Spectroscopic and topographic characterization of the effect of monomer feed ratio in electrocopolymerization of N-vinylcarbazole-co-3-methylthiophene on carbon fiber

Abstract

In the case of conductive polymer films, with thickness in the nanometer range, electrografted onto carbon fiber, the characterization is difficult and requires the development of new analysis procedures and methods. Recently we have successfully applied the reflectance FTIR method for the characterization of electrocoated thin conductive polymeric films (poly[carbazole-coacrylamide], and poly[carbazole-co-methylthiophene]) [1–3] onto carbon fiber. Atomic force microscopy (AFM) analysis was performed on highly oriented pyrolytic graphite (HOPG) as a model system [4], and the adhesion properties of Poly[carbazole-coacrylamide] on carbon fiber has been determined [5]. These methods allow a non-destructive characterization of the surface coating and can give information on the structure of electrocoated polymers and copolymers. In this paper we have investigated the electrografting of the copolymer poly[N-vinylcarbazoleco-3-methylthiophene] (hereafter NVCzMeTh) onto carbon fiber by reflectance FTIR, X-ray photoelectron spectroscopy (XPS) and AFM. Reflectance FTIR analysis was carried out on a single fiber. AFM was used to gain information about the morphology of the copolymer electrografted onto carbon fiber. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis were also performed to study the morphology and composition of such coatings. Polyacrylonitrile (PAN) based, Hexcel AS4C 12 K carbon fibers (12 000 single filaments in a roving) were used for the electrocopolymerization (diameter of ∼5– 6 μm). The electrocopolymerization procedure was carried out as described previously [3]. Electrodeposition of polymers on the carbon fiber microelectrodes was performed galvanostatically at 40 ◦C at a constant current density of ∼10 A/cm2, using the carbon fibers as anode. For sample NVCzMeTh1 the initial concentration of monomer used was [NVCz]0 = 0.05 M (Fluka), [MeTh]0 = 0.067 M (Fluka, >98%); for sample NVCzMeTh4 the initial concentrations were [NVCz]0 = 0.017 M and [MeTh]0 = 0.240 M. The solvent was DMF (Fluka, puriss. grade) containing 0.1 M TMAP (Fluka) as supporting electrolyte. After the electrolysis, the carbon fibers were washed thoroughly with water and distilled acetone and with THF