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oai:www.ideals.illinois.edu:2142/99288 2023-07-11 col_2142_5131 col_2142_14787 com_2142_5130 com_2142_9630 com_2142_234

Ewoldt, Randy H. Carey-De La Torre, Olivia 2018-03-13T15:44:44Z 2018-03-13T15:44:44Z 2017-09-20 2017-12 "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." Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2018-03-13 without embargo terms The student, Olivia Carey-De La Torre, accepted the attached license on 2017-09-08 at 14:39. The student, Olivia Carey-De La Torre, submitted this Thesis for approval on 2017-09-08 at 14:52. This Thesis was approved for publication on 2017-09-20 at 14:44. DSpace SAF Submission Ingestion Package generated from Vireo submission #11638 on 2018-03-13 at 10:03:32 Made available in DSpace on 2018-03-13T15:44:44Z (GMT). No. of bitstreams: 2 CAREY-DELATORRE-THESIS-2017.pdf: 7939801 bytes, checksum: 2fd2d98164a4218e54bc9ee324a66177 (MD5) LICENSE.txt: 4221 bytes, checksum: 5f147bec8b244a6afb33f6d21b279bc9 (MD5) Previous issue date: 2017-09-20 application/pdf http://hdl.handle.net/2142/99288 en Copyright 2017 Olivia Carey-De La Torre Stiffening Asymptotic nonlinearity Medium amplitude oscillatory shear (MAOS) Elastic stiffening in PVA-Borax studied with experimental medium amplitude oscillatory shear text text Mechanical Sci & Engineering Mechanical Engineering University of Illinois at Urbana-Champaign Thesis M.S.