TORCh: Thermally Optimized Ramped Chirps for the Efficient Generation of Rheological Master Curves

Recent improvements in the design of optimally windowed chirps, combined with their implementation into commercial rheometer software, streamline methods for thermorheological characterization of polymeric materials and enhance ease and robustness of data processing. We explore a novel test strategy for master curve generation by simultaneously imposing a thermal ramp and a sequence of windowed chirps to sweep rapidly through frequency and temperature space. By careful consideration of the effects of thermal diffusivity and the rate of material change, we develop a Thermally Optimized Ramped Chirp (TORCh) protocol for accurate characterization of thermorheologically simple materials, which is two- to five-fold faster and yields approximately 10-fold higher data density (when compared to conventional discrete frequency sweeps). The temperature dependence of the resulting shift factors is well described by the WLF equation, and the data density enables precise tracking of the locus of the thermorheological glass transition (max(tan δ)) through temperature and frequency space.