The glass transition is relevant for performance definition in rubber products. For extrapolation to high-frequency behavior, time-temperature superposition is usually assumed, although most complex rubber compounds might be outside of its area of validity. Fast differential scanning calorimetry (FDSC) with cooling rates up to 1500 K/s and broadband dielectric spectroscopy (BDS) with frequencies up to 20 MHz are applied here to directly access both kinetics and dynamics of glass formation in a wide frequency range. For the first-time, the relation between the thermal vitrification and the dielectric relaxation is studied on vulcanized styrene-butadiene rubber, showing that both cooling rate and frequency dependence of its glass transition can be described by one single Vogel-Fulcher-Tammann-Hesse equation. The results indicate the validity of the Frenkel-Kobeko-Reiner equation. Another focus is the sample preparation of vulcanized elastomers for FDSC and BDS as well as the temperature calibration below 0 C.

The piezoelectric shear gauge (PSG) [Christensen and Olsen, Rev. Sci. Instrum. 66, 5019 (1995)] is a rheometric technique developed to measure the complex shear modulus of viscous liquids near their glass transition temperature. We report recent advances to the PSG technique: (1) The data extraction procedure is optimized, which extends the upper limit of the frequency range of the method to between 50 and 70 kHz. (2) The measuring cell is simplified to use only one piezoelectric ceramic disk instead of three. We present an implementation of this design intended for liquid samples. Data obtained with this design revealed that a soft extra spacer is necessary to allow for thermal contraction of the sample in the axial direction. Model calculations show that flow in the radial direction is hindered by the confined geometry of the cell when the liquid becomes viscous upon cooling. The method is especially well-suited for—but not limited to—glassy materials.

An efficient use of plasticizers in rubber compounds requires an understanding of their miscibility behavior. Besides the chemical properties of both rubber and plasticizer, the rigidity of the plasticizer plays an important role for their miscibility. The miscibility is investigated here using the glass transition measured by differential scanning calorimetry and broadband dielectric spectroscopy (BDS). Additionally, the interfacial relaxation and phase separation measured by BDS are confirmed by transmission electron microscopy. While the flexible plasticizer, poly-(α-methylstyrene), stays miscible in a silica-filled polybutadiene rubber compound, the more rigid plasticizer, indenecoumarone (IC), shows a phase separation at high concentrations. The phaseseparated IC tends to accumulate at the silica surface.