Positron annihilation doppler broadening spectroscopy of carbon black and carbon black-filled rubber polymers

Abstract

We have used positron annihilation Doppler Broadening Spectroscopy to investigate the effects of filling various rubber polymers with different amounts and types of carbon blacks. The S parameter was measured for a wide variety of samples. The results show direct correlation between the S parameter and the various physical characteristics of the carbon black. The S parameter is found to decrease with carbon black particle and aggregate diameter, to increase with carbon black surface area, and to decrease as more carbon black is added to the polymer samples. This behavior can be understood as due to a combination of reduction in positronium formation as carbon black is added to the polymer, and the decrease in positron annihilation with valence electrons in the sample as the amount of carbon black-polymer links are increased. No effect on the S parameter is observed for sample mixing times longer than 45 seconds. The authors express their thanks to Dr. Michel Gerspacher and Dr.Leszek Nikiel, Sid Richardson Carbon and Gasoline Co., Ft. Worth Tx, for providing the samples and for many helpful discussions.