Materials & Nanotechnology Masters Theses
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Item Lignin and Cellulose Nanofibers Enhanced Corn-Based Thermoplastic Composites(North Dakota State University, 2021) Chen, YanlinThe goal of this project is to develop biobased thermoplastics and composites using corn as the main raw material. Corn contains mainly starch, zein, and oil. Thermoplastic starch/zein blends were prepared through internal mixing and extrusion. Lignin was used as a compatibilizer to refine the phase structure of the blend and increase the mechanical properties of the product. Scanning electron microscopy study showed that the incorporation of lignin significantly reduced the domain size of the zein phase in the blends. Modulus and tensile strength of the blend were increased greatly. Thermogravimetric analysis showed that the thermal stability of the blends was slightly improved after the incorporation of lignin. Cellulose nanofibrils (CNFs), a biobased nanomaterial, were also tested as a reinforcement for the blend. The incorporation of CNFs further enhanced the modulus and strength of the blends, suggesting a strong synergy between lignin and CNFs in reinforcing the corn-based thermoplastics.Item Investigating the Reduction of Fogging Behavior of Natural Fiber-Filled Polymers(North Dakota State University, 2021) Thanki, Nidhi ModhaSynthetic fibers such as glass and carbon are used as reinforcement in polymer composites due to their high strength and modulus. However, synthetic fibers are non-biodegradable and contribute to high costs. In literature, various natural fibers, including banana and sisal fiber, as reinforcement in a polymer matrix, are investigated for mechanical and thermal properties to overcome this challenge. Nevertheless, natural fibers bring their issues such as degradation and emissions of Volatiles Organic Compounds (VOCs), resulting in the fogging phenomena when exposed to heating-cooling cycles. In this study, effectiveness of addition of porous fillers in reducing VOCs emissions in biocomposites reinforced with natural fibers is investigated. Mechanical testing exhibited that adding the porous filler into the biocomposites did not hinder mechanical properties. It is hypothesized that adding the porous filler in the biocomposites could reduce the VOCs emission due to the pore structures absorbing the VOCs.Item The Effects of Doping on the Lithium Ionic Conductivity of LLZO Solid-State Electrolyte(North Dakota State University, 2020) Altayaran, Fadhilah AhmedLithium-ion batteries (LIBs) employing solid-state electrolytes are considerably safer and might potentially generate a higher energy density compared. The goal of this thesis is to investigate the synthesis and stability of doped Li₇La₃Zr₂O₁₂ (LLZO). The reason of adopting LLZO is to presents a high conductivity, good electrochemical stability against metallic lithium. The investigation method involves preparing LLZO powder, pressing it to pellets, sintering the pellets at 1230 ºC and coating metal electrodes on them, followed by the measurement of the lithium ionic conductivity through Electrochemical Impedance Spectroscopy, Scanning Electron Microscopy, and X-ray diffraction. Doping has proven to be an effective way to improve the lithium ionic conductivity. In our research, multi-doped LLZO with Al and Ta and F presented the highest conductivity σ = 1.67×10-4 Scm-1 at room temperature. Our study suggests that the adoption may lead to a significant increase in the lithium ionic conductivity of LLZO solid-state electrolyte.Item Single-Wall Carbon Nanotube Films Dip-Coating by Colloidal Nanocrystals Bilayer Films(North Dakota State University, 2019) Altayyar, AmalA wrinkling approach was used to study the mechanics of hybrid nanotube/nanocrystal coatings adhering to soft polymer (PDMS) substrates. We focused on three thicknesses: 10 nm, 30 nm, and 40 nm. The approach we used is the Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIFMM) technique, which allows measurement of the SWCNT film mechanics by the buckling wavelength and the film thickness by inducing a compressive stress in the films at different strains; 2%, 4%, 6%, 8%, 10%, and 12%. In this thesis, dip-coating method with colloidal nanocrystals was used to enhance the rigidity of the carbon nanotube films by filling the pores of the nanotube network. Our results show an almost two-fold enhancement in the Young modulus of a thin SWCNT film related to the presence of a thin interpenetrating over-layer of the semiconductor nanocrystal.Item Bending and Force Recovery in Polymer Films and Microgel Formation(North Dakota State University, 2018) Elder, Theresa MarieTo determine correlation between geometry and material three different model films: polymethylsiloxane (PDMS), polystyrene (PS), and polycarbonate (PC), were singly bent and doubly bent (forming D-cones). Bends were chosen as they are fundamental in larger complex geometries such as origami and crumples. Bending was carried out between two plates taking force and displacement measurements. Processing of data using moment equations yielded values for bending moduli for studied films that were close to accepted values. Force recovery showed logarithmic trends for PDMS and stretched exponential trends for PS and PC. In a separate experiment a triblock copolymer of polystyrene–polyacrylic acid–polystyrene was subjected to different good and bad solvent mixing with any resulting particle morphology examined. Particles formed more uniformly with high water concentration, particles formed with high toluene concentration and agitation yielded three separate morphologies.Item 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.Item Development of Bio-based Wood Adhesive by Using Cellulose Nanofiber Reinforcement and Crosslinking Agent for Improved Bonding Strength(North Dakota State University, 2017) Oh, MyungkeunEngineered 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.Item Mechanical Properties of Multilayers of Carbon Nanotube Polystyrene Nanocomposites(North Dakota State University, 2017) Almutairi, Eid AliWe 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.Item The Free and Restricted Diffusion of Silicon Nanocrystal Clusters(North Dakota State University, 2015) Elbaradei, Ahmed BahgatBiological 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.Item Electrochemical Impedance Spectroscopy Study of the Ultraviolet Exposure of Ballistic Resistant Polymer Matrix Composites(North Dakota State University, 2012) Pavlacky, Drew AdamThis 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.Item Temperature Dependent Optical Properties of Silicon Quantum Dot/Polymer Nanocomposites(North Dakota State University, 2012) Van Sickle, Austin ReedThe 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.