Date of Award
Doctor of Philosophy in Chemistry
Jimmie C. Oxley
A variety of intermolecular interactions occurs when an energetic material responds to its surroundings. With a better grasp of these energetic material contacts, improved performance on plastic-bonded explosives, superior swab materials for explosives detection, and novel insensitive munitions are possible. In order to further understand these interactions, the following relationships were researched: adhesion between energetic materials and polymer substrates; quantitative collection and detection of energetic materials on electrostatically charged swabs; and noncovalent derivative investigation between energetic material pairs.
A number of explosives detectors rely on introduction of the analyte to the instrument via swabs. However, most swab materials are burdened by either poor sorption (pickup) or poor desorption (release). Therefore, finding a swab that can both easily sorb and desorb an explosive is highly desirable. Atomic force microscopy (AFM), while normally employing a sharp (~5 nm) tip for topographic and force measurements, can also be used to measure adhesion between a material and substrate surface. AFM force curve experiments were performed on eleven polymers with nine energetic materials, organic explosives, and energetic salts. Teflon was the least adhesive polymer to all energetic materials, while no distinct trend could be elucidated among the other polymers or energetics.
Rather than create a novel swab material for explosives detection, improving current commercial off the shelf (COTS) swabs would be a fast and cost-effective way to increase analyte detection on existing security instrumentation. For this reason, the viability of electrostatically charging COTS swabs was explored. COTS swabs were charged both triboelectrically and inductively, and voltage degradation both in time and through changes in relative humidity was determined. For collection efficiency, transfer efficiency, and uncharged swab comparison, quantification of energetic materials on a triple quadrupole liquid chromatograph/mass spectrometer was performed. Limits of quantification for trace amounts of energetic material were typically in the single nanogram level. In addition to adsorption of energetic material comparable to traditional uncharged swabs, electrostatically charged swabs can also adsorb material at standoff, introducing a new noncontact sampling method.
The synthesis of the next generation of explosives is increasingly difficult because available novel reagents and synthetic techniques are limited. Energetic material solvates have been known for nearly 65 years, but cocrystallization of an energetic material and another solid has only been demonstrated in the last decade. Relying on noncovalent derivatives (NCDs), cocrystals can tailor explosive properties such as density and detonation velocity, potentially yielding a new energetic material without novel molecule synthesis. The most common synthons for pharmaceutical cocrystallization involve carboxylic acid and amide functionalities, but the majority of common energetic materials are devoid of these groups. With the wealth of knowledge from pharmaceutical cocrystals, utilizing these groups could yield more effective screening for energetic cocrystal pairs. Herein, we present the TNT-nicotinamide cocrystal, an energetic cocrystal with an amide synthon.
Swanson, Devon S., "Intermolecular Interactions of Energetic Materials" (2016). Open Access Dissertations. Paper 503.