Showing papers on "Surface modification published in 1992"

Evidence of a transition temperature for the optimum deposition of grafted monolayer coatings

Abstract: TECHNIQUES for surface modification are of considerable technological interest for the fabrication of water-repellent and anti-fouling coatings. Silanization1 (the chemical grafting of organic molecules onto a substrate via a trichlorosilane group) stands out among these techniques by virtue of its ability to provide highly compact coatings of optical quality, extreme chemical inertness and adjustable wettability2. Although the silanization reaction has been extensively characterized3–8, the properties of the grafted layers are still too variable for most commercial applications; for example, the quality of the grafted layers depends critically on the presence of trace amounts of water, and on the temperature at which the silanization reaction takes place9. Here we provide evidence for the existence of a near-ambient temperature threshold, Tc, which represents an upper bound for obtaining the highest-quality films. This threshold temperature is found to be an intrinsic property of the silane molecules: it depends linearly on their chain length, but is independent of the solvent used for the reaction. We suggest that Tc is analogous to the triple point in the phase diagram of Langmuir monolayers.

Surface modification of Kapton film by plasma treatments

Abstract: Kapton films were treated with seven plasmas: Ar-, N2-, O2-, CO-, CO2-, NO-, and NO2- plasmas. Surface properties and chemical composition of the plasma-treated Kapton films were investigated from the contact angle measurement, and the IR and XPS spectra. The plasmas, especially NO- and NO2-plasma, made the Kapton film surface hydrophilic. The XPS and IR spectra showed that the plasma led to the modification of the imide groups in the Kapton film to secondary amide and carboxylate groups.

Adsorption of catechols on fractured glassy carbon electrode surfaces

Abstract: Glassy carbon surfaces exposed by fracturing a glassy carbon rod in the electrolyte solution exhibit fast electron transfer kinetics compared to conventionally polished surfaces, implying that glassy carbon is inherently active toward electron transfer before any intentional surface modification. The adsorption of dopamine and related compounds was examined on fractured glassy carbon surfaces and compared to polished or electrochemically prretreated (ECP) surfaces

Microanalytical Characterization and Surface Modification of TiNi Orthodontic Archwires

Abstract: Orthodontic archwires (equiatomic TiNi alloy) of both used (4 weeks) and unused conditions were microanalyzed by optical and scanning electron microscopes, energy dispersive X-ray spectroscopy, and electron diffraction to characterize the surface layers. They were also subjected to immersion and polarization corrosion tests in a 0.9% NaCl aqueous solution. Based on results obtained from these analytical and experimental studies, surfaces of TiNi archwires were further electrochemically treated to etch away nickel selectively and reform the surface morphology to uniform and porous surface layers. Main conclusions were: (a) surface layers of used archwires were covered contaminants causing the discoloration, and the contaminants were identified as mainly KCl crystals, (b) surfaces of both used and unused wires were observed to be irregular features characterized by lengthy island-like structures, where nickel was selectively dissolved, (c) corrosion tests in a 0.9% NaCl aqueous solution in immersion and polarization methods indicated that by increasing temperature from 3 degrees to 60 degrees C and acidity from pH 11 to pH 3, calculated corrosion rates increased, and (d) surface layers of TiNi archwires can be electrochemically modified to selectively etch nickel away, leaving a Ti-enriched surface layer and forming a uniformly distributed porous surface that may reduce the coefficient of friction against the orthodontic brackets.

Surface modifications of polyaniline films by graft copolymerization

Abstract: Both pristine and argon plasma treated emeraldine (EM) base films were subjected to near-UV light-induced graft copolymerization with acrylamide, sodium styrenesulfonate (NaSS) and acrylic acid (AAc). It was found that in each case, the density of surface grafting is enhanced by plasma treatment. Surface grafting with the three polymers also leads to a more hydrophilic film. Grafting with NaSS and AAc polymers readily gives rise to a self-doped or self-protonated EM surface structure. However, a substantial proportion of the grafted protonic acid groups at the surface remains free for further surface modification and functionalization

Surface modified niobium oxide catalyst: synthesis, characterization, and catalysis

Abstract: The molecular structures and reactivity of surface modified niobium oxide catalysts were determined by Raman spectroscopy, pyridine adsorption as well as the methanol oxidation reaction. Metal oxides (Re 2 O 7 CrO 3 , WO 3 , MoO 3 , and V 2 O 5 ) and acids (phosphate and sulfate) form a surface overlayer on the niobia support, and possess a structure similar to the metal oxide ionic species present in acidic solutions (ReO 4 − , Cr 3 O 2− 10 , W 12 O −8 40 , Mo 8 O 4− 26 , V 10 O 6− 28 , H 2 PO − 4 , and HSO − 4 ) when the surface is hydrated. Upon dehydration, only one dehydrated surface ReO 4 species is present on niobia. For the CrO 3 , WO 3 , MoO 3 , V 2 O 5 , P 2 O 5 , and sulfate supported on niobia two dehydrated surface metal oxide species, highly distorted and slightly distorted structures, are present. Acidity and BET studies reveal that the presence of the surface metal oxide species stabilizes the surface acidic properties and surface area of niobia during high calcination temperatures (500°C). The 1% V 2 O 5 and 1% P 2 O 5 on Nb 2 O 5 samples possess a high concentration of surface acid sites as well as surface area, and the strength of surface Lewis acid sites on 1% P 2 O 5 /Nb 2 O 5 is stronger than the other systems. In addition, the surface V 2 O 5 , MoO 3 , CrO 3 , and Re 2 O 7 sites on niobia behave as redox sites and the surface WO 3 , P 2 O 5 , and sulfate sites on niobia behave as acid sites during methanol oxidation. The weak interaction between the surface rhenia species and the niobia support results in volatilization of surface rhenia during methanol oxidation and a corresponding low activity. Thus, the surface properties of niobia catalysts could be altered by the addition of surface metal oxide overlayer.

Analysis of air-corona-treated polypropylene and poly(ethylene terephthalate) films by contact-angle measurements and X-ray photoelectron spectroscopy

Abstract: Contact-angle measurements in air and water environments and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface properties of air-corona-treated polypropylene (PP) and poly(ethylene terephthalate) (PET) films. Surface properties were examined as a function of the storage time at various temperatures. Corona treatment forms water-soluble, low-molecular-weight oxidized materials on both polymer films. Corona-treated PP and corona-treated PET films have markedly different responses to aging. For corona-treated PP stored at ambient temperatures, only a slight decrease in wettability was observed. This decrease was attributed to the reorientation of oxidized functionalities within the surface region. At elevated storage temperatures, migration of oxidized species out of the surface region occurred under some conditions. For corona-treated PET, extensive migration and reorientation of oxidized groups occurred even at ambient temperatures, leading to significant decreases in wettability...

Surface modification of UHSPE fibers through allylamine plasma deposition. II. Effect on fiber and fiber/epoxy interface

Abstract: The surface of ultra-high strength polyethylene (UHSPE) fibers was modified using allylamine plasma deposition to improve their adhesion to epoxy resins. Allylamine plasma polymerization was investigated at different power inputs and polymerization times. The adhesion of treated fibers to epoxy resin was studied by single-fiber, pull-out tests. A special silicon rubber mold was developed to embed the single fiber in epoxy resin. The results show that the interfacial shear strength (IFSS) increased by a factor of 2 to 3 after allylamine plasma treatments. The greatest improvement, by a factor of 3.25, was obtained at 30 W for 10 min. Scanning electron microscopy (SEM) was also used to study the surface topography of fibers pulled from the epoxy resin. In most cases, it was observed that pull-out failure occurred at the interface, as evidenced from clean fiber surfaces. In a few cases, however, fibrils were peeled from fibers. The fiber strength decreased, but initial modulus increased after the plasma treatments. The decrease in fiber strength was insignificant for treatments at a lower power input, but was significant at higher power inputs. Treatment time, however, had no significant effect on fiber strength.

A glow discharge treatment to immobilize poly(ethylene oxide)/poly(propylene oxide) surfactants for wettable and non-fouling biomaterials

Abstract: A non-fouling (protein resistant) polymer surface was achieved using an argon glow discharge treatment of a polyethylene surface which had been precoated with various poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) (PEO-PPO-PEO) tri-block copolymer surfactants. The surfactant is first deposited on the polymer surface via a solvent swelling and evaporation method. Then the coated surfactant is immobilized on the substrate surface by an inert gas discharge treatment. ESCA and water contact angle () measurements on treated and solvent washed surfaces show significant increases in both surface O/C ratios and surface water wettability (0 < 30°) compared to LDPE control surfaces, revealing the presence of PEO on the treated surfaces. A great reduction of fibrinogen adsorption on the modified surfaces is also observed for the highest PEO content surfactants. This simple surface modification process may have wide applicability to obtain wettable polymer surfaces in general, and non-fouling biomate...

Feature articls. Doped glassy carbon: a new material for electrocatalysis

Abstract: Glassy carbon is an important material for electrochemical catalysis, particularly as an electrode material. Current methods for the preparation of glassy carbon are described, together with a discussion of recent progress in the modification of the surface of glassy carbon. Surface modification of glassy carbon, with the intent of mediating its electrochemical behaviour, remains an important research topic. Methods to achieve this goal, including surface absorption of electrochemically active species, covalent attachment of active species and coating the surface of glassy carbon with thin films, are reviewed briefly. We describe a new low-temperature approach to preparing homogeneously modified, rather than surface modified, glassy carbon, using the thermolysis of poly(phenylene diacetylene)s as the carbon solid precursor. This methodology is compatible with the introduction of a wide variety of heteroatoms, including nitrogen, silicon and fluorine, and allows the preparation of thin films of glassy carbon. The incorporation of platinum in various oxidation states is described and the electrochemical response of the platinum-doped glassy carbons is described.

Surface modification of polyethylene powder using plasma reactor with fluidized bed

Abstract: The fluidization technique was applied for the surface modification of powder by plasma, and whether the technique was a practically useful one in the surface modification of powder or not was discussed. Polyethylene powder was used as a specimen to be modified. The oxygen plasma treatment of the polyethylene powder in the fluidized state showed a capability that the surface of the powder was changed from hydrophobic to hydrophilic. The contact angle of water for the treated powder surface was 51°C, which was estimated from the dynamic wicking data. The hydrophilic surface modification of the polyethylene powders in the fluidized bed required the operation of the plasma treatment for at least 3 h. The requirement of the plasma operation for long time rises mainly from large surface area of the powder. The oxygen plasma treatment led to the formation of oxygen functionalities including C O and C(O)O groups at the outermost layer of the powder. The concentration of the CO and C(O)O functionalities reached 10 and 6% of the total carbon elements being in the XPS sampling depth, respectively. From these results we conclude that the fluidization technique is a useful manner in the surface modification of powder by plasma.

Polymerization in microemulsion. 2. Surface control and functionalization of microparticles

Abstract: Mixtures of similarly and oppositely charged surfactants are used to examine the sensitivity of the microemulsions to impurities or dopants in the surfactant layer. Subsequently, the influence of functional monomers and block copolymers on the latex particle size and structure is studied. In all cases, synergistic stabilization as well as a poisoning of the parent microemulsions can be observed. The results of thesesynthetic procedures are chemically highly active surfaces which could be used for catalysis.

Surface modification by accelerated plasma or ions

Abstract: The present invention is a surface modification process which provides a means of rapidly heating a thin layer of a polymer surface or a thin coating of material on a coated substrate and various surfaces produced by such a process.

Surface modification of UHSPE fibers through allylamine plasma deposition. I: Infrared and ESCA study of allylamine plasma formed polymers

Abstract: Allylamine (CH2CHCH2NH2) was polymerized through rf generated plasma at varying powers and times. Chemical groups and elemental compositions in the polymers were studied using ESCA and infrared spectroscopy. It was observed that plasma derived polymers contained a significant number of primary amines, along with some secondary and tertiary amines, imines, and nitrile groups. Plasma derived polymers had a complex structure and contained unsaturated groups. A considerable amount of oxygen, primarily from residual air in the plasma reaction chamber, and possibly from atmosphere when plasma polymers were exposed to air, was responsible for carbonyl, amide, ether, and hydroxyl groups found in the polymer structure. Some silicon was also detected in the plasma deposited films.

Control of selectivity during chemical vapor deposition of copper from copper (I) compounds via silicon dioxide surface modification

Abstract: The selective chemical vapor deposition of the compounds, (hfac)CuL, where hfac=1,1,1,5,5,5‐hexafluoroacetylacetonate and L=trimethylphosphine (PMe3); 1,5‐cyclooctadiene (1,5‐COD); vinyltrimethysilane (VTMS), and 2‐butyne onto W in the presence of SiO2 has been studied as a function of surface pretreatment. Cleaning the substrates with hot aqueous H2O2, followed by washing and drying resulted in blanket copper deposition (except for L=PMe3). In contrast, the nucleation of copper onto SiO2 can be controlled by reacting the SiO2 surface with chlorotrimethylsilane regardless of the nature of L. Transmission FTIR studies of (hfac) Cu(VTMS) adsorbed on a model (Cab‐O‐Sil) SiO2 surface in the presence and absence of chlorotrimethylsilane suggested that the chlorotrimethylsilane interacted with the surface hydroxl groups to reduce the number of sites at which (hfac) Cu(VTMS) can adsorb and react, therefore providing selectivity.

Surface oxidation of polyethylene, polystyrene, and PEEK: the synthon approach

Abstract: It is found that surface modification of a polymer by an oxygen glow discharge can be modeled by vacuum-UV oxidation However, during plasma treatment, competing etching/ablation processes also occur which continuously expose unreacted polymer; this does not happen during UV irradiation and therefore a greater depth of oxidation is found with the latter; UV/O 2 -treated PEEK gives the most highly oxidized surface