Research in nanoparticle-reinforced composites is predicated by the promise for
exceptional properties. However, to date the performance of nanocomposites has not
reached its potential due to processing challenges such as inadequate dispersion and
patterning of nanoparticles, and poor bonding and weak interfaces. The main objective
of this dissertation is to improve the physical properties of polymer nanocomposites at
low nanoparticle loading. The first step towards improving the physical properties is to
achieve a good homogenous dispersion of carbon nanofibers (CNFs) and single wall
carbon nanotubes (SWNTs) in the polymer matrix; the second step is to manipulate the
well-dispersed CNFs and SWNTs in polymers by using an AC electric field.
Different techniques are explored to achieve homogenous dispersion of CNFs and
SWNTs in three polymer matrices (epoxy, polyimide and acrylate) without detrimentally
affecting the nanoparticle morphology. The three main factors that influence CNF and
SWNT dispersion are: use of solvent, sonication time, and type of mixing. Once a dispersion procedure is optimized for each polymer system, the study moves to the next
step. Low concentrations of well dispersed CNFs and SWNTs are successfully
manipulated by means of an AC electric field in acrylate and epoxy polymer solutions.
To monitor the change in microstructure, alignment is observed under an optical
microscope, which identifies a two-step process: rotation of CNFs and SWNTs in the
direction of electric field and chaining of CNFs and SWNTs. In the final step, the
aligned microstructure is preserved by curing the polymer medium, either thermally
(epoxy) or chemically (acrylate). The conductivity and dielectric constant in the parallel
and perpendicular direction increased with increase in alignment frequency. The values
in the parallel direction are greater than the values in the perpendicular direction and
anisotropy in conductivity increased with increase in AC electric field frequency. There
is an 11 orders magnitude increase in electrical conductivity of 0.1 wt% CNF-epoxy
nanocomposite that is aligned at 100 V/mm and 1 kHz frequency for 90 minutes.
Electric field magnitude, frequency and time are tuned to improve and achieve desired
physical properties at very low nanoparticle loadings.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2352 |
| Date | 15 May 2009 |
| Creators | Banda, Sumanth |
| Contributors | Ounaies, Zoubeida |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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