Nanometer-thin single-walled carbon nanotube (CNT) films collected from the aerosol chemical deposition reactors have gathered attention for their promising applications. Densification of these pristine films provides an important way to manipulate mechanical, electronic, and optical properties. To elucidate the underlying microstructural level restructuring, which is ultimately responsible for the change in properties, we perform large scale vector-based mesoscopic distinct element method simulations in conjunction with electron microscopy and spectroscopic ellipsometry characterization of pristine and densified films by drop-cast volatile liquid processing. Matching with the microscopy observations, pristine CNT films with a finite thickness are modeled as self-assembled CNT networks comprising entangled dendritic bundles with branches extending down to individual CNTs. Simulations of these films under uniaxial compression uncover a soft deformation regime extending up to an ∼75% strain. When removing the loads, the pre-compressed samples evolve into homogeneously densified films with thickness values depending on both the pre-compression level and the sample microstructure. The significant reduction in thickness is attributed to the underlying structural changes occurring at the 100 nm scale, including the zipping of the thinnest dendritic branches.
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We acknowledge useful discussions with Adam Boies, James Elliott, Kris Wise, and Ben Jensen. Computational resources supporting this work were provided by the NASA High End Computing Program through the NASA Advanced Supercomputing Division at Ames Research Center, by the Minnesota Supercomputing Institute, and by SkolTech. The authors thank Mr. Boris Zabelich for partial help with TEM imaging and acknowledge the OtaNano— Nanomicroscopy Center of Aalto University for a part of this research. This work was supported by NASA NNX16AE03G and by the University of Minnesota MnDrive and Grant-in-Aid programs. I.O. acknowledges financial support from the Russian Foundation for Basic Research (RFBR) under Grant No. 18-18-29-19198. Y.G. acknowledges financial support from RFBR under Grant No. 18-29-20032. A.G. and A. G.N. acknowledge RFBR under Grant No. 19-32-90143. A.P.T. acknowledges the EDUFI Fellowship (No. TM-19-11079) from the Finnish National Agency for Education and the Magnus Ehrnrooth Foundation (the Finnish Society of Sciences and Letters) for personal financial support. T.D. greatly acknowledges support from the Fulbright U.S. Scholars program.
© 2020 Author(s).