Showing papers on "Surface modification published in 1995"

Hybrid Organic-Inorganic Composites

Abstract: Some General Trends in the Area of Organic-Inorganic Composites Organic-Inorganic Hybrids with a Crystalline Polymer Matrix Inorganic-Protein Interactions in the Synthesis of a Ferrimagnetic Nancomposite Ion-Exchange Intercalation into the MPS[3 Layered Compounds: Design of Nanocomposites with Unusual Magnetic Electrical, and Nonlinear Optical Properties Preparation and Characterization of Nanocomposites of Poly(ethylene oxide) with Layered Solids Polymer-Clay Hybrids (Perfluorosulfonate Ionomer)-(Inorganic Oxide) Nanocomposites: Organic Modification of Surfaces of Silicon Oxide Nanoparticles Grown In Situ Nanostructured Organic-Inorganic Hybrid Materials Synthesized Through Simultaneous Processes Multiple Size Scale Structures in Silica-Siloxane Composites Studied by Small-Angle Scattering Composite Polymer Colloid Nucleated by Functionalized Silica Vinyl-Polymer-Modified Hybrid Materials and Photoacid-Catalyzed Sol-Gel Reactions Hybrid Organic-Inorganic Interpenetrating Networks A New Route to Polymer-Filled Glass: Hybrid Interpenetrating Networks with Appreciable Toughness Solidification of Colloidal Crystals of Silica Thermo-irreversible Gelation and Percolation-Based Mechanical Response via Metal-Olefin Coordination in Diene Polymers Hybrid Organic-Inorganic Silica Materials: Chemical Evidence for Organization in the Solid Hybrid Organic-Inorganic Materials: The Sol-Gel Approach Sol-Gel-Derived Silica-Siloxane Composite Materials: Effect of Reaction Conditions in Polymer-Rich Systems Hypervalent Spiro Polysiliconate and Polygermylate Ionomers: Novel Ladder and Network Materials Hexylene- and Phenylene-Bridged Polysiloxane Network Materials Structural Design of High-Performance Polymers for Sol-Gel Processing Preparation and Properties of High-Clarity Polyamide-Silica Hybrid Materials Preparation and Mechanical Properties of Polybenzoxazole-Silica Hybrid Materials Morphological Studies of Conductive Polyemers Deposited onto High-T[c Superconductors Novel Organic-Inorganic Composite Materials for Photonics Inorganic-Organic Hybrid Coatings for Metals and Glass Surfaces Surface Modification of Carbon Fibers for Advanced Composite Materials

Dextran modified self-assembled monolayer surfaces for use in biointeraction analysis with surface plasmon resonance

Abstract: The development of a surface modification method based on self-assembled monolayers on gold surfaces has proved to be a successful basis for the functionalization of sensor surfaces intended for use in biospecific interaction analysis. The dextran coated alkanethiol layer shows high chemical stability towards various conditions employed for different analytical sequences. Optimized synthesis sequences yield highly reproducible sensor surfaces in terms of surface coverage and biomolecule binding capacities. Immobilization chemistries adapted for coupling various biomolecules and other ligands were developed for the dextran coated surface and used in bioanalysis techniques based on surface plasmon resonance. This mass sensitive, real-time analysis technique with label-free detection has developed as a universal tool for analysis of various qualitative and quantitative biospecific interactions, including affinity and kinetic rate constant determinations.

Zeta Potential Measurements on Conducting Polymer-Inorganic Oxide Nanocomposite Particles

Abstract: We describe some of our recent results on the characterization of aqueous colloidal dispersions of conducting polymer-inorganic oxide nanocomposite particles. Such colloids are easily prepared by synthesizing the conducting polymer in the presence of commercially available ultrafine silica (or tin(IV) oxide) particles in aqueous media. In the present study we present electrokinetic data as a function of pH for the following systems: polypyrrole-silica, carboxylic acid-functionalized polypyrrole-silica, amine-functionalized polypyrrole-silica, polyaniline-silica, and polypyrrole-tin(IV) oxide colloids. These data show that both the isoelectric points and zeta potentials of these nanocomposite dispersions are governed primarily by the nature of the charged groups at the inorganic oxide surface rather than by the conducting polymer component. This suggests that the inorganic oxide is the major component at the particle surface, which is consistent with the excellent long-term colloid stability of these dispersions. The aqueous electrophoresis measurements also indicate that our surface functionalization experiments were successful: Carboxylic acid groups can be incorporated via copolymerization using an appropriate functional pyrrole comonomer, while amine groups can be introduced via derivatization of the silica component using 3-aminopropyl triethoxysilane.

A comparison of gas-phase methods of modifying polymer surfaces

Abstract: Oxidation is the most common surface modification of polymers. This paper presents a comparison of five gas-phase surface oxidation processes: corona discharge, flame, remote air plasma, ozone, and combined UV/ozone treatments. Well-characterized biaxially oriented films of polypropylene and poly(ethylene terephthalate) were treated by each of the five techniques. The surface-treated films were then analyzed by X-ray photoelectron spectroscopy (XPS or ESCA), contact-angle measurements, and Fourier-transform IR (FTIR) spectroscopy. Corona, flame, and remote-plasma processes rapidly oxidize polymer surfaces, attaining XPS O/C atomic ratios on polypropylene of greater than 0.10 in less than 0.5 s. In contrast, the various UV/ozone treatments require orders of magnitude greater exposure time to reach the same levels of surface oxidation. While corona treatment and flame treatment are well known as efficient means of oxidizing polymer surfaces, the ability of plasma treatments to rapidly oxidize polymers is no...

Surface modification of ultrafiltration membranes by low temperature plasma. I. Treatment of polyacrylonitrile

Abstract: Excitation with low temperature helium or helium/water plasma and subsequent exposure to air of polyacrylonitrile (PAN) ultrafiltration membranes was used to hydrophilize the surface of these materials. We analyzed the effectiveness of this approach as a function of' plasma operating variables including gas phase composition, plasma power, treatment time, and system pressure. Following the changes in physical and chemical composition of the PAN surface resulting from these modifications was a major aspect of this work. Techniques such as the captive bubble contact angle method, ellipsometry, ESCA, and FTIR-ATR were all used. In addition, the formation and lifetime of peroxides during these processes were determined. At low powers (≤25 W) and short treatment periods (≤30 s), the main chemical conversion of PAN surfaces was simultaneous hydrophilization and stabilization via PAN cyclization. Relatively small water permeability changes were observed as a result of such treatment

Prevention of biofilm formation by polymer modification

Abstract: Bacterial biofilm formation on synthetic polymers plays an important role in industry and in modern medicine, leading, for example, to difficult-to-treat infections caused by colonized foreign bodies. Prevention of biofilm formation is a necessary step in the successful prophylaxis of such infections. One approach is to inhibit bacterial adherence by polymer surface modification. We have investigated polymer modification by glow discharge treatment in order to study the influence of the modified surface on bacterial adherence. Surface roughness, surface charge density and contact angles of the modified polymers were determined and related to the adherence of Staphylococcus epidermidis KH6. Although no influence of surface roughness and charge density on bacterial adherence was noticed, a correlation between the free enthalpy of adhesion (estimated from contact angle measurements) and adherence was observed. There seems to exist a certain minimum bacterial adherence, independent of the nature of the polymer surface. Modified polymers with negative surface charge allow for bacterial adherence close to the adherence minimum. These polymers could be improved further by the ionic bonding of silver ions to the surface. Such antimicrobial polymers are able to prevent bacterial colonization, which is a prerequisite for biofilm formation. It is suggested that modification of polymers and subsequent surface coupling of antimicrobials might be an effective approach for the prevention of bacterial biofilm formation.

Electronics of Colloidal Nanometer Particles

Abstract: Small colloidal particles * ) and clusters * ) of semiconductors and metals exhibit unusual properties and may be considered as a new physico-chemical dimension between the molecules and the bulk materials. The surface to volume ratio is extremely large; small-particle research therefore constitutes a combination of solid state and surface science. The electronic properties of the particles (light absorption, colour, fluorescence, catalytic and photocatalytic activity, electrochemistry etc.) depend on particle size. Chemical surface modification affects these properties and allows one to prepare new nano-structures in solution, in layers, and in the crystalline state. No attempt is made in the present article to review the whole field, but to describe this new branch of colloid chemistry by focussing on a few selected topics.

Lubricious hydrogel surface modification

Abstract: New and improved lubrifying coatings for reducing the coefficients of friction of surfaces on medical devices include hydrophilic copolymers derived monoethylenically-unsaturated monomers including some monomers having pendant primary amine functionality and some monomers having pendant tertiary amine functionality. The lubricious hydrogel coatings are covalently bondable to epoxy functionalized surfaces on the medical equipment to provide firmly adherent hydrogel coatings that are slippery when wet. Epoxy functionalized surfaces are provided by epoxy functional or epoxy group containing silane coupling agents. The pendant tertiary amine moieties are readily convertible at alkaline pH to quaternary ammonium cations to which anionic anti-thrombogenic agents may be bonded. Three dimensional copolymer matrices may also be provided as coatings on the surfaces by crosslinking the copolymers before or after attachment to the surface being treated.

Sizing Removal and Functionalization of the Carbon-fiber Surface Studied By Combined Tof Sims and Xps

Abstract: Time-of-flight secondary ion mass spectrometry (TOF SIMS) and X-ray photoelectron spectroscopy (XPS) have been jointly used to study a two-step surface processing of AS4 carbon fiber: extraction of sizing in CH2Cl2 and functionalization with trimellitic anhydride. The combined information on molecular specificity obtained with TOF SIMS and quantification obtained with XPS allows us to follow qualitatively and quantitatively the changes in functional groups on the carbon surface. The results show that the sizing on AS4 contains at least four different compounds. These compounds can be extracted in CH2Cl2 and the elimination is almost complete for silicone. The functionalization of AS4 with trimellitic anhydride has been realized. The reaction takes place between the amine groups on the carbon fiber and the two types of functional groups in trimellitic anhydride.

Gas‐phase photoinduced graft polymerization of acrylic acid onto polyacrylonitrile ultrafiltration membranes

Abstract: Heterogeneous surface modification of polyacrylonitrile (PAN) ultrafiltration (UF) membranes is realized with UV irradiation-initiated graft polymerization of acrylic acid (AA) from the gas phase onto photoinitiator (benzophenone, BP)-coated samples. In the absence of monomer, PAN functionalization by ketyl radicals dominates after UV excitation of sorbed BP. With AA, graft and total polymer yield increase with BP loading and UV irradiation time. Average molecular weight and distribution of PAA homopolymer—formed in parallel during graft polymerization—are analyzed with gel permeation chromatography. Morphology of PAN-gr-AA UF membranes is checked with scanning electron micrographs (SEMs) and atomic force microscopy. Chemical changes are characterized with FTIR-ATR spectroscopy and SEM/EDX analyses, indicating a pronounced surface selctivity of the graft polymer modification (localized in the upper 5-μm membrane thickness). The amount of grafted PAA systematically reduces membrane permeability and increases dextrane retention, as verified in UF experiments. Photo graft polymer modificationof UF membranes will be applied to adjust membrane performance by controlling surface hydrophilicity and permeability using other monomers and/or further graft polymer functionalization. © 1995 John Wiley & Sons, Inc.

Surface Functionalization of Poly(ethylene terephthalate) Film and Membrane by Controlled Wet Chemistry: Chemical Characterization of Carboxylated Surfaces

Abstract: Surface functionalization of poly(ethylene terephthalate) (PET) film or track-etched membrane was performed using the methods of organic synthesis conducted at the solid-liquid interface. Basic hydrolysis in aqueous acetonitrile followed by permanganate oxidation in diluted sulfuric acid created new carboxylic chain-ends. These reactive functions were assayed as follows: (i) activation with water soluble carbodiimide; (ii) coupling to H-3-labeled amino acids; and (iii) liquid scintillation counting of the sample-associated radioactivity. Some samples were also analyzed by X-ray photoelectron spectroscopy. Depending on the experimental conditions (temperature and duration of treatment), about 1-2% of the surface repeated units could be functionalized without deterioration of the polymer bulk. This study establishes the best conditions for the covalent anchorage of bioactive substances on the PET surface. (C) 1995 Academic Press, Inc.

Surface treatment of magnetic recording heads

Abstract: Surface modification of magnetic recording heads using plasma immersion ion implantation and deposition is disclosed. This method may be carried out using a vacuum arc deposition system with a metallic or carbon cathode. By operating a plasma gun in a long-pulse mode and biasing the substrate holder with short pulses of a high negative voltage, direct ion implantation, recoil implantation, and surface deposition are combined to modify the near-surface regions of the head or substrate in processing times which may be less than 5 min. The modified regions are atomically mixed into the substrate. This surface modification improves the surface smoothness and hardness and enhances the tribological characteristics under conditions of contact-start-stop and continuous sliding. These results are obtained while maintaining original tolerances.

Interfacial modification of polypropylene composites filled with magnesium hydroxide

Abstract: The mechanical behaviour of polypropylene composites containing magnesium hydroxide is considered with reference to the influence on properties of filler surface modification. Compared to composites containing untreated filler, mechanical properties can be strongly affected by the chemical nature and amount of surface treatment applied. In particular, very significant improvements in toughness are obtained using sufficiently high levels of magnesium stearate to ensure complete coverage of the magnesium hydroxide surface. Results are discussed in terms of the observed deformation mechanism in the polymer matrix.

Plasma and ion beam surface treatment of polyethylene

Abstract: Plasma treatment is a widely used technique for altering the surface properties of polymers. The present paper deals with the surface modification of polyethylene foils in a capacitively coupled industrial r.f. (13.56 MHz) plasma system. The treated surfaces were investigated by scanning electron microscopy and contact angle measurement. Also etch rates of PE for different plasma parameters were measured. Different sample positions, directly upon the cathode and inside the plasma, distinguished by different ion bombardment due to a d.c. self bias of the cathode, were used for processing. This caused different etch rates, surface structures and roughness. Owing to the creation of polar groups on the surface, the surface tension generally increases with the duration of the plasma treatment. Depending on the sample position, different contributions of polar and dispersion components of the surface tension were found. Even short plasma treatments showed good spatial homogeneity of surface tension. This was independent of the spatial distribution of the plasma density. Ion beam treatment generally showed results similar to those with the plasma treatment, although the effect of the ion energy was more significant for ion beam treatment.

Chemical Vapor Surface Modification of Porous Glass with Fluoroalkyl-Functionalized Silanes. 2. Resistance to Water

Abstract: Smooth and porous glass surface substrates were modified with fluoroalkyltrichlorosilanes (CF 3 (CF 2 ) n -CH 2 CH 2 SiCl 3 , n=0, 3, 7, FAS) by means of chemical adsorption from the gas phase to give rise to highly hydrophobic surfaces. The hydrophobicity was found to increase with increasing molecular size of the adsorbates, accompanied by the more regular molecular orientation confirmed by the analysis of the X-ray photoelectron spectra (XPS). The resistance of the FAS layer to liquid H 2 O was examined by following the variations in the contact and critical tilting angles with time after immersion in boiling H 2 O. In all the samples tested, the contact angle (θ s ) decreases and the critical tilting angle (α) increases with time. For the same FAS treatment, the decreasing rate of θ s is much smaller in the surface porous substrate, while the increasing rate of α is greater. These noticeable facts were rationalized in terms of the data of Fourier-transformed infrared attenuated total reflection and XPS measurements. Also, the former data reveal that the FAS molecules are anchored via interfacial Si s -O-Si bonds and intermolecular Si c -O-Si c bonds in the monolayer formation process and partially desorbed by hydrolysis during immersion in HaO. Molecular orbital calculations of the clusters employed as a model of the FAS molecule chemically bonding to the surface of SiO 2 were also carried out in order to obtain information on the electronic distribution and the reactivity with H 2 O, suggesting that the crucial step of the deterioration is the nucleophilic attack of the interfacial Si atoms accompanied by cleavage of the intermolecular Si c -O-Si, bonds. On the basis of these results, the deterioration mechanism was discussed

An overview of the basic aspects of polymer adhesion. Part II: Application to surface treatments

Abstract: The main surface treatments of materials (metals and plastics in particular) to be joined are presented. It is observed that these treatments modify the roughness, morphology, and chemical composition of the surface. As a result of these operations, the substrate surface energy is generally increased. A correlation is often noted between the increased surface energy and the assembly adhesive qualities.

Hydrophilization of porous polystyrene-based continuous rod column.

Abstract: Reactive porous rods of poly[(chloromethyl)styrene-co-divinylbenzene] have been prepared for the first time by copolymerization of the monomers in the presence of a porogenic diluent. A two-step modification process involving reaction with ethylenediamine followed by reaction with gamma-gluconolactone leads to a porous medium that has highly hydrophilic surface functionalities. Preliminary chromatographic evaluation with both small molecules such as alkylbenzenes in reversed-phase mode and large proteins in hydrophobic adsorption and ion-exchange modes demonstrates that the surface of the modified rods possesses a hydrophilicity that is comparable to that of the best hydrophilic HPLC packings.

Polymer treatment in the flowing afterglow of an oxygen microwave discharge: Active species profile concentrations and kinetics of the functionalization

Abstract: The surface treatment of different polymers and their corresponding model surfaces in the flowing afterglow of an oxygen microwave plasma is investigated. The concentration profiles of tire long-lived species issued from the plasma are measured and calculated in the downstream area The influence of atomic and singlet molecular oxygen in the behavior of different polymers is investigated. It appears that the evolution of the surface energy can be explained by an initiation of the functionalization by the oxygen atoms impinging upon the surface followed by reaction of the radicals formed with molecular oxygen. The concentration of functions at the sureface is limited due to their destruction by reaction with oxygen atoms. Furthermore, the functionalization level is higher in the /lowing afterglow than in the plasma, without any significant degradation of the polymer surface. Therefore, the treatment in the flowing afterglow is more efficient to increase suface energy in particular, for polymers which undergo high backbone chain scission.

The Chemistry of Self-Assembled Long-Chain Alkanethiol Monolayers on Gold

Abstract: The aggregation of organic compounds at electrode surfaces has long been recognized. Structurally well-defined organic monolayers on solid surfaces allow experimenters to simplify and model a large variety of interfacial phenomena that are often difficult to study at interfaces due to heterogeneous or poorly defined structure. Recent research reports indicate that the building of organic compound structures on electrode surfaces is quickly emerging as a promising new methodology for surface modification with the potential to attain very well-defined morphologies. Three main approaches are under evaluation: (1) Langmuir–Blodgett transfer of a organic compound monolayer from the air/solution interface to the electrode/solution interface. (2) Covalent attachment (or chemisorption) of the amphiphilic monomers to the electrode surface. So far, only examples involving electroinactive amphiphilies have been reported. (3) Self-assembly of organic molecules at electrode surfaces contacting dilute organic compounds solutions. This approach, which is probably the simplest one, has been investigated widely in recent years.

Development of “stainless” aluminum alloys by surface modification

Abstract: In a research project devoted to the elimination of toxic materials in methods of corrosion protection, surface modification processes have been developed to improve the pitting resistance of aluminum alloys without the use of chromates. These processes use chemical treatments in various cerium salt solutions and an electrochemical treatment in a molybdate solution. The details of the surface modification method depend on alloy composition. For Al 6061 and Al 6013 treated by immersion in hot Ce(NO3)3 and CeCl3 followed by anodic polarization in Na2MoO4, pitting did not occur during immersion in 0.5 M NaCl for 60 days. Surface modification of Al 7075-T6 and Al 2024-T3 involves immersion in boiling Ce(NO3)3, anodic polarization in Na2MoO4 and immersion in boiling CeCl3. Very corrosion-resistant surfaces were produced on Al 7075-T6 after applying an electrochemical pretreatment step which removes copper from the outer surface layers. During exposure of Al 7075 in 0.5 M NaCl for 30 days no measurable corrosion was indicated by continuous monitoring with electrochemical impedance spectroscopy and by visual observation. For Al 2024, significant improvements in the resistance to localized corrosion were also obtained with these processes. A further modification of the CeMo process which is very effective for Al 2024 consists of immersion in hot cerium acetate, anodic polarization in Na2MoO4 and immesion in hot Ce(NO3)3. Impedance data collected in 0.5 M NaCl remained capacitive for 30 days, which is indicative of lack of localized corrosion. Surface anlaysis showed increased levels of Ce and Mo at sites where Cu-containing compounds are located. Apparently local cathodes are eliminated during the surface modification process, thereby reducing the driving force for pitting.