Thermally induced microstructural changes and its influence on electrical conductivity of a polymer-based bakelite RPC detector material: A positron lifetime study

Annealing studies have been carried out to understand the temperature induced microstructural changes in Bakelite (P120 NEMA LI-1989 Grade XXX) Resistive Plate Chamber (RPC) detector material using Positron annihilation lifetime spectroscopy (PALS), Fourier transform infrared spectroscopy (FTIR), and XRD. The variation of positron lifetime parameters viz., ortho-Positronium lifetime (s3) and free volume size (Vf) increases marginally above glass transition temperature Tg as a result of structural changes due to segmental mobility. The drastic increase of free volume parameters above 240 o C attributed to the reduction in strength of CAH bond of the aliphatic bridges and cleavage of methylene bridges of the polymer network, which is supported by the FTIR results. The XRD results show the reduction in crystallinity and average crystallite size of Bakelite on annealing correlates well with the free volume and electrical conductivity. The temperature induced electrical conductivity and activation energy is also correlated with the positron lifetime parameters. (C) 2013 Wiley Periodicals, Inc.