Resolution of controversy concerning the morphology of polyacetylene

Abstract

A free standing film of polyacetylene, first obtained by Ito et al.¹, has been shown by electron micrograph (EM) to consist of fibrils with average diameter of 20 nm. The results were confirmed by us² and many other laboratories. To eliminate any morphological changes resulting from post polymerization handling of the specimen, we have developed the technique of direct polymerization onto EM grids^2,3. The 20–100 nm thick polyacetylene films thus obtained were found to have 3-nm diameter microfibrils as the ultimate morphological entity which aggregate to form the more abundant 20-nm fibrils. Electron diffraction showed the polymer chain axis to be along the fibre axis^3–5. In marked contrast Wegner and co-workers^6–11 reported that polyacetylene particles contain irregularly shaped lamellae ∼5–20 nm in thickness connected into ribbon-like aggregates with polymer chain axis perpendicular to the aggregate direction^6,7, and proposed an irregular chain folded lamellar morphology, highly cross-linked with the average length of linear chain segments of ∼20 units. We have resolved this controversial observation by reproducing the work of Wegner et al. and show here that such specimens were readily transformed to smooth fibrillar morphology by washing with methanolic-HCl.