy in the normalized conductivity with sigma parallel to/sigma-perpendicular to approximately 3 in accord with hopping conductivity in the anisotropic undoped emeraldine base. In contrast, the dc conductivity of oriented emeraldine hydrochloride salt shows a 10-fold increase in dc conductivity for sigma-parallel to as compared with unoriented material, with sigma-parallel to/sigma-perpendicular to approximately 3.5. Both sigma-parallel to and sigma-perpendicular to vary as exp[-(T0/T)1/2] with T0 parallel to approximately 5500 K and T0 perpendicular to approximately 6500 K, indicating that the dc conductivity is dominated by quasi-one-dimensional variable-range hopping in the amorphous regions between the crystalline areas.