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Title:Elastic stiffening in PVA-Borax studied with experimental medium amplitude oscillatory shear
Author(s):Carey-De La Torre, Olivia
Advisor(s):Ewoldt, Randy H.
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
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.
Issue Date:2017-09-20
Rights Information:Copyright 2017 Olivia Carey-De La Torre
Date Available in IDEALS:2018-03-13
Date Deposited:2017-12

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