Paper Number
PO125
Session
Poster Session
Title
Rheology-guided direct-write printing of carbon nanotube structures
Presentation Date and Time
October 23, 2019 (Wednesday) 6:30
Track / Room
Poster Session / Ballroom C on 4th floor
Authors
- Owens, Crystal E. (Massachusetts Institute of Technology)
- McKinley, Gareth H. (Massachusetts Institute of Technology, Department of Mechanical Engineering)
- Hart, Anastasios J. (Massachusetts Institute of Technology)
Author and Affiliation Lines
Crystal E. Owens, Gareth H. McKinley, and Anastasios J. Hart
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA
Speaker / Presenter
Owens, Crystal E.
Text of Abstract
The bulk properties of components fabricated by direct-write 3D printing are governed by the key characteristics of the original ink in combination with structure imposed by the printing process. Nanomaterials can provide novel properties not exhibited in bulk materials, and provide a route to functional inks that, for instance, can enable 3D printing of electronic and sensing components. In particular, carbon nanotubes (CNTs) have been measured to have outstanding electrical conductivity and current carrying capacity. Here, we present the development and direct-write printing of aqueous CNT inks in the interest of establishing novel manufacturing methods for printed electronics.
CNTs at high concentrations (>0.5%wt) entangle and act rheologically as thixo-elasto-viscoplastic materials. As CNTs behave as rigid rods in solution, strong shear and extensional flow have been shown to create flow-induced alignment. Due to strong shape anisotropy, the axial alignment of component CNTs is known to systematically affect ultimate strength and electrical conductivity of macroscopic CNT objects.
We print by dispensing CNT ink from a needle onto a motorized substrate, optionally extruding beneath a coagulating liquid that precipitates the CNTs, rapidly locking flow-oriented CNT structures in place. By tailoring the flow kinematics during our printing process, we enforce external control over the development of the microstructure, thus directing the final properties. We describe the effect of solution concentration on the rheology of single-walled CNTs dispersed in water, and explore the impact of shear-driven and extension-driven alignment on morphology and final properties of printed structures. We report the influence of processing parameters such as the rate of elongation, nozzle height, and shear rates on the feature resolution and conductivity of extruded features, and suggest relationships that connect rheological properties of the ink to printability of controllable and fine features.