When 9:30 AM - 11:30 AM Jan 10, 2017
Where GM Room, Lurie Engineering Center
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Electrostatically Induced Carbon Nanotube Alignment for Polymer Composite Applications


Wesley Chapkin
Thesis Defense

The ability to manipulate nanoparticles to tailor composite properties is a growing area of interest in nanotechnology. Precise control of nanotube alignment has been shown to be an important factor in creating nanocomposites with enhanced electrical and mechanical properties; however, in-depth analyses of alignment dynamics within polymer matrices has typically been limited to end state specimens, which inhibits the development of an accurate model to describe the dynamics of CNT alignment. We have developed a non-invasive technique utilizing polarized Raman spectroscopy to measure changes in CNT alignment in situ and in real time in a polymer matrix under an applied electric field. With this technique, we have confirmed the prediction of faster alignment for CNTs under electric fields of greater frequency and potential. We also show discrete levels of alignment as a function of CNT length based on an electrostatic potential energy model, which demonstrates the interconnectedness of the various processing steps. Real-time polarized Raman spectroscopy also allows us to demonstrate the loss of CNT alignment that occurs after the electric field is removed, which reveals the need for fast polymerization steps or the continued application of the aligning force during polymerization to lock in CNT alignment. Furthermore, through a study on the effect of polymer viscosity on the rate of CNT alignment, we have determined that shear viscosity serves as the controlling mechanism for CNT rotation, a finding that matches theoretical work concerning rigid rod mobility in a polymer melt. This indicates that the manipulation of temperature (and indirectly the viscosity of the matrix) will have a direct effect on the rate of CNT alignment, which could prove useful in expediting the manufacturing of CNT-reinforced composites cured at elevated temperatures. Nanoparticle additions to carbon fiber reinforced plastics (CFRPs) are another growing area of research. With applied electric fields, we show the ability to generate enhanced electric field gradients within the carbon fiber gaps, which lead to increased levels of alignment. These measurements have been corroborated with COMSOL modeling. This finding could potentially lead to the development of CFRPs with CNT additions that selectively enhance the composite properties outside the carbon fiber interphase in the neat epoxy.

DISSERTATION COMMITTEE:

Chair:

Prof. Alan Taub, MSE

Members:

Prof. John Kieffer MSE

Prof. Michael Thouless, ME, MSE

Cognate:

Prof. Wei Lu, ME