Positron annihilation spectroscopy of polyacrylonitrile-based carbon fibers embedded with multi-wall carbon nanotubes

Polyacrylonitrile (PAN)-based carbon fibers, embedded with multi-wall carbon nanotubes (MWCNT) in different concentrations, have been prepared by an electrospinning technique and investigated using scanning electron microscopy, Raman, and positron annihilation spectroscopy. An analysis of the positron lifetime and Doppler broadened spectral line shape has been made. Positron lifetime spectra for all the samples give best fit for three distinct lifetime components. Raman data has been used to estimate the sp(2) mole fraction in the fiber. It is found that the gradual changes incorporated in the fiber due to the addition of MWCNTs are reflected as well defined changes in the positron lifetime and the S parameter of the Doppler broadened spectral line. Annihilation parameters are discussed from the point of view of formation of distinct positron trapping sites in the form of vacancy type defects at the interfaces of MWCNTs and the PAN matrix, and their variations in concentration due to different amount of MWCNTs added. (c) 2005 Elsevier Ltd. All rights reserved.