Experimental Investigation on Patterning of Anchored and Unanchored Aligned Carbon Nanotube Mats by Fluid Immersion and Evaporation

Pattern formation by capillary forces in a nanoscale system was studied experimentally. Densely packed, vertically aligned mats of order 100 microns in height comprised of 20 nm diameter multi-walled carbon nanotubes were fabricated and treated with various liquids. The carbon nanotubes deflected and rearranged under the action of surface tension as the liquids evaporated, and remained fixed once dried. The size analysis of the resulting patterns in these experiments and in the literature showed they are distributed within one standard deviation from the mean, and there are, in general, many more small sizes than large ones within a pattern. Preexisting defects in the mats were found to play a significant role in the pattern formation process, both in this work and in the literature, whereas the properties of the specific liquid used and the height of the mats did not. A novel method for anchoring the aligned mats within another material using spin-coating was developed. An anchored mat made in this way was successfully held in place even under the application of a 5.5 m/s water jet. The anchoring method allowed the first known investigation of the role of boundary conditions in this pattern formation process. Under identical experimental conditions to cases where patterns are formed in the unanchored mats, it was found that no pattern formation occurs in the anchored mats. A population balance model based on conservation of area was applied to the pattern formation process, but sufficient details are lacking to make predictions. The anchoring method and its prevention of pattern formation is a very important finding, and is relevant to applications of the aligned mats, such as field emission displays, supercapacitors, tissue culture scaffolds, and friction drag reducing surfaces.