Shape-driven Arrest of Coffee Stain Effect Drives the Fabrication of Carbon-Nanotube-Graphene-Oxide Inks for Printing Embedded Structures and Temperature Sensors
Carbon nanotube (CNT) based binder-free, syringe-printable inks, with graphene oxide (GO) being used as the dispersants, have been designed and developed. We discover that such a printability of the ink is directly attributed to the uniform deposition of the GO-CNT agglomerates, as opposed to the ‘coffee-staining’ despite these aggregates being micron-sized. We explain that the ellipsoidal nature of the micron-scale GO-CNT agglomerates/particles enables these particles to severely perturb the air-water interface, triggering a large long-range capillary interaction that causes the uniform deposition by overcoming the “coffee-stain”-forming forces from the evaporation-mediated flows. We measure the properties of this ink and identify a temperature-dependent resistance with a negative temperature coefficient of resistance (TCR) α ~ −2.2×10−3/0C. Finally, the printing is conducted on flat and curved surfaces, for developing polymer-ink embedded structures that might serve as precursors to syringe-printable CNT-based nanocomposites, and for fabricating sensors-like patterns that demonstrate α ~ −1.7×10−3/0C with large averaged resistance drop (per unit temperature) of −20 Ω/0C.