This thesis investigates new processing methods and bone tissue engineering applications of cross-linked cellulose nanocrystal (CNC) aerogels. Aerogels are highly porous, low-density materials that have been praised for their high surface area and interconnected pores, but criticized for their brittleness. This prompted a search for new aerogel “building blocks” to produce more flexible materials; CNCs meet this need and chemically cross-linked CNC aerogels have good compressive strength and shape recovery properties in air and liquid environments. CNCs are high aspect ratio, non-toxic and renewably-sourced nanoparticles. Literature has demonstrated CNC aerogel production using cryo-templating with controlled drying. In this work, we produce aerogels using a new scalable process called pressurized gas expansion (PGX) and compare them to conventional cryo-templated aerogels. PGX aerogels were found to have more expanded fibrillar morphology, a range of mesopore sizes and smaller macropores, in contrast to cryo-templated aerogels that had a sheet-like morphology surrounding larger macropores. Additionally, PGX aerogels had higher specific surface area and porosity, but lower compressive strength due to a lower cross-link density. While neither CNC aerogel type dispersed in water, PGX aerogels partially shrank whereas cryo-templated aerogels did not; this is attributed to their morphological differences. This work shows that new aerogel processing methods can introduce new properties and thus broaden the potential applications of CNC aerogels. One specific biomedical application was evaluated for CNC aerogels – their use as bone tissue scaffolds. Cryo-templated aerogels comprised of CNCs with different surface chemistries, either sulfate or phosphate groups, were found to have attractive chemical, physical and mechanical properties for bone tissue engineering. This work shows that both types of CNC aerogels can facilitate cell proliferation, favorable differentiation, and can nucleate uniform hydroxyapatite growth. These positive in vitro results and the bimodal pore morphology of CNC aerogels make them promising bone scaffolds for in vivo studies. / Thesis / Master of Applied Science (MASc) / Aerogels are light, porous, sponge-like materials that are essentially 99% air by volume. In this work, the aerogels are made from non-toxic plant-based nanoparticles called cellulose nanocrystals (CNCs). This thesis investigates: 1) new ways to control CNC aerogel properties and pore size through different processing methods and 2) the use of CNC aerogels to aid in the repair of damaged bones. High-resolution microscopy and nano-characterization tools show that CNC aerogels have tunable properties, which may extend their possible applications. The internal structure, sponge-like mechanical properties and biocompatibility of CNC aerogels allowed them to be successfully utilized to support bone cells and grow bone-like mineral.

Cellulose nanocrystal (CNC) has found application in a variety of novel products due to its spectrum of properties. Notably, the CNC-polymer systems have seen numerous applications in special materials like Pickering emulsions, foams and gels etc. CNC interacts with different polymers to a different extent. These interactions include molecular level and bulk interactions. Subsequently, they modify the interfacial properties. Though vibrant, the CNC-polymer molecular interaction is still unclear. We took this void in our understanding as our motivation to explore these interactions. In this work, we tried to understand why CNC interacts differently with different polymers and what drives the adsorption of polymer on CNC. Our work can also help us to understand the configurations and origins of CNC-polymer system properties. The broad range of length and time scales covered by this physical process requires a multiscale simulation approach. In this thesis, we start with the all-atom molecular simulation and focus on the specific energetic interactions between CNC surfaces and unrealistically short polymer chains. In future work, we will build on this model and develop a multiscale modeling approach for capturing the full scope of CNC-polymer interaction, including the configuration and dynamics of realistic long polymer chains around CNCs. We propose that there are two driving forces for adsorption based on the free energy difference values obtained via PMF (potential of mean force) calculations done on eight systems with different physical components. Overall, we conclude that the balance between polymer's ability to form hydrogen bonds with the surface and their interactions with the bulk solvent control the adsorption and desorption phenomenon. A larger coarse-grained model developed from our simulations will help to understand these systems better. This presented work deals with the specific energy interactions and information which we will need for the systematic coarse-graining of these systems. / Thesis / Master of Applied Science (MASc)

Since the Eu3+ ion can occupy different cation sites in a host material, it can serve as a useful probe of nanocrystalline structures to gain more insight into the structural changes that can occur when the particle size is reduced from the bulk to nanometer regime. The use of laser spectroscopy to probe two nanocrystalline structures, Eu3+:Y2O3 and Eu3+:CaO, was investigated. The nanocrystalline structures were prepared by the laser-vaporization-gas-phase condensation of the bulk oxides. The particle size distribution and dominant particle diameters of the nanocrystals were determined by transmission electron microscopy. The particle size dependency results of Eu3+:Y2O3 revealed three distinct phases: (1) the sharp lines of the monoclinic Y2O3 were dominant in the larger particles; (2) the C2 site of the cubic phase, which appears in the smaller particles; and (3) the amorphous phase that increases in intensity as the particle size decreases. The observation of distinct spectral lines from the monoclinic phase confirms the presence of a crystalline phase for all of particle sizes studied. The site-selective results of various concentrations of 13-nm Eu3+:CaO showed that the laser-vaporization-gas-phase condensation method of preparation produced two europium-containing phases at most concentrations: cubic CaO and monoclinic Eu2O3. Results showed that the monoclinic Eu2O3 phase could be reduced by 95% by annealing at 800 0C for 30 minutes without particle growth. Since the Eu3+ ion and the Y3+ ion are isovalent, the substitution of a Eu3+ ion into Y2O3 is considered a trivial case of extrinsic disorder since the impurity is neutral relative to a perfect crystal1. As a result, it is not necessary to have any other defects present in the crystals to maintain charge neutrality. With Eu3+:CaO, the dopant and host cation charges are different and therefore the dopant distribution can be investigated by site-selective spectroscopy. Since the experimental dopant distribution results for nanocrystalline Eu3+:CaO were inconclusive, a model to predict the theoretical change in the dopant distribution in Eu3+:CaO as a function of particle size was developed. The model predicts that the defect chemistry is affected when the particle size is approximately 50 nm and smaller. / Ph. D.

Nanoparticle usage continues to increase in everyday products, from cosmetics to food preservation coatings, drug delivery to polymer fillers. Their characterization and synthesis is of utmost importance to ensure safety and improved product quality. Nanoparticles can be sourced naturally or synthetically fabricated. Cellulose nanocrystals (CNCs) are rod-like nanoparticles that can be isolated from nature. Reliable methods of characterization are necessary to ensure quality control. However, their physical characteristics cause challenges for imaging under transmission electron microscopy (TEM) with a high enough resolution for dimensional analysis. Heavy metal staining such as radioactive uranyl acetate is often used to increase contrast and TEM sample substrate preparation techniques often use expensive equipment such as glow discharge in order to prevent CNC agglomeration. A method to reliably produce TEM images of CNCs without using radioactive stains or expensive glow discharge equipment was developed, using a vanadium-based stain branded NanoVan® and bovine serum albumin to keep CNCs dispersed while drying on the TEM substrate. Due to their aspect ratio, there is also concern of toxicity to the lungs. The concentration of CNCs in air in production facilities must be monitored, but there is currently no method tailored to CNCs. A method using UV-vis spectroscopy, dynamic light scattering, TEM, and scanning mobility particle sizer in conjunction with impinger collectors was developed for monitoring aerosolized CNC concentration. Synthetic nanoparticles are often used for controlled drug delivery systems. A new peptide drug termed αCT1 has been shown to interact with cell communication in a way that promotes wound healing, reduces inflammation and scarring, and aids in cancer therapy. However, the peptide's half-life in the body is estimated to be less than a day, which is not conducive to long-term treatments. Controlling its release into the body over several weeks can decrease the number of doses required, which is especially useful for glioblastoma treatment. Poly(lactic-co-glycolic acid) (PLGA) is often used for drug encapsulation since it hydrolyzes in the body and is biocompatible. Two methods of αCT1 encapsulation in PLGA were explored. It was found that flash nanoprecipitation increased loading of αCT1 in the particles by 1-2 orders of magnitude compared with the double emulsion method. Particles released αCT1 over three weeks and were non-cytotoxic. / PHD / Nanoparticle usage continues to increase in everyday products, from cosmetics to food preservation coatings, drug delivery to polymer fillers. Understanding the nature of nanoparticles is important to ensure safety and quality of commercial products, and production of particles allows for tailoring for specific applications. In this work, a technique to more easily create samples of cellulose nanocrystals (CNCs) for electron microscopy is developed. Electron microscopy can then be used to measure the size of these rod-like particles. Then, the technique is used to help develop a method to measure the concentration of CNCs in air. CNCs may irritate the lungs, so development of a way to measure their concentration in air is important to ensure safety of plant workers and consumers of CNCs. Characterization techniques of CNCs were used for synthesized particles used for brain cancer treatment. Synthesized particles contain the drug αCT1, which has been shown to reduce glioblastoma, or brain cancer, from becoming resistant to chemotherapy. These particles were made using poly(lactic-co-glycolic acid) (PLGA), a polymer that degrades in the body into lactic acid and glycolic acid. PLGA particles released αCT1 over three weeks and are of a size that is compatible with the brain. However, loading of the drug was low when using the first synthesis method. By switching particle synthesis methods, drug loading in the particles was increased by 1-2 orders of magnitude.

Titanium been used industrially for nearly a century. Ever since it was first reduced to its elemental form, concerted efforts have been made to improve the material and to reduce the cost of production. In this thesis, titanium is mechanically alloyed with cellulose nanocrystals followed by powder consolidation and sintering to form a solid titanium metal matrix composite. Cellulose nanocrystals (CNCs) were chosen as the particle reinforcement as they are a widely abundant and natural material. Additionally, the nanocrystals can be derived from waste materials such as pistachio shells. This offers a unique advantage to act as a green process to enhance the mechanical properties of the titanium as well as to reduce to cost of production. Vibrational milling using a SPEX 8000M mill was used to mechanically alloy titanium powder with varying concentrations of CNCs. Additionally, the milling time was varied. This process showed that varying the concentrations of CNCs between 0.5% - 2% by weight did not noticeably alter the microstructural or mechanical properties of the materials. Conversely, changing the milling time from 0.5 hours to 5 hours proved to greatly alter the microstructural and mechanical properties of the titanium matrix metal composites. Further increasing the milling time to 10 and 25 hours caused the materials to become exceedingly brittle thus, the majority of experiments focused on samples milled between 0.5 hours and 5 hours. The hardness values for the Ti-1%CNC materials increased from 325-450-600-800 for the samples milled for 0.5, 1, 2, and 5 hours respectively. The other concentrations used were found to yield similar values and trends. SEM micrographs showed that small precipitates had formed within the grains except materials milled at 5 hours, which showed the production of very coarse particles at the grain boundaries. Similarly, an attrition mill was used to mechanically alloy titanium with varying CNC concentrations. Milling time was also varied. The powders were consolidated, sintered and characterized. It was found that increasing CNC content at low milling times caused a reduction in hardness. The X-ray diffractograms also showed a trend in that the diffraction patterns shifted to the lower angle with increasing CNC concentration, thereby suggesting that the increase in CNC content facilitated the removal of oxygen atoms housed within the interstitial sites. The oxygen was observed to diffuse and precipitate platelet titanium dioxide particles. These particles were found to be located within the titanium grains and coarsened with milling time. Generally, increasing the milling time to 15 hours was found precipitate particles at the grain boundaries as well as to excessively dissolve oxygen into the titanium lattice leading to embrittlement. The materials milled for 5 hours showed the best increase in strength while maintaining good ductility. / Master of Science / Titanium has only been used industrially since the early 1940’s thanks in large to the modern advances to reduce titanium ore to its elemental state. Titanium gained much interest as a structural material because of its corrosion resistance and its exceptional strength for a lightweight metal, making the material ideal for medical and aerospace applications. Pure titanium was found to be soft and had poor wear resistance, therefore, efforts were made to create titanium alloys which mitigated these weaknesses. Often titanium is alloyed with costly and toxic elements to enhance its strength properties, making it dangerous to use in the medical field. One way to enhance the strength properties of titanium without the addition of these harmful alloying elements is to create a titanium composite by adding strong inert particles to a titanium matrix. One method to create titanium metal matrix composites is to violently mix titanium powder with the reinforcement material, through a process called mechanically alloying. Following the mixing process the powder is then compacted and heated to form a solid part through a process called sintering. While these powder processing methods are known and viable for forming titanium metal matrix composites, some of the reinforcement materials can be expensive. In this thesis, cellulose nanocrystals (CNCs) will be added as reinforcement to titanium by means of two mechanical alloying processes, vibratory milling (shaking) and attrition milling (stirring). CNCs can be derived from plant matter which is widely abundant and inexpensive. The viability of CNCs to be used as a reinforcement material, as well as the mechanical alloying processes were investigated to determine the effect on the titanium strength properties. The powder processing steps were found to cause the CNCs to react with the surrounding titanium matrix which caused beneficial oxides to form as the reinforcement materials. In general, it was found that vibratory milling caused the final titanium metal matrix composite to be hard and brittle. Attrition milling was found to be more favorable as some materials were observed to be strong yet ductile.

This thesis identifies a facile and versatile technique for creating multi-scale porous titania with tunable meso-scale morphology. Three templating approaches were simultaneously utilized in achieving this; namely, soft-templating by template-free self-assembly of an aligned macroporous structure, freeze-casting for the preservation of particle dispersion found in suspension, and hard-templating by the use of cellulose nanocrystals (CNCs) as sacrificial material. A systematic study was conducted wherein three synthesis parameters (water content, alcohol solvent content, and drying method) were varied in the hydrolysis of titanium tetra-isopropoxide (TTIP) by the sol-gel method to determine their contribution to the formation of multi-scale porous titania exhibiting aligned macrochannels and mesoporosity. The optimal synthesis settings for producing multi-scale porous titania were identified as H2O/TTIP molar ratio of 30, without any isopropanol (acting as solvent), and freeze-drying after freezing at -40°C. Subsequently, CNCs were added in various quantities (0-50vol%) to the hydrolysis of TTIP using these optimized settings to achieve more direct and precise control of the final titania meso-structure. Morphological studies revealed that the final titania bodies maintained the formation of macrochannels 1-3 μm in diameter as a result of hydrolysis in excess water in the absence of an organic solvent and exhibited successful templating mutually affected by CNC addition and freeze-casting. Freeze-drying preserved particle dispersion in the colloid suspension, hindering agglomeration otherwise found after oven-drying and enhanced the CNCs' role of disrupting titania aggregation and increasing interconnectivity. Thus, meso-structured multi-scale porous titania was prepared by a combined templating strategy using template-free self-assembly, freeze-casting, and CNC hard-templating. / MS / Titanium dioxide (TiO₂) has been shown to exhibit desirable properties including physical and chemical stability and biocompatibility making it a material of great interest in a variety of fields including pigments and biomedicine. Furthermore, the material’s photocatalytic activity (i.e. ability to absorb light energy to generate usable charge) has led to its implementation in solar cells, in the production of hydrogen as an eco-friendly fuel, and in decontaminating water from organic pollutants. While TiO₂ has shown great promise in these applications, there remains a need to identify a simple strategy to synthesize TiO₂ with a tunable multi-scale porous structure with pores of different sizes and shapes to improve its performance. To this end, a facile and versatile procedure was used to prepare multi-scale porous TiO₂ with tunable morphology. In investigating the effect of water content, alcohol content and drying method on the final morphology, a multi-scale structure was achieved by synthesizing TiO₂ in the absence of an alcohol solvent and within a new moderate range of water content that had not been previously explored. Lacking an effective and easy strategy to further manipulate the multi-scale morphology, this self-assembly technique was modified by incorporating cellulose nanocrystals (CNCs) into the synthesis procedures to further tune the structure on the nanometric scale by altering the final porosity and surface area. The final TiO₂ samples exhibited multi-scale porous structures that could be manipulated by combining the self-assembly and CNC-templating techniques in an adaptable strategy to tailor the TiO₂ morphology for its various uses in photocatalysis and biomedicine.

Synthetic plastics are intrinsic to modern human existence. Unfortunately, many challenges exist related to the accumulation of plastic waste, including greenhouse gas emissions, contamination of natural environments, and entrance into the food chain through microplastics. Therefore, new polymers are being developed that both compete with the capabilities and costs of petroleum-based plastics and have assured biodegradability. Through decades of research, plant oils have emerged as one of the leading options for alternative starting materials because of their feasibility for use in polymerization reactions, wide availability, renewability, and cost-effectiveness. In this work, cottonseed oil (CSO) and soybean oil (SBO) are successfully utilized to synthesize polymers with a range of promising properties. A nanocomposite was produced by incorporating cellulose nanocrystals (CNCs) into an epoxidized CSO (ECSO) polymer matrix. A significant improvement in properties such as tensile stiffness and strength, without any substantial decrease in extensibility or thermal integrity has been observed. This demonstrated that CNCs can be used to tune the CSO- based polymer properties. Enzymes are excellent alternatives to traditional catalysts as they eliminate the necessity of elevated reaction temperatures and pressures. Epoxidized SBO (ESBO) was polymerized using immobilized candida antarctica lipase B (Novozyme N435). The resulting polymer was inhomogeneous, with soluble waxy and insoluble solid components. Analyses of the soluble component indicated the formation of a multi-branched polymer, showing that a greener system may be used to produce ESBO-based polymers. It is necessary to test the biodegradability of biobased polymers to confirm their validity as alternatives to traditional plastics. Degradation of the CNC-incorporated CSO-based network polymer was characterized by submersing specimens into various aqueous media, including artificial seawater and saltwater, to simulate realistic end-of-use scenarios. Decomposition occurred due to hydrolysis of the many ester linkages within the polymer structure. The presence of CNCs appeared to enhance the rate of degradation. Overall, the hydrolytic susceptibility of the CSO-based network polymer was observed as enhanced by incorporating CNCs. In summary, this work demonstrates the viability of using plant oils and CNCs to produce biodegradable polymers with a range of properties, thus aiding in the effort to replace traditional plastics.

Chalcogenide perovskites with a distorted ABX3 structure (A: Ca, Ba, Sr; B: Zr, Hf; X: S, Se) are a prominent focus in optoelectronic materials. One of these is BaZrS3 which has garnered significant attention in perovskite materials due to its distinctive distorted perovskite structure and valuable optical properties that are viable for a single-junction solar cell and present a compelling option for tandem solar cell configurations. Another promising material is SrZrS3 which exists in two phases: needle-like non-perovskite α-SrZrS3 and distorted perovskite β-SrZrS3. The distorted perovskite phase shows promising luminescence properties in bulk, making it potentially viable for LED applications. In this work, we show that the non-perovskite α-SrZrS3 was accessed through colloidal synthesis at 330 °C and 365 °C by increasing concentrations of precursors. In order to favor the perovskite phase, we conducted alloying experiments incorporating varying percentages of doped Sr2+ into BaZrS3 to first synthesize a distorted perovskite Ba(1-x)SrxZrS3. Through varying percentages and varying reaction conditions such as temperature, time of reaction, and doping concentrations, we aim to optimize the synthesis of colloidal Ba(1-x)SrxZrS3 nanocrystals.

No / Exploring nucleation processes by molecular simulation can provide a mechanistic understanding at the atomic level and also enables kinetic and thermodynamic quantities to be estimated. However, whilst the potential for modeling crystal nucleation and growth processes is immense, there are specific technical challenges to modeling [that need to be tackled]. In general, rare events, such as nucleation cannot be simulated using a direct ¿brute force¿ molecular dynamics approach. In recent years, the limited time and length scales that are accessible by conventional molecular dynamics simulations have inspired a number of advances to tackle problems that were hitherto considered outside the scope of molecular simulation. While general insights and features could be explored from efficient generic models, The newer methods have paved the way to realistic crystal nucleation scenarios. The association of single ions in solvent environments, the mechanisms of motif formation in solvents, the nucleation process itself, ripening reactions, role of additives, as well as the self-organization of nanocrystals can now all be investigated at the molecular level. The insights gained should complement experiments and enhance our fundamental understanding of the processes involved and facilitate the rational design of new materials.

Yes / Ultrasmall SnO2 nanocrystals as anode materials for lithium-ion batteries (LIBs) have been synthesized by bubbling an oxidizing gas into hot surfactant solutions containing Sn-oleate complexes. Annealing of the particles in N2 carbonifies the densely packed surface capping ligands resulting in carbon encapsulated SnO2 nanoparticles (SnO2/C). Carbon encapsulation can effectively buffer the volume changes during the lithiation/delithiation process. The assembled SnO2/C thus deliver extraordinarily high reversible capacity of 908 mA.h.g(-1) at 0.5 C as well as excellent cycling performance in the LIBs. This method demonstrates the great potential of SnO2/C nanoparticles for the design of high power LIBs. / National Natural Science Foundation of China (21103039), Anhui Province Natural Funds for Distinguished Young Scientists, https://bradscholars.brad.ac.uk/browse?order=ASC&rpp=20&sort_by=-1&etal=-1&offset=6150&type=authorResearch Fund for the Doctoral Program of Higher Education of China (20110111120008), Beijing National Laboratory for Molecular Sciences (BNLMS), and Deutsche Forschungsgemeinschaft Grant (DFG): H1113/3-5. C.Y. acknowledges the support from the “Thousand Talents Program” and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).