Materials & Nanotechnology

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Research from the Department of Materials & Nanotechnology. The interdisciplinary department website may be found at https://www.ndsu.edu/materials_nanotechnology/

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The Development, Characterization and Testing of Mg-rich Primers
(North Dakota State University, 2012) Battocchi, Dante
Aluminum alloys are widely used in aircraft industry for their strength and light weight. Those alloys that are hardened by precipitation, especially the Copper-rich of the 2000 series, are prone to corrosion and are protected against it using chromate containing coatings. The primary component of these coating systems is Chromium 6+ (CrVI) that has been found to be very toxic in the environment and carcinogenic, toxic and mutagenic in humans. The Mg-rich primer development is the result of a successful multi-year project funded by the US Air-force with its objective the replacement of coatings based on CrVI with a class of coatings less toxic and with comparable protective performances. The Mg rich primer fulfilled the USAF requirements and it is currently undergoing commercial and military qualifications testing. The use of Mg as one of the active pigments in coatings allows the primer to protect the underlying Al sacrificially, not considered possible for this substrate until now. Mg is anodic to most of the other structural metals and when particulate Mg became available commercially, the concept of the primer was first developed by analogy to Zn-rich coatings for steel. When Mg and Al are in contact and immersed in a corrosive environment, magnesium corrodes preferentially and protects the aluminum.
Electrochemical Impedance Spectroscopy Study of the Ultraviolet Exposure of Ballistic Resistant Polymer Matrix Composites
(North Dakota State University, 2012) Pavlacky, Drew Adam
This study examined the effect of ultraviolet radiation on ballistic resistant polymer matrix composites. Two composite systems studied included a phenolic matrix with either S2 Glass® or Kevlar® fiber laminates. These composites were weathered in ultraviolet conditions and the effects were quantified with multiple destructive and non-destructive testing. Electrochemical impedance spectroscopy (EIS) was used as a non-destructive evaluation method which is a commonly used experiment in the corrosion community. Circuit modeling the EIS spectra produced both resistive and capacitive characteristics inherent of the composite materials. Surface characterization was performed to determine if degradation was occurring at the composite surface. Techniques included: color, gloss, surface profilometry, and water contact angle. Tensile and flexural destructive experimentation revealed the influence of the ultraviolet exposure on the mechanical properties. It was determined that the resistive portion of the EIS response correlated well with the ultimate tensile strength of the S2 Glass® fiber composites.
Temperature Dependent Optical Properties of Silicon Quantum Dot/Polymer Nanocomposites
(North Dakota State University, 2012) Van Sickle, Austin Reed
The photoluminescent properties of silicon quantum dots embedded in a stabilizing polymer matrix are relevant to a number of potential applications of these unique nanomaterials such as drug delivery, temperature sensing, and photovoltaics. Aspects of how these photoluminescent properties change with respect to variations in such parameters as excitation intensity, polymer interactions, particle size and particle polydispersity are investigated here. Improving the photostability and understanding the nature of how this is achieved will be critical for realizing the potential of silicon quantum dots in a number of applications. Improvements in photoluminescent stability related to fluorescence intermittency, radiative lifetime, emitted intensity, and wavelength shifts are shown to be due to decreased exposure to oxygen, increased particle packing, decreased temperature, and increased monodispersity of the quantum dots.
Synthesis of Sustainable Polymers from Vegetable Oil: Applications in Coatings and Nanoparticle Surface Modification
(North Dakota State University, 2013) Kalita, Harjyoti
Polymeric materials are increasing being used in many household, industrial, and health and personal care products. These materials, being either non-degradable or slow degradable, remain in the environment for a long time and are posing increasingly significant threats to the ecosystem components including mammals, birds, fish, reptiles, and crustaceans. Renewable resource based materials are the best raw materials for the development of sustainable products. Vegetable oil and polyglycol based novel copolymers have been synthesized in this research. Poly(2-VOES-r-TEGEVE) copolymers were synthesized from 2-(vinyloxyethyl) soyate (2-VEOS) and tri(ethylene glycol) ethyl vinyl ether (TEGEVE) via cationic polymerization. They were used in waterborne coating as self-dispersible polymers and as surfmers. Four different copolymers were synthesized having 2-VOES wt% as 10, 15, 25, 50 and rest being TEGEVE. In addition to that water insoluble poly(2-VOES) copolymers were synthesized from soybean oil. All copolymers were used as self-dispersible polymers and their coating property were analyzed by measuring glass transition temperature, drying time, gloss, transparency, contact angle, hysteresis, tensile strength, and hardness. Results showed that the coatings can be cured by autoxidation drying process within 6.1 to 8.2 h. Results also showed high transparency (coated in glass panel) with maximum 2% absorbance which is comparable to uncoated substrate (clean glass). Copolymer having 2-VOES wt% 15 and 50 were used as surfmers to disperse poly(2-VOES) and they were cured using autoxidation method. Results showed that the curing of film can be achieved within 2.6 to 8.0 h. High gloss and transparency confirmed that the surfmers get copolymerized with poly(2-VOES). Another set of poly(2-VOES-r-TEGEVE) copolymers with 2-VOES wt% 15, 25, 50, 75 and 85 were synthesized and then functionalized with a carboxyl group. These carboxyl functionalized polymer were used to coat nanoscale zero-valent iron (NZVI) to enhance their colloidal stability in aqueous media with an objective of using the coated particles for groundwater remediation. Structure property analysis of the coated NZVI showed that carboxyl functional copolymer with 15 wt% 2-VOES and 85 wt% TEGEVE had the best colloidal stability of the coated NZVI (CNZVI). Treatability study with CNZVI was carried out using trichloroethylene (TCE) and arsenic [As(V)] as model contaminants. Treatability data indicated that CNZVI can degrade 85 % of TCE (initial concentration 15 mgL-1) within 6 h and remove 99% of As(V) (initial concentration 15 mgL-1) within 0.5 h. Results also showed that CNZVI has higher contaminant (TCE and arsenic) removable rate compared to NZVI. The biodegradation behaviors of carboxyl functionalized poly(2-VOES-r-TEGEVE) copolymers were analyzed by respirometric, microbial growth, and gel permeation chromatography (GPC) studies. Respirometic test confirmed 90% degradations of carboxyl functionalized poly(2-VOES-r-TEGEVE) copolymers within 28 d. Microbial growth and GPC studies also support the data obtained from respirometic tests.
Biomimetic Nanoclay Scaffolds for Bone Tissue Engineering
(North Dakota State University, 2014) Ambre, Avinash Harishchandra
Tissue engineering offers a significant potential alternative to conventional methods for rectifying tissue defects by evoking natural regeneration process via interactions between cells and 3D porous scaffolds. Imparting adequate mechanical properties to biodegradable scaffolds for bone tissue engineering is an important challenge and extends from molecular to macroscale. This work focuses on the use of sodium montmorillonite (Na-MMT) to design polymer composite scaffolds having enhanced mechanical properties along with multiple interdependent properties. Materials design beginning at the molecular level was used in which Na-MMT clay was modified with three different unnatural amino acids and further characterized using Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD). Based on improved bicompatibility with human osteoblasts (bone cells) and intermediate increase in d-spacing of MMT clay (shown by XRD), 5-aminovaleric acid modified clay was further used to prepare biopolymer (chitosan-polygalacturonic acid complex) scaffolds. Osteoblast proliferation in biopolymer scaffolds containing 5-aminovaleric acid modified clay was similar to biopolymer scaffolds containing hydroxyapatite (HAP). A novel process based on biomineralization in bone was designed to prepare 5-aminovaleric acid modified clay capable of imparting multiple properties to the scaffolds. Bone-like apatite was mineralized in modified clay and a novel nanoclay-HAP hybrid (in situ HAPclay) was obtained. FTIR spectroscopy indicated a molecular level organic-inorganic association between the intercalated 5-aminovaleric acid and mineralized HAP. Osteoblasts formed clusters on biopolymer composite films prepared with different weight percent compositions of in situ HAPclay. Human MSCs formed mineralized nodules on composite films and mineralized extracellular matrix (ECM) in composite scaffolds without the use of osteogenic supplements. Polycaprolactone (PCL), a synthetic polymer, was used for preparing composites (films and scaffolds) containing in situ HAPclay. Composite films showed significantly improved nanomechanical properties. Human MSCs formed mineralized ECM on films in absence of osteogenic supplements and were able to infiltrate the scaffolds. Atomic force microscopy imaging of mineralized ECM formed on composite films showed similarities in dimensions, arrangement of collagen and apatite with their natural bone counterparts. This work indicates the potential of in situ HAPclay to impart polymeric scaffolds with osteoinductive, osteoconductive abilities and improve their mechanical properties besides emphasizing nanoclays as cell-instructive materials.
Laser-Assisted Advanced Assembly for MEMS Fabrication
(North Dakota State University, 2014) Atanasov, Yuriy Andreev
Micro Electro-Mechanical Systems (MEMS) are currently fabricated using methods originally designed for manufacturing semiconductor devices, using minimum if any assembly at all. The inherited limitations of this approach narrow the materials that can be employed and reduce the design complexity, imposing limitations on MEMS functionality. The proposed Laser-Assisted Advanced Assembly (LA3) method solves these problems by first fabricating components followed by assembly of a MEMS device. Components are micro-machined using a laser or by photolithography followed by wet/dry etching out of any material available in a thin sheet form. A wide range of materials can be utilized, including biocompatible metals, ceramics, polymers, composites, semiconductors, and materials with special properties such as memory shape alloys, thermoelectric, ferromagnetic, piezoelectric, and more. The approach proposed allows enhancing the structural and mechanical properties of the starting materials through heat treatment, tribological coatings, surface modifications, bio-functionalization, and more, a limited, even unavailable possibility with existing methods. Components are transferred to the substrate for assembly using the thermo-mechanical Selective Laser Assisted Die Transfer (tmSLADT) mechanism for microchips assembly, already demonstrated by our team. Therefore, the mechanical and electronic part of the MEMS can be fabricated using the same equipment/method. The viability of the Laser-Assisted Advanced Assembly technique for MEMS is demonstrated by fabricating magnetic switches for embedding in a conductive carbon-fiber metamaterial for use in an Electromagnetic-Responsive Mobile Cyber-Physical System (E-RMCPS), which is expected to improve the wireless communication system efficiency within a battery-powered device.
Synthesis and Characterization of Novel Hierarchically Functionalized Carbon Nanofibers for Energy Conversion and Storage Applications
(North Dakota State University, 2014) Zhou, Zhengping
Among various energy conversion and storage devices available in the market, supercapacitors are deemed as an effective, competitive solution to the increasing demand for high-power density energy-storage devices. Yet, supercapacitors usually carry relatively low energy density compared to batteries. Nanostructured electrode materials are expected being able to greatly enhance the electrochemical performance of supercapacitors. This research aims at rational synthesis and electrochemical characterization of novel hierarchically functionalized carbon nanofibers (CNFs) for use as advanced electrode materials of supercapacitors. These novel CNFs [(i.e., graphene-beaded CNFs (G/CNFs) and carbon nanotube (CNT)-grown CNFs (CNT/CNFs)] were successfully synthesized. The unique synthesis routes consist of electrospinning the precursor polymer nanofibers, followed by controlled carbonization, chemical vapor deposition (CVD) for CNT growth, and in situ polymerization for coating nanostructured conducting polymer. These new electrode materials carry the advantages of G/CNFs and CNT/CNFs (e.g., unique nanostructural continuity, large specific surface area, low intrinsic contact electric resistance, etc.) and conducting polymers (e.g., high pseudocapacitance), and therefore show excellent electrochemical performance including high specific capacitance, superior energy and power densities, and excellent cyclability. In addition, this work also provides the experimental study on parameter dependency of conic angle in electrospinning and scalable fabrication of core-shell nanofibers via needleless emulsion electrospinning.
Multicomponent Doped Barium Strontium Titanate Thin Films for Tunable Microwave Applications
(North Dakota State University, 2014) Alema, Fikadu Legesse
In recent years there has been enormous progress in the development of barium strontium titanate (BST) films for tunable microwave applications. However, the properties of BST films still remain inferior compared to bulk materials, limiting their use for microwave technology. Understanding the film/substrate mismatch, microstructure, and stoichiometry of BST films and finding the necessary remedies are vital. In this work, BST films were deposited via radio frequency magnetron sputtering method and characterized both analytically and electrically with the aim of optimizing their properties. The stoichiometry, crystal structure, and phase purity of the films were studied by varying the oxygen partial pressure (OPP) and total gas pressure (TGP) in the chamber. A better stoichiometric match between film and target was achieved when the TGP is high (> 30 mTorr). However, the O2/Ar ratio should be adjusted as exceeding a threshold of 2 mTorr in OPP facilitates the formation of secondary phases. The growth of crystalline film on platinized substrates was achieved only with a lower temperature grown buffer layer, which acts as a seed layer by crystallizing when the temperature increases. Concurrent Mg/Nb doping has significantly improved the properties of BST thin films. The doped film has shown an average tunability of 53%, which is only ~8 % lower than the value for the undoped film. This drop is associated with the Mg ions whose detrimental effects are partially compensated by Nb ions. Conversely, the doping has reduced the dielectric loss by ~40 % leading to a higher figure of merit. Moreover, the two dopants ensure a charge neutrality condition which resulted in significant leakage current reduction. The presence of large amounts of empty shallow traps related to NbTi localize the free carriers injected from the contacts; thus increase the device control voltage substantially (>10 V). A combinatorial thin film synthesis method based on co-sputtering of two BST sources doped with Mg/Nb and Ce, respectively, was applied. The composition and the dielectric properties of the deposited film were correlated and the optimal concentration of dopants corresponding to high tunability and low dielectric loss was determined in a timely fashion.
Optical Properties and Ensemble Characteristics of Size Purified Silicon Nanocrystals
(North Dakota State University, 2014) Miller, Joseph Bradley
Nanotechnology is at the forefront of current scienti c research and nanocrystals are being hailed as the `arti cial' atoms of the 21st century. Semiconducting silicon nanocrystals (SiNCs) are prime candidates for potential commercial applications because of silicon's already ubiquitous presence in the semiconductor industry, nontoxicity and abundance in nature. For realization of these potential applications, the properties and behavior of SiNCs need to be understood and enhanced. In this report, some of the main SiNC synthesis schemes are discussed, including those we are currently experimenting with to create our own SiNCs and the one utilized to create the SiNCs used in this study. The underlying physics that governs the unique behavior of SiNCs is then presented. The properties of the as-produced SiNCs are determined to depend strongly on surface passivation and environment. Size puri cation, an important aspect of nanomaterial utilization, was successfully performed on our SiNCs though density gradient ultracentrifugation. We demonstrate that the size-puri ed fractions exhibit an enhanced ability for colloidal self-assembly, with better aligned nanocrystal energy levels which promotes greater photostability in close-packed lms and produces a slight increase in photoluminescence (PL) quantum yield. The qualities displayed by the fractions are exploited to form SiNC clusters that exhibit photostable PL. An analysis of SiNC cluster (from individual nanocrystals to collections of more than one thousand) blinking and PL shows an improvement in their PL emitting `on' times. Pure SiNC lms and SiNC-polymer nanocomposites are created and the dependence of their PL on temperature is measured. For such nanocomposites, the coupling between the `co ee-ring' e ect and liquid-liquid phase separation is also examined for ternary mixtures of solvent, polymer and semiconducting nanocrystal. We discover that with the right SiNC-polymer concentration and polymer molecular weight, phase separation can be supressed; we use this to build a prototype nanocomposite printing device. Finally, the nanocrystals are PEGylated and introduced into an aqueous biological environment to demonstrate their potential for use in biological labelling and sensing devices. The development of superlattice structures from monodisperse SiNC fractions and their use in solid-state lighting and solar cell applications are also explored.
Experimental Evaluation of Multiscale Behavior of Human Bone
(North Dakota State University, 2014) Gu, Chunju
Bone is the most important structural member of the human body. It has a unique hierarchical structure and its primary constituents, collagen molecules and hydroxyapatite, are arranged in a staggered pattern at nanometer scale. Osteogenesis imperfecta (OI) is an inheritable disease characterized by the fragility of bones and other tissues rich in the type I collagen. OI provides an interesting platform for investigating how alterations of collagen at the molecular level cause changes in the structure of bone. In this dissertation, multi-scale-, particularly nanometer and sub-micro scale-, behaviors of both normal and OI (putative type I) human bones have been evaluated experimentally. Since chemical treatment influences collagen or mineral structure, we have used ―undisturbed bone samples‖ that are not subjected to any chemicals as previously done in literature. Photoacoustic-Fourier transform infrared spectroscopy (PA-FTIR) experiments reveal orientational differences in stoichiometry of hydroxyapatite. FTIR, electron microscopy, scanning probe microscopy, and nanomechanical tests also show that the OI disease results in a distorted microstructure in bone and that the mineralization of hydroxyapatite in OI is also altered. Modulus mapping test displays the distribution of mineralized fibril and extrafibrillar mineral according to the spatial variation of elastic properties. Dynamic nanomechanical behaviors of OI bone and normal bone indicates that the viscoelasticity of intact bone is mostly determined by the mineral. Also investigated are molecular composition and nanomechanical properties of different anatomical positions in the diaphysis of an OI human tibia. Our study on OI bone describes unique differences in collagen as previously described but also elaborates on unique influence of the non-collagenous proteins on mineralization of bone in OI. The fundamental premise of this work is investigation of the molecular basis of this highly debilitating bone disease.
Synthesis, Characterization, and Modeling of New Molecule-Based Magnets
(North Dakota State University, 2015) Olson, Christopher Samuel
The chemical bond and its role as a mediator of magnetic exchange interaction remains an important aspect in the study of magnetic insulators and semiconductors. The M[TCNE] (M = transition metal, TCNE = tetracyanoethylene) class of organic-based magnets has attracted considerable interest since VII[TCNE]x (x ~ 2) exhibits one of the highest critical temperatures for its class – Tc ~ 400 K – in addition to highly spin-polarized conduction and valance bands (Eg ~ 0.5 eV), thus foreseeing potential spintronic application. The magneto-structural factors underlying this exceptional behavior remain elusive, however, due to the amorphous nature of the material. To address this, a novel synthetic route was utilized to produce new polycrystalline M[TCNE] solids (whose crystal structures have been resolved) with varying transition metal centers (Ni, Mn, Fe) and lattice dimensionality (2D-3D), exhibiting a wide range of Tc (40-170 K). Spectroscopic and magnetometric studies were performed and demonstrate that in 2D [MII(TCNE)(NCMe)2]X structures (M = Ni, Mn, Fe; X = diamagnetic anion), strong ligand-to-metal transfer of electron density from the organic TCNE radical plays a significant role in the formation of magnetic exchange pathways, while single-ion anisotropy strongly influences the critical temperature and below-Tc spin disorder for magnets in this material class. Additionally, using quantum-computational modeling, magnetic spin-density transfer trends, spin-polarized electronic structures, and electronic exchange coupling constants have been identified and interpreted in terms of 3d-orbital filling and dimensionality of magnetic interaction. These findings offer new perspectives on the stabilization of magnetic order in M[TCNE] solids.
Synthesis of Cellulose Nanofiber Composites for Mechanical Reinforcement and Other Advanced Applications
(North Dakota State University, 2015) Xu, Xuezhu
Cellulose nanofibers from bioresources have attracted intensive research interest in recent years due to their unique combination of properties including high strength and modulus, low density, biocompatibility/biodegradability and rich surface chemistry for functionalization. The nanofibers have been widely studied as nanoreinforcements in polymer nanocomposites; while the nanocomposite research is still very active, new research directions of using the nanofibers for hydrogels/aerogels, template for nanoparticle synthesis, scaffold, carbon materials, nanopaper, etc. have emerged. In this Ph.D. thesis, fundamental studies and application developments are performed on three types of cellulose nanofibers, i.e. cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs) and bacterial cellulose (BC). First CNCs and CNFs are systematically compared in terms of their effects on the mechanical properties, crystallization and failure behavior of the nanocomposites, which provides a guideline for the design of cellulose nanofiber reinforced composites. Second, CNFs and BC are used to develop core-shell carbon fibers and flexible carbon aerogels for energy storage applications. This part is focused on developing nanocarbon materials with multi-scale features. Lastly, hybrid CNC/CNF nanopaper with superior optical, mechanical, and electrical properties is developed and its application is demonstrated on a LED device.
The Free and Restricted Diffusion of Silicon Nanocrystal Clusters
(North Dakota State University, 2015) Elbaradei, Ahmed Bahgat
Biological applications for silicon nanocrystals (SiNCs) have recently gained more attention because of silicon’s low toxicity. But, to be able to use SiNCs in applications such as biological sensors, labeling or drug delivery we need to understand their transport in different environments and their interaction with cell membrane. I will review some different methods for the synthesis of, and I will give an accounting of encapsulating SiNCs with PEGylated phospholipids to make them soluble in water. I also studied the free diffusion of these micelles in water, as well as their restricted diffusion and interaction with giant unilamellar vesicles (GUVs). I studied their restricted diffusion in oil emulsions. I was able to calculate the diffusion coefficient for a large number of micelles moving freely in water. I also measured the effect of water on the SiNC micelles intensity and observed the difference between the restricted diffusion in liposomes and emulsions.
First Principle Study on Interfacial Energetic Alignment and Charge Transfer in Quantum Dots Functionalized via Metal-Organic Dye
(North Dakota State University, 2016) Cui, Peng
Quantum dots (QDs) are promising materials for applications in solar energy conversion because of tunable band gap, multi-exciton generation, photon-upconversion, etc. One of the main challenges of increasing solar energy conversion is to extend the lifetime of photoexcited charge-carriers in conduction band, and one of the strategies is to functionalize QD with mediator molecules. Functionalizing QD with metal-organic dye serves as the additional channel of manipulating charge transfer – the key process increasing solar energy conversion. When metal-organic dye is attached to QD, the interfacial charge transfer direction as well as the rates are determined by a balance between the energetic alignment, QD-dye interaction as well as charge-carrier relaxation dynamics. In this dissertation, we explore the effect of dye functionalization on these elements. We change the metal ion, organic ligands as well as binding geometry of dye, size of QD, polarity of solvent, and use density functional theory to study their effects on energetic alignment. Embedding density functional calculation is used to study the dipole interaction between QD and dye providing additional controllability on charge transfer excitation. At last, we apply Tully surface hopping scheme in combining with density functional theory in time domain to study the charge-carrier relaxation dynamics and charge transfer across the heterogeneous interface in QD/dye nanocrystal composite.
Properties of Block-Copolymer Interfaces
(North Dakota State University, 2016) Rozairo, Damith P.
There is considerable interest in the fabrication and mechanism of soft spheres and capsules because of their use in a large number of applications ranging from targeted drug delivery systems to cosmetically active agents. The performance of these soft spheres depends on the enhancement of the mechanical properties of these materials. This dissertation is focused on studying the fundamental physics of these soft spheres. First, we study a simple fluid-fluid system covered by a diblock copolymer. Specifically, we use laser confocal microscopy to adapt a sessile drop geometry to a measurement of the static properties of an ensemble of polystyrene-b-poly(ethylene oxide) (PS-PEO) stabilized oil droplets. We present a simple model derived from Bashforth-Adams model for sessile drops. This method can be used to measure the surface tension of any fluid-fluid interface using a simple optical microscope without looking at the full geometry of a deformed droplet. We then synthesize a polystyrene-b-poly(acrylic acid)-b-polystyrene (PS-PAA-PS) elastic-shell-coated emulsion drop that shows an identical deformation to the fluid-like PS-PEO droplets. Both systems, in sessile geometry, can be related to their basic material properties through appropriate modeling. We find that the elastic shell is dominated by its surface tension, easily enabling it to match the static response of a purely fluid drop. Motivated by the sessile drop geometry, we study how these idealized cargo carrying spheres interact with a hard wall. As a polymer covered droplet approaches a flat wall, it buckles in and traps an amount of the outer fluid. This fluid is slowly drained out through a narrow channel covered with a polymer brush. A simple scaling model predicts the drainage rate of the fluid through the polymer brush. Finally, we look at how a long diblock copolymer (PS-PEO) molecule is packed at an oil-water interface and how it affects the surface tension. We find that as the polymer to oil concentration is reduced, it goes from the critical concentration at which no more chains can be fitted to the bare oil interface quickly. Furthermore, we find that the outer brush thickness (PEO) increases as the PS-PEO concentration is increased.
An Insilico Design of Nanoclay Based Nanocomposites and Scaffolds In Bone Tissue Engineering
(North Dakota State University, 2016) Sharma, Anurag
A multiscale in silico approach to design polymer nanocomposites and scaffolds for bone tissue engineering applications is described in this study. This study focuses on the role of biomaterials design and selection, structural integrity and mechanical properties evolution during degradation and tissue regeneration in the successful design of polymer nanocomposite scaffolds. Polymer nanocomposite scaffolds are synthesized using aminoacid modified montmorillonite nanoclay with biomineralized hydroxyapatite and polycaprolactone (PCL/in situ HAPclay). Representative molecular models of polymer nanocomposite system are systematically developed using molecular dynamics (MD) technique and successfully validated using material characterization techniques. The constant force steered molecular dynamics (fSMD) simulation results indicate a two-phase nanomechanical behavior of the polymer nanocomposite. The MD and fSMD simulations results provide quantitative contributions of molecular interactions between different constituents of representative models and their effect on nanomechanical responses of nanoclay based polymer nanocomposite system. A finite element (FE) model of PCL/in situ HAPclay scaffold is built using micro-computed tomography images and bridging the nanomechanical properties obtained from fSMD simulations into the FE model. A new reduction factor, K is introduced into modeling results to consider the effect of wall porosity of the polymer scaffold. The effect of accelerated degradation under alkaline conditions and human osteoblast cells culture on the evolution of mechanical properties of scaffolds are studied and the damage mechanics based analytical models are developed. Finally, the novel multiscale models are developed that incorporate the complex molecular and microstructural properties, mechanical properties at nanoscale and structural levels and mechanical properties evolution during degradation and tissue formation in the polymer nanocomposite scaffold. Overall, this study provides a leap into methodologies for in silico design of biomaterials for bone tissue engineering applications. Furthermore, as a part of this work, a molecular dynamics study of rice DNA in the presence of single walled carbon nanotube is carried out to understand the role played by molecular interactions in the conformation changes of rice DNA. The simulations results showed wrapping of DNA onto SWCNT, breaking and forming of hydrogen bonds due to unzipping of Watson–Crick (WC) nucleobase pairs and forming of new non-WC nucleobase pairs in DNA.
Development of Bio-based Wood Adhesive by Using Cellulose Nanofiber Reinforcement and Crosslinking Agent for Improved Bonding Strength
(North Dakota State University, 2017) Oh, Myungkeun
Engineered woods, plywood, particle board, and oriented strand board, are widely used as a low-cost wood replacement in many applications. Many of the currently used wood adhesives contain chemicals that are harmful to human health and the environment. Increasing environmental and human health concerns have made the development of safe bio-based adhesives a priority. In this study, two plant proteins, zein from corn and wheat gluten, were used to develop wood adhesives. To increase their bond strength, cellulose nanofibers were added to create nanocomposite adhesives and a crosslinking agent was also used. Single-lap shear test, flexural and internal bond tests were performed on dry and water-immersed samples to measure the bond strength. Fractured bond surfaces were studied using optical observation and scanning electron microscopy (SEM) to determine bond failure mechanisms. Thermal and chemical properties of the adhesives were evaluated using thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR), respectively.
Synthesis and Utilization of Si6H12 and Si6X12 (X = Cl, Br) for the Generation of Novel Silicon Materials
(North Dakota State University, 2017) Frohlich, Matthew T.
Cyclohexasilane (Si6H12) and its derivatives, Si6X12 (X = Cl, Br), have chemical and physical properties different from linear and branched polysilanes, thus creating interest in their use as starting materials for a variety of applications. The liquid nature and lower activation energy of Si6H12 give it advantages as a starting material for silicon based materials including quantum dots (SiQDs), nanorods (SiNRs) and nanowires (SiNWs), as well as novel processing methods such as roll to roll deposition of silicon thin films. The electronegative elements on Si6X12 create Lewis acid sites above and below the ring, giving it the ability to form novel salts and 1-dimensional stacked polymers. This work developed a new route toward Si6H12 and Si6Cl12 by focusing on the production of the precursor [Si6Cl142-] dianion salts and studying their physical and chemical properties. This thesis also describes the preparation of novel Si6X12 based materials.
Agricultural Residues and Other Carbon-Based Resources as Feedstocks for Supercapacitor Electrodes
(North Dakota State University, 2017) Wang, Yong
Agricultural residues are generally considered as renewable, economical and environmental-friendly sources to produce carbon-based materials with many advanced applications. Agricultural residues and by-products generated from the agricultural industry, such as distiller's dried grains with solubles (DDGS), are produced every year on a large scale but lack of proper utilization. As a result, seeking high-value applications based on agricultural residues is essential for the promotion of the economy in agricultural states like North Dakota, USA. With the fast development of nanotechnology in recent years, carbon-based nanomaterials have attracted intense research interests in the fields of chemistry, materials science and condensed matter physics due to many unique properties (e.g., chemical and thermal stability, electrical conductivity, mechanical strength, etc.). The development of low-cost nanomaterials using agricultural residues as feedstocks can be a promising route for the sustainable development of the agricultural industry. In this dissertation, the preparation of carbon-based materials from agricultural residues is explored. Many advanced applications are investigated, especially in the field of energy storage devices. The development of porous activate carbons were investigated in detail, and their application as electrode materials of supercapacitors was demonstrated. Hydrothermal carbonization of biomass to produce carbonaceous materials was also covered in this dissertation. In addition to traditional raw materials such as cellulose produced from wood industry, novel material sources such as bacterial cellulose were used to prepare nanocomposites that can be used for the electrodes of supercapacitors. This dissertation contributes to the sustainable development of the agricultural industry in North Dakota.
Mechanical Properties of Multilayers of Carbon Nanotube Polystyrene Nanocomposites
(North Dakota State University, 2017) Almutairi, Eid Ali
We have studied the mechanical behavior of multi-layered composite films comprised of single-wall carbon nanotubes and polystyrene polymer, where we focused on three targeted layer thicknesses; 10 nm, 20 nm, and 40 nm. The approach we used is the Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIFMM) technique, which allows us to measure the Young modulus of the films as a function of layer thickness and the number of layers by inducing a compressive stress in the films at different strains; 1 %, 2.5 %, 5 %, 7.5 %, and 10 %. Polystyrene was added in an effort to reduce the plasticity of the carbon nanotube films by filling the pores of the nanotube network. We found that the strongest synergistic effect in this regard occurred for the composite with a layer thickness near 20 nm, while the composite films have reached bulk behavior by the sixth layer.

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