Plasma-Surface Interaction at Atmospheric Pressure: from Mechanisms with Model Polymers to Applications for Sterilization

Cold temperature atmospheric pressure plasma (APP) produces many types of chemically reactive species and is capable of modifying materials at atmospheric pressure. Studying plasma-surface interaction (PSI) at such pressure has been challenging due to the small mean-free-path (< 100 nm) which prohibits the conventional method of using independently controlled beams of ions/neutrals to isolate the role of each species. In this dissertation, we developed an alternative approach of studying PSI at atmospheric pressure using well-controlled source-ambient-sample systems and comprehensive surface/gas phase characterization techniques. In this new approach, we emphasize the controlled generation of reactive species from the plasma source, the regulated transportation of reactive species to the target surfaces, as well as the simplified material structure subjected to plasma treatment. To isolate and identify the role of certain reactive species on materials, a plasma source is selected with its operating conditions carefully tuned for the delivery of such species to target surface. Plasma-induced effects on model polymers and biomolecules were characterized and then quantitatively correlated to the gas phase species. Due to the multi-phase nature of PSI, many characterization techniques, including that of plasma/gas phases such as optical emission spectroscopy (OES), Fourier transform infrared spectroscopy (FTIR) and UV absorption, and that of material surfaces such as X-ray photoelectron spectroscopy (XPS), attenuated total reflection (ATR) FTIR and Ellipsometry were adopted. Using this approach, we were able to evaluate the effect of both short- and long-lived reactive neutrals on many types of surface moieties. For example, we find that atomic O and OH radicals are able to cause fast material removal but moderate oxidation on the etched surface. We also find that O3 can participate in the chemical modification of aromatic rings, i.e. cleavage and their conversion into ether, ester carbonyls and surface organic nitrate groups, both on surface and in the polymer bulk. We also find evidence for (1) the competition between etching and surface modification processes when a high density of short-lived reactive species is involved, and (2) three polymer transformation stages when large fluxes of long-lived reactive species are interacting with styrene-based polymers. Lastly, we extended our work to explore the potential application of APP reactors for disinfecting raw foods and evaluated bacterial inactivation mechanisms

A skeleton/skin strategy for preparing ultrathin free-standing single-walled carbon nanotube/polyaniline films for high performance supercapacitor electrodes

One of the most critical aspects in the preparation of single-walled carbon nanotubes (SWCNTs)/ conducting polymer hybrid electrodes is to improve the energy density without seriously deteriorating their high power capability. Here, we report a ‘‘skeleton/skin’’ strategy for the preparation of freestanding, thin and flexible SWCNT/polyaniline (PANI) hybrid films by a simple in situ electrochemical polymerization method using directly grown SWCNT films with a continuous reticulate structure as template. In situ electrochemical polymerization can achieve effective deposition of PANI onto the surface of SWCNT bundles in the films and control the morphology and microstructure of the SWCNT/PANI hybrid films. In a SWCNT/PANI hybrid film, the directly grown SWCNT film with continuous reticulate architecture acts as the skeleton and PANI layers act as the skin. This unique continuous ‘‘skeleton/skin’’ structure ensures that these hybrid films have much higher conductivity compared to SWCNT/PANI composite films based on post-deposition SWCNT films. Flexible supercapacitors have been fabricated using the SWCNT/PANI hybrid films as both electrodes and charge collectors without metallic current collectors. High energy and power densities (131 W h kg 1 and 62.5 kW kg 1, respectively) have been achieved for the optimized assembly. The high electrical conductivity and flexibility, in combination with continuous porous architecture, suggests that the asprepared ultrathin free-standing SWCNT/PANI hybrid films have significant potential as promising electrode materials for thin, lightweight and flexible energy storage devices with high performance

A comparative study of biomolecule and polymer surface modifications by a surface microdischarge

Cold atmospheric plasma (CAP) sources are attractive sources of reactive species with promising industrial and biomedical applications, but an understanding of underlying surface mechanisms is lacking. A kHz-powered surface microdischarge (SMD) operating with N2/O2 mixtures was used to study the biological deactivation of two immune-stimulating biomolecules: lipopolysaccharide (LPS) and peptidoglycan (PGN), found in bacteria such as Escherichia coli and Staphylococcus aureus, respectively. Model polymers were also studied to isolate specific functional groups. Changes in the surface chemistry were measured to understand which plasma-generated species and surface modifications are important for biological deactivation. The overall goal of this work is to determine which effects of CAP treatment are generic and which bonds are susceptible to attack. CAP treatment deactivated biomolecules, oxidized surfaces, and introduced surface bound NO3. These effects can be controlled by the N2 fraction in O2 and applied voltage and vary among different target surfaces. The SMD was compared with an Ar/O2/N2-fed kHz-powered atmospheric pressure plasma jet and showed much higher surface modifications and surface chemistry tunability compared to the jet. Possible mechanisms are discussed and findings are compared with recent computational investigations. Our results demonstrate the importance of long-lived plasma-generated species and advance an atomistic understanding of CAP-surface interactions

A “skeleton/skin” strategy for preparing ultrathin free-standing single-walled carbon nanotube/polyaniline films for high performance supercapacitor electrodes

One of the most critical aspects in the preparation of single-walled carbon nanotubes (SWCNTs)/conducting polymer hybrid electrodes is to improve the energy density without seriously deteriorating their high power capability. Here, we report a “skeleton/skin” strategy for the preparation of free-standing, thin and flexible SWCNT/polyaniline (PANI) hybrid films by a simple in situ electrochemical polymerization method using directly grown SWCNT films with a continuous reticulate structure as template. In situ electrochemical polymerization can achieve effective deposition of PANI onto the surface of SWCNT bundles in the films and control the morphology and microstructure of the SWCNT/PANI hybrid films. In a SWCNT/PANI hybrid film, the directly grown SWCNT film with continuous reticulate architecture acts as the skeleton and PANI layers act as the skin. This unique continuous “skeleton/skin” structure ensures that these hybrid films have much higher conductivity compared to SWCNT/PANI composite films based on post-deposition SWCNT films. Flexible supercapacitors have been fabricated using the SWCNT/PANI hybrid films as both electrodes and charge collectors without metallic current collectors. High energy and power densities (131 W h kg−1 and 62.5 kW kg−1, respectively) have been achieved for the optimized assembly. The high electrical conductivity and flexibility, in combination with continuous porous architecture, suggests that the as-prepared ultrathin free-standing SWCNT/PANI hybrid films have significant potential as promising electrode materials for thin, lightweight and flexible energy storage devices with high performance