Sharif Digital Repository

Understanding the flow of liquids and particularly water in nanochannels is important for scientific and technological applications, such as for filtration and drug delivery. In this study, we perform molecular dynamics simulations to investigate the transfer of single-file water molecules across straight or nonstraight single-walled carbon nanotubes (SWCNTs). In contrast with the macroscopic scenario, the nonstraight nanostructure can increase the water permeation. Remarkably, compared with the straight SWCNT, the nonstraight SWCNT with the minimal bending angle of 30° in the simulations can enhance the water transport up to 3.9 times. Also increasing length and diameter of carbon nanotubes... 

Nowadays, water desalination is a widely-used method for producing clean and fresh water. Recent researches in this area have mostly focused on Reverse Osmosis technology which is one of the most efficient technologies in water desalination. A new idea to increase the efficiency of a recently-designed reverse osmosis membrane called “Honeycomb Carbon Nanotube Membrane” is presented through molecular dynamics simulation. Although in this study only the inlet area of the honeycomb structure which is a Y-shaped entrance, is modeled and studied, but obviously, any improvement in the membrane inlet, equals better results at outlet which means a more efficient desalination process. Present thesis... 

This thesis is devoted to the simulation of biomolecules manipulation using Molecular dynamics (MD). In order to investigate the manipulation behavior, we have used the Ubiquitin as biomolecule, a single-walled carbon nanotube (SWCNT) as manipulation probe, a graphene sample as substrate. Along this line, a lot of simulations are conducted to study the effects of different conditions on the success of manipulation process. These conditions include tip diameter, vertical gap between tip and substrate, initial orientation of protein, and the simulation environment (dry or wet). The results demonstrate that tips with bigger diameters and smaller distances with respect to the substrate increase... 

This research describes a new and relatively general method to grow well-aligned carbon nanotubes (CNTs) on cobalt-deposited stainless steel by thermal chemical vapor deposition (CVD) of ethylenediamine precursor. The CNTs are vertically aligned at high density over large areas on the surface. Different effective parameters in growth of carbon nanotubes, as type of substrate, surface treatment, temperature of growth , feeding carbon supplies have been studied. Finally, aligned carbon nanotubes have been prepared by 100-150 nm diameter and 9µ length. CoOx•nH2O–MWCNTs nanocomposites were successfully synthesized, using a cathodic electrochemical reduction of H2O2 to deposit cobalt... 

In some concrete projects, the consolidation of concrete is quite challenging due to the congestion of rebar and the complex concrete placement. Self-compacting concrete (SCC) can overcome these problems. On the other hand, nanomaterials in concrete can be used to improve the engineering properties of concrete and adverse environmental effects. This study uses aluminum-nano oxide and carbon-nano tubes (by replacing 1, 3, and 5% by weight of cementitious materials) to enhance the physical and mechanical properties of SCC. Additionally, adverse environmental effects of SCC improve by replacing 35% of cement with combustion furnace slag. Experimental results showed that with increasing... 

Carbon nanotubes are cylinders in Nano scale formed of carbon atoms with covalent bonds that contain a significant electrical and mechanical features. Carbon nanotubes are divided into two main types: multi-walled carbon nanotubes (MWCNTs) and single walled carbon nanotubes (SWCNTs). A SWCNT is a rolled graphene sheet (graphene is in fact a single sheet of graphite). SWCNTs has lately been considered as one of most interesting research cases. The reason why researchers have been fond of investigating about graphene has been its unconventional quantum hall effects, high room-temperature electrical conductivity and its mechanical stability despite of being composed of single layer atom... 

Due to high cost and ineffectiveness of molecular models a new method for coupling continuum models with molecular models is used. In this method, the continuum and molecular domains are overlapped. Comparing the results obtained from the concurrent simulations and molecular dynamic simulations proves the accuracy of the method used. The method is used for modeling single layered graphene sheets, stress contours are presented for multiscale and both static and dynamic simulations of concurrent. For multiscale simulations two different carbon nano tubes are investigated and strees-bond angle and strees-bond length are also presented  

During the last decade, thanks to a combination of exploding computational power and improved physical insight into material behavior, continuum and atomistic simulations improved greatly. Both classes of methods are now used to solve problems, which are more complicated than ever with greater accuracy than ever before. Nevertheless, there still exist problems for which neither method alone is sufficient. In general, atomistic simulations cannot be used for such length scales due to the restrictions on the number of atoms that can be simulated, along with the time scales, which they can be simulated for. In contrast, continuum simulations tend to fail at the atomic scale, for example due to... 

According to human needs and in line with the development of advanced technologies, different biomedical Engineering fields like hard tissue implants are growing rapidly. Despite significant biotechnology Developments in recent years, some problems to the recognition of implants related osseointegration phenomena persist. The deficient osseointegration and implant-associated infections are key issues for the long-term clinical success of titanium and titanium alloy implants, while development of multifunctional surfaces that can simultaneously overcome these problems remains highly challenging. Therefore, the ultimate goal of this paper was to improve bone cell attachment and simultaneously... 

An impedimetric human papilloma virus (HPV) DNA biosensor based on gold nanotubes (AuNTs) in label free detection was materialized. The AuNTs decorated nanoporous polycarbonate (AuNTs-PC) template as biosensor electrode was fabricated by electrodeposition method. The single strand DNA (ss-DNA) probe was covalently immobilized onto the AuNTs-PC electrode. The hybridization of target sequences with the ss-DNA probe was observed by the electrochemical impedance spectroscopy (EIS). The biosensor showed high selectivity and could differentiate between the complementary, mismatch and non-complementary DNA sequences. The EIS measurements were matched to Randle's equivalent circuit. The... 

This thesis presents a research on the physical behavior of water inside carbon nanotubes (CNTs). Molecular simulations are carried out using the Monte Carlo method in the canonical and grand canonical ensembles. Due to the difference between the inter-molecular forces in the axial and radial directions, the anisotropic pressure tensor is calculated for water confined inside the CNTs with the diameters of 0.88, 1.08, 1.28, and 1.48 nm at different densities using the Monte Carlo simulations. Using the assumption of effective extended Lennard-Jones interactions between the nearest neighbors, a set of new equations of state for water confined inside the CNTs is derived and shown to be... 

Detection and determination of ultra-trace electroactive materials using electrochemical methods have been widely employed by researchers since they offer a fast, easy and reliable approach. In this way, developing of new nanoelectrodes with special and unique properties plays a profound role on the achievement of better results.
Gold nanoelectrode ensembles are one of the most important nanoelectrodes which due to the high surface area, chemical, electrochemical and physical stability, and integration of a large number of individual nanoelectrodes, introduce excellent opportunities to be employed as promising nanoelectrodes in determinations applications.
In this work, preparation... 

In this research we focus on fabrication, characterization and performance of biosensors based on vertically aligned carbon nanotubes. Carbon nanotubes have been used as high density carbon nanotubes and nanoelectrode array. Carbon nanotubes have been grown using plasma enhanced chemical vapor deposition method. Characterization and performance of biosensors have been studied by cyclic voltammetry and electrochemical impedance spectroscopy methods.
The mediator-less glutamate biosensor is prepared based on covalently attached glutamate dehydrogenase on vertically aligned carbon nanotubes. The biosensor has a low detection limit of 57 nM, two linear range of 0.1-20 µM with sensitivity of... 

We have studied binary structures contain; as grown thin film of carbon nanotubes (CNTs) , CNT rich polymeric composite, Pd doped WO3 thin film, and also hybrid thin film which was mixed CNTs and WO3 nanoparticles and ternary structure which was obtained by adding Pd to hybrid structure as a hydrogen gas sensor. The structure, morphology, chemical composition and quality of as–grown and functionalized CNTs and sensitive films were studied by SEM, TEM, XRD, XPS, DLS, FTIR and Raman spectroscopy methods. Variation of film’s electrical resistance after exposure gases is utilized as the principle of gas sensing. Multi-Walled Carbon Nanotube (MWCNTs) films were obtained by Thermal Chemical Vapor... 

In this project, two multiscale modeling procedures have been implemented to study the mechanical behavior of SWCNT/polymer composites. First, a new three-phase molecular structural mechanics/ finite element (MSM/FE) multiscale model has been introduced which consists of three components, i.e. a carbon nanotube, an interphase layer and outer polymer matrix. The nanotube is modeled at the atomistic scale using MSM, whereas the interphase layer and polymer matrix are analyzed by the FE method. Using this model, we have investigated the macroscopic material properties of nanocomposite with and without considering the interphase and compared the results with molecular dynamics (MD) simulations.... 

In this research, initially, thin film of TiO2 nanotube arrays (TNA) was deposited on Titanium foil (Ti), using anodization technique under an optimized applied voltage of 60 V, for 200 minutes. Highly smooth and ordered TNA formed by effective two-step anodization method. The TNA synthesized by this procedure, showed a better surface smoothness and tube order as compared with the TNA prepared in one-step anodization process. The electrolyte which was utilized for the anodization process, contained 90% of Ethylene Glycol (EG) in volume, 10% de-ionized water (DI) in volume, 0.1M Ammonium Fluoride (NH4F), and 0.5 ml Phosphoric Acid (H3PO4) 1M in order to adjust the pH about 5.6. Moreover, the... 

The use of nanocomposite materials in various industries such as aerospace, oil and gas, automotive, etc. has become increasingly widespread due to its unique thermal and mechanical properties. Due to the problems and costs of the production process and experimental testing for optimal construction, it is necessary to propose a low-cost method for estimating the mechanichal properties of these materials. In this research, the mechanical properties of polymetric nano carbon nanocomposites have been estimated by multi-scale method with using finite element analysis by Abaqus software. the mechanical properties of nanocarbon composites have been extracted by using the multi-scale method that... 

The increasing growth of composite materials in various industries and the use of these materials in the production of the main structures, recognized study and simulation of accurate behavior of these materials at different scales. On the other hand, the appearance of Nano-scale materials with amazing physical and mechanical properties and the use of these nanoparticles as reinforcement in the structure of polymer composites, further highlights the importance of simulating the behavior of polymer nanoparticles at different scales. One of the issues that is considered in various industries, especially in the airspace industry, is the phenomenon of fatigue. The complexity of the fatigue... 

The goal of this research is investigation and analysis of a surface consists of vertically aligned carbon nanotubes (VACNTs) using continuum mechanics modeling. Today these kinds of surfaces also known as the darkest material have a particular importance in industries. Knowing the properties of a material is one of the most important things in analysis and designing using that kind of material, so extraxting the stiffness matrix of a material could be a big step for starting analyzing it. In this thesis a lattice of VACNTs with two different layouts and several unique geometrics is simulated using molecular dynamics approach using the Lammps software. The general stiffness matrix of the... 

Nowadays, composites have wide applications in different industries especially in aerospace industry because of their high strength to weight ratio. Epoxy 5052 for its relatively good mechanical properties and high thermal resistance has vaidly use for manufacturing of large composite components. However; fracture toghness of epoxy resins is not good in comparison to their other exceptional properties. Therefore, researchers have endeavored to improve this characteristic with different approaches. One of these methods is nanotechnology. Since the components in aerospace industry are often under impact loads and impact strength of these materials has been less studied, effect of carbon...