IntroductionThe plasma state, recognized as the fourth state of matter, is broadly defined as a gaseous environment composed of charged and neutral species with a net zero electric charge. This manifestation of matter can be generated by increasing the energy content of atoms and molecules regardless the nature of the energy source. Consequently plasma can be created by involving caloric, radiant, or mechanical energy sources. Plasma states can be divided in two main categories according to their intrinsic energy content: hot plasmas (or near-equilibrium plasmas) and cold plasmas (nonequilibrium plasmas) often called silent discharges or glow discharges. Hot plasmas are characterized by near thermodynamic equilibrium and very high degrees of ionization, and are composed of neutral and charged molecular and atomic species, and electrons having extremely high energies (e. g., electric arcs, rocket jets, plasmas generated by nuclear reactions). Actually, it is estimated that more than 90 % of the known Universe exists under the plasma state. All active celestial bodies are hot plasma environments. Cold plasmas are composed of low energy atomic and molecular charged and neutral species and of energetic electrons. However, due to the low caloric capacity of the electrons the energy is not distributed to the reactor walls and consequently, these plasmas operate at reactor temperatures comparable to room temperature. These plasmas are also characterized by very low degrees of ionization. Consequently, these plasmas are suitable for the modification of organic substrates.Besides natural plasmas like the ionosphere, lightning, the rarefied interplanetary-space-plasma, man-made plasmas can be initiated by increasing the energy content of a gaseous system. Plasmas are loosing energy toward the walls which confine them by collision and radiation, and consequently energy must be supplied in a continuous manner to sustain the plasma state. The easiest way to meet this requirement is by using electrical energy; and this is the reason why the most common plasmas are electrical discharges.An electrical discharge (e. g. cold plasma) is initiated when omnipresent free electrons (due to cosmic radiation) of a low-pressure gaseous environment are accelerated to kinetic energy levels capable of inducing ionization and fragmentation processes. The newly resulted electrons will also be accelerated leading to further elastic and inelastic collisions and to the generation of the plasma state.It is noteworthy that the energy levels of the cold plasma species (1-10 eV; predominantly 0.5-3 eV) are comparable to the chemical bond energies, and consequently this state represents a novel and very significant way for modifying the structure of volatile organic and inorganic matter. The plasma species can also interact with solid-phase substances generating chemical and morphological changes in the very top layers of the plasma-exposed substrates. These features make electrical discharges an excellent tool for generating unconventional reaction m...
It has been demonstrated that surfaces coated with poly(ethylene glycol) (PEG) are capable of reducing protein adsorption, bacterial attachment, and biofilm formation. In this communication cold-plasma-enhanced processes were employed for the deposition of PEG-like structures onto stainless steel surfaces. Stainless steel samples were coated under 1,4,7,10-tetraoxacyclododecane (12-crown-4)-ether and tri(ethylene glycol) dimethyl ether (triglyme)-radio frequency (RF)-plasma conditions. The chemistry and characteristics of plasma-coated samples and biofilms were investigated using electron spectroscopy for chemical analysis (ESCA), atomic force microscopy (AFM), and water contact angle analysis. ESCA analysis indicated that the plasma modification resulted in the deposition of PEG-like structures, built up mainly of -CH 2 OCH 2 OO-linkages. Plasma-coated stainless steel surfaces were more hydrophilic and had lower surface roughness values compared to those of unmodified substrates. Compared to the unmodified surfaces, they not only significantly reduced bacterial attachment and biofilm formation in the presence of a mixed culture of Salmonella typhimurium, Staphylococcus epidermidis, and Pseudomonas fluorescens but also influenced the chemical characteristics of the biofilm. Thus, plasma deposition of PEG-like structures will be of use to the food-processing and medical industries searching for new technologies to reduce bacterial contamination.
Polyester (PET) swatches are treated with an electrical discharge plasma of a reactive atmosphere (tetrachlorosilane) to graft chlorosilane groups, subsequently hydrolyzed to very hydrophilic hydroxysilane groups. The Kawabata evaluation system for fabrics (KES-FB), high resolution microscopy, and surface tension measurements are used to investigate the physical properties of the fabrics before and after plasma exposure. The results show that the surface parameters are considerably modified by the treatment.
A novel plasma-enhanced coating for wood substrates has been developed which diminishes the degradation of wood under simulated harsh environmental conditions. Reflective (zinc oxide) and electromagnetic radiation (EMR)-absorbent (benzotriazole, 2-hydroxybenzophenone, phtalocyanine, and graphite) substances were incorporated into a liquid phase, high-molecular-weight polydimethylsiloxane and deposited as thin layers on wood surfaces. The macromolecular films, containing the dispersed materials, were then converted into a three-dimensional solid state network by exposure to a 30 kHz-oxygen-RF-plasma. The discharge induced chemistry and altered surface topographies in the surface layers were monitored by survey and high resolution Electron Spectroscopy for Chemical Analysis, Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy, and Scanning Electron Microscopy. The surface characteristics and the resistance to weathering of the plasma treated substrates were evaluated and compared to the properties of un-modified samples. Keywords Southern yellow pine Weathering degradation Cold-plasma-induced surface modificationBrought to you by | University of Manchester Authenticated Download Date | 5/25/15 9:26 PM Fig. 22. Percent weight loss of PDMSO matrix coated wood samples ( 0: un-treated; 1: only PDMSO; 2: benzotriazole/PDMSO; 3: ZnO/PDMSO; 4:hydroxybenzophenone/PDMSO; 5: phthalocyanine/PDMSO; 6: graphite/PDMSO).Fig. 23. Water contact angle of reflective and EMR-containing PDMSO matrix, before and after simulated weathering test (solid bars represent data for un-weathered samples and hatched bars represent data for 2-week-weathered samples; 0: un-treated; 1: only PDMSO; 2: benzotriazole/PDMSO; 3: ZnO/PDMSO; 4:hydroxybenzophenone/PDMSO; 5: phthalocyanine /PDMSO; 6:graphite/ PDMSO). Brought to you by | University of Manchester Authenticated Download Date | 5/25/15 9:26 PM
ABSTRACT:To improve the overall performance of wood-plastic composites, appropriate technologies are needed to control moisture sorption and to improve the interaction of wood fiber with selected hydrophobic matrices. The objective of this study was to determine the surface thermodynamic characteristics of a wood fiber and to correlate those characteristics with the fiber's water vapor adsorption behavior. The surface thermodynamic properties, determined by inverse gas chromatography at infinite dilution or near zero surface coverage, were the dispersive component of the surface energy, surface acid-base free energy and enthalpy of desorption of acid-base probes, and surface acid-base acceptor and donor parameters (K A and K D ). Water vapor adsorption was expressed in terms of the percentage of weight gain (⌬W%) resulting from water vapor adsorption on the wood particles, calculated relative to their initial weight after preconditioning in a vacuum dessicator at room temperature. The results showed a strong correlation between ⌬W% and K A , and between ⌬W% and surface acid-base free energy of water desorption (⌬H AB water ), calculated from experimental K A and K D and values in the literature for acceptor and donor values of water. These results suggest that for substrates such as wood, whose surface Lewis acid-base properties are characterized by a relatively stronger tendency to accept electrons, the key to controlling water vapor adsorption is to manipulate the magnitude of ⌬H AB water , primarily via K A , and to a lesser extent via K D .
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