چكيده به لاتين
This study aimed to research on the effect of the carbon nanotubes (CNT) with structural defects on the properties of the CNT/epoxy nanocomposite at atomic levels using molecular dynamics (MD) simulation and quantum calculations . The simulation models are constructed via an in-situ curing process performed using the LAMMPS software and an in-house code. The obtained thermomechanical properties of the cross-linked pure polymer and comparing the results with experimental counterparts demonstrate the validity of the curing process, and highlights the importance of curing process in the modeling of thermoset polymers. In order to choose the correct simulation model, in the present study, the non-equilibrium MD simulation was utilized to consider the influence of the CNT length on the nanocomposites stiffness through the isothermal isobaric ensemble. The results indicated that reinforcing efficiency of the embedded CNT is not constant and reduce for shorter CNTs. On the other hand, due to the Van der Waals interactions between the CNT and polymer atoms, the CNT-polymer bonding could not be assumed as a perfect bound. Subsequently, a relationship formula was derived to predict the effective stiffness of an embedded CNT in terms of its length. This relationship is used to predict more accurate elastic modulus of nanocomposite, that was validated using published experimental data.
Based on our pervious findings, the continuous single wall carbon nanotube (SWCNT) as a long nanofiber has been considered to construct the nanocomposite representative volume elements (RVEs). The mechanical behavior of RVEs has been studied in the presence of pristine SWCNT and the SWCNTs including Thrower-Stone-Wales and vacancy defects. The results indicated that despite the enhancement of longitudinal and transverse Young's moduli, the shear moduli of the nanocomposite including the pristine SWCNT were reduced compared to the pure polymer. It was shown that although the presence of defects weakens the elastic properties of isolated SWCNTs, they improve the nanocomposite properties. To explain these findings, the influence of defects on the structural integrity of nanocomposite and interfacial bonding strength have been investigated. Also, the CNT-polymer interface was studied to analyze the mechanism of load transfer through interfacial shear strength simulation test. The distribution analysis of the polymer around the CNT indicated that the polymer properties at a certain distance from the CNT surface, differ from the pure polymer. Therefore, the defects cause to increase the longitudinal and transverse shear moduli through improvement of the CNT-polymer interaction and consequently enhancement of interfacial shear strength.
Furthermore to study the extreme states of impurity defects, additional simulations were performed, in which the performance of carbon, silicon carbide and boron nitride nanotubes are compared.
