Date of Award

7-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Aerospace, Physics, and Space Sciences

First Advisor

Mary Helen McCay

Second Advisor

Karen Lozano

Third Advisor

Razvan Rusovici

Fourth Advisor

James R. Brenner

Abstract

In this study, the electromagnetic interference (EMI) shielding effectiveness (SE) of vapor grown carbon nanofiber (VGCNF) reinforced polyvinylidene difluoride (PVDF) composite and PVDF/VGCNF thermally sprayed with magnetite (Fe3O4) and graphite has been investigated. EMI SE evaluations were performed in the frequency range of 30 kHz-1.5 GHz. The developed nanocomposite (NC) system was fabricated by high shear mixing using a Banbury type mixer. The material was then subjected to compression molding. Subsequently, the films were thermally sprayed using Fe3O4/graphite powder. The NC and coated NC films had average thicknesses of 0.82 mm and 0.93 mm, respectively. The NC films were subjected to physico-thermal, electrical, and EMI characterization. For the NC material, a morphological analysis was performed by scanning electron microscopy, and characterization complemented with Fourier transform infrared spectroscopy, and X-ray diffraction analyses. The thermal properties of the uncoated NC films were studied by differential scanning calorimetry and thermogravimetric analysis, which revealed the influence of VGCNFs on thermal stability and phase transitions. For the coated NC material, the features and morphologies were observed by optical microscopy and scanning electron microscopy. The surface properties were explored by XRD, X-ray photoelectron spectroscopy, and Raman analyses. Tensile adhesion test showed improvements from previously reported values in the range of 6-15 MPa. The NC film electrical conductivity measurements for in-plane and through plane was gradually enhanced by increasing the VGCNF loading up to 10-4 S/cm, while the coated NC film showed a significant increase for in-plane conductivity up to 10-2 S/cm and no change was observed in through-plane electrical measurements. Resistivity for in-plane measurements decreased by up to three orders of magnitude between the uncoated and coated NCs. The EMI SE value observed for the layered composite system increased to an average of 52 dB. This study illustrates the processing, structure, properties, and material relationships for lightweight, multi-layered films with significantly enhanced electrical conductivity and EMI shielding for aerospace and aircraft applications.

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