ENERGETIC BIOCIDAL MATERIALS AND SPORE NEUTRALIZATION

Abstract

The objective of this dissertation is to explore a more accurate and versatile approach to investigating the neutralization of spores suffered from ultrafast heating and biocide based stresses, and further to explore and understand novel methods to supply ultrafast heating and biocides through nanostructured energetic materials

A surface heating method was developed to apply accurate (± 25 ˚C), high heating rate thermal energy (200 - 800 ˚C, ~103 - ~105 ˚C/s). Uniform attachment of bacterial spores was achieved electrophoretically onto fine wires in liquids, which could be quantitatively detached into suspension for spore enumeration. The spore inactivation increased with temperature and heating rate, and fit a sigmoid response. The neutralization mechanisms of peak temperature and heating rate were correlated to the DNA damage at ~104 ˚C/s, and to the coat rupture by ultrafast vapor pressurization inside spores at ~105 ˚C/s. Humidity was found to have a synergistic effect of rapid heating and chlorine gas to neutralization efficiency. The primary neutralization mechanism of Cl2 and rapid heat is proposed to be chlorine reacting with the spore surface.

The stress-kill correlation above provides guidance to explore new biocidal thermites, and to probe mechanisms. Results show that nano-Al/K2S2O8 released more gas at a lower temperature and generated a higher maximum pressure than the other nano-Al/oxysalts. Given that this thermite formulation generates the similar amount of SO2 as O2, it can be considered as a potential candidate for use in energetic biocidal applications. The reaction mechanisms of persulfate and other oxysalts containing thermites can be divided into two groups, with the reactive thermites (e.g. Al/K2S2O8) that generate ~10× higher of pressure and ~10× shorter of burn time ignited via a solid-gas Al/O2 reaction, while the less reactive thermites (e.g. Al/K2SO4) following a condensed phase Al/O reaction mechanism. These different ignition mechanisms were further re-evaluated by investigating the roles of free and bound oxygen. A constant critical reaction rate for ignition was found which is independent to ignition temperature, heating rate and free vs. bound oxygen.