Behrouz Arash

A review on the application of nonlocal elastic models in modeling of carbon nanotubes and graphenes

Recent research studies on the application of the nonlocal continuum theory in modeling of carbon nanotubes and graphene sheets are reviewed, and substantial nonlocal continuum models proposed for static and dynamic analyses of the nano-materials are introduced. The superiority of the nonlocal continuum theory to its local counterpart, and the necessity of calibration of the small-scale parameter as the key parameter revealing small-scale effects are discussed. The nonlocal beam, plate, and shell models are briefly presented and potential areas for future research are recommended. It is intended to provide an introduction to the development of the nonlocal continuum theory in modeling the nano-materials, survey the different nonlocal continuum models, and motivate further applications of the nonlocal continuum theory to nano-material modeling.

Mechanical properties of carbon nanotube/polymer composites

The remarkable mechanical properties of carbon nanotubes, such as high elastic modulus and tensile strength, make them the most ideal and promising reinforcements in substantially enhancing the mechanical properties of resulting polymer/carbon nanotube composites. It is acknowledged that the mechanical properties of the composites are significantly influenced by interfacial interactions between nanotubes and polymer matrices. The current challenge of the application of nanotubes in the composites is hence to determine the mechanical properties of the interfacial region, which is critical for improving and manufacturing the nanocomposites. In this work, a new method for evaluating the elastic properties of the interfacial region is developed by examining the fracture behavior of carbon nanotube reinforced poly (methyl methacrylate) (PMMA) matrix composites under tension using molecular dynamics simulations. The effects of the aspect ratio of carbon nanotube reinforcements on the elastic properties, i.e. Youngs modulus and yield strength, of the interfacial region and the nanotube/polymer composites are investigated. The feasibility of a three-phase micromechanical model in predicting the elastic properties of the nanocomposites is also developed based on the understanding of the interfacial region.

Vibration of Single- and Double-Layered Graphene Sheets

Free vibration of single- and double-layered graphene sheets is investigated by employing nonlocal continuum theory and molecular dynamics simulations. Results show that the classical elastic model overestimated the resonant frequencies of the sheets by a percentage as high as 62%. The dependence of small-scale effects, sizes of sheets, boundary conditions, and number of layers on vibrational characteristic of single- and double-layered graphene sheets is studied. The resonant frequencies predicted by the nonlocal elastic plate theory are verified by the molecular dynamics simulations, and the nonlocal parameter is calibrated through the verification process. The simulation results reveal that the calibrated nonlocal parameter depends on boundary conditions and vibrational modes. The nonlocal plate model is found to be indispensable in vibration analysis of grapheme sheets with a length less than 8 nm on their sides.

A review on nanomechanical resonators and their applications in sensors and molecular transportation

Nanotechnology has opened a new area in science and engineering, leading to the development of novel nano-electromechanical systems such as nanoresonators with ultra-high resonant frequencies. The ultra-high-frequency resonators facilitate wide-ranging applications such as ultra-high sensitive sensing, molecular transportation, molecular separation, high-frequency signal processing, and biological imaging. This paper reviews recent studies on dynamic characteristics of nanoresonators. A variety of theoretical approaches, i.e., continuum modeling, molecular simulations, and multiscale methods, in modeling of nanoresonators are reviewed. The potential application of nanoresonators in design of sensor devices and molecular transportation systems is introduced. The essence of nanoresonator sensors for detection of atoms and molecules with vibration and wave propagation analyses is outlined. The sensitivity of the resonator sensors and their feasibility in detecting different atoms and molecules are particularly discussed. Furthermore, the applicability of molecular transportation using the propagation of mechanical waves in nanoresonators is presented. An extended application of the transportation methods for building nanofiltering systems with ultra-high selectivity is surveyed. The article aims to provide an up-to-date review on the mechanical properties and applications of nanoresonators, and inspire additional potential of the resonators.

Mechanical properties of carbon nanotube reinforced polymer nanocomposites: A coarse-grained model

Abstract In this work, a coarse-grained (CG) model of carbon nanotube (CNT) reinforced polymer matrix composites is developed. A distinguishing feature of the CG model is the ability to capture interactions between polymer chains and nanotubes. The CG potentials for nanotubes and polymer chains are calibrated using the strain energy conservation between CG models and full atomistic systems. The applicability and efficiency of the CG model in predicting the elastic properties of CNT/polymer composites are evaluated through verification processes with molecular simulations. The simulation results reveal that the CG model is able to estimate the mechanical properties of the nanocomposites with high accuracy and low computational cost. The effect of the volume fraction of CNT reinforcements on the Youngs modulus of the nanocomposites is investigated. The application of the method in the modeling of large unit cells with randomly distributed CNT reinforcements is examined. The established CG model will enable the simulation of reinforced polymer matrix composites across a wide range of length scales from nano to mesoscale.

Carbon Nanotube-Based Sensors for Detection of Gas Atoms

The potential of single-walled carbon nanotubes as nanosensors in detection of noble gases via a vibration analysis is investigated using molecular dynamics simulations. An index based on frequency shifts of the nanotubes in an environment of noble gas atoms is defined and examined to measure the sensitivity of the sensors. The effects of density of gas atoms on the tube sensors, the diameter and length of the tubes, and the type of restrained boundary of the tubes on the sensitivity are studied. The simulation results indicate that the resolution of a sensor made of a (8, 8) carbon nanotube with a length of 4.92 nm can achieve an order of 10−6 fg and the sensitivity can be enhanced by nanotubes with smaller sizes and stiffer boundary conditions.

Tensile fracture behavior of short carbon nanotube reinforced polymer composites: A coarse-grained model

Abstract Short-fiber-reinforced polymer composites are increasingly used in engineering applications and industrial products owing to their unique combination of superior mechanical properties, and relatively easy and low-cost manufacturing process. The mechanical behavior of short carbon nanotube (CNT) polymer composites, however, remains poorly understood due to size and time limitations of experiments and atomistic simulations. To address this issue, the tensile fracture behavior of short CNT reinforced poly (methyl methacrylate) (PMMA) matrix composites is investigated using a coarse-grained (CG) model. The reliability of the CG model is demonstrated by reproducing experimental results on the strain–stress behavior of the polymer material. The effect of the nanotube weight fraction on the mechanical properties, i.e. the Young’s modulus, yield strength, tensile strength and critical strain, of the CNT/polymer composites is studied in detail. The dependence of the mechanical properties of the composites on the orientation and length-to-diameter aspect ratio of nanotube reinforcements is also examined.

A coarse-grained model for the elastic properties of cross linked short carbon nanotube/polymer composites

Abstract Short fiber reinforced polymer composites have found extensive industrial and engineering applications owing to their unique combination of low cost, relatively easy processing and superior mechanical properties compared to their parent polymers. In this study, a coarse-grained (CG) model of cross linked carbon nanotube (CNT) reinforced polymer matrix composites is developed. A characteristic feature of the CG model is the ability to capture the covalent interactions between polymer chains, and nanotubes and polymer matrix. The dependence of the elastic properties of the composites on the mole fraction of cross links, and the weight fraction and distribution of nanotube reinforcements is discussed. The simulation results reveal that the functionalization of CNTs using methylene cross links is a key factor toward significantly increasing the elastic properties of randomly distributed short CNT reinforced poly (methyl methacrylate) (PMMA) matrix. The applicability of the CG model in predicting the elastic properties of CNT/polymer composites is also evaluated through a verification process with a micromechanical model for unidirectional short fibers.

Gene Detection With Carbon Nanotubes

The potential of carbon nanotubes (CNTs) as nanosensors in detection of genes through a vibration analysis is investigated with molecular dynamics. The carbon nanotube based nanosensor under investigation is wrapped by a gene whose structure includes a single strand deoxyribose nucleic acid (DNA) with a certain number of distinct nucleobases. Different genes are differentiated or detected by identifying a differentiable sensitivity index that is defined to be the shifts of the resonant frequency of the nanotube. Simulation results indicate that the nanosensor is able to differentiate distinct genes, i.e., small proline-rich protein 2 A, small proline-rich protein 2B, small proline-rich protein 2D, and small proline-rich protein 2E, with a recognizable sensitivity. The research provides a rapid, effective, and practical method for detection of genes.

Thermal Buckling of Multiwalled Carbon Nanotubes Using a Semi-Analytical Finite Element Approach

In this article, a semi-analytical finite element approach based on the nonlocal elastic shell model is proposed to study the thermal buckling of multiwalled carbon nanotubes (MWCNTs). By taking nonlocality into consideration, the small scale effect is incorporated into the model presented herein. Based upon the Eringen nonlocal elasticity, the displacement field equations coupled by the van der Waals interaction force are derived. Comprehensive results for the thermal buckling of multiwalled carbon nanotubes are given. The influences of the small scale parameter and boundary conditions on the thermal instability of MWCNTs are examined. It is indicated that the possibility of the radial buckling mode of deformation due to radially elevated temperature is significantly higher than that of axial buckling mode of deformation due to uniformly reduced temperature when carbon nanotubes experience thermal loads.