Study on damping mechanism based on the free volume for CIIR by PALS.

The influences of the free volume and the termperature on the damping property of chlorinated isoprene-isobutylene rubber (CIIR) were first investigated by positron annihilation lifetime spectroscopy (PALS), dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC), respectively. From the variations of ortho-positronium (o-Ps) lifetimes as a function of temperature, two transition temperatures can be observed, i.e., Tg and T B . We found that there exists a pre-rubbery state between the glass transition temperature Tg and T B . The DMA results indicate that the tan 6 peak of CIIR has a very broad temperature distribution because of the existence of a liquid-liquid transition (T II ). The temperature dependence of the average free volume size can be linearly fitted below Tg and above T B , respectively. It is very interesting that the difference spectrum of the free volume size between the results fitted by two lines (below Tg and above T B ) and experimental data is very similar to the dynamic mechanical spectrum of CIIR. In order to clarify the damping mechanics, the Williams-Landel-Ferry (WLF) equation based on free volume theory has been successfully used to establish a direct quantificational relationship between the free volume and the damping property, which indicates that the free volume plays an important role in determining the damping property.