Elastic stiffening in PVA-Borax studied with experimental medium amplitude oscillatory shear

Carey-De La Torre, Olivia

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https://hdl.handle.net/2142/99288 Copy

Description

Title

Elastic stiffening in PVA-Borax studied with experimental medium amplitude oscillatory shear

Author(s)

Carey-De La Torre, Olivia

Issue Date

2017-09-20

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

Ewoldt, Randy H.

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Stiffening
• Asymptotic nonlinearity
• Medium amplitude oscillatory shear (MAOS)

Abstract

"In this thesis, we seek to understand the mechanisms of strain-stiffening and shear-thickening often observed in transient or associative polymer hydrogels; specifically, Poly(vinyl) alcohol (PVA) crosslinked with Sodium tetraborate (Borax), or PVA-Borax. We use medium amplitude oscillatory shear (MAOS) as a tool to measure asymptotically nonlinear viscoelastic material functions across a range of compositions of PVA-Borax with storage moduli ranging from $G_0 \approx 100-3000$~Pa. The material functions can be related to model parameters to gain physical insight into the structure of the material system. We demonstrate that with a ""good"" structure-rheology model \cite{AshwinModel}, a single nonlinear parameter scales the asymptotically nonlinear material functions, and we argue that finite-extensibility is the sub-dominant cause of nonlinearity ($<5$\%) compared to stretch-induced crosslinking. Furthermore, we validate the model by using first-harmonic MAOS measures to predict third-harmonic MAOS via a single nonlinear model parameter. Finally, we define a universal nonlinear parameter to compare the strength of nonlinearities across a range of strain-stiffening materials."

Graduation Semester

2017-12

Type of Resource

text

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http://hdl.handle.net/2142/99288

Copyright and License Information

Copyright 2017 Olivia Carey-De La Torre

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