Novel understandings of yielding in soft materials through recovery rheology techniques

Griebler, James J.

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https://hdl.handle.net/2142/129834 Copy

Description

Title

Novel understandings of yielding in soft materials through recovery rheology techniques

Author(s)

Griebler, James J.

Issue Date

2025-07-01

Director of Research (if dissertation) or Advisor (if thesis)

Rogers, Simon A.

Doctoral Committee Chair(s)

Rogers, Simon A

Committee Member(s)

• Kong, Hyun J
• Sing, Charles E
• Hutchens, Shelby

Department of Study

Chemical & Biomolecular Engr

Discipline

Chemical Engineering

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Yield Stress
• Rheology
• Recovery Rheology
• Soft Matter

Language

eng

Abstract

his thesis develops and applies the framework of recovery rheology to better understand complex behaviors in yield stress fluids and other soft materials. Recovery rheology acknowledges that strain can be experimentally decomposed into recoverable and unrecoverable parts, allowing for a direct physical interpretation of how materials store and dissipate energy when deformed or stressed. By leveraging this framework, it is shown that a wide range of phenomena that have remained poorly understood can be accurately accounted for by experimental studies and described by the construction of rheo-physical models. Using iterative recovery protocols, it is shown that everyday commercial products such as Cool Whip and Cream Cheese exhibit universal recovery behavior akin to model yield stress fluids. The concept of strain shift is introduced and developed in novel ways which reveals continuous flow even below the traditionally defined yield stress, challenging longstanding assumptions about solid-like behavior in this regime. Strain shift is then utilized further to clarify the nature of a phenomenon often called ’double yielding’, demonstrating that the so-called two-step transition - seen when two overshoots are present in the loss modulus of an amplitude sweep - is not due to multiple yield points, but rather an elastic softening followed by yielding. Finally, this work resolves the phenomenon delayed yielding through iterative creep and recovery tests, showing that flow initiates immediately upon stress application, and the delay is a consequence of the recoverable strain dominating the unrecoverable until some delay time is reached. Finally, this work ends in a historical journey through recovery tests in the field of rheology. This is done by starting with the earliest works by Lord Kelvin and Ludwig Boltzmann, through K. Weissenberg and J. M. Burgers, to the modern day understanding of recovery rheology. In addition, this work examines the history of the Boltzmann superposition principle, revealing that its foundation in Hookean elasticity is inadequate for fluids and proposes a new constitutive model to use in place of Hooke’s law for the superposition principle, consistent with observations from recovery rheology. Altogether, this work establishes recovery rheology as a unifying lens through which fundamental rheological behaviors can be viewed and understood. Specifically this work shows novel methods and understandings specifically for yield stress fluids, with applications that apply to any soft materials. It offers not only new experimental protocols and analytical tools but also a conceptual shift in how we define the main concepts in rheology.

Graduation Semester

2025-08

Type of Resource

Text

Handle URL

https://hdl.handle.net/2142/129834

Copyright and License Information

Copyright 2025 James J. Griebler

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