Frequency-sweep medium-amplitude oscillatory shear (MAOS)

Abstract

Medium-amplitude oscillatory shear (MAOS) is asymptotically nonlinear and a valuable tool for inferring structure from rheology. However, a drawback of conventional MAOS is the time and material intensive nature of experiments. Many strain amplitude sweeps, and typically multiple sample loadings, are required to obtain frequency-dependent properties. Here, we propose a new MAOS methodology that is much faster (fewer data points) and cheaper (fewer material loadings): The frequency-sweep MAOS. Similar to conventional frequency-sweep SAOS (small-amplitude oscillatory shear), we use only a frequency-sweep. A key challenge is that measurable MAOS data lie within a narrow and frequency-dependent domain between the instrument resolution (at small strain amplitudes) and nonlinear behavior beyond asymptotic nonlinearity (at large strain amplitudes). This necessitates a nonconstant strain amplitude γ0(ω) for the frequency-sweep instead of a single constant strain amplitude. We provide guidelines for finding this γ...