Mechanical hole-burning spectroscopy: Demonstration of hole burning in the terminal relaxation regime

We have developed a mechanical spectral hole-burning (MSHB) scheme that is analogous to dielectric and magnetic spectral hole-burning techniques. Previous dielectric nonresonant spectral hole-burning experiments have been performed close to the glass temperatures of glass-forming materials and interpreted in terms of dynamic heterogeneity. The present study focuses on polymeric systems far above the glass temperature and in the terminal (reptation) regime. Theoretically, we examine Kaye-Bernstein-Kearsley-Zapas and Bernstein-Shokooh nonlinear viscoelastic constitutive models, which do not invoke an explicit heterogeneous dynamics for the relaxation response, to study MSHB, and find that both models fail to capture the subtle mechanical holes observed in the experiments. Experimentally, we successfully burned mechanical holes and show that the hole intensities vary as a function of "waiting time" and pump amplitude. The results suggest that MSHB is a potentially powerful tool with which to examine the dynamics of complex fluids.