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Amanda Way_ETD 2.pdf (5.93 MB)

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Stimuli-Responsive Nanofiber Composite Materials: From Functionalized Cellulose Nanocrystals to Guanosine Hydrogels

Way, Amanda E
http://rave.ohiolink.edu/etdc/view?acc_num=case1390388160

Abstract Details

2014, Doctor of Philosophy, Case Western Reserve University, Macromolecular Science and Engineering.
This dissertation focuses on different classes of stimuli-responsive materials, and in particular, on materials withnon-covalent fiber interactions. Chapters 2-4 focus on the functionalization of fibers within mechanically adaptive polymer nanocomposites and how this effects their mechanical properties. Chapter 5 highlights how altering fibers within a supramolecular guanosine hydrogel can effect the gel’s stability and mechanical properties. First, the effect of functionalization of cellulose nanocrystals (CNCs) is investigated, followed by the properties of their resulting nanocomposites in various polymer matrices. CNCs functionalized with carboxylic acid and amine moieties were prepared and the modulus of the CNC dispersions were shown to be sensitive to pH. When these CNCs were used as fillers in poly(vinyl acetate) (PVAc) nanocomposites it was demonstrated that pH- responsive films are obtained. Along these lines, negatively charged carboxylated CNCs were functionalized with uncharged propyl amine groups in order to alter the CNC surface charge. Three different CNC surface charges were synthesized, PVAc nanocomposites were made, and the mechanical properties and swelling characteristics of the nanocomposites were investigated. It was demonstrated that CNC surface charge does not effect the mechanical properties of the composites in the wet or dry state. However, as surface charge increases, the swelling and rateof mechanical switching increases. CNCs were also functionalized with temperature-responsive poly(oligoethylene glycol)monomethyl ether (meth)acrylates tocreate PVAc and poly(ethylene-co-vinyl acetate) (PEVA) reversible, heat-induced stiffening nanocomposites. When placed in water below LCST the nanocomposites stay soft but exhibit dramatic stiffening when heated above the LCST. Supramolecular guanosine hydrogels are an interesting class of stimuli-responsive materials that hold promise for biomedical applications. We show that that multi-valent polymeric 8-methoxy-guanosine derivatives can act as supramolecular crosslinking units between fibers of the hydrogelator, 8-methoxy-2¿,3¿,5¿-tri-O-acetylguanosine (8OMeTAcG) at biologically relevant saltconcentrations. These non-gelling polymeric derivatives resulted in a significant enhancement in the mechanical properties of the 8OMeTAcG gels as a result of fiber crosslinking. Furthermore, the modulus and shear sensitivity of the gels can be controlled by simply varying the ratio of the two gel components. Lastly, a number of the above stimuli-responsive materials were created via Radical Addition Fragmentation Chain Transfer (RAFT) polymerizations. As part of these studies, we investigated new types of RAFT agents thatmay be beneficial interms of access to new monomers or to new polymer architectures. A common precursor disulfide molecule, bis(dodecylsulfanyl thiocarbonyl)disulfide, was demonstratedto produce controlled, low PDI polymers in a RAFT-type mechanism, yielding access to polymers with high end- functionality, useful for further functionalization.
Stuart Rowan, Dr. (Advisor)
LaShanda Korley, Dr. (Committee Member)
Horst von Recum, Dr. (Committee Member)
Ica Manas-Zloczower, Dr. (Committee Member)
283 p.
Nanotechnology; Polymer Chemistry; Polymers
Cellulose nanocyrstals, guanosine, RAFT polymerization, nanocomposites

Recommended Citations

Citations

  • Way, A. E. (2014). Stimuli-Responsive Nanofiber Composite Materials: From Functionalized Cellulose Nanocrystals to Guanosine Hydrogels [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1390388160

    APA Style (7th edition)

  • Way, Amanda. Stimuli-Responsive Nanofiber Composite Materials: From Functionalized Cellulose Nanocrystals to Guanosine Hydrogels. 2014. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1390388160.

    MLA Style (8th edition)

  • Way, Amanda. "Stimuli-Responsive Nanofiber Composite Materials: From Functionalized Cellulose Nanocrystals to Guanosine Hydrogels." Doctoral dissertation, Case Western Reserve University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1390388160

    Chicago Manual of Style (17th edition)

case1390388160
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© 2013, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.