Low-Temperature Thermal, Dielectric, and Acoustic Properties of Amorphous Polymers

The thermal conductivity λ, the specific heat c, the thermal expansion α, the acoustic and dielectric properties of polycarbonate (PC), of polystyrene (PS) and of an epoxy resin were measured in the temperature ranges between 0.1 K and 80 K (λ c) and between 4 K and 300 K (α). The measurements show the typical low-temperature behavior of amorphous solids. Below 20 K the results can be explained in the framework of the soft potential model. Above 20 K with increasing temperature λ, and α show between 30 K and 50 K a distinct decrease in slope of the temperature dependence. The sound velocity shows for PC and PS the typical decrease with increasing temperature. For PC the maximum in the dielectric losses shifts with increasing frequency and at increasing pressure to higher temperature.