The viscoelastic relaxation dynamics of a series of poly(methyl methacrylate) [PMMA] based nanocomposites filled with carbon nanotubes have been studied using dynamic mechanical analysis and broadband dielectric spectroscopy. The networks were prepared using four methods: (i) melt mixing, (ii) solution processing, (iii) in-situ polymerization, and (iv) polymer grafting. Nanotube modifications included surface oxidation via acid exposure and surface functionalization for polymer grafting. The effect of variations in processing method and nanotube modification on glass transition temperature (Tg) and relaxation dynamics was investigated. The relaxation behavior of the nanocomposites was sensitive to processing method and nanotube functionalization. Nanotube loading (to 5 wt%) led to a progressive increase in rubbery modulus, with the increase more pronounced in the solution-processed samples owing to enhanced nanotube dispersion. In the case of the oxidized nanotubes, loading led to an increase in modulus, but also a systematic decrease in Tg of ~ 15°C with 3 wt% nanotubes. For in-situ polymerized (PMMA/MWNT-ox) nanocomposites, there was no readily discernable trend in Tg. Composites prepared via in-situ polymerization in the presence of methyl methacrylate functionalized tubes (i.e., polymer grafting) displayed a positive shift in Tg of nearly 20°C at 1 wt% loading. Investigation of the dielectric relaxation of the PMMA/MWNT composites indicated a percolation threshold between 0.3 and 0.4 wt% MWNT.
| Identifer | oai:union.ndltd.org:uky.edu/oai:uknowledge.uky.edu:gradschool_theses-1063 |
| Date | 01 January 2010 |
| Creators | Placido, Andrew Jonathan |
| Publisher | UKnowledge |
| Source Sets | University of Kentucky |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | University of Kentucky Master's Theses |
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