Doping effect upon the molecular order of thin films of conducting polymers

Based in a linear dichroism analysis in the infrared region, we present a preliminary investigation of the effect of FeCl3 doping upon the molecular order of Langmuir-Blodgett films prepared from mixtures of poly-hexadecylthiophene (PHDT) and behenic acid (BA) at different relative concentrations. Low values of γ, the orientation angle of the alkyl chains relative to the normal to the substrate, are normally associated to a higher degree of molecular order. For pristine films, γ is maximum at intermediate values of the relative concentrations of the mixtures. Upon doping, disorder increases and it is most noticeable in the more organized films.