IMPROVEMENT OF MAGNETIC CARBON NANOTUBE DISPERSION BY SURFACE TREATMENT WITH DIAZONIUM SALT FOR AEROSPACE POLYMER NANOCOMPOSITES

Open Access
- Author:
- Trivedi, Shreya Shailesh
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 09, 2018
- Committee Members:
- Namiko Yamamoto, Thesis Advisor/Co-Advisor
- Keywords:
- Aerospace
Materials
Composites
Carbon nanotubes
Polymer nanocomposites
Magnetic Assembly
Covalent functionalization
Diazonium salt - Abstract:
- Polymer nanocomposites (PNCs) reinforced with carbon nanotubes (CNTs) can be potentially integrated into fiber reinforced plastics (FRPs) to improve interlaminar strength and transport properties, but application of CNT-PNCs is currently limited due to difficulty in scalable fabrication. FRPs, or composites, find applications in commercial aircraft and spacecraft structures due to their high mass-specific strength and stiffness instead of other metal alternatives. However, due to their multi-layer structure, the composites experience delamination under in-plane compressive loads, and have poor thermal and electrical transport properties. Recently, integration of nanofillers into these composites has been investigated to overcome these limitations. Nanofillers, due to the size scale, have high crystallinity, and thus superior mechanical and transport properties. Among many nanofillers, carbon nanotubes uniquely have very high aspect ratio and exceptional multi-functional properties, and thus CNT-PNCs are sought-after novel materials in aerospace applications for their tailorable and advanced mechanical, electrical, thermal, and actuation/sensing properties. However, their application is currently limited, because CNTs have a strong tendency to agglomerate, and cannot be implemented in a controlled manner, especially in bulk. Without proper control of nanofiller distribution, property enhancement cannot be achieved. This work involves experimental investigation of effective dispersion and active assembly of CNTs using surface functionalization and external magnetic fields, as a scalable and energy-efficient manufacturing process for structuring CNT-PNCs. The CNTs are first processed to be magnetically responsive, by e-beam coating the CNT tips with Nickel (Ni), after oxygen plasma functionalization to ensure Ni-CNT adhesion. The Ni-coated CNTs are then functionalized by in-situ formation of diazonium salt on their surfaces, to improve their dispersion and promote covalent bonding with the bisphenol-F based epoxy matrix (EPON 862). CNT alignment is achieved within the viscous matrix (~70 cP), after the short (~40 min) magnetic field application of small strength (~400 G vs. ~50 G of a typical refrigerator magnet). The steps to fabricate and functionalize the Ni-coated CNTs and to structure and cure CNT-PNCs are developed and improved in terms of the effective magnetic responsiveness, functionalization degree, and alignment degree. This work demonstrated the unique and scalable fabrication method of CNT-PNCs by improving CNT dispersion through the in-situ surface treatment that is critical for magnetic structuring of CNTs. In future, more detailed studies will be conducted about the damages caused to CNTs by this functionalization process, such as CNT graphitic structures, CNT lengths, and Ni coating adherence, and more. In addition, CNT assembly within polymer matrices using various magnetic fields will be explored to achieve 2D and 3D, potentially anisotropic CNT structures; CNT structure-property relationship studies will be conducted about mechanical, transport, and potentially actuation properties.