November 19
@
4:00 PM
–
5:00 PM
Simon Rogers
Department of Chemical Engineering
University of Illinois Urbana-Champaign
Champaign, IL
Recovery Rheology
Rheological studies of real-world behaviors use idealized protocols to elucidate the underlying constitutive relations and are typically based on measurements of the stress response to strains or strain rates or vice versa. Strains and rates can therefore be thought of as rheological “atoms”, from which any complicated protocol can be built. It is commonly observed, however, that when stresses are removed, some of the deformation is recovered. Strain is therefore a composite parameter and can be decomposed into recoverable and unrecoverable components by iteratively performing constrained recovery steps during any experiment. By acknowledging strain’s composite nature, we not only get more information about how materials respond to forces that can be used to construct more accurate constitutive relations, we must also face the limitations of our current nomenclature and some of the assumptions that underly modern rheology.
Case studies are presented to highlight the benefits of forming rheological investigations around a desire to understand the recoverable and unrecoverable behaviors of soft materials. An initial focus will be on yield stress fluids, where recovery rheology has provided answers to long-standing problems, and has led to the formation of new constitutive relations for viscoelastic and yield stress fluids. Gelation is another area that has benefited from a recovery rheology analysis. I’ll show how a simple model built on recovery principles is able to capture the complex rheology observed during gelation. Furthermore, recovery rheology is shown to lead to conceptually clearer definitions of common parameters, as well as dimensionless groups such as the Deborah and Weissenberg numbers without the difficulty of addressing nonlinear relaxation times or experimental timescales.