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Stimuli-responsive Materials and Structures with Electrically Tunable Mechanical Properties

Auletta, Jeffrey (2017) Stimuli-responsive Materials and Structures with Electrically Tunable Mechanical Properties. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Electricity, a convenient stimulus, was used to manipulate the mechanical properties of two classes of materials, each with a different mechanism. In the first system, macroscale electroplastic elastomer hydrogels (EPEs) were reversibly cycled through soft and hard states by sequential application of oxidative and reductive potentials. Electrochemically reversible crosslinks were switched between strongly binding Fe3+ and weak to non-binding Fe2+, as determined by potentiometric titration. With the incorporation of graphene oxide (GO) into the EPE, a significant enhancement in modulus and toughness was observed, allowing for the preparation of thinner EPE samples, which could be reversibly cycled between soft and hard states over 30 minutes. Further characterization of this EPE by magnetic susceptibility measurements suggested the formation of multinuclear iron clusters within the gel.

Copper-derived EPEs which exploited the same redox-controlled mechanism for switching between hard and soft states were also prepared. Here, the density of temporary crosslinks and the mechanical properties were controlled by reversibly switching between the +1 and +2 oxidation states, using a combination of electrochemical/air oxidation and chemical reduction. In addition to undergoing redox-controlled changes in modulus, these EPEs exhibited shape memory.

In the second system, electroadhesion between ionomer layers was exploited to create laminate structures whose rigidity depended on the reversible polarization of the dielectric polymers. The role of the counter-ion in determining the intrinsic and electroadhesive properties of poly(ethylene-co-acrylic acid) ionomers in bi- and tri-layered laminate structures was examined. PEAA ionomers were prepared with three tetraalkylammonium cations (NR4+, R = methyl, TMA+; ethyl, TEA+; and propyl, TPA+). Reflecting the increasing hydrophobicity of the longer alkyl chains, water uptake changed as a function of counterion with TMA+ > TEA+ > TPA+. The glass transition temperatures, electrical resistivities, elastic moduli, and coefficients of friction were measured and found to depend on the cation identity. Overall, the cation-influenced mechanical properties of the ionomer determined the flexural rigidity range, but not the magnitude of the rigidity change, between the on and off states.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Auletta, Jeffreyjta15@pitt.edujta150000-0002-7857-8780
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairMeyer,
Committee MemberWaldeck,
Committee MemberClark,
Committee MemberStar,
Date: 20 June 2017
Date Type: Publication
Defense Date: 30 March 2017
Approval Date: 20 June 2017
Submission Date: 5 April 2017
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 203
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Stimuli resonsive, polymer, mechanical properties, redox
Date Deposited: 20 Jun 2017 20:23
Last Modified: 20 Jun 2017 20:23


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