Free-volume changes at nanoscale in doped polyacrylic acid studied by positron annihilation spectroscopy

Polyacrylic acid (PAA) doped with carbon black (CB), chromium oxide (Cr2O3) and cupferron with different wt% (0.25%, 0.50%, 0.75%, and 1%) was studied using positron annihilation lifetime (PAL) technique and Doppler broadening of annihilation radiation (DBAR). Ortho-positronium lifetime components (τ3 and I3) were used to estimate the nanoscale free-volume hole sizes (Vf) and its fractions (f). It was found that the hole size Vf and its fractions f as well as S-parameters decreased at high value of doping concentration due to dopants-polymer formation. These results are supported by a significant narrowing in the nanoscale free-volume hole size distributions.The correlation between positron annihilation parameters and electric conductivity are discussed.