Electrochemical studies of volume phase transitions of temperature -responsive polymeric gels.
Item
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Title
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Electrochemical studies of volume phase transitions of temperature -responsive polymeric gels.
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Identifier
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AAI3115304
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identifier
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3115304
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Creator
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Zhang, Weimin.
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Contributor
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Adviser: Malgorzata Ciszkowska
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Date
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2004
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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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Chemistry, Analytical
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Abstract
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The objective of this project is to study volume phase transition of polymeric gels utilizing electroanalytical techniques. Two types of gels, poly(N-isopropylacrylamide), (NIPA), and poly(N-isopropylacrylamide- co-acrylic acid), (NIPA-AA), were studied in our project.;The oxidation of electroactive probes, which include 1,1' -ferrocenedimethanol (Fc(MeOH)2), 4-hydroxy-tempo (TEMPO), Ferrocenylmethyltrimethylammonium ion (FcTMA+) and Hexaammineruthenium(III) ion (Ru(NH6)3+) was studied in aqueous solutions and swollen state NIPA and NIPA-AA gels using Pt microdisk electrodes. The diffusion coefficient (D) of Fc(MeOH)2 in swollen state of gels is only about 15%--55% smaller than that in aqueous solution. However, the viscosity of these gels is approximately 5 orders of magnitude greater than that of aqueous solution. The value of activation energy ( Ea) for the diffusion of Fc(MeOH)2 in aqueous solution and in NIPA and NIPA-AA gels was almost identical. These data suggest that microscopic viscosity of solvent trapped in swollen gel network is similar to that in aqueous solutions.;A decrease of the D of a probe in swollen gels was analyzed in terms of "obstruction effect" and "hydration effect". A new model was developed to explain this phenomenon and experimental results were compared with predictions of that model.;For NIPA gels, after the volume phase transition, the D of Fc(MeOH)2 in collapsed gels decreased approximately 2 orders of magnitude when the gel collapsed. D of Fc(MeOH)2 in collapsed NIPA-AA gels does not change significantly.;Voltammetric experiments were also carried out for positively charged FcTMA+ and Ru(NH3)63+ in NIPA-AA gels with and without supporting electrolyte. After the volume phase transition occurs, a decrease of the D of both probes was observed. Such decrease is more pronounced in NIPA-AA gel without supporting electrolyte than that with supporting electrolyte.;UV-vis spectroscopy was used to study the distribution of Fc(MeOH) 2 between the collapsed polymer phase and released solution during the volume phase transition. The estimated concentration of Fc(MeOH)2 in collapsed phase is 4.5 times higher than that in the original swollen gel and 6 times higher than that in released liquid. The concentration of Fc(MeOH)2 in collapsed NIPA-AA gel is about 20% higher than that in original swollen gels.
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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.
