Samieh Haghighi

The tensile properties and fracture mechanism of hydroxyl-functionalized silicon carbide nanotubes (O-fSiCNTs) inserted into polymer matrices are explored and the outcomes are compared to results for the hydroxyl-functionalized carbon nanotubes (O-fCNTs) incorporated in similar matrices. The molecular dynamics (MD) method is used and the simulations are based on the notion of representative volume elements (RVEs). The incorporation of chemisorbed nanotubes in polymers has a profound effect on the enhancement of their mechanical properties. The O-fSiCNTs inside the polyethylene (PE) and polypropylene (PP) (O-fSiCNTs/PE and O-fSiCNTs/PP) possess lower Young’s modulus, maximum stress, and strain energy as compared to the O-fCNTs/PE and O-fCNTs/PP. The zigzag O-fSiCNTs/polymer experiences lower bearable maximum strains in response to imposed loads in comparison with the O-fCNTs/polymer which is opposite to what occurs in the armchair O-fSiCNTs and O-fCNTs/polymer. The more the functionalization degree is, the weaker the structure is and its stiffness, tensile strength, tolerable strain before fracture, and ability to absorption of internal energy decline. Not only are the zigzag O-fSiCNTs/polymer stiffer than the armchair O-fSiCNTs/polymer in every percent of functionalization, but also as compared to the armchair ones, they show a lower decrease in the variation of Young’s modulus with increasing the functionalization percentage.

Tensile properties such as Young’s modulus and ultimate tensile force are important properties in understanding the characteristics of nanocomposites. Besides, the importance of functionalization methods in modification of the unique mechanical and elastic properties of carbon nanotubes (CNTs) is being widely recognized. In this paper, the tensile properties of CNTs functionalized with carbene under physisorption of polymer chains, i.e., aramid and polyketone chains, are investigated by using a series of molecular dynamics (MD) simulations. The results illustrated that Young’s modulus of carbene-functionalized CNTs (cfCNTs) decreases by rising the weight percentage of carbene. By contrast, Young’s modulus of cfCNTs under physisorption of polymer chains (cfCNTs/polymers) increases as the carbene weight rises. In a particular carbene weight, Young’s modulus of cfCNTs/polymers decreases by increasing the chains of non-covalent functional groups. Moreover, it is shown that similar to Young’s modulus, ultimate tensile force of cfCNTs reduces by increasing the weight percentage of carbene whereas the ultimate tensile force of cfCNTs/polymers has an increasing trend with raising the carbene weight.

The average pull-out force and interaction energy of polyethylene (PE) cross-linked functionalized carbon nanotubes (cfCNTs) embedded in polymer matrices (PE-cfCNTs@polymers) was studied using molecular dynamics (MD) simulations. Accordingly, the pull-out process of PE-cfCNTs from inside polymer matrices, i.e., Aramid and PE, was performed under displacement control. The results obtained were compared with those of pure carbon nanotube (CNT) incorporated into polymer matrices (pure CNT@polymers). The influence on the pull-out force and interaction energy between the CNT and polymer of the structure of polymer matrices, the weight percentage and two types of distribution patterns of cross-linked PE chains, namely mapped and wrapped, was investigated. The results indicate that the structure of the polymers and distribution patterns of cross-linked PE chains strongly affect important parameters related to interfacial properties. The average pull-out force of mapped and wrapped PE-cfCNTs@polymers increases as the weight of attached PE chains on the CNT surface increases. The effect of wrapped structures on increasing the pull-out force is greater than that of the mapped configurations. Also, the PE-cfCNTs@polymers show higher average pull-out forces than those of their pure counterparts. As the CNT pulls out from the polymer matrix, an approximately linear reduction in the absolute value of interaction energy with the pull-out displacement is observed. However, this trend is changed to some extent by imposing instability through the wrapped PE-cfCNTs.

Based on molecular dynamics (MD) simulations, the buckling analysis of a perfect carbon nanotorus is presented herein. First of all, the minimum length of single-walled carbon nanotubes (SWCNTs) with different radii is determined at which perfect toroidal CNTs can be formed without any ripple at the inner side of the rings. According to the results, by increasing the radius of SWCNT (r), the radius of its corresponding perfect nanotorus (R) increases. Also, for SWCNTs with various lengths, it is found that the buckling force and strain of related carbon nanotoruses increase by increasing R/r. In addition, as the perfect toroidal CNTs are arranged vertically in a column form in accordance with two different schemes, the effects of increasing the radius (R) and the number of carbon nanotoruses (the height of the column made by nanotoruses) on the buckling force and strain are investigated. Based on the results, as a fixed number of carbon nanotoruses with the same radius are arranged vertically in the column form, the buckling force and strain increase by increasing R/r. By contrast, increasing the height of the column made by carbon nanotoruses with similar radius leads to the reduction of buckling force and strain.