Microstructure and charge transport in hybrid metallophthalocyanine/rigid rod polymer fibers

Abstract

Strong, environmentally stable, electrically conductive fibers can be fabricated from solutions of nickel phthalocyanine (Ni(Pc)) and the ultra-high modulus polymers poly-( p -phenyleneterephthalamide) (PPTA, Kevlar) or poly- p -phenylenebenzobisthiazole) (PBT) by dry-jet, wet-spinning techniques, followed by chemical or electrochemical doping. The fiber mechanical strength s at a particular composition is a simple linear function of the Ni(Pc) I volume fraction Φ c : s ≈ s p (1− Φ c), where s p is the of a pure PPTA or PBT fiber. The electrical conductivity σ for Φ c>0.17 obeys the empirical relationship: 1n( σ) = Φ c1n( σ c) + (1 − Φ c) 1n( σ p) where σ c represents the conductivity of polycrystalline Ni(Pc)I and σ p denotes the conductivity of pure PPTA or PBT. The temperature dependence of σ is thermally-activated and can be fit to a fluctuation-induced carrier tunnelling model. In contrast, the thermoelectric power S of the fibers is p-type and metal-like (S ∼ T), strongly resembling that of Ni(Pc) I single crystals. X-ray diffraction shows microstructural evidence for phase separation and the presence of a fine (domain size <50 nm) Ni(Pc) I dispersion embedded in the PPTA or PBT matrix.