(352i) Time-Strain Superposition in Soft Glasses

Soft glassy materials are typified by large relaxation times and thus it is imperative to probe their long time responses. Most of these systems are athermal, and thus the conventional time-temperature superposition (TTS) approach has not proven to be suitable for accessing long time behaviors. We report a simple time-strain superposition (TSS) procedure that can be used instead to create rheological maps of soft glassy dynamics spanning over unprecedented time-scales. Experimental results from model soft nanoparticle suspensions as well as self-suspended nanoparticle fluids are presented. The roles of temperature and strain in assisting the relaxation in materials that exhibit TTS and TSS, respectively, are found to be analogous; the shift factors are shown to exhibit a WLF like dependence on strain in TSS. The generality of the approach is confirmed by theoretical calculations using the soft glassy rheology (SGR) model that also predict similar behavior, thus suggesting that time-strain superposition is a generic feature of all soft glasses.