Abstract:
The physics behind the mechanism of memory formation and loss in soft materials is of great interest to understanding the behavior of biological, environmental, and industrial materials. The traditional rheological memory function quantifies the rate at which memory is lost and assumes that the memory originates from application of a step strain, making it difficult to apply to arbitrary transient rheological protocols. Recent studies of memory apply cyclic shearing and implement a stroboscopic protocol for determining differences and similarities in structural measures but have yet to connect the transient rheology to memory formation and loss. In this work, we propose a generalized memory function and apply it to the analysis of rheo-X-ray photon correlation spectroscopy (rheo-XPCS) experimental data from an aggregated fumed silica gel and predictions from a continuum model under dynamic shearing. Our proposal is defined in terms of changes in the ultimate recoverable strain over an interval and includes the traditional definition of memory in response to a small step strain, but generalizes it to any linear or nonlinear deformation or loading protocol, allowing for the determination of when and how quickly memories are imparted and forgotten. Our rheo-XPCS data show that the aggregate-level structure recorrelates whenever the change in recoverable strain over some interval is zero. The macroscopic recoverable strain is therefore a measure of the nano-scale structural memory. We further show that the magnitude of the structural recorrelation determined in rheo-XPCS is proportional to how much of the applied strain is recoverable. We therefore equate the property of memory with the behavior of recovery. Our proposed memory function is generic, as it can be equally applied to any soft materials under any deformation protocol. This work emphasizes the critical role of recoverable strain in connecting structural measures to bulk rheological responses, and adds another chapter to a building literature on the fundamental nature of recoverable strain.
Krutarth M. Kamani1 , Yul Hui Shim1, James Griebler1, Suresh Narayanan2, Qingteng Zhang2, and Simon A. Rogers1. 1Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign. 2X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
Bio: Simon A. Rogers is an Associate Professor in the Department of Chemical and Biomolecular Engineering at the University of Illinois at Urbana-Champaign and a 2022-2023 I. C. Gunsalus Scholar. Dr. Rogers uses experimental and computational tools to understand and model advanced colloidal, polymeric, and self-assembled materials. He joined the department in 2015. He received his BSc in 2001, BSc (Hons) in 2002; and his PhD from Victoria University of Wellington in New Zealand in 2011. He completed his postdoctoral research at the Foundation for Research and Technology in Crete, the Jülich Research Center in Germany, and the Center for Neutron Research at the University of Delaware. He has received the ACS PRF Doctoral New Investigator grant, the NSF CAREER award, the School of Chemical Sciences Teaching Award from UIUC, and is the 2022 recipient of the Arthur B. Metzner Early Career Award from the Society of Rheology.
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