The aim of this thesis is to advance the field of solid lubrication science by developing coatings that provide reliable performance in ambient conditions, work on rough surfaces, and are amenable to industrial size and design complexities. Two different coating systems, Ti3C2Tx-MoS2 and Ti3C2Tx-Graphene Oxide blends, were studied in this work. The Ti3C2Tx-MoS2 nanocomposites were spray-coated onto rough 52100-grade steel surfaces, and their tribological performance was evaluated in a ball-on-disk configuration in a unidirectional sliding mode. The test results indicate that Ti3C2Tx-MoS2 coatings achieved superlubricity, which has not been previously reported for either pristine material under macroscale sliding conditions. The observed synergistic mechanism enabled the superlative performance, which was explained by the in-situ formation of a robust tribolayer responsible for sustained lubricity even at high contact pressures (>1.1 GPa) and sliding speeds (0.1 m/s). Processing, structure, and property correlation studies were conducted to understand the underlying phenomena. Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to reveal the formation of the tribolayer. The Ti3C2Tx-Graphene Oxide blends were also spray-coated onto rough-bearing steel surfaces, and their tribological assessment was carried out in ambient environmental conditions and high contact pressures in a ball-on-disc experimental setup. The coatings led to substantial friction reduction compared to uncoated and single-component-coated surfaces, with a friction coefficient as low as 0.065 at 1 GPa contact pressure and 100 mm/s sliding speed, surpassing the state-of-the-art. The coatings also provided excellent protection against wear loss of the substrate and counter-face. The results were explained based on the observations from Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and nanoindentation measurements. The in-operando formation of a dense, hard, and stiff tribolayer was observed, which was responsible for the sustained lubricity even at high test loads and sliding speeds. This thesis presents a holistic exploration and correlation of structure-property-processing for the advancement of solid lubrication science. It provides insights into the development of solid lubricant materials and their tribological performance, which can be useful for various industrial applications.

Plastics are a class of materials known for their cost and property advantages, increasing significantly in their usage worldwide. Unfortunately, these benefits come with an increasingly concerning environmental impact. A combination of inadequate disposal options and combinations of materials have led to environmental disasters that will impact generations. One of the worst areas for plastic waste is food packaging. Plastic as a material generally excels at durability and longevity, but as food packaging, it outlives its intended purpose by several orders of magnitude. This leads to plastic food packaging materials sitting in landfill or leading to the environment for hundreds of years. Because of this, there is a strong motivation to develop food packaging materials that are biodegradable, yet still maintain the properties that make plastic better than other classes of materials. Food packaging has many forms, but in general, the most important aspects are cost, mechanical, and oxygen and water barrier properties. To achieve an end-product that excels in these aspects, combinations of materials called composites may be developed. Nanocomposites are a subcategory of composites composed of a matrix material and nanomaterials, separate phases that interact with one another in a number of ways. This research is focused on increasing the mechanical and barrier properties of polyvinyl alcohol, the most commercially-viable biodegradable polymer. The nanomaterials used were graphene oxide (GO) and cellulose nanofibers (CNF) for mechanical and barrier reinforcement. Five sample compositions were produced: a control PVA, CNF, 1 wt% GO, 5 wt% GO, and 10 wt% GO, which were drawn down on uncoated paper and cast by themselves. Testing of these nanocomposites included oxygen transmission, mechanical, and thermal property analysis, and various solvent-interaction testing including absorption of water and oil, Cobb testing, and water vapor permeation. With the addition of CNF and GO to PVA, there was an observed increase in barrier properties through a reduction of hydrophilicity and water absorption, and oxygen permeability.

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Grafenoxid (GO) har potential att användas i läkemedelsleveransapplikationer. Dess stora specifika yta gör det intressant som en effektiv bärare och skyddare av olika aktiva substanser för genterapi, såsom DNA och mRNA. Denna studie har fokuserat på att undersöka förhållandena för att ladda negativt laddat mRNA på GO. Kitosan (CS) och linjär polyetylenimin (PEI) har preadsorberats på GO för att underlätta mRNA-adsorption. Studien undersökte vid vilka förhållanden zeta-potentialen av GO/polyelektrolyt för det negativt laddade GO blir positivt. Dessa komplexerades sedan med mRNA vid olika N/P-förhållanden. Dessutom bedömde studien mRNA-frisättningskapaciteten genom att reducera pH.  GO/CS-komplexet vid förhållandet 1:2 visade positiv zeta-potential med N/P-förhållandena som sträcker sig från 1:1 till 10:1 visade att all mRNA och polyA har adsorberat till komplexet. N/P-förhållandet 10:1 var den enda som uppnådde en neutral zeta-potential, vilket tyder på tillräckligt mRNA för mättnad. Genom att öka koncentrationen av CS, kunde zeta-potentialen skifta till positivt vilket potentiellt förbättrar transfektionseffektiviteten. Visade en förbättring i signalen av det fria mRNA ökade när GO/CS/mRNA-komplexet utsattes för ett mer surt pH. Detta tyder på en potentiell frisättning när vektorn transfekteras in i cellen, eftersom den transporteras till lysosomerna som kännetecknas av sin sura miljö. GO/PEI-komplex visade endast negativ zeta-potential vid GO:PEI-förhållanden som når upp till 1:10, och därmed kommer det negativt laddade mRNA inte att adsorbera på dessa GO/PEI-komplex.  Resultaten tyder på en lovande utgångspunkt för pre-formuleringen av GO/CS-komplexet för vidare forskning. Detta arbete ger ett bidrag för framtida studier inom detta område. / Graphene oxide (GO) has a potential to be used in drug delivery applications. The large surface-to-mass ratio makes it interesting as efficient carrier and protector of various substances aimed for therapy, including DNA and mRNA. This study has focused on determining the ideal conditions for loading negatively charged mRNA onto GO using chitosan (CS) and linear polyethyleneimine (PEI) to facilitate mRNA adhesion. This was achieved by examining at what ratios of GO/polyelectrolyte the zeta potential of the negatively charged GO becomes positive, which were then subjected to mRNA complexation at different N/P (nitrogen/phosphate) ratios. Moreover, the study assessed the mRNA release capability by altering the pH.  The GO/CS complex at ratio 1:2 showed positive zeta potential with the N/P ratios ranging from 1:1 to 10:1 presented 100% loading efficiency of the added nucleic acids. With the N/P ratio 10:1 standing out as it achieved a neutral zeta potential, suggesting enough mRNA for saturation. By increasing the concentration of CS, the zeta potential could shift to positive potentially enhancing transfection efficiency. During the release assessment, the GO/CS/mRNA complex displayed increased amount of unbound mRNA when subjected to a more acidic pH. This suggests potential release when transfected into the cell, as the vector is transported to the lysosomes characterized by their acidic environment. GO/PEI complexes demonstrated only negative zeta potential at GO:PEI ratios reaching to 1:10, and thus the negatively mRNA will not adsorb on these GO/PEI complexes.  The findings suggest a promising starting point for the pre-formulation of the GO/CS complex for further research. This work provides a solid foundation for future studies in this area.

Prosthetic joint infection (PJI) poses a significant risk to implanted patients, requiring multiple surgeries with high rates of reinfection. The primary cause of such infections is otherwise innocuous bacterial species present on the skin that have survived sterilization protocols. Antibiotic drugs have significantly reduced efficacy due to the lack of vasculature in the newly implanted site, allowing microbes to form biofilms with even greater resistance. Graphene oxide (GO) is known to have good biocompatibility while providing drugless antimicrobial properties. The focus of this study is on the development and characterization of a robust coating for titanium alloy implants to promote bone regeneration while inhibiting microbial biofilm adhesion to the implant surface. The novelty of this study is the use of proprietary coal-derived graphene oxide (c-GO) in a biomedical application. c-GO has been demonstrated to have a greater number of functional oxygen groups to promote cell adhesion, while also maintaining thinner layers than possible with graphite exfoliation methods. As an alternative to powerful antimicrobial drugs, it was hypothesized that an advanced coating of graphene-oxide would provide a defensive, passively antimicrobial layer to a titanium implant. While GO is typically quite expensive, the newly developed process provides an economical and environmentally friendly method of producing GO from coal (c-GO). The result is a coating that is inexpensive and capable of halving the biofilm formation of MRSA on titanium-alloy surgical screws in addition to providing improved bone cell adhesion and hard tissue compatibility. / Master of Science / Any time a patient receives implantation surgery, there is a chance of microbes entering the body. These are typically naturally occurring skin flora, harmless but opportunistic. On the surface of implants within the body, these bacteria can form colonies called biofilms, leading to severe and potentially deadly infections, called prosthetic joint infection (PJI). PJI often requires multiple surgeries to remedy, but rates of reinfection are relatively high. As with any surgery, patients are given antibiotic drugs, but implants to not receive blood flow as the body normally would, reducing the effectiveness of antibiotics. Once biofilms are formed, the bacteria become even hardier and resistant even to powerful antibiotics. Graphene oxide (GO) is a carbon material known to have good biocompatibility (i.e., non-toxic) while providing antimicrobial properties. The focus of this study is on the development and characterization of a robust coating for titanium alloy implants to promote bone healing while reducing microbial biofilm colonization on the implant's surface. The novelty of this study is the use of proprietary coal-derived graphene oxide (c-GO) in a biomedical application. c-GO has been demonstrated to have a different chemical makeup than graphite-derived GO, which may improve its efficacy as an antimicrobial coating. As an alternative to powerful antimicrobial drugs, it was hypothesized that a coating of graphene-oxide would provide a defensive, passively antimicrobial layer to a titanium implant. While GO is typically quite expensive, the newly developed one-pot process provides an economical and environmentally friendly method of producing GO from coal (c-GO). The result is a coating that is inexpensive and capable of halving the biofilm formation of MRSA on titanium-alloy surgical screws in addition to providing improved bone cell adhesion and hard tissue compatibility.

Poly(lactic acid) is biodegradable polymer derived from renewable resources and non-toxic, which has become most interested polymer to substitute petroleum-based polymer. However, it has low glass transition temperature and poor gas barrier properties to restrict the application on hot contents packaging and long-term food packaging. The objectives of this research are: (a) to reduce coagulation of graphene oxide/single-walled carbon nanotube (GOCNT) nanocomposite in poly(lactic acid) matrix and (b) to improve mechanical strength and oxygen barrier property, which extend the application of poly(lactic acid). Graphene oxide has been found to have relatively even dispersion in poly(lactic acid) matrix while its own coagulation has become significant draw back for properties of nanocomposite such as gas barrier, mechanical properties and thermo stability as well as crystallinity. Here, single-walled carbon nanotube was hybrid with graphene oxide to reduce irreversible coagulation by preventing van der Waals of graphene oxide. Mass ratio of graphene oxide and carbon nanotube was determined as 3:1 at presenting greatest performance of preventing coagulation. Four different weight percentage of GOCNT nanocomposite, which are 0.05, 0.2, 0.3 and 0.4 weight percent, were composited with poly(lactic acid) by solution blending method. FESEM morphology determined minor coagulation of GOCNT nanocomopsite for different weight percentage composites. Insignificant crystallinity change was observed in DSC and XRD data. At 0.4 weight percent, it prevented most of UV-B light but was least transparent. GOCNT nanocomposite weight percent was linearly related to ultimate tensile strength of nanocomposite film. The greatest ultimate tensile strength was found at 0.4 weight percent which is 175% stronger than neat poly(lactic acid) film. Oxygen barrier property was improved as GOCNT weight percent increased. 66.57% of oxygen transmission rate was reduced at 0.4 weight percent compared to neat poly(lactic acid). The enhanced oxygen barrier property was ascribed to the outstanding impermeability of hybrid structure GOCNT as well as the strong interfacial adhesion of GOCNT and poly(lactic acid) rather than change of crystallinity. Such a small amount of GOCNT nanocomposite improved mechanical strength and oxygen barrier property while there were no significant change of crystallinity and thermal behavior found. / Master of Science

Grafenoxid (GO) ar en lovande kandidat som nano-tillsats i medicinska byggnadsstallningar for benregenerering. GO kan forbattra den biologiska kompatibiliteten och osteogena prestandan hos polymerbaserade byggstallningar, och ocksa vasentligt bidra till forbattringen av materialets mekaniska egenskaper. I detta arbete ympades nano-grafenoxid (nGO) kovalent pa ytan av poly (e-kaprolakton) (PCL) genom att fdrst modifiera polymerytan via aminolys. Med anvandning av 1,6-hexandiamin / isopropanol infordes fria amingrupper framgangsrikt pa PCL-ytan for efterfoljande immobilisering av nGO. En optimerad ympningsprocess utvecklades via en losningsmedelsassisterad metod med vatten som losningsmedel for att kovalent binda nGO pa ytan av PCL byggnadsstallningar. De initiala nGO koncentrationerna var 0,5 och 1 mg / ml. fourier-transform infrarodspektroskopi (FTIR) och termogravimetrisk analys (TGA) verifierade bindningen mellan de funktionella gruppema pa nGO och de fria aminema. Svepelektronmikroskopi (SEM) visade en homogen fordelning av nGO pa ytan av de porosa byggnadsstallningarna. De mekaniska testema som utfordes demonstrerade · en 50 och 21 % okning av kompressionsstyrkan :for byggnadsstallningarna ympade med de initiala nGO-koncentrationema pa 0,5 och 1 mg / ml. In vitro-mineraliseringstester visade bildandet av mineralfallningar pa ytan av byggnadsstallningama som okade i storlek med hogre nGO-halt. A ven nGO: s potential som nano-barare av ett antibiotikum studerades i detta arbete. Pa grund av sitt overflod av kemiska funktionaliteter kan nGO effektivt adsorbera foreningar genom olika sekundara interaktioner. I denna studie optimerades dessa sekundara interaktioner genom att reglera losningens pH for maximal adsorption av ciprofloxacin, ett bredspektrum antibiotikum som anvands vid behandling av osteomyelit. Ciprofloxacin befanns kunna adsorberas starkast i sin katjonform vid pH 5, dar 1t-1t elektron­donatoracceptor (EDA) -interaktioner dominerar. Sammanfattningsvis bekraftar de resultat som presenteras i detta arbete potentialen hos nGO som egenskapsforbattrare och lakemedelsbarare i applikationer inom vavnadsregenerering. / Graphene oxide (GO) is a promising candidate as nano-filler material in scaffolds for bone regeneration. It has been demonstrated to enhance the biological compatibility and osteogenic performance of polymer-based scaffolds, aside from its substantial contribution to the improvement of the material's mechanical properties. In this work, nano-graphene oxide (nGO) was covalently grafted to the surface of poly( e-caprolactone) (PCL) by first modifying the polymer surface via aminolysis. Using 1,6-hexanediamine/isopropanol, free amine groups were successfully introduced to the PCL surface for the subsequent immobilization of nGO. An optimized grafting pathway, which implements the solvent-assisted method and uses water as a solvent, was developed to covalently attach nGO using initial concentrations of 0.5 and 1 mg/mL. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) both verified the successful attachment of nGO through the free amines. Scanning electron microscopy (SEM) depicts a homogeneous dispersion of nGO over the polymer matrix. Mechanical tests were performed and demonstrate a 50 and 21 % increase in compressive strength for the scaffolds grafted using initial nGO concentrations of 0.5 and 1 mglmL. In vitro mineralization tests showed the formation of mineral precipitates on the surface of the scaffolds that increased in size with higher nGO content. The potential of nGO as a nano-carrier of an antibiotic drug was also explored in this work. As it comprises of an abundance of chemical functionalities, nGO is able to efficiently adsorb compounds through various secondary interactions. In this study, these secondary interactions were optimized by controlling the solution pH for the maximum adsorption of ciprofloxacin, a broad-spectrum antibiotic used in the treatment of osteomyelitis. Ciprofloxacin was found to be adsorbed most strongly in its cationic form at pH 5, in which 1t-1t electron-donor acceptor (EDA) interactions predominate. Overall, the results presented in this work validate the potential of nGO as nano-enhancer and drug carrier in tissue engineering scaffold applications.