Self-organization of nanopolyacetylene
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Self-organization of Nanoparticles and Vibrational Coherence in Gels and Composites of Nanopolyacetylene (V.M.Kobryanskii, International Congress of Nanotechnology, November 2005, San Francisco, E-mail:

The capability of self-organizing leading to formation of highly ordered structures is one of the delightful properties of nano-dimensional materials. However, the possibility to create material with three-dimensional order of nanoparticles located significantly distant from each other does remain not clear. The present work for first time shows vibrational coherence between nanoparticles in gels and composites of nanopolyacetylene.

Nanopolyacetylene was obtained by polymerization of acetylene in the solution of polyvinyl butyral in 1-butanol on the rhenium catalyst. During the polymerization the viscosity of the reaction solution increases with the formation of gelatinous mixture. Gel dissolves in the surplus of 1-butanol during mixing and it easily forms films when it dries. The obtained material possesses high cross section of Raman scattering and high stability under influence of laser irradiation. Both of these phenomena result from excitation of coherent vibrations in polyacetylene chains [1,2].

Two methods of preparation of nanopolyacetylene films were used in the present work. In the first method (A) the films were formed from the reaction mixture by slow evaporation of solvent at horizontally located supports. In the second one (B) the reaction mixture was placed in a large amount of water. In this case the slow precipitation of polyvinyl butyral occurred and a substance similar to the gum containing remainders of solvents (50% by weight) was formed. The films were prepared from the gum by extrusion. Films A and B with thickness of 5 microns and 50 microns were prepared and studied.

Figure 1 shows the absorption spectra of thin films A and B. One can see from the figure that the position of absorption bands coincides for both films. The spectrum of the film A is characterized by a fine structure of absorption bands of cis- and trans- forms. At the same time in the absorption spectra of film B the fine structure is absent but high intensity background absorption is observed.

Absorption spectra of thin films A and B

Figure 2 shows Raman scattering spectra of thick films A and B. One can see from this figure that the intensity of the Raman scattering of the film obtained through the process of precipitation of reaction mixture is hundreds times lower than the one of the film obtained from gel.

Raman scattering spectra of thick films A and B. Excitation  1064 nm

We assume that polymerization of acetylene in solution of polyvilyl butyral is accompanied by formation of gel with three-dimensional order of polyacetylene nanoparticles. In this case, distribution of nanoparticles remains highly ordered after evaporating of solvent and formation of solid composites. The process of precipitation of reaction mixture is accompanied by change of the conformation of the macromolecules of polyvinyl butyral and by breaking the bond between macromolecules of polyvinyl butyral and polyacetylene nanoparticles. In this case the order between nanoparticles is disrupted and the contribution of vibrational coherence between nanoparticles to the intensity of Raman scattering becomes negligible.

[1] Paraschuk D. Yu., Kobryanskii V. M., Phys. Rev. Lett., (2001), 87, 207402.
[2] Adachi Sh., Kobryanskii V. M., Kobayashi T., Phys. Rev. Lett., (2002), 89, 027401.