Abstract
There are various arguments and models connecting the characteristic length associated with the boson peak vibrations ξ to the length scale of dynamical heterogeneity Lhet. ξ is usually defined as the ratio of the transverse sound velocity to the boson peak frequency. Here we present pressure, temperature, and molecular weight dependencies of ξ , estimated using light scattering, in a few molecular and polymeric glass formers. These dependencies are compared with respective dependencies of the activation volume V # in the same materials. Good agreement is found for the pressure and molecular weight dependencies of ξ and V # measured at the glass transition temperature Tg. These results provide more evidence for a possible relationship between the sensitivity of structural relaxation to density (activation volume) and the heterogeneity volume. However, contrary to the expectations for Lhet, ξ does not decrease with temperature above Tg in most of the studied materials. The temperature dependence of ξ is compared to that of Lhet in glycerol and orthoterphenyl (OTP) estimated from literature data. The analysis shows a clear difference in the behavior of ξ (T) and V #(T) at temperatures above Tg, although V #(T)1/3 and Lhet(T) have similar temperature dependence. Possible reasons for the observed difference are discussed.
