Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 103-110). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 103-110). Also available on the Internet.

The main cause of spacecraft failures is due to the harsh space environment; therefore, rigorous testing of materials used in modern spacecraft is imperative to ensure proper operation during the life span of the mission. Enhancing the capabilities of ground-based test facilities allows for more accurate measurements to be taken as it better simulates the environment to which spacecraft will be exposed. The range of temperature measurements has been significantly extended for an existing space environment simulation test chamber used in the study of electron emission, sample charging and discharge, electrostatic discharge and arcing, electron transport, and luminescence of spacecraft materials. This was accomplished by incorporating a new two-stage, closed-cycle helium cryostat, which has an extended sample temperature range from 450 K, with long-term controlled stability of -7Pa) that can simulate diverse space environments. These existing capabilities include controllable vacuum and ambient neutral gases conditions (< 10-7 to 10-1 Pa), electron fluxes (5 eV to 30 KeV monoenergetic, focused, pulsed sources ranging from 10-4 to 1010 nA-cm-2), ion fluxes (<0.1 to 5keV monoenergetic sources for inert and reactive gases with pulsing capabilities), and photon irradiation (numerous continuous and pulsed monochromatic and broadband IR/VIS/UV [0.5 to 7 eV] sources). The original sample mount accommodates one to four samples of 1 cm to 2.5 cm diameter in a low-temperature carousel, which allows rapid sample exchange and controlled exposure of the individual samples. Multiple additional sample mounts have been added to allow for standalone use for constant voltage measurements, radiation induced and conductivity tests, as well as extended capabilities for electron-induced luminescent measurements to be conducted using various material sample thickness in the original existing space environment simulation test chamber.

Developing a fundamental understanding of the interactions of chemical warfare agents (CWAs) with surfaces is essential for the rational design of new sorbents, sensors, and decontamination strategies. The interactions of chemical warfare agent simulants, molecules which retain many of the same chemical or physical properties of the agent without the toxic effects, with amorphous silica were conducted to investigate how small changes in chemical structure affect the overall chemistry. Experiments investigating the surface chemistry of two classes of CWAs, nerve and blister agents, were performed in ultrahigh vacuum to provide a well-characterized system in the absence of background gases. Transmission infrared spectroscopy and temperature-programmed desorption techniques were used to learn about the adsorption mechanism and to measure the activation energy for desorption for each of the simulant studied. In the organophosphate series, the simulants diisopropyl methylphosphonate (DIMP), dimethyl methylphosphonate (DMMP), trimethyl phosphate (TMP), dimethyl chlorophosphate (DMCP), and methyl dichlorophosphate (MDCP) were all observed to interact with the silica surface through the formation of a hydrogen bond between the phosphoryl oxygen of the simulant and an isolated hydroxyl group on the surface. In the limit of zero coverage, and after defect effects were excluded, the activation energies for desorption were measured to be 57.9 ± 1, 54.5 ± 0.3, 52.4 ± 0.6, 48.4 ± 1, and 43.0 ± 0.8 kJ/mol for DIMP. DMMP, TMP, DMCP, and MDCP respectively. The adsorption strength was linearly correlated to the magnitude of the frequency shift of the ν(SiO-H) mode upon simulant adsorption. The interaction strength was also linearly correlated to the calculated negative charge on the phosphoryl oxygen, which is affected by the combined inductive effects of the simulants' different substituents. From the structure-function relationship provided by the simulant studies, the CWA, Sarin is predicted to adsorb to isolated hydroxyl groups of the silica surface via the phosphoryl oxygen with a strength of 53 kJ/mol. The interactions of two common mustard simulants, 2-chloroethyl ethyl sulfide (2-CEES) and methyl salicylate (MeS), with amorphous silica were also studied. 2-CEES was observed to adsorb to form two different types of hydrogen bonds with isolated hydroxyl groups, one via the S moiety and another via the Cl moiety. The desorption energy depends strongly on the simulant coverage, suggesting that each 2-CEES adsorbate forms two hydrogen bonds. MeS interacts with the surface via a single hydrogen bond through either its hydroxyl or carbonyl functionality. While the simulant work has allowed us to make predictions agent-surface interactions, actual experiments with the live agents need to be conducted to fully understand this chemistry. To this end, a new surface science instrument specifically designed for agent-surface experiments has been developed, constructed, and tested. The instrument, located at Edgewood Chemical Biological Center, now makes it possible to make direct comparisons between simulants and agents that will aid in choosing which simulants best model live agent chemistry for a given system. These fundamental studies will also contribute to the development of new agent detection and decontamination strategies. / Ph. D.

Developing a fundamental understanding of the interactions of chemical warfare agents (CWAs) with surfaces is essential for the rational design of new sorbents, sensors, and decontamination strategies. The interactions of chemical warfare agent simulants, molecules which retain many of the same chemical or physical properties of the agent without the toxic effects, with amorphous silica were conducted to investigate how small changes in chemical structure affect the overall chemistry. Experiments investigating the surface chemistry of two classes of CWAs, nerve and blister agents, were performed in ultrahigh vacuum to provide a well-characterized system in the absence of background gases. Transmission infrared spectroscopy and temperature-programmed desorption techniques were used to learn about the adsorption mechanism and to measure the activation energy for desorption for each of the simulant studied. In the organophosphate series, the simulants diisopropyl methylphosphonate (DIMP), dimethyl methylphosphonate (DMMP), trimethyl phosphate (TMP), dimethyl chlorophosphate (DMCP), and methyl dichlorophosphate (MDCP) were all observed to interact with the silica surface through the formation of a hydrogen bond between the phosphoryl oxygen of the simulant and an isolated hydroxyl group on the surface. In the limit of zero coverage, and after defect effects were excluded, the activation energies for desorption were measured to be 57.9 ± 1, 54.5 ± 0.3, 52.4 ± 0.6, 48.4 ± 1, and 43.0 ± 0.8 kJ/mol for DIMP. DMMP, TMP, DMCP, and MDCP respectively. The adsorption strength was linearly correlated to the magnitude of the frequency shift of the ν(SiO-H) mode upon simulant adsorption. The interaction strength was also linearly correlated to the calculated negative charge on the phosphoryl oxygen, which is affected by the combined inductive effects of the simulants’ different substituents. From the structure-function relationship provided by the simulant studies, the CWA, Sarin is predicted to adsorb to isolated hydroxyl groups of the silica surface via the phosphoryl oxygen with a strength of 53 kJ/mol. The interactions of two common mustard simulants, 2-chloroethyl ethyl sulfide (2-CEES) and methyl salicylate (MeS), with amorphous silica were also studied. 2-CEES was observed to adsorb to form two different types of hydrogen bonds with isolated hydroxyl groups, one via the S moiety and another via the Cl moiety. The desorption energy depends strongly on the simulant coverage, suggesting that each 2-CEES adsorbate forms two hydrogen bonds. MeS interacts with the surface via a single hydrogen bond through either its hydroxyl or carbonyl functionality. While the simulant work has allowed us to make predictions agent-surface interactions, actual experiments with the live agents need to be conducted to fully understand this chemistry. To this end, a new surface science instrument specifically designed for agent-surface experiments has been developed, constructed, and tested. The instrument, located at Edgewood Chemical Biological Center, now makes it possible to make direct comparisons between simulants and agents that will aid in choosing which simulants best model live agent chemistry for a given system. These fundamental studies will also contribute to the development of new agent detection and decontamination strategies. / Ph. D.

Reflection absorption infrared spectroscopy was used as the primary analysis technique to study the interfacial chemistry of surfaces relevant to chemical and biological warfare agent defense. Many strategies utilized by the military to detect and decompose chemical and biological warfare agents involve their interaction with surfaces. However, much of the chemistry that occurs at the interface between the agents and surfaces of interest remains unknown. The surface chemistry plays an important role in efficacy of both detection and decontamination technology, and by obtaining a deeper understanding of that chemistry, researchers might be able to develop more sensitive detection devices and more effective decontamination strategies. Our efforts have focused on three different areas of surface chemistry relevant to chemical and biological warfare agent defense: 1) The development of a surface synthesis strategy to create and control the structure of antibacterial self-assembled monolayers (SAMs). Our work demonstrated a successful strategy for creating SAMs that contain long-chain quaternary ammonium groups, which were synthesized and subsequently characterized using RAIRS and X-ray photoelectron spectroscopy (XPS). 2) The determination of the surface conformation, orientation, and relative surface density of immobilized antimicrobial peptides. Our results revealed that the peptides consisted of tilted (50-60°), α-helices on the surface, regardless of solution conditions. 3) The design and construction of a new ultrahigh vacuum surface science instrument that allows for the study of gas-surface reactions with up to three gases simultaneously. 4) The study of the adsorption of chemical warfare agent simulants to silica nanoparticulate films. Our work demonstrated that the adsorbate structure was dependent on the number of hydrogen-bonding groups, and the adsorption consists of a pressure-dependent two part mechanism. The results presented here will help increase the understanding of the surface chemistry of three interfaces relevant to chemical and biological defense. Future researchers may apply the new information to develop more effective detection and decontamination strategies for chemical and biological warfare agents. / Ph. D.

Constructing a detailed understanding of the heterogeneous oxidation of atmospheric organic aerosols, both from a mechanistic and kinetic perspective, will enable researchers to predict the fate and lifetime of atmospheric gases and the particles with which they interact. In an effort to develop a more complete understanding of the interfacial reactions of ozone with vinyl-containing organic thin films, self-assembled monolayers that contain vinyl groups positioned precisely at the gas/surface interface were synthesized as model systems for atmospheric organic aerosols. To isolate the reactions of background gases with ozone or surface products, an ultrahigh vacuum surface analysis instrument was designed and constructed to explore the reactions of ozone with the atmospheric model systems. The surface reactions can be monitored in real-time with reflection absorption infrared spectroscopy (RAIRS) and mass spectrometry. The chemical identity of adsorbates on a surface can also be determined before or after a reaction with X-ray photoelectron spectroscopy (XPS). Disordering of the monolayers concurrent with the disappearance of the vinyl group was observed with RAIRS. New bands within the RAIR spectra were observed and assigned to carbonyl or carboxylic acids bound to the surface. Little oxidation of the sulfur head groups and no significant loss of carbon during the reaction was observed with XPS. A mechanism is proposed that includes the cross linking of the hydrocarbon chains within the monolayer, which impedes further oxidation of the sulfur head group and limits desorption of the chains. By RAIRS, the kinetics of the oxidation of the vinyl groups were tracked and an observed rate constant was determined by monitoring the changes in IR absorbance of the C=C bond. With the aid of the rate constant, an initial reaction probability for the collisions of ozone with vinyl groups positioned precisely at an interface was determined. The reaction probability is approximately three orders of magnitude greater than the reaction probability for an analogous gas-phase reaction, which demonstrates that the gas/surface interface plays an important role in this reaction. The results presented in this thesis should help develop a more detailed understanding of the interfacial reactions of pure ozone at surfaces. / Ph. D.

Ultrahigh vacuum (UHV) surface science experiments were designed to study reaction kinetics and mechanisms of gas-phase NO₃ radicals with well-organized, highly characterized, organic thin films. The surface reactions were monitored in situ with reflection-absorption infrared spectroscopy (RAIRS). The oxidation states of surface-bound molecules were identified with X-ray photoelectron spectroscopy (XPS). Consumption of vinyl groups was observed concurrently with formation of organic nitrates in RAIRS. XPS spectra showed little oxidation of sulfur head groups. The observed rate constant was determined based on the consumption of carbon-carbon double bonds and the formation of organic nitrates. Using this rate constant, the initial reaction probability was determined to be (3 ± 1) X 10⁻³. This reaction probability is approximately two orders of magnitude higher than that for the reactions between the same surface and pure O₃, which is due to the higher electron affinity of NO₃ relative to O₃. These results led to the development of a proposed mechanism that involves electrophilic addition of NO₃ to the double bonds. Reactions between NO₃ and a methyl-terminated SAM were also monitored in situ with RAIRS. In the CH3-SAM studies, hydrogen abstraction was observed during NO3 exposure. The results presented in this thesis should help develop an understanding of the fundamental interfacial reaction dynamics of NO₃ radicals with organic surfaces. / Master of Science

Reactions of strongly oxidizing pollutants with unsaturated hydrocarbon surfaces are important to many areas of scientific interest. For example, reactions of unsaturated hydrocarbons on the surface of tropospheric aerosols could have a great effect on the oxidizing capacity of the troposphere while the reaction products could be involved in the formation of clouds and smog. These reactions are also important in understanding the toxic effect inhalation of these pollutants have on the pulmonary surfactant of the lung, the only amicable air-water interface of the body. The fatty acids of this surfactant are as much as 30% unsaturated, and exposure to oxidizing pollutant is known to alter both the composition and function of the surfactant. Understanding the reaction mechanism will further the knowledge of how this toxicity occurs. While the reactions of strongly oxidizing pollutants, such as ozone and nitrogen dioxide, with alkenes in the gas and solution phases are well known, the interfacial reaction mechanisms of these species is not fully understood. The goal of this study is to determine the reaction mechanism when an unsaturated hydrocarbon monolayer at the gas-surface interface is exposed to gas phase nitrogen dioxide. An olefin-terminated thiol was synthesized and a self-assembled monolayer on Au(111) made and characterized using Reflection-Absorption Infrared Spectroscopy (RAIRS). This unsaturated surface was then exposed to NO2 at a pressure of 1x10-4 mbar in a UHV (Ultrahigh Vacuum) chamber. Time-resolved RAIRS was preformed in situ to monitor the reaction during exposure. X-ray Photoelectron Spectroscopy and RAIRS determined the surface reaction product as an aldehyde. While the mechanism can not be precisely determined, two mechanisms involving either the hydrogen abstraction or radical addition of the NO2 to yield an aldehyde are proposed. / Master of Science

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 209-217).