Slow dynamics, aging, and glassy rheology in soft and living matter

Abstract

We explore the origins of slow dynamics, aging and glassy rheology in soft and living matter. Non-diffusive slow dynamics and aging in materials characterised by crowding of the constituents can be explained in terms of structural rearrangement or remodelling events that occur within the jammed state. In this context, we introduce the jamming phase diagram proposed by Liu and Nagel to understand the ergodic-nonergodic transition in these systems, and discuss recent theoretical attempts to explain the unusual, faster-than-exponential dynamical structure factors observed in jammed soft materials. We next focus on the anomalous rheology (flow and deformation behaviour) ubiquitous in soft matter characterised by metastability and structural disorder, and refer to the Soft Glassy Rheology (SGR) model that quantifies the mechanical response of these systems and predicts aging under suitable conditions. As part of a survey of experimental work related to these issues, we present x-ray photon correlation spectroscopy (XPCS) results of the aging of laponite clay suspensions following rejuvenation. We conclude by exploring the scientific literature for recent theoretical advances in the understanding of these models and for experimental investigations aimed at testing their predictions.

Unexpected drop of dynamical heterogeneities in colloidal suspensions approaching the jamming transition

“…It is unlikely that such a correlation exists for events occurring in non-overlapping regions; in contrast, successive events in the same region will lead to partially correlated changes of phase when the direction of displacement persists during several events. Thus, p = 1.65 indicates intermittent supradiffusive motion, a behaviour close to the ballistic motion reported for many jammed systems 19,20 . Figure 3b shows the 1/σ 2 φ -dependence of χ * .…”

“…Surprisingly, as ϕ increases β grows above one, finally saturating around 1.3. A similar 'compressed' exponential relaxation has been observed in single 19,20 and multiple 21 scattering experiments on systems close to jamming, usually associated with ultraslow ballistic motion.…”

Stress relaxation in aging soft colloidal glasses

“…Generically, these materials are characterized by slow dynamics and often fail to achieve equilibrium within time scales that can be achieved in the laboratory [1]. They are therefore classified as soft glassy materials and serve as excellent model systems in the understanding of the non-equilibrium glass transition in hard condensed matter systems [2,3]. As a direct consequence of the particle crowding that exists in these materials, the constituent entities are arrested in a cage formed by their neighbors.…”

“…It is generally observed that for concentrations above 1 volume %, an aqueous suspension of Laponite undergoes ergodicity breaking soon after mixing Laponite powder in water [6,7]. During the last decade, various optical tools have been employed to investigate such ergodicity breaking and the subsequent aging dynamics in this system [3]. The intensity autocorrelation function measured in dynamic light scattering (DLS) experiments is seen to exhibit a two-step decay.…”

Aging of a homogeneously quenched colloidal glass-forming liquid

“…The non-stationary, slowly-evolving dynamics of deeply quenched fluids, referred to as aging, has been the subject of considerable attention over the last decade [1,2]. Concentrated emulsions [3], colloidal gels [4], and aqueous clay suspensions [5] are some examples of aging systems.…”