Surface chemistry

This research tests the use of sensitized lanthanide ions to determine if they can
detect water-borne explosive traces and produces two designs for a field-deployable
underwater explosive trace detector. 1,1 0-phenanthroline and thenoyltritluoroacetone are
evaluated as sensitizing ligands to absorb energy and initiate the fluorescence process in
europium ions. Different compounds obtained via ligand choice and mixing order are
evaluated for their ability to produce a large fluorescence differential between explosive-laden
and explosive-absent solutions. Optimal excitation and emission wavelengths for
several different compounds are determined, as well as practical wavelengths to be
applied in the field. The effect of methanol as a solvent to deliver the reagents is
evaluated and rough solubility limits are determined. The effects of seawater constituents
on detection are investigated and explosive detection limits are determined. It was found
that this method and device are viable for underwater explosive trace detection. A field-deployable
device is designed, characterized, and proven.

The degradation of polymer composites in moist environments is a limiting
factor in the advancement of composite technology. The key to mitigate this
degradation is to maintain the integrity of the fiber/matrix (F/M) interface. In this
study, the F/M interface of carbon/vinyl ester composites has been modified by
treating the carbon fiber with polyhedral oligomeric silsesquioxane (POSS). Two
POSS systems, namely octaisobutyl and trisilanolphenyl, have been
investigated. A set of chemical and mechanical procedures has been developed
to coat carbon fibers with POSS, and fabricate layered composites using vinyl
ester resin. lnterlaminar shear, transverse tension, and low velocity impact tests
on composites have indicated around 10-38% improvement in mechanical
properties with respect to control samples. Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) tests have also shown
significant improvement in glass transition temperature (T9). Hygrothermal tests,
under various environments, have demonstrated that POSS reduces water
absorption by 20-30%.

The effect of the hydrophobicity of organic compounds on their micelle-water partition coefficients was investigated. The micelle-water partition coefficients were obtained by UV/VIS spectroscopy and correlated with their octanol-water partition coefficients. The octanol-water partition coefficient of an organic compound is a measure of its hydrophobicity. Hydrophobicity alone did not influence the micelle-water partition coefficients. Further research is required to substantiate present findings and obtain additional related information.

Low Energy Electron Diffraction is used to determine the different structures formed by the CO adsorption on the Ni(110) surface at two coverages. At full coverage the superlattice is Ni(110)-(2 x 1)2CO. For this superlattice, the CO molecules adsorb at the short bridge sites with a 20 degrees common tilt in the +-[001] directions. The Ni-C and the C-O bond lengths are 1.85 A and 1.15 A, respectively. In the Ni(110)-c(2 x 4)3CO superlattice structure, which is formed at an intermediate coverage, the CO molecules adsorb at the top sites with two types of configurations on alternate (110) rows. Half the rows are filled with CO molecules having a 9 degrees zig-zag common tilt in the $\pm$ (001) directions, and half the rows are half filled with untilted CO molecules. The Ni-C and the C-O bond lengths are 1.67 A and 1.15 A, respectively. The possible role of hydrogen in the formation of the surface structure is discussed.

The purpose of this thesis is to provide a comprehensive overview of an important technique (low energy electron diffraction) used in the study of surface phenomena. Within this context, the LEED studies of NO adsorbed on the Ni(110) surface and of Fe-33%Ni(111) near its Martensitic transition temperature were done to determine their surface structures.

The generation and multiplication of dislocations in Gallium Arsenide (GaAs) and Indium Phosphide (InP) single crystals grown by the Vertical Gradient Freeze (VGF) process is predicted using a transient crystallographic finite element model. This transient model is developed by coupling microscopic dislocation motion and multiplication to macroscopic plastic deformation in the slip system of the grown crystals during their growth process. During the growth of InP and GaAs crystals, dislocations are generated in plastically deformed crystal as a result of crystallographic glide caused by excessive thermal stresses. The temperature fields are determined by solving the partial differential equation of heat conduction in a VGF crystal growth system. The effects of growth orientations and growth parameters (i.e., imposed temperature gradients, crystal radius and growth rate) on dislocation generation and multiplication in GaAs and InP crystals are investigated using the developed transient crystallographic finite element model. Dislocation density patterns on the cross section of GaAs and InP crystals are numerically calculated and compared with experimental observations. For crystals grown along [001] and [111] orientations, the results show that more dislocations are generated as the temperature gradient, the crystal growth rate and the crystal radius increase. For the same growth process, it shows that the crystal grown along [111] orientation is a favorable growth direction to grow lower dislocation density crystals. All the results show a famous "W" shape and four fold symmetry dislocation density pattern in GaAs and InP crystals grown from both orientations regardless of crystal growth parameters, which agree well with the patterns observed in actual grown crystals. Therefore, this developed crystallographic model can be employed by crystal grower to design an optimal growth parameters and orientations for growing low dislocation density in advanced semiconductor and optical crystals.

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.

This research focuses on carbon fiber treatment by nitric acid and 3- (trimethoxysilyl)propyl methacrylate silane, and how this affects carbon/vinyl ester composites. These composites offer great benefits, but it is difficult to bond the fiber and matrix together, and without a strong interfacial bond, composites fall short of their potential. Silanes work well with glass fiber, but do not bond directly to carbon fiber because its surface is not reactive to liquid silanes. Oxidizing surface treatments are often prescribed for improved wetting and bonding to carbon, but good results are not always achieved. Furthermore, there is the unanswered question of environmental durability. This research aimed to form a better understanding of oxidizing carbon fiber treatments, determine if silanes can be bonded to oxidized surfaces, and how these treatments affect composite strength and durability before and after seawater exposure. Nitric acid treatments on carbon fibers were found to improve their tensile strength to a constant level by smoothing surface defects and chemically modifying their surfaces by increasing carbonyl and carboxylic acid concentrations. Increasing these surface group concentrations raises fiber polar energy and causes them to cohere. This impedes wetting, resulting in poor quality, high void content composites, even though there appeared to be improved adhesion between the fibers and matrix. Silane was found to bond to the oxidized carbon fiber surfaces, as evidenced by changes in both fiber and composite properties. The fibers exhibited low polarity and cohesion, while the composites displayed excellent resin wetting, low void content, and low seawater weight gain and swelling. On the contrary, the oxidized fibers that were not treated with silane exhibited high polarity and fiber cohesion.