Exposure to high impact velocity is the principle limiting factor of material performance in ballistic applications for use in civilian and defense industries. Graphene has emerged as a material of scientific interest due to its exceptional mechanical and thermal properties. When incorporated appropriately in a polymer matrix, graphene can significantly improve properties of polymers at small loading, while preserving the integrity of the polymer. Graphene based polymer nanocomposites provide a novel approach for material design for ballistic applications. The reliability of graphene/polymer nanocomposites on end use applications depends on understanding the effect of structure-property relationship of nanocomposite. A first approach to engineering nanocomposite for ballistic applications requires thorough understanding of physical properties change with incorporation of nanofillers in polymer matrix. One significant class of properties tremendously affected by inclusion of nanofiller is thermodynamic properties. Therefore, a first investigative study, we explore non-linear elastic behavior of graphene using first principle method, specifically Density-Functional Theory (DFT), and atomistic simulation. Using DFT, we calculated the equation of state (EOS) and elastic constants of graphene. The results are in agreement with experimental and other theoretical studies using DFT. However, accuracy of atomistic simulations is limited by empirical potentials. Nevertheless, general anisotropic, non-linear mechanical behavior of graphene is evident on both approaches. Additionally we use molecular dynamics (MD) simulations to study effect of graphene nanofiller on thermo‑mechanical properties of polyurethane. We have calculated thermodynamic, structural and mechanical properties of the amorphous polyurethane and its graphene nanocomposite. Our results show significant enhancement of thermal-mechanical properties. The final part of this dissertation, we used non-equilibrium molecular dynamics (NEMD) simulations to investigate dynamic response behavior of polyurethane and its graphene nanocomposite. Calculation of Hugoniot states of polyurethane agrees with experimental studies. However, a phase change phenomenon observed in experimental work was not visible in the present work. This is due to bond breaking and formation, which is a clear characterization of phase changes. Graphene-polyurethane nanocomposites demonstrate similar shock wave propagation illustrating characteristics of impeding shock wave when subjected to different particle velocities. This is due to graphene inducing stress concentrations in the composite, which may increase yield strength.

Biobased polymers are a critical research topic as they may serve as replacement to traditional unsustainable petro-chemical polymers. It is vital to widen its range of applications by improving its physical and mechanical properties via light weighting and strength improvements. Light weighting can be accomplished by introducing foam morphology to the material while mechanical strength improvements can be achieved by inserting stiff filler material to the base polymer to form a composite. This study explores the physical, mechanical, thermal, rheological and morphological properties of blends, foams and composites between biobased PLA and PHBV matrix polymers and biobased chitin nanowhisker filler. It was found that foams produced from PLA and PHBV blends exhibits refined cellular morphology which leads to light weighting and good strength preservation while chitin nanowhiskers was determined to be a very effective filler for mechanical property improvements in both solid and porous materials.

Hospital-acquired infections are a significant contributor to clinically-related morbidity and mortality. The majority of these infections are associated with the use of invasive medical devices, where urinary catheters account for ~36% of cases. Current preventative strategies have shown short-term (<7 days) success, however their long-term (>28 days) efficacy is unclear. This thesis explores the use of solution-cast polyurethane nanocomposite (PUNC) materials for antimicrobial drug delivery in urinary applications. It is hypothesised that the enhanced barrier properties of PUNCs, afforded by the incorporation of well-dispersed nanoinclusions, would allow for the sustained release of an antimicrobial agent. The objectives of this research were to investigate the antibacterial, mechanical and barrier properties of PUNCs incorporating various silicates modified using antimicrobials, hypothesised to also act as dispersing agents. Organically modified silicates (OMS) were prepared at 110%, 200% and 300% cationic exchange capacity (CEC) using the biocide, chlorhexidine diacetate (CHX), which was hypothesised to perform the dual functions; dispersant and antibacterial agent. Resulting OMS were incorporated at 1wt% and 5wt% loadings into a PU matrix to produce PUNCs; PEU-CHX1.1MMT, PEU-CHX2.0MMT, and PEU-CHX3.0MMT, respectively. CHX performed well as a dispersant, producing intercalated to partially exfoliated PUNCS. Antibacterial activity was dependent on OMS type and loading. PEU-CHX1.1MMT materials had poor antibacterial properties, but the addition of free CHX into the materials significantly improved their efficacy, demonstrating long-term sterility in an in vitro urinary tract (UT) model. PEU-CHX2.0MMT and PEU-CHX3.0MMT at 5wt% OMS loadings had partially exfoliated structures and excellent antibacterial activity. Cytotoxicity was evident in all materials, although to a lesser extent in the latter. Overall, intermediate OMS loadings of CHX2.0MMT would be expected to produce PUNCs with favourable antibacterial activity and cytocompatibility. PUNC drug-release profiles demonstrated sustained release compared to pristine PU, indicative of enhanced barrier properties. Their ultimate tensile properties decreased with increased OMS loading or addition of free CHX.Higher cationic-exchanged OMS caused significant reductions in strain. Young's modulus increased in response to higher %CEC OMS and loading. PUNCs show promise as antibacterial biomaterials for long-term urinary applications, where antimicrobial release and mechanical properties can be modulated through organic modification and OMS loading.

The use of polymer nanocomposites (NCs) in industrial applications has received growing attention over the past decade due to their improved mechanical properties. However, little work has been reported which analyses the efficacy of NCs in biological applications, including drug delivery systems and implantable materials. This thesis examines the effect of the chemistry of the organic modifier (OM) on the structure and biological performance of poly(ether)urethane NCs (PUNCs) and the influence of the method of drug incorporation on interactions between drug and NC. Organically modified silicates (OMS) were prepared using OMs varying in terminal functionality and alkyl chain length. PUNCs were solvent cast containing 1 and 3wt% OMS and particle dispersion analysed using X-ray diffraction and transmission electron microscopy. Findings revealed that use of an OM with methyl terminal, dodecylamine (12CH3), resulted in superior dispersion of OMS compared with a carboxyl terminated OM, aminododecanoic acid (12COOH), of equivalent alkyl chain length. This is believed to result from increased self interaction of 12COOH compared with 12CH3. Additionally, increased alkyl chain length was shown to improve NC dispersion with a chain length of sixteen units resulting in the optimum dispersion with a partially exfoliated NC structure. Analysis of cellular interactions with the PUNCs revealed a significant difference in both fibroblast and platelet adhesion to NCs incorporating 12CH3 compared with 12COOH. Surface analysis using ToF-SIMS demonstrated the presence of 12CH3 fragments on the NC surface supporting the hypothesis that surface expressed OMs alter cellular interactions with the NC. Altering the alkyl chain length also affected cellular interaction with an alkyl chain length of twelve units or greater, substantially reducing fibroblast adhesion without affecting cell growth inhibition or viability. Incorporation of a model drug, crystal violet, into the PUNCs demonstrated a lower degree of disruption to OMS dispersion when loaded post NC fabrication compared with pre fabrication. This is believed to result from interactions between the drug and NC constituents which also impacted on drug release from the NC system. Results show PUNC properties and biological interactions can be modulated through OM variation and fabrication method, thus showing potential for use in biomedical applications.

The use of polymer nanocomposites (NCs) in industrial applications has received growing attention over the past decade due to their improved mechanical properties. However, little work has been reported which analyses the efficacy of NCs in biological applications, including drug delivery systems and implantable materials. This thesis examines the effect of the chemistry of the organic modifier (OM) on the structure and biological performance of poly(ether)urethane NCs (PUNCs) and the influence of the method of drug incorporation on interactions between drug and NC. Organically modified silicates (OMS) were prepared using OMs varying in terminal functionality and alkyl chain length. PUNCs were solvent cast containing 1 and 3wt% OMS and particle dispersion analysed using X-ray diffraction and transmission electron microscopy. Findings revealed that use of an OM with methyl terminal, dodecylamine (12CH3), resulted in superior dispersion of OMS compared with a carboxyl terminated OM, aminododecanoic acid (12COOH), of equivalent alkyl chain length. This is believed to result from increased self interaction of 12COOH compared with 12CH3. Additionally, increased alkyl chain length was shown to improve NC dispersion with a chain length of sixteen units resulting in the optimum dispersion with a partially exfoliated NC structure. Analysis of cellular interactions with the PUNCs revealed a significant difference in both fibroblast and platelet adhesion to NCs incorporating 12CH3 compared with 12COOH. Surface analysis using ToF-SIMS demonstrated the presence of 12CH3 fragments on the NC surface supporting the hypothesis that surface expressed OMs alter cellular interactions with the NC. Altering the alkyl chain length also affected cellular interaction with an alkyl chain length of twelve units or greater, substantially reducing fibroblast adhesion without affecting cell growth inhibition or viability. Incorporation of a model drug, crystal violet, into the PUNCs demonstrated a lower degree of disruption to OMS dispersion when loaded post NC fabrication compared with pre fabrication. This is believed to result from interactions between the drug and NC constituents which also impacted on drug release from the NC system. Results show PUNC properties and biological interactions can be modulated through OM variation and fabrication method, thus showing potential for use in biomedical applications.

In this work, I start by introducing a relatively recently innovated thin film architecture which offers a new direction in strain control, the vertically aligned nanocomposite (VAN). I first present the literature in the field, explaining the advantages and unique novel properties stemming from VAN structures. Next, I introduce the work I did to examine the unique strain states of Ba0.6Sr0.4TiO3–Sm2O3 VAN structures. It was found that the strain states in the functional Ba0.6Sr0.4TiO3 phase are unconventional compared to those in planar thin films. 3-dimensional strain was found to be acting on the Ba0.6Sr0.4TiO3 phase in the VAN structure. The origin of the strain was explained using a simple model which takes into account thermal expansion mismatch as well as lattice mismatch and elastic coefficients. The ferroelectric properties of the films were presented in relation to the observed strain states. I next present the work I did on the influence of strain on the magnetic properties in VAN film of Sm0.34Sr0.66MnO3–Sm2O3. Ferromagnetism was achieved in an otherwise antiferromagnetic Sm0.34Sr0.66MnO3. The effect was explained by a strain induced transition from super-exchange to double exchange coupling in the material. Last but not least, the potential of scalability of VAN films was explored by using sputtering to grow VAN structures instead of the commonly-used PLD growth. BaTiO3–Sm2O3 was used as a primary study material due to its well reported VAN properties. Preliminary results showing indications of a VAN structure. Some basic physical property characterization is also presented and compared to the properties of PLD-grown films in the literature. Limitations and challenges that arise due to the fundamental differences between sputtering and PLD are also described.

Metal-polymer nanocomposite materials were found to have highly tunable opti- cal properties. Density functional theory-based calculations were employed to study trends in Ag/polyvinylidene fluoride nanocomposite optical properties. The frequency- dependent imaginary part of the dielectric constant was calculated from dipolar inter- band transitions. The metallic inclusion introduced both occupied and unoccupied states into the large polymer band gap. Thus, higher inclusion volume fractions generally led to stronger composite optical response. Spectra from monodisperse sys- tems correlated well with nanoparticle quantum confinement models. A polydisperse system exhibited optical properties that correlated best with interparticle distances along the field direction. Nanodisk and nanorod-shaped inclusions had tunable re- sponse from field polarization, aspect ratio, crystallographic projections, and nanorod end-cap morphology. / Graduate / 0495

Polymer nanocomposites are prepared by appropriately dispersing nanoscale fillers into polymer matrices. Graphene, a two-dimensional nano-carbon material with outstanding physical properties, has been widely studied as a conductive filler for nanocomposites. In this work, a gum Arabic aqueous solution was proposed as a new media to exfoliate graphite into few-layer graphene by liquid-phase sonication. Successful exfoliation was confirmed by Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. Four types of graphene nanoplatelets were used to study the effects of the filler's aspect ratio. The one with the largest aspect ratio showed the best performance, where the conductivity of neat epoxy was increased by five orders of magnitude at 10 wt.%. Using a hot sonication technique and adding a small amount of second fillers further improved the electrical conductivities. The highest conductivity obtained in this study was 0.025 S/cm, which met the requirements of electromagnetic shielding material.

Flexibility, low cost, versatility, miniaturization and multi-functionality are key aspects driving research and innovation in many branches of the electronics industry. With many anticipated emerging applications, like wearable, transparent and biocompatible devices, interest among the research community in pursuit for novel multifunctional miniaturized materials have been amplified. In this context, multiferroic polymer-based nanocomposites, possessing both ferroelectricity and ferromagnetism, are highly appealing. Most importantly, these nanocomposites possess tunable ferroelectric and ferromagnetic properties based on the parameters of their constituent materials as well as the magnetoelectric effect, which is the coupling between electric and magnetic properties. This tunability and interaction is a fascinating fundamental research field promising tremendous potential applications in sensors, actuators, data storage and energy harvesting. This dissertation work is devoted to the investigation of a new class of multiferroic polymer-based flexible nanocomposites, which exhibits excellent ferromagnetism and ferroelectricity simultaneously at room temperature, with the goal of understanding and optimizing the origin of their magnetoelectric coupling. The nanocomposites consist of high aspect ratio ferromagnetic nanowires (NWs) embedded inside a ferroelectric co-polymer, poly(vinylindene fluoride-trifluoroethylene), P(VDF-TrFE) matrix. First, electrochemical deposition of ferromagnetic NWs inside anodic aluminum oxide membranes is discussed. Characterization of electrodeposited iron, nickel and highly magnetostrictive iron-gallium alloy NWs was done using XRD, electron and magnetic force microscopy. Second, different nanocomposite films have been fabricated by means of spin coating and drop casting techniques. The effect of incorporation of NWs inside the ferroelectric polymer on its electroactive phase is discussed. The remanent and saturation polarization as well as the coercive field of the ferroelectric phase are slightly affected. Third, effects of NW alignment on the magnetic properties of nanocomposites are discussed. Nanocomposites with aligned NWs showed anisotropic magnetic properties while the ones without showed isotropic properties. Forth and last, the effects of NWs loading, alignment and material on the magnetoelectric properties of the nanocomposites are analyzed. Low NW concentrations are found to promote the electroactive phase of the nanocomposite, whereas high concentrations lower it. Nanocomposites with aligned NWs showed an anisotropic magnetoelectric effect. Higher magnetostrictive NWs exhibited a higher magnetoelectric coupling, demonstrating the advantage of galfenol-based nanocomposites, which are reported in this thesis for the first time.

Five series of PT-30/organoclay (Cloisite 10A, Cloisite 30B, Nanomer I.28E, Nanomer I.30E and Nanomer I.44PA) composites were prepared and characterized. The dispersion of clay tactoids in PT-30 resin was studied by XRD and TEM. XRD analyses determined that the d-spacings of each nanoclays of these were expanded upon dispersing in the PT-30 matrix versus the as-received clay. TEM micrographs further demonstrated that the intercalation of clay layers by PT-30 occurred during the curing process. Histograms of clay tactoids distributions were generated based on the combination of XRD and TEM results. The glass transition temperatures (Tg) of selected PT-30/clay composites were measured by DSC and compared. Partial clay exfoliation with some resin intercalation was demonstrated. The average flexural strengths and flexural moduli of all composites were obtained using three-point bending tests.