Langston, Tye A.

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.

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.