Positron Annihilation Lifetime Spectroscopy of Carbon Black- and Silica-Filled Rubber

Abstract

Lifetime spectroscopy has been used to investigate different grades of carbon black (CB) and silica mixed into a variety of rubbers as a function of CB or silica loading. The spectra were analyzed into three lifetimes. The results show that: (1) The longest observed lifetime, tau (3), attributed to ortho positronium formation depends on the rubber but not on filler loading or type of CB. The free volume size in the rubber is not affected by the addition of the filler. (2) The intensity, I-3, of ortho positronium formation depends both on the loading and on the type of CB, but is less dependent on loading in the case of silica. (3) The intermediate lifetime, tau (2), depends both on the loading of the filler and on the type of CB. For CB, this indicates that tau (2) is not simply the additive result of bulk annihilation in the rubber and CB. Rather the CB loading creates new trapping sites at the CB-rubber interface that depend on the type of CB.