Constrained Bucking Analysis Of Carbon Nanotube With Molecular Dynamics Simulation And Beam Model

Carbon nanotubes (CNTs), besides the promising applications in nanoelectronics, reinforced composite due to their extraordinary electrical and mechanical properties, have the potential performance in nanobiology and nanomedicine because the high surface area feature and excellent chemical stability enable CNTs adsorb and conjugate with a variety of therapeutic and diagnostic agents, such as drugs, genes, antibodies and biosensors. Scientists proved that CNTs are capable of penetrating into the cell directly and delivering drug without metabolism in the body. However, it is required that the length of CNTs is suitable to enter the cell, and the toxicity of CNTs is dependent the length, which requries the understanding of CNTs-cells interaction mechanism and investigation on mechanical stability of CNTs constrained by surrrounding cells. As for CNTs-cell interaction and deformation of CNTs with the cell constraint, only the entry of CNTs into cell has been well studied and explained, relatively little is known about how CNTs deform and interact with cell constraints after entry. Therefore, to understand the CNTs-cells interaction, the length-dependent toxicity and ultimately advance the development of nanotechnology in biomedicine, it is required to elucidate the mechanical stability of ultra-long CNTs constrained by cells or tissues under compression.In this paper, we used Molecular Dynamics (MD) method to study the buckling and post-buckling behavior of the constrained single-walled carbon nanotube (SWCNT). A rigid nanotube, the diameter of which is much larger than that of SWCNT, is modeled the constraint tube to restrict the movement of SWCNT. With the outer tube fixed, the inner tube is compressed with different strain rates and temperature to investigate the mechanical stability of constrained SWCNT.MD simulations reveal an unusual twice-buckling mode for CNTs with constraint, the first buckling mode can be Euler buckling or sinusoidal buckling under different strain rate and temperature, while the second buckling mode is helical buckling before the final collapse. To compare the results of MD, an Euler buckling beam model is established to predict the behavior of SWCNT, and a simple formula is derived for the critical strain and the freestanding length of post-buckling. In addition, the theoretical profile of adhesive and helical CNTs is given, which is compared with the profile by MD simulations. The analytical model is capable of obtaining the accurate parameter values characterizing the different buckling mode, which is verified by MD simulations.