Nanoscience and Nanotechnology Commons^™

Effect Of Oxidation Of Graphene On Agglomeration And The Mechanical Properties Of Thermosetting Resins, Matthew A. Reil

Electronic Theses and Dissertations

Thermosetting resins are used extensively worldwide in applications ranging from adhesives to structural components. However, these resins generally fail in a brittle fracture mode which is undesirable in most situations. Graphene (G) and its derivatives have been considered as additives to epoxy for material property enhancement and varied results have been reported in the literature. In this work, the effects of the oxidation of G to graphene oxide (GO) on polymer interactions and plate agglomeration were studied by classical molecular dynamics (MD). Results from those simulations concluded that agglomerates were likely present in all G-based nanocomposites. The effect of these …

Atomistic Simulations Of Twin Facets Associated With Three-Dimensional { []011 } Twins In Magnesium, Qiyu Zeng, Mingyu Gong, Houyu Ma, Yao Shen, Jian-Feng Nie, Jian Wang, Yue Liu

Department of Mechanical and Materials Engineering: Faculty Publications

Twinning is a deformation mechanism that creates three-dimensional (3D) twin domains through the migration of twin facets. This occurs via the nucleation and glide of twinning disconnections (TDs), which can pile up to create twin facets. A comprehensive under- standing of twin facets associated with 3D twins, including their atomic structures and energies, is crucial for understanding deformation twinning. In this study, we propose a molecular statics/dynamics (MS/MD) approach to determine characteristic twin facets enclosing 3D non-equilibrium/equilibrium { [] 011 } twin domains, which has been much less studied than the counterpart { [] 012 } twin domains. The stability …

Molecular Modeling Of High-Performance Polymers, Sagar Umesh Patil

Dissertations, Master's Theses and Master's Reports

High-performance polymers are extensively used in the aerospace and aeronautics industries due to their low density, high specific strength, and high specific stiffness. These properties along with better infiltration with reinforcements [carbon nanotubes (CNTs), glass, etc.] capability make them an excellent candidate to fabricate Polymer Matrix Composites (PMCs) tailored for specific applications. The applications range from products used daily to deep space exploration. These materials are subjected to varying temperatures and pressures during fabrication and in service. Therefore, the evolution of their intrinsic properties needs to be studied and their ability to sustain extreme environmental conditions in outer space needs …

Graphene/Oxide Interactions With Polymer Networks Modeled Using Molecular Dynamics, Matthew Alan Reil

Electronic Theses and Dissertations

Due to its unique physical properties, graphene has shown great promise as an additive to Polymer Matrix Composites (PMCs) for material property enhancement. Achieving homogeneous dispersion of the graphene platelets within a polymeric network is critical to realizing these enhancements. Research has shown that achieving homogeneous dispersion of graphene platelets within PMCs is challenging as graphene is immiscible with most polymeric networks. This work used Molecular Dynamics (MD) simulations to demonstrate dispersion of graphene platelets within PMCs is inhibited by molecular surface charge potentials. Further simulations were conducted to demonstrate functionalized forms of graphene, specifically graphene oxide, have altered surface …

Coarse-Grained Dynamically Accurate Simulations Of Ionic Liquids At Vacuum-Interface, Tyler D. Stoffel

Theses and Dissertations--Mechanical and Aerospace Engineering

Ionic liquids, possessing improved properties in many areas of technical application, are excellent candidates as components in development of next-generation technology, including ultra-high energy batteries. If they are thus applied, however, extensive interfacial analysis of any selected ionic configuration will likely be required. Molecular dynamics (MD) provides an advantageous route by which this may be accomplished, but can fall short in observing some phenomena only present at larger time/length scales than it can simulate. Often times this is approached by coarse-graining (CG), with which scope of simulation can be significantly increased. However, coarse-grained MD systems are generally known to produce …

Interactions Between Dislocations And Three-Dimensional Annealing Twins In Face Centered Cubic Metals, Yanxiang Liang, Xiaofang Yang, Mingyu Gong, Guisen Liu, Qing Liu, Jian Wang

Department of Mechanical and Materials Engineering: Faculty Publications

Annealing twins often form in metals with a face centered cubic structure during thermal and mechanical processing. Here, we conducted molecular dynamic (MD) simulations for copper and aluminum to study the interaction processes between {1 1 1}1/2 <1 1 0> dislocations and a three-dimensional annealing twin. Twin boundaries are characterized with Σ3{1 1 1} coherent twin boundaries (CTBs) and Σ3{1 1 2} incoherent twin boundaries (ITBs). MD results revealed that dislocation-ITB interactions affect slip transmission for a dislocation crossing CTBs, facilitating the nucleation of Lomer dislocation.

Metal Segregation During The Solidification Of Titanium-Aluminum Alloys For 3d Printing Applications, Jwala Parajuli

Master's Theses

Titanium-Aluminum alloys are one of the widely used alloys in multiple engineering applications. They are highly preferred in Selective Laser Melting (SLM) processes due to their low density, high melting temperature, and good strength. Segregation occurs during the solidification of most alloys and produces a non-uniform distribution of atoms. In SLM, segregation may depict the type of adhesion between the two deposited interfacial layers and the strength between the interphase between an already solidified layer and a new one, and overall, the quality of the printed part. In order to avoid segregation, the understanding of the segregation behavior at atomistic …

Atomistic Simulations Of Novel Nanoscale Semiconductor Devices: Resistance Switches And Two-Dimensional Transistors, Joseph P. Anderson, Mahbubul Islam, David Guzman, Alejandro Strachan

The Summer Undergraduate Research Fellowship (SURF) Symposium

As transistors get smaller, we are achieving record levels of memory density. However, there is a limit to how small transistors can be made before their functionality breaks down. Thus alternatives to traditional transistor technology are needed. The two such technologies we examined are: resistance switching devices, which reversibly grow metal filaments through a dielectric, and two-dimensional transistors, which are capable of breaking through the scalability limit of traditional transistors. In order to design resistance switching devices which create filaments with some level of consistency, the dynamics of the filament formation need to be explored. Herein we model this process …

Modal Phonon Transport Across Interfaces By Non-Equilibrium Molecular Dynamics Simulation, Yang Zhong, Tianli Feng, Xiulin Ruan

The Summer Undergraduate Research Fellowship (SURF) Symposium

Phonons represent the quantization of lattice vibration, responsible for heat transfer in semiconductors and dielectrics. Phonon heat conduction across interfaces is crucially important for the thermal management of real-life devices such as smartphones, electric vehicles, and satellites. Although recent studies have broadly investigated spectral phonon contribution to lattice thermal conductivity, the mechanism of phonon modal transport across interfaces is still not well-understood. Previous models, including the acoustic mismatch model (AMM) and diffuse mismatch model (DMM), only consider elastic process while neglecting inelastic phonon contributions. Herein, we employ spectral Non-Equilibrium Molecular Dynamics Simulation (NEMD) to probe the temperature and heat flux …

Molecular Dynamics Simulations Of Dna-Functionalized Nanoparticle Building Blocks On Gpus, Tyler Landon Fochtman

Graduate Theses and Dissertations

This thesis discusses massively parallel molecular dynamics simulations of nBLOCKs using graphical processing units. nBLOCKs are nanoscale building blocks composed of gold nanoparticles functionalized with single-stranded DNA molecules. To explore greater simulation time scales we implement our nBLOCK computational model as an extension to the coarse grain molecular simulator oxDNA. oxDNA is parameterized to match the thermodynamics of DNA strand hybridization as well as the mechanics of single stranded DNA and double stranded DNA. In addition to an in-depth review of our implementation details we also provide results of the model validation and performance tests. These validation and performance tests …

Computational Optimization And Characterization Of Molecularly Imprinted Polymers, Jacob Jordan Terracina

Legacy Theses & Dissertations (2009 - 2024)

Molecularly imprinted polymers (MIPs) are a class of materials containing sites capable of selectively binding to the imprinted target molecule. Computational chemistry techniques were used to study the effect of different fabrication parameters (the monomer-to-target ratios, pre-polymerization solvent, temperature, and pH) on the formation of the MIP binding sites. Imprinted binding sites were built in silico for the purposes of better characterizing the receptor – ligand interactions. Chiefly, the sites were characterized with respect to their selectivities and the heterogeneity between sites.

Molecular Modeling Of Aerospace Polymer Matrices Including Carbon Nanotube-Enhanced Epoxy, Matthew Radue

Dissertations, Master's Theses and Master's Reports

Carbon fiber (CF) composites are increasingly replacing metals used in major structural parts of aircraft, spacecraft, and automobiles. The current limitations of carbon fiber composites are addressed through computational material design by modeling the salient aerospace matrix materials. Molecular Dynamics (MD) models of epoxies with and without carbon nanotube (CNT) reinforcement and models of pure bismaleimides (BMIs) were developed to elucidate structure-property relationships for improved selection and tailoring of matrices.

The influence of monomer functionality on the mechanical properties of epoxies is studied using the Reax Force Field (ReaxFF). From deformation simulations, the Young’s modulus, yield point, and Poisson’s ratio …

Experimentally Validated 3d Md Model For Afm-Based Tip-Based Nanomanufacturing, Rapeepan Promyoo

Open Access Dissertations

In order to control AFM-based TBN to produce precise nano-geometry efficiently, there is a need to conduct a more focused study of the effects of different parameters, such as feed, speed, and depth of cut on the process performance and outcome. This is achieved by experimentally validating a MD simulation model of nanomachining, and using it to conduct parametric studies to guide AFM-based TBN. A 3D MD model with a larger domain size was developed and used to gain a unique insight into the nanoindentation and nanoscratching processes such as the effect of tip speed (e.g. effect of tip speed …

Dislocation Engineering In Novel Nanowire Structures, Christopher Y. Chow, Samuel T. Reeve, Alejandro Strachan

The Summer Undergraduate Research Fellowship (SURF) Symposium

Leveraging defects is a cornerstone of materials science, and has become increasingly important from bulk to nanostructured materials. We use molecular dynamics simulations to explore the limits of defect engineering by harnessing individual dislocations in nanoscale metallic specimens and utilizing their intrinsic behavior for application in mechanical dampening. We study arrow-shaped, single crystal copper nanowires designed to trap and control the dynamics of dislocations under uniaxial loading. We characterize how nanowire cross-section and stacking-fault energy of the material affects the ability to trap partial or full dislocations. Cyclic loading simulations show that the periodic motion of the dislocations leads to …

Nanoscale Phonon Thermal Conductivity Via Molecular Dynamics, Jonathan M. Dunn

Open Access Theses

Molecular dynamics (MD) simulations provide a useful and simple means of calculating the nanoscale thermal properties of materials, which requires special analysis since the thermal properties of materials change when their dimensions reach the nanoscale. In this research, MD is used to investigate the nanoscale phonon thermal transport of materials that are attracting much interest in the areas of materials science and nuclear physics. In order to evaluate two distinct methods of calculating the thermal conductivity of materials using MD, the simulation methods are first applied to Si. Once an understanding of each simulation method is established, they are then …

Traction-Separation Relationships For Hydrogen-Induced Grain Boundary Embrittlement In Nickel Via Molecular Dynamics Simulations, Wesley Allen Barrows

Graduate Theses and Dissertations

The deleterious effects of atomic and molecular hydrogen on the mechanical properties of metals have long been observed. Although several theories exist describing the mechanisms by which hydrogen negatively influences the failure of materials, a consensus has yet to be reached regarding the exact mechanism or combination of mechanisms. Two mechanisms have gained support in explaining hydrogen’s degradative role in non-hydride forming metals: hydrogen-enhanced localized plasticity and hydrogen-enhanced decohesion. Yet, the interplay between these mechanisms and microstructure in metallic materials has not been explained. Accordingly, for this thesis, the three main objectives are: (i) to develop a numerical methodology to …

Multiscale Modeling Of The Hierarchical Structure Of Cellulose Nanocrystals, Fernando Luis Dri

Open Access Dissertations

Cellulose constitutes the most abundant renewable polymeric resource available today. It considered an almost inexhaustible source of raw material, and holds great promise in meeting increasing demands for environmentally friendly and biocompatible products. Key future applications are currently under development for the automotive, aerospace and textile industries. When cellulose fibers are subjected to acid hydrolysis, the fibers yield rod-like, highly crystalline residues called cellulose nanocrystals (CNCs). These particles show remarkable mechanical and chemical properties (e.g. Young Modulus ~200 GPa) within the range of other synthetically-developed reinforcement materials. Critical to the design of these materials are fundamental material properties, many of …

Molecular Dynamics Study Of Diffusion Of O2 Penetrates In Uncrosslinked Polydimethysiloxane (Pdms), Crosslinked Pdms, And Pdms-Based Nanocomposites, Varun Ullal

Graduate Theses and Dissertations

Molecular dynamics simulations are used to study diffusion of O₂ molecules in pure polydimethysiloxane (PDMS), crosslinked PDMS, and PDMS-based nanocomposites. The PDMS chains and penetrates are modeled using a hybrid interatomic potential which treats the Si-O atoms along the chain backbone explicitly while coarse-graining the methyl side groups and penetrates. By tracking the diffusion of penetrates in the system and subsequently computing their mean-squared displacement, diffusion coefficients are obtained. In pure PDMS models of varying molecular weight, diffusivity of the O₂2 penetrates is found to have an inverse relationship with chain length. Simulation models with longer chains …

Structures And Energetics Of Si Nanotubes From Molecular Dynamics And Density Functional Theory, Amritanshu Palaria, Gerhard Klimeck, Alejandro Strachan

Birck and NCN Publications

We use molecular dynamics (MD) with a first principles-based force field (ReaxFF) and density functional theory (DFT) to predict the atomic structure, energetics and elastic propoerties of Si nanotubes. We find various low-energy and low-symmetry hollow structures with external diameters of about 1 nm. These are the most stable structures in this small-diameter regime reported so far and exhibit properties very different from the bulk. While the cohesive energies of the four most stable nanotubes reported here are similar (from 0.638 to 0.697 eV above bulk Si), they have disparate Young's moduli (from 72 to 123 GPa).