Disorder and staging in iodine-doped polyacetylene

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Abstract
Iodine doping of highly oriented trans-polyacetylene films has been studied using in situ x-ray diffraction of vapor- and solution-doped samples. In either case the initial doping transition is marked by coexistence of undoped polymer and that of an intermediate doped phase. At higher dopant concentrations the samples undergo additional structural evolution. Structure-factor calculations of suggestive models, in comparison to the equatorial profiles, indicate that the stepwise formation of well-ordered structural phases (i.e., staging) does not occur. An alternative model of the doping process is proposed whereby dopant uptake occurs in two distinguishable steps. Initially, a systematic ‘‘disordered’’ packing of quasi-one-dimensional iodine columns forms within the polymer host matrix, and, thereafter, the doping process is dominated by intercalation of unoccupied galleries to form layered iodine sheets.