Study On Preparation And Characterization Of Helical Fibers

Helical fibers, one of the typical representatives of chiral materials, having been attracted more and more attention for the controllable and adjustable advantages such as composition, structure, morphology, permittivity parameter, permeability parameter and chiral parameters.Regular helical nanofibers are prepared by the chemical vapor deposition of acetylene with copper nanocrystals as a catalyst at the low temperature of 250℃. The copper nanocatalyst used in this study is obtained from the thermal decomposition of copper tartrate precursor. The morphologies of the fibers could be simply controlled by adjusting reaction temperature, calefaction speed, and the acetylene flow rate.It could be known by TEM and SEM analysis that these helical nanofibers grown over single copper nanocrystal exhibited a mirror-symmetric growth mode: the two helical nanofibers had identical coil diameter, coil pitch, cycle number, and fiber diameter, but had absolutely opposite helical senses. The morphologies of the fibers could be changed in the processes of fibers growth, and the shape of copper nanocrystals changed from irregular (circular, oblong) to regular(rhombic, triangular, quadrangular, and polygonal) during the processes of fibers growth. The shape and dimension of the catalyst particles have a great influence on the morphology of the fibers. Helical structure is apt to generate over the catalyst particles with small dimension and shape regularity. The shape changes are caused by the changes in surface energy resulting from the acetylene-adsorption on the copper nanocrystals.The XRD, IR, and elemental analysis revealed that the chemical structure of helical fibers was a kind of poly(acetylene)-like polymer, and helical fibers were amorphous. The reaction proceeded mainly by the polymerization of acetylene over copper nanocrystals, accompanied by some side reactions. With increasing the reaction temperature, of the C/H ratio of helical fibers increased, but the chemical structure of helical fibers little changed.The as-prepared helical fibers are insulator, and exhibits room temperature (300K) ferromagnetic behavior.