Cold Plasma Conditions Research Articles

Template Polymerization From Cold-Plasma-Enhanced-Crystallinity Polymer Surfaces.

Cold-plasma conditions are suitable for producing high concentrations of free radicals even on the most inert polymeric substrates and to etch preferentially amorphous and crystalline zones of polymer surface morphologies. This opens up a novel way for initiation of replica-type graft-polymerization reactions with plasma treated substrates. Use of crystallinity-enhanced and activated natural polymeric surfaces as polymerization initiators is significant since it allows a better understanding of the sterical order of natural polymers and also permits the synthesis of synthetic macromolecules "encoded" by the sterical order of the natural "host" polymer. Template graft-polymerization of acrylonitrile (AN) and styrene (ST) were performed on RF-plasma enhanced-crystallinity cellophane surfaces through plasma-induced polymerization mechanisms. The influence of plasma treatment time on the surface crystallinity of the natural substrates and the presence of ordered synthetic polymeric layers on the host-polymers were investigated by atomic force microscopy (AFM). The presence of surface functionalities on virgin and plasma-treated surfaces were monitored by survey and high resolution X-ray photoelectron spectroscopy (ESCA) and by differential, attenuated total reflectance infrared spectroscopy (ATR-FTIR).

Some Terpenes and Related Derivatives Synthesized in Cold Plasma Systems

The synthesis of bicyclo-[2.2.1]-heptane and bicyclo-[7.2.0]-undec-4-ene derivatives under cold plasma conditions are reported. The reaction systems involve gaseous mixtures at an interface with ice surfaces. The reactions are sensitive to the feed mixture and the ice trapped compounds.

Surface Functionalization of Polymers under Cold Plasma Conditions-A Mechanistic Approach.

Cold plasma conditions offer a novel route for synthesizing and depositing macromolecular structures on various organic and inorganic surfaces, and to functionalize in a controlled manner even the most inert polymeric substrates. The energies of active species of plasma are high enough to split all chemical bonds from organic and organometallic derivatives and consequently, tailored macromolecular structures can be created through controlled recombination of plasma generated charged and neutral molecular fragments. Non- macromolecular forming active species of organic- or inorganic-origin can interact with polymeric surfaces creating desired, new thin layer structures through in situ or ex-situ recombination mechanisms initiated between the plasma generated active sites of the condensed and gaseous phases. Understanding the plasma induced reaction mechanisms developed in the gas phase and on the surfaces which limit the discharge opens up rational ways to create materials with advanced surface characteristic, such as chemical inertness, advanced hydrophobicity or hydrophilicity, selective reactivity (molecular recognition), intense surface roughness, etc.

Primary Amine Implantation Onto Polypropylene Surfaces from Melamine and Urea RF Plasmas.

The possibility of generating tailored surface characteristics (adhesion, biocompatibility, wettability, etc.) from plasma modified surfaces by derivatization and grafting reactions, opens up new possibilities for the creation of advanced materials. Implantation of reactive amine (primary amine) functionalities onto synthetic polymeric surfaces under cold plasma conditions- one of the potential approaches to surface functionalization has been the subject of numerous investigations of recent years. It has been shown that ammonia plasmas do not implant primary amine groups efficiently and consequently, a large number of amine-group containing compounds were tested as alternatives. However, the low volatilities of many of potential aminating agents limit considerably their plasma processing. In this contribution a novel approach of surface amination of PP samples from melamine and urea precoated surfaces is presented. ESCA, ATR-FTIR and ex-situ post plasma grafting reaction data indicate that simultaneous plasma induced evaporation, fragmentation and primary amine implantation processes can be successfully developed. The surface primary-amine concentrations were evaluated by chemical derivatization technique, and the influence of plasma treatment time on the amine group concentrations was investigated.

Structure and properties of tin‐containing polymers deposited from tetramethyltin HF plasma

AbstractThere has been an increasing interest in depositing metal or metal‐containing thin films through plasma polymerization for various applications. This work deals with the plasma graft polymerization of tetramethyltin (TMT) on polypropylene surfaces with an aim of producing special electrical and optical coatings. The fragmentation of TMT under cold plasma conditions and the recombination of discharge‐generated active species were studied by analyzing the resulting molecular mixture trapped outside of the plasma zone by HR‐MS and GC‐MS techniques. It was found that the predominant ionic fragment is m/z = 165, and the most probable intermediate structure of the polymer formation mechanism is hexamethylditin. The structure of polymeric layers deposited on various substrates were investigated by ESCA and FT‐IR methods. Intense oxidation of tin‐based polymeric layers were observed under open laboratory conditions. The existence of weak SnSn and SnC bonds in the polymeric structure is suggested to be responsible for this reaction. This phenomenon was associated with enhanced UV transparency. Based on analytical data a plasma‐enhanced polymerization mechanism of TMT is proposed. © 1995 John Wiley & Sons, Inc.

Characterization of ionization and matrix suppression in inductively coupled ‘cold’ plasma mass spectrometry

A parametric study of plasma power and central gas flow was carried out to study the transition from normal analytical conditions to cooler plasma conditions using an inductively coupled plasma mass spectrometer having a balanced load coil. ‘Cold plasma' conditions (low power and high central gas flow) permit the determination of K, Ca and Fe at trace levels. The effect of changing the position of the ground reference of the load coil was investigated. Trace element ionization is consistent with thermal ionization at low electron density. Ion–molecule chemistry (charge transfer) with NO+ or O2+ may be important at the cooler plasma temperature. Suppression of analyte signals by concomitant matrix elements is partially correlated with the ionization potentials of the matrix element. If the analyte ion signals are normalized to that for NO+, the suppression of signals appears to be independent of the matrix element, and a modest dependence on the ionization potential of the analyte element is apparent. For high concentrations of elements of low ionization potential, an additional or enhanced mechanism of ionization is evident. The onset for this enhanced ionization is sharply defined by a characteristic ionization potential near 6.0 eV. The sensitivity for trace elements does not appear to be affected by this enhanced ionization. The appearance of the enhanced ionization is made evident by a change in the ratio of the NO+ and O2+ signals. Use of cold plasma conditions for the determination of K, Ca and Fe in high-purity waters and acids is evident. It appears that the method may also be used for samples having moderate salt content if the analytical protocol includes measurement of the background ions NO+ and O2+.

Silicon contamination of substrates in fluorocarbon plasmas produced in glass reactors

AbstractExtensive research has been carried out in recent years using fluorocarbon plasmas for modification and depositions on polymer substrates. In some cases anomalous results have been obtained that are not explainable based on conventional fluorine chemistry. In this investigation pure polypropylene films were exposed to carbon tetrafluoride plasmas in a Pyrex glass reactor. At short reaction times (less than 1 min) significant amount of silicon was detected by ESCA on the surface of the films. Analysis of liquid nitrogen trapped fluorocarbon plasma gases and molecular fragments indicated high concentrations of silicon and carbon containing species, the former indicative of ablation and etching reactions of the glass reactor walls. The production of a relatively high quantity of fluorosilicon derivatives was explained by the greater affinity of silicon for fluorine than for carbon, with the tendency to readily form SiF4. These fluorosilicon radical and ionic species generated under cold plasma conditions can easily react with polymeric substrates causing unexpected surface modifications. In addition Si–F bonds could be readily hydrolyzed to SiOH islands on the surface of the substrate to impart anomalous characteristics. © 1994 John Wiley & Sons, Inc.

Boltzmann equation and Monte Carlo analysis of electron-electron interactions on electron distributions in nonthermal cold plasmas.

Electron distribution functions in nonthermal cold plasmas generated by classical electrical discharges have been calculated from a powerful Boltzmann equation solution and an original Monte Carlo simulation. In these two methods both classical (i.e., elastic, inelastic, and superelastic) electron-atom (or molecule) collisions and electron-electron interactions are taken into account. The approximations considered to include long-range (electron-electron) and short-range (electron-atom) interactions in the same Monte Carlo algorithm are first validated by comparing with Boltzmann equation results. Then, the influence of electron-electron interactions on electron distribution functions, swarm parameters, and reaction rates under nonthermal cold plasma conditions are analyzed and discussed as a function of reduced electric field E/N and ionization degree ${\mathit{n}}_{\mathit{e}}$/N for different atomic and molecular gases.

Surface modification and grafting of natural and synthetic fibres and fabrics under cold plasma conditions

Natural and synthetic fibres and fabrics have been modified in cold plasma conditions in order to impart new qualities to support materials. Both static and dynamic installations designed to this aim are presented. Improved hydrophilicity, dyeability and flamme retardancy properties were achieved by grafting with either monomeric or polymeric substances.

Polymerization of some potential „grafting‐monomers”︁ for natural and synthetic fibres in cold plasma conditions

AbstractPlasma induced solid‐state polymerization of some potential „grafting‐monomers”︁ (acrylamide, benzidine and alphanaphthylamine) for natural and synthetic fibres has been studied. Polymerization mechanisms have been suggested on the basis of the analytical data (IR, NMR, ESR spectroscopy, elemental analysis, gel‐filtration, swelling properties, DTA measurements) of the polymers obtained in cold plasma conditions.

Synthesis of purine and pyrimidine bases and nucleosides under the cold plasma conditions (IX).

Living-matter precursors are obtained by the action of the high-frequency electrical discharges on a methane-ammonia-water mixture. Some purine and pyrimidine bases as well as nucleosides are detected and estimated quantitatively by column chromatography, one- and two-dimensional paper chromatography, paper chromatography with standard addition, colour tests as well as by optical density measurement within the UV region.

Abiotic synthesis of some polysaccharide-like and polypeptide-like structures in cold plasma

Starting from methane, ammonia and water vapors polypeptide-like and polysaccharide-like structures have been synthesized in cold plasma conditions. By gel filtration analysis of the raw product eight fractions of different molecular weight have been separated. The partial chemical nature of each fraction and of the hydrolysis products has been determined using elementary analysis, IR spectroscopy, paper, thin-layer and gas-chromatography. It is noteworthy that higher proportions of H 2O in the feed composition increase the amount of sugar and polysaccharide-like compounds in the reaction product.

Synthesis of some amino acids, sugars, and peptides in cold plasma abiotic synthesis of some high-molecular-weight proteid-like structures (V).

AbstractThe synthesis of some high‐molecular‐weight protenoid structures in radiofrequency cold plasma conditions are discussed. The fractionation results of the raw product and the spectrum of free and protenoid‐bound amino acids are given. The uv analysis of these compounds is presented.A protein‐forming mechanism that might have existed on the primitive earth is proposed.

The reaction of atomic fluorine with fluorobenzene

The reaction of atomic fluorine with fluorobenzene under cold plasma conditions leads to the formation of three difluorobenze isomers. The isomer distributions confirm the selective introduction of atomic fluorine into the aromatic ring as previously found in the reaction of atomic fluorine and bromobenzene. A comparison of the isomer distribution indicates that the presence of a fluorine atom in a ring has greater inhibiting effect on ortho substitution than the corresponding bromine atom.

Synthesis of some amino acids, sugars, and peptides in cold plasma. Electron‐microscopic studies on some proteid forms (III)

AbstractElectron‐microscopic studies of some proteid structures (synthesized in RF electrical discharge) and corresponding individual compounds resulting from acid hydrolysis were investigated. Some superior precellular structures with peptide linkages in cold plasma conditions were observed.