Insight into Geometry-Controlled Mechanical Properties of Spiral Carbon-Based Nanostructures Ali Sharifian, † Mostafa Baghani, † Jianyang Wu, ‡ Gregory M. Odegard, § and Majid Baniassadi* ,†,∥ † School of Mechanical Engineering, College of Engineering, University of Tehran, P.O. Box 11155-4563, Tehran 1417466191, Iran ‡ Department of Physics, Jiujiang Research Institute and Research Institute for Biomimetics and Soft Matter, Fujian Provincial Key Laboratory for Soft Functional Materials Research, Xiamen University, Xiamen 361005, P. R. China § Department of Mechanical Engineering-Engineering Mechanics, Michigan Technological University, Houghton, Michigan 49931, United States ∥ University of Strasbourg ICube/CNRS, 2 Rue Boussingault, 6700 Strasbourg, France * S Supporting Information ABSTRACT: The spiral structures of carbon-based materials such as coiled carbon nanotube (CCNT) and graphene helicoid have attracted great attention for use in electrical and mechanical nanodevices. There are a couple of main reasons for this attitude such as striking properties and behavioral diversity with regard to the ever-increasing need for miniaturization of devices. In this research, using atomistic simulations, the effects of geometric parameters (e.g., cross- sectional shape, pitch angle, inner diameter, and outer diameter) on the mechanical properties of CCNT are studied. Interestingly, the results show that the mechanical properties (e.g., Young’s modulus, stretchability, etc.) have a heavy reliance on CCNTs’ geometric parameters. The stretching of the CCNT increases with the raising inner radius. Geometric changes affect the various stages that the CCNTs encounter during tensile and compression tests. The different mechanical behavior of various types of CCNTs leads to their diverse applications. Thus, these results can give an insight to design and develop new-generation nanodevices. 1. INTRODUCTION Over the past decades, carbon-based materials such as graphene and carbon nanotubes (CNTs) have attracted a great deal of interest in different fields of nanoscience and nanotechnology because of their unique combination of thermal, mechanical, and electrical properties. 1−11 Their distinctive properties have triggered intensive studies into a wide variety of applications. They can now be used in nanoelectronic devices, 12−14 biological sensors, 4,15,16 nano- switches, 17−20 nanocomposites, 21,22 and nanoelectromechan- ical devices. 19,23,24 Particularly, coiled CNTs (CCNTs) and graphene helicoids (GHs) are greatly used in fabricating artificially new structures because of their fantastic properties and unique morphology. 25−28 CCNT fibers acting as ideal nanosprings are utilized to store and release energy because of their helical 3D structure. Considering the miniaturization mission of nanotechnology, CCNT is a major candidate for a new formation of electrical and mechanical nanodevices. Theoretically, the atomic structure of CCNTs was first suggested by Ihara et al. 29,30 So far, several researchers have described the structure of CCNTs and relationships between geometric parameters (e.g., diameter, length, and position of defects). 31−35 Chuang et al. 36,37 introduced a generalized classification for helical CNTs (HCNTs) and expressed that CCNTs are composed of the hexagonal network together with nonhexagonal pairs such as pentagon−heptagon or quadri- laterals−octagon pairs. These nonhexagonal pairs induce positive and negative curvatures. Experimentally, Zhang et al. 38 have synthesized regular shapes of CCNTs in certain laboratory-settings and described the fabrication procedure for thin-coiled nanotubes. In more recent studies, researchers have successfully synthesized high quality of CCNTs. 39,40 To date, there have been several experiments that investigated the mechanical properties of CCNTs with different geometrical parameters. 41−44 Chen et al. 45 employed atomic force microscopy (AFM) cantilevers to perform tensile loading on an individual CCNT. They observed that CCNT behaves like an elastic spring at low strains with spring constant of 0.12 N/m. In another research, Poggi et al. 46 examined mechanical response of a multiwalled carbon nanospring in compression with AFM and showed that nonlinear response of the nanospring is consistent with compression and buckling of Received: December 22, 2018 Revised: January 14, 2019 Published: January 15, 2019 Article pubs.acs.org/JPCC Cite This: J. Phys. Chem. C 2019, 123, 3226-3238 © 2019 American Chemical Society 3226 DOI: 10.1021/acs.jpcc.8b12269 J. Phys. Chem. C 2019, 123, 3226−3238 Downloaded via NORTHWESTERN UNIV on October 24, 2019 at 02:16:53 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.