Heterogeneity of the structural relaxation of jammed state in particle-filled elastomers

The Payne effect is a low-strain hysteretic softening in particle-filled elastomers which we recognize as part of jamming physics [1-2]. We find that in particle-filled elastomers aging at a fixed oscillatory strain $\gamma _{a}$ produces a spectral hole in the loss modulus vs strain spectrum which is localized near the aging strain [3]. Sequential aging at two strains reveals that when $\gamma _{a1}>\gamma _{a2}$ the resulting dynamic spectra appear to be a combination of that aged at $\gamma _{a1 }$and $\gamma _{a2}$; whereas for $\gamma _{a1}<\gamma _{a2}$, the resulting dynamic spectra only reflect the characteristic hole burning of the second strain after holding at $\gamma _{a2}$. This remarkable behavior of particle-filled elastomers suggests that structural relaxations in jammed state are heterogeneous and aging at a fixed strain $\gamma_{a}$ only affects part of the relaxation spectra. \newline \newline [1] \textit{Phys. Rev. E}, \textbf{2005}, 72 (3), 031406; \newline [2] \textit{Phys. Rev. Lett.}, \textbf{2005}, 95, 075703; \newline [3] \textit{Europhys. Lett.}, \textbf{2006}, 76(2) 278.