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Fig. 4. A) Aligned straight fibers with a single fiber shown in the enlarged inset; B) Aligned sinusoidal fibers with a single fiber shown in the enlarged inset; C) Aligned helical fiber with a single fiber shown in the enlarged inset. (All scale bars in inset images are 1 µm).
This and the next image are from:
Sumit Khatri, Jizhe Cai and Mohammad Naraghi (Department of Aerospace Engineering, Texas A&M University, 3409 TAMU, College Station, TX 77843-3409, United States),
“Formation of wavy carbon nanofibers and nanocoils via precursor constrained microbuckling”, Journal of the Mechanics and Physics of Solids, Vol. 134, Article 103763, January 2020, https://doi.org/10.1016/j.jmps.2019.103763
ABSTRACT: Flexible carbon nanosprings and wavy nanofibers can be used in micro and nanoelectromechanical system devices, deployable structures, flexible displays, energy storage, catalysis, nanocomposites and a multitude of other uses. A novel method to produce wavy and helical carbon nanofibers (CNFs) is presented here. The CNFs with controlled geometry were fabricated via pyrolysis of electrospun polyacrylonitrile (PAN) nanofibers as the precursor. The waviness/helicity of nanofibers was achieved by subjecting the precursor nanofibers to constraint buckling inside a thermally shrinking matrix. The much higher tendency of the matrix to shrink, compared to PAN nanofibers, was achieved by controlling the microstructure and crystallinity of the precursors. The formation of the wavy/helical geometry was explained quantitatively via mechanistic models, by minimizing the total mechanical energy stored in the PAN-matrix system during the matrix shrinkage. Despite its simplicity in considering elastic deformations only, the model provided reasonably quantitative matching with the experiments. Compared to existing methods in generating wavy/helical nanofibers, such as chemical vapor deposition growth methods, our method provides a more controllable geometry which is suitable for large scale production of aligned buckled CNFs.
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