High Pressure Induced Binding Between Linear Carbon Chains and Nanotubes
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High Pressure Induced Binding Between Linear Carbon Chains and Nanotubes Gustavo Brunetto2, Nádia F. Andrade1, Douglas S. Galvão2, and Antônio G. Souza Filho1 1 Physics Department, Federal University of Ceará, 60440-900, Fortaleza, Ceará, Brazil 2 Applied Physics Department, State University of Campinas, 13083-970 Campinas, São Paulo, Brazil. ABSTRACT Recent studies of single-walled carbon nanotubes (CNTs) in aqueous media have showed that water can significantly affect the tube mechanical properties. CNTs under hydrostatic compression can preserve their elastic properties up to large pressure values, while exhibiting exceptional resistance to mechanical loadings. It was experimentally observed that CNTs with encapsulated linear carbon chains (LCCs), when subjected to high hydrostatic pressure values, present irreversible red shifts in some of their vibrational frequencies. In order to address the cause of this phenomenon, we have carried out fully atomistic reactive (ReaxFF) molecular dynamics (MD) simulations for model structures mimicking the experimental conditions. We have considered the cases of finite and infinite (cyclic boundary conditions) CNTs filled with LCCs (LCC@CNTs) of different lengths (from 9 up to 40 atoms). Our results show that increasing the hydrostatic pressure causes the CNT to be deformed in an inhomogeneous way due to the LCC presence. The LCC/CNT interface regions exhibit convex curvatures, which results in more reactive sites, thus favoring the formation of covalent chemical bonds between the chain and the nanotube. This process is irreversible with the newly formed bonds continuing to exist even after releasing the external pressure and causing an irreversibly red shift in the chain vibrational modes from 1850 to 1500 cm−1. INTRODUCTION Recently, studies on single-walled CNTs behavior on aqueous media were reported [1,2]. These studies showed that water can significantly affect the tube mechanical, but the compressed structures still preserve their elastic strength properties and an exceptional resistance to mechanical loading. These studies are suggestive that CNTs can be good platforms for applications in nanofluidic devices. It was experimentally observed [3] that when subjected to high pressures, linear carbon chains (LCCs) inside carbon nanotubes (CNT) present irreversible red shifts for some of their vibrational frequencies due to the LCC coalescences induced by the external pressure. In this work we have investigated, through fully atomistic molecular dynamics (MD) simulations, the behavior of single LCC confined inside CNT and subject to extreme high external hydrostatic pressures (up to 10 times higher than used to merge two LCC). Our results show that depending on the applied pressure values, the induced structural deformations can lead to the formation of covalent chemical bonds between the LCC and the tube walls. These newly formed bonds remain stable even when the applied pressures are removed. Similarly to the case where two LCC are merged, some vibrational frequencies are
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