Applications of recovery rheology: Psychorheology, thixotropy, and beyond

The field of rheology seeks to understand the viscoelastic nature of materials. Presently, most rheological studies examine only the total strain acquired by materials. Recovery rheology is a way of rheological thinking that acknowledges that the total strain consists of two components: the recoverable and unrecoverable strains. This thesis demonstrates that understanding the composite nature of strain leads to new ways of thinking about outstanding problems, new ways of interpreting data, and garners new insights from data. In particular, this thesis develops the use of recovery rheology to address problems in several areas of outstanding research including psychorheology, thixotropy, and the mathematics of oscillatory flows. Psychorheology is a subfield of rheology interested in studying the connection between the fundamental physics of materials and what people perceive while interacting with them. Whereas studies have historically emphasized studying individuals’ sensory evaluations as described by the individual on an arbitrary scale, in this work we examine physical forces applied by individuals as they probe materials in situ. Study of subjects’ transient signals allows for definitions of behaviors with direct rheological equivalencies. These definitions are easily adapted to corresponding rheological experiments, and thus the establishment of direct relationships between sensory perceptions and the transient material properties that evoke them. Thixotropy is a rheological phenomenon associated with the microstructural evolution of materials. Specifically, it deals with changes in material properties due to the prior shear history that the material experienced. In this work, thixotropic materials are examined in terms of recoverable and unrecoverable strains in creep and oscillatory flows to show that thixotropy is apparently a purely viscous effect – a view not always reflected in the literature. The results are also used to highlight how superficial analysis of the dynamic moduli can lead to misleading or incorrect interpretation of thixotropy. Oscillatory tests are very commonly used in rheology to characterize materials. Historically, recovery rheology tests have been time consuming to perform since they are usually measured iteratively. By thinking about oscillatory flows in terms of strain components, this work provides mathematical proof that oscillatory recovery tests can be greatly expedited by introducing a new experimental protocol. The new protocol takes about as much time as a traditional oscillatory test. The protocol is applied to model and other materials. The mathematics are applied to well-known empirical rules such as the Cox-Merz rules and Laun’s rules. They are also used to develop a simple nonlinear model which captures all common amplitude sweep behaviors. The principles of recovery rheology are further examined in the context of defining material parameters, particularly in the context of oscillatory and arbitrary flows. Existing definitions, such as the dynamic moduli, are shown to have shortcomings, and new definitions are proposed. Discussion and experimental examples are provided. In summary, this thesis advances the understanding of the entire field of rheology by demonstrating new experimental and analytical methods that provide more information about materials than those used as the standard today. Problems in several different areas of interest are explored and, in some cases, solved.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Burgeson, Eric Michael

Contributors dc:contributor

• Rogers, Simon A
• Kong, Hyunjoon
• Statt, Antonia
• Sing, Charles E

• Rheology
• Recovery Rheology
• Psychorheology
• Thixotropy

Statement dc:rights

• Copyright 2024 Eric Michael Burgeson

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/125672

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F125672