University of Cambridge > > Engineering - Mechanics and Materials Seminar Series > Carbon Nanotube Mechanics: nano and macro; liquid and solid; stiff and soft—but always conductive

Carbon Nanotube Mechanics: nano and macro; liquid and solid; stiff and soft—but always conductive

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Certain materials properties are viewed as contradictory. For example, high electrical and thermal conductivity are associated with hard, crystalline materials such as metals or graphite. Conversely, softness is associated with biological materials, polymers, colloids, and disordered structures, which are also thermally and electrically insulating. We have essentially accepted that certain ostensible contradictions cannot be resolved. For example, we have no material that is electrically conductive and can be sutured or sewn, despite the obvious need in medical devices and wearable electronics. This ostensible contradiction has caused an interesting split between “soft” and “hard” condensed matter. Within soft condensed matter, we split liquids between colloids and solutions—perhaps artificially so.

The combination of nanoscale properties of “solid” carbon nanotubes (CNTs), and their translation at the macroscopic scale, and their behavior in liquids, are making us rethink these artificial divisions between “soft” and “hard”, and between colloidal and solution behavior in complex fluids. In this lecture, I will discuss how CNT in liquid phases can and should be viewed as hybrids between polymer molecules and colloidal particles, and how this approach can be used to design directed assembly routes for soft conductors.

Even at minute concentrations, CNTs form complex fluid phases with intriguing properties. In ultra-dilute solutions, CNT behave as ideal semiflexible Brownian filaments; surprisingly (or not?), their bending stiffness follows continuum scaling laws. In crowded environments (e.g., gels), CNTs reptate like stiff polymers; surprisingly, the small bending flexibility of CNTs strongly enhances their motion. In thermodynamic solvents, slender CNTs form liquid crystalline phases at minuscule concentrations. CNTs solutions can be used for making transparent, conducting, flexible films and coatings, as well as highly porous, soft three-dimensional foams. At high concentration, CNTs liquid crystals can be spun into well-aligned, packed macroscopic fibers. Because of their near-perfect microstructure, these fibers are ideal for studying the relationship between “molecular” CNT properties and macroscale CNT material behavior. CNT fibers and foams combine high conductivity, strength, and the emergent property of softness. As soft conductors, CNT fibers provide a natural interface to the electrical function of the body as restorative sutures for electrically damaged heart tissue as well as electrodes for stimulating and sensing the activity of the brain.

This talk is part of the Engineering - Mechanics and Materials Seminar Series series.

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