Nanostructured materials

Nanoscale silica particles are functionalized and ultrasonically dispersed into a
mixture of polyethylene glycol and ethanol, and then reinforced with Kevlar. The stab or
puncture resistance of the flexible nanophased materials system supersedes recent
advances made in this area. Through SEM scans, thermal and chemical analysis, it is
evident that the functionalized nanoparticles offer multiple facets of resistance to
penetration of a sharp impactor. The improvement in protection is traced to the
formation of siloxane bonds during functionalization. The framework for a theoretical
model is established to estimate penetration depth under low velocity impact of a sharp
object through the flexible composite. For comparison ofthese novel fabric composites,
a method is also introduced to evaluate penetration resistance quantitatively. The method
is capable of showing subtle changes that would otherwise be missed.

The technical and scientific challenges to provide reliable sources energy for US
and global economy are enormous tasks, and especially so when combined with strategic
and recent economic concerns of the last five years. It is clear that as part of the mix of
energy sources necessary to deal with these challenges, fuel cells technology will play
critical or even a central role. The US Department of Energy, as well as a number of the
national laboratories and academic institutions have been aware of the importance such
technology for some time. Recently, car manufacturers, transportation experts, and even
utilities are paying attention to this vital source of energy for the future. In this thesis, a
review of the main fuel cell technologies is presented with the focus on the modeling, and
control of one particular and promising fuel cell technology, aluminum air fuel cells. The
basic principles of this fuel cell technology are presented. A major part of the study
consists of a description of the electrochemistry of the process, modeling, and simulations
of aluminum air FC using Matlab Simulink™. The controller design of the proposed
model is also presented. In sequel, a power management unit is designed and analyzed as an alternative source of power. Thus, the system commutes between the fuel cell output
and the alternative power source in order to fulfill a changing power load demand. Finally,
a cost analysis and assessment of this technology for portable devices, conclusions and
future recommendations are presented.

With the goal of improving chemical detection methods for buried improvised explosive
devices (IED’s), the intention of this study is to show that functionalized nano-particles
improve the sensing properties of a polymer applied to gas sensors. The approach was
reinforcing the polymer, Nafion, with acid-functionalized carbon nanotubes (CNT’s).
Ammonia was chosen as the analyte for its similarity to IED byproducts without the
dangers of toxicity or explosion. Two sensor platforms were investigated: Quartz crystal
microbalances (QCM’s) and microcantilevers (MC’s). Preliminary evaluation of treated
QCM’s, via frequency analyzer, showed improvements in sensitivity and fast reversal of
adsorption; and suggested increased stability. Tests with coated MC’s also supported the
findings of QCM tests. Amplitude response of MC’s was on average 4 times greater
when the Nafion coating contained CNT’s. Quantitative QCM testing with gas-flow
meters showed that with CNT inclusion: the average number of moles adsorbed increased
by 35% (>1.2 times frequency response); sensitivity improved by 0.63 Hz/ppt on average; although the detection threshold decreased marginally; but reusability was
much better after extended exposures to concentrated ammonia.

The focus of this thesis is to develop lanthanide (Ln) luminescent materials through the exploration of coordination polymers and nanomaterials. Herein, dimethyl-3,4- furanedicarboxylate acid undergoes hydrolysis under hydrothermal conditions to form coordination polymers with lanthanide ions. The resulting coordination polymers exhibited luminescent properties, with quantum yields and lifetimes for the Eu-and Tb-CP of 1.14+-0.32% and 0.387=-0.0001 mx, and 3.33=-0.82% and 0.769=-0.006 ms, respectively. While the incorporation of lanthanides was not achieved in this work, progress toward the production of pure phase InP in the nanoregime has been made, using a low-cost, hydrothermal method. Through SEM and PXRD conflict, it is believed that pure INP particles with a size range of 58-81 nm were successfully synthesized.

Classical trajectory molecular dynamics methods are used to investigate open ended free standing single wall carbon nanotubes ("SWT"). Total energy calculations performed using classical three-body interatomic potentials with periodic boundary conditions along the tube axis, showed that the minimum strain energy varied as 1/$R\sp2$ relative to an unstrained graphite sheet. We discuss the development of a parallel code to simulate short-ranged empirical potentials such as those of Stillinger and Weber, Tersoff, and Tersoff-Brenner. We then use the Tersoff and Tersoff-Brenner potentials to examine SWT and the tube response to axial stretching and compression. Data collected are used to calculate Young's modulus for the tubes and to develop a simple formula that approximates Young's modulus over a range of tube radii. The investigation of the free standing SWT leads to a suggestion for the possible mechanism responsible for holding the tubes open during the growth process.

Classical trajectory molecular dynamics methods are used to investigate the critical strain of single-walled carbon nanotubes ("SWT") and the strength and extent of the interactions between 3D Ge structures on the surface of Si(001). The discrete model is capable of giving some insight into the critical strain of the SWT's beyond the limits of the continuous model and allow us to investigate the effects of lattice distortion due to the placement of Ge structures on the surface of a Si substrate. Total energy calculations performed using classical three-body interatomic potentials with appropriate boundary conditions for each case are used to investigate the two systems. We discuss the development of a parallel code to simulate short-ranged empirical potentials such as those of Stillinger and Weber, Tersoff, and Tersoff-Brenner. We then use the Tersoff potential to model C and Si/Ge system. Data collected are used to examine the behavior of the two systems.

In this investigation, polymer precursor of syntactic foam has been reinforced with SiC nanoparticles to enhance mechanical and fracture properties. Derakane 8084 vinyl ester resin was first dispersed with 1.0 wt% of SiC particles using a sonic cavitation technique. In the next step, 30.0 wt% of microspheres (3M hollow glass borosilicate, S-series) were mechanically mixed with the nanophased vinyl ester resin, and cast into rectangular molds. A small amount of styrene was used as dilutant to facilitate mixing of microspheres. The size of microspheres and SiC nanoparticles were 20-30 um and 30-50 nm, respectively. Tension, compression, and flexure tests were conducted following ASTM standards and a consistent improvement in strength and modulus within 20-35% range was observed. Fracture toughness parameters such as KIC and GIC were also determined using ASTM E-399. An improvement of about 11-15% was observed. Samples were also subjected to various environmental conditions and degradation in material properties is reported.

My study sought to acquire quantitative data from the surface of lithic tools and use that data to discriminate tools used on different contact materials. An experimental archaeological wear production method was conceived, whereby I and several volunteers produced wear on chert, heat-treated chert, and obsidian flakes by using those flakes on several contact materials. The flakes were then analyzed using a laser scanning confocal microscope, which recorded three-dimensional surface data from each tool. The data was analyzed using cluster analysis to find the ideal combination of parameters which correctly discriminated the flakes based on use-wear data. After finding acceptable parameters which grouped flakes appropriately through cluster analysis, those groups were subjected to a discriminant analysis. Each analysis returned a p-value under .05, meaning that the clustering based on the parameters Sq and Sfd produced by the cluster analysis was not random, but indicative of these variables' ability to discriminate lithic use-wear. The major advantage of the approach developed in this study is that it can quantitatively discriminate use-wear produced by different contact materials on flakes with no a priori information at all.

This thesis investigates the use of nanotechnology in an extensive literature search in the field of cement and concrete. A summary is presented. The research was divided into two categories: (1) nanoparticles and (2) nanofibers and nanotubes. The successes and challenges of each category is documented in this thesis. The data from the literature search is taken and analyzed using statistical prediction by the use of the Monte Carlo and Bayesian methods. It shows how statistical prediction can be used to analyze patterns and trends and also discover optimal additive dosages for concrete mixes.

Enhancement of mechanical, thermal and hygrothermal properties of carbon fiber/vinyl ester (CFVE) composites through nanoparticle reinforcement has been investigated. CFVE composites are becoming more and more attractive for marine applications due to two reasons : high specific strength and modulus of carbon fiber and low vulnerability of vinyl ester resin to sea water. However, the problem with this composite system is that the fiber matrix (F/M) interface is inherently weak. This leads to poor mechanical properties and fast ingress of water at the interface further deteriorating the properties. This investigation attempts to address these deficiencies by inclusion of nanoparticles in CFVE composites. Three routes of nanoparticle reinforcement have been considered : nanoparticle coating of the carbon fiber, dispersion of nanoparticles in the vinyl ester matrix, and nanoparticle modification of both the fiber and the matrix. Flexural, short beam shear and tensile testing was conducted after exposure to dry and wet environments. Differential scanning calorimetry and dynamic mechanical analysis were conducted as well. Mechanical and thermal tests show that single inclusion of nanoparticles on the fiber or in the matrix increases carbon/vinyl ester composite properties by 11-35%. However, when both fiber and matrix were modified with nanoparticles, there was a loss of properties.