Structural analysis and applications of polymer networks formed from surface-active copolymers in aqueous solvents.
Item
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Title
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Structural analysis and applications of polymer networks formed from surface-active copolymers in aqueous solvents.
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Identifier
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AAI9130383
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identifier
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9130383
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Creator
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Varelas, Charalambos G.
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Contributor
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Adviser: Carol A. Steiner
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Date
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1991
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Chemical | Chemistry, Polymer | Engineering, Materials Science
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Abstract
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The structure and properties of dispersed phase hydrogels made from surface-active graft copolymers have been investigated using fluorescence spectroscopy, rheology and calorimetry. In addition, the solute retention and release properties of these gels have been investigated with an eye toward applications in controlled drug release devices. A mathematical model was developed which we will ultimately use to predict the release behavior of our gels from their structure.;The graft copolymer used in this study is hydrophobically modified hydroxyethyl cellulose (HMHEC). It is composed of a water-soluble backbone to which hydrophobic grafts are covalently bonded. We have shown that the polymer phase-separates in water/alcohol solvents due to the inherent incompatibility of certain of the polymer segments with water. That leads to the formation of amphiphilic hydrogels that exhibit unique swelling properties in the solvents. These hydrogels are clear, flexible and viscoelastic. They are composed of hydrophobic microdomains dispersed throughout the bulk phase, that can sequester hydrophobic solutes and release them over time. These unique properties make these hydrogels potentially advantageous in applications such as separation processes and controlled release of pharmaceutical agents.;The results presented here are divided into 4 principal conclusions. First, the best hydrogels form at 50/50 (v/v) ethanol/water solvents and at polymer concentrations higher than 0.6% (w/w). By best gels we mean the most stable in structure with the highest storage modulus. Second, the hydrogels are characterized by microdomains which are hydrophobic, not in contact with water and stable to drying and swelling. At low shear stress, the microdomains behave as temporary linkages of finite lifetimes. The molecular weight between microdomains was found to be independent of the volume fraction of polymer in the gel. The number of linkages per backbone ranges from 22.8 {dollar}\pm{dollar} 1.3 to 26.2 {dollar}\pm{dollar} 1.5 over the frequency range 30-50 rad/sec. Third, 1% HMHEC gels can absorb tryptophan and theophylline at average levels 73 {dollar}\pm{dollar} 3%, and 50 {dollar}\pm{dollar} 7% higher than water and release the solutes at a constant rate for 8 and 10 h, respectively. Fourth, the mathematical model developed can be used in conjunction with our structural characterization results to predict the optimum gel composition for a particular release profile.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
