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GEL FORMATION OF METALLO-SUPRAMOLECULAR POLYMERS

WENG, WENGUI
http://rave.ohiolink.edu/etdc/view?acc_num=case1194555000

Abstract Details

2008, Doctor of Philosophy, Case Western Reserve University, Macromolecular Science.
Utilizing metal-ligand binding as the driving force for the self-assembly a series of mechanically-strong metallo-supramolecular gels, which exhibit dramatic reversible responses to a variety of stimuli, including thermal, mechanical and chemical, have been prepared in the presence of a ZnII alone or with a small percentage of lanthanide metal ion (LaIII). Microscopic examination reveals that the supramolecular metal-ligand coordination species, in acetonitrile solvent, form globular colloidal particles, which appear to exhibit spherulitic structure, indicating crystallization and phase separation accompany the gelation process. The responsive nature of the gels can be tailored by the metal ion salts used to form the gels and by external electrolytes, such as formic acid and tetrabutyl ammonium perchlorate. The disruption of this network by mechanical shear, and its facile reformation when shear is removed, are the origin of the pronounced thixotropic behavior of the gels. Increase of the concentration of LaIII prechlorate ions in the sonicated gels decreases the gel modulus, which correlates to a decrease in crystallinity and size of the spherulitic particles. Utilizing mixed solvent systems consisting of a good solvent (DMSO) with either a non-solvent (water) or poor solvent (ethylene glycol) we are able to systematically vary the morphology and responsive behaviors of the metallo-supramolecular gels, formed by a metallo-supramolecular polymer, E5:Zn. By tailoring the solvent composition it is possible to produce highly transparent gels, which are very strong, but which are also highly mechano-responsive, i.e. they exhibit pronounced yielding and thixotropic behavior. Gelation kinetics was found to be very dependent on thermomechanical history of the samples, i.e. shaking, thermal quenching, and exposure to air all lead to much faster gel formation. Gels containing lanthanum(III) ions were readily formed in solvent mixtures. The gelation time and gel strength was found to be dependent on the amount of LaIII added. Higher LaIII content leads to longer gelation times and lower gel strengths. The effect is more significant when lanthanum(III) nitrate is used, compared to the crosslinking salt, lanthanum(III) perchlorate. Gelation of metallo-supramolecular polymers from E4 and E6, monomer with tetraethylene glycol and hexaethylene glycol cores, respectively, was also achieved in the presence of transition metal ion ZnII. It was found that these slight changes in the core length of the monomer lead to substantial change in the gel characteristics compared to E5:Zn. Whereas transparent gels of E5:Zn and E6:Zn can be easily prepared, no transparent gel could be formed using E4:Zn. This phenomenon was attribute to the lower solubility of the E4:Zn polymer.
Alexander Jamieson (Advisor)
435 p.
Gel; Metallo-supramolecular polymer; rheology; responsive; colloidal

Recommended Citations

Citations

  • WENG, W. (2008). GEL FORMATION OF METALLO-SUPRAMOLECULAR POLYMERS [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1194555000

    APA Style (7th edition)

  • WENG, WENGUI. GEL FORMATION OF METALLO-SUPRAMOLECULAR POLYMERS. 2008. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1194555000.

    MLA Style (8th edition)

  • WENG, WENGUI. "GEL FORMATION OF METALLO-SUPRAMOLECULAR POLYMERS." Doctoral dissertation, Case Western Reserve University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1194555000

    Chicago Manual of Style (17th edition)

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This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.