Dataset for Probing cage dynamics in concentrated hardsphere suspensions and glasses with high frequency rheometry

The cage concept, a central microscopic mechanism for glassy dynamics, has been utilized inconcentrated colloidal suspensions to describe a number of phenomena. Here, we probe the evolutionof cage formation and shear elasticity with increasing volume fraction in hard sphere suspensions, withemphasis on the short-time dynamics. To this end, we utilize linear viscoelastic (LVE) measurements, bymeans of conventional rotational rheometers and a home-made HF piezo-rheometer, to probe thedynamic response over a broad range of volume fractions up to the very dense glassy regime inproximity to random close packing. We focus on the LVE spectra and times shorter than thosecorresponding to the dynamic shear modulus G0 plateau, where the system approaches transientlocalization and cage confinement. At these short times (higher frequencies), a dynamic cage has notyet fully developed and particles are not (strictly) transiently localized. This corresponds to an effectivesolid-to-liquid transition in the LVE spectrum (dynamic moduli) marked by a high frequency (HF)crossover. On the other hand, as the volume fraction increases caging becomes tighter, particlesbecome more localized, and the onset of the localization time scale becomes shorter. This onset oftransient localization to shorter times shifts the HF crossover to higher values. Therefore, the study ofthe dependence of the HF crossover properties (frequency and moduli) on volume fractions providesdirect insights concerning the onset of particle in-cage motion and allows direct comparison withcurrent theoretical models. We compare the experimental data with predictions of a microscopicstatistical mechanical theory where qualitative and quantitative agreements are found. Findings includethe discovery of microscopic mechanisms for the crossover between the two exponential dependencesof the onset of the localization time scale and the elastic shear modulus at high volume fractions as aconsequence of emergent many body structural correlations and their consequences on dynamicconstraints. Moreover, an analytic derivation of the relationship between the high frequency localizedshort-time scale and the elastic shear modulus is provided which offers new physical insights andexplains why these two variables are experimentally observed to exhibit nearly-identical behaviors.