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

"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 G₀ \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."

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2018

Author dc:creator

• Carey-De La Torre, Olivia

Contributors dc:contributor

• Ewoldt, Randy H.

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

Statement dc:rights

• Copyright 2017 Olivia Carey-De La Torre

Language dc:language

en

Handle dc:identifier

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

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/99288