In-situ positron annihilation lifetime measurements of strained isoprene rubber filled with carbon black

Abstract

The free volume in carbon-black filled isoprene rubber is determined by in-situ positron annihilation lifetime measurements on the rubber subject to tensile strain using ortho-positronium as a probe. The dependence of free volume on the elongation and carbon black loading in the strained state is investigated to clarify the reinforcement mechanism of carbon black in synthetic rubber. Although no change in the ortho-positronium lifetime is detected, the ortho-positronium formation probability sharply decreases with increasing elongation and carbon black concentration in the strained state. The percent reduction is enhanced at high elongations and carbon black loadings. This result indicates the formation of both a bound rubber layer around the CB fillers and regions in the strained rubber phase with oriented molecular chains characterized by lower mobility, where ortho-positronium formation is suppressed.