Showing papers on "Surface modification published in 1996"

Synthesis of Nanosized Gold−Silica Core−Shell Particles

Abstract: Gold colloids have been homogeneously coated with silica using the silane coupling agent (3-aminopropyl)trimethoxysilane as a primer to render the gold surface vitreophilic. After the formation of a thin silica layer in aqueous solution, the particles can be transferred into ethanol for further growth using the Stober method. The thickness of the silica layer can be completely controlled, and (after surface modification) the particles can be transferred into practically any solvent. Varying the silica shell thickness and the refractive index of the solvent allows control over the optical properties of the dispersions. The optical spectra of the coated particles are in good agreement with calculations using Mie's theory for core−shell particles.

Preparation of bioactive Ti and its alloys via simple chemical surface treatment.

Abstract: A simple chemical method was established for inducing bioactivity of Ti and its alloys. When pure Ti, Ti-6A1-4V, Ti-6A1-2Nb-Ta, and Ti-15Mo-5Zr-3A1 substrates were treated with 10M NaOH aqueous solution and subsequently heat-treated at 600 degrees C, a thin sodium titanate layer was formed on their surfaces. Thus, treated substrates formed a dense and uniform bonelike apatite layer on their surfaces in simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. This indicates that the alkali- and heat-treated metals bond to living bone through the bonelike apatite layer formed on their surfaces in the body. The apatite formation on the surfaces of Ti and its alloys was assumed to be induced by a hydrated titania which was formed by an ion exchange of the alkali ion in the alkali titanate layer and the hydronium ion in SBF. The resultant surface structure changed gradually from the outermost apatite layer to the inner Ti and its alloys through a hydrated titania and titanium oxide layers. This provides not only the strong bonding of the apatite layer to the substrates but also a uniform gradient of stress transfer from bone to the implants. The present chemical surface modification is therefore expected to allow the use the bioactive Ti and its alloys as artificial bones even under load-bearing conditions.

Properties and modification methods for vegetable fibers for natural fiber composites

Abstract: SYNOPSIS Studies on structure and properties of natural vegetable fibers (NVF) show that composites made of NVF combine good mechanical properties with a low specific mass. The high level of moisture absorption by the fiber, its poor wettability, as well as the insufficient adhesion between untreated fibers and the polymer matrix lead to debonding with age. To build composites with high mechanical properties, therefore, a surface modification of the fibers is necessary. The existing physical and chemical NVF modification methods-e.g., plasma treatment or graft copolymerization-which are used for the development of NVF-polymer composite properties is discussed. It is shown that modified cellulose fiber-polymer interaction mechanisms are complex and specific to every definite system. By using an coupling agent, like silanes or stearin acid, the Young's modulus and the tensile strength increases, dependent on the resin, until 50%. Simultaneously, the moisture absorption of the composites decreases for about 60%. With other surface modifications, similar results are obtained. 0 1996 John Wiley & Sons, Inc

Control of Electron Transfer Kinetics at Glassy Carbon Electrodes by Specific Surface Modification

Abstract: Various well-established and novel surface modification procedures were used on glassy carbon (GC) electrodes to yield surfaces with low oxide content or which lack specific oxide functional groups. In addition, monolayers of several different adsorbates were formed on GC surfaces before electrochemical evaluation. Both the nonspecific monolayer adsorbates and reagents which chemisorb to specific functional groups were observed on the surface with Raman and photoelectron spectroscopy. The various GC surfaces were then evaluated for their electron transfer reactivity with nine redox systems in aqueous electrolyte, including Ru(NH3)62+/3+, Fe(CN6)3-/4-, ascorbic acid, and Feaq3+/2+. The nine systems were categorized according to their kinetic sensitivity to surface modification. Several, including Ru(NH3)62+/3+, are insensitive to surface modifications and are considered outer sphere. Feaq3+/2+, Vaq2+/3+, and Euaq2+/3+ are catalyzed by surface carbonyl groups and are very sensitive to the removal of surface...

Plasma Surface Modification and Plasma Polymerization

Abstract: In current materials R&D, high priority is given to surface modification techniques to achieve improved surface properties for specific applications requirements. Plasma treatment and polymerization are important technologies for this purpose. This book provides a basic and thorough presentation of this subject. This is probably the first book

Polymer surface modification : relevance to adhesion

Abstract: This book documents the proceedings of the Fourth International Symposium on Polymer Surface Modification: Relevance to Adhesion held under the auspices of MST Conferences, LLC in Orlando, FL, June 9-11, 2003. Polymers are used for a variety of purposes in a host of technological applications and even a cursory look at the literature will evince that currently there is tremendous interest and RD 2. Other / Miscellaneous Surface Modification Techniques; and 3. General Papers. The topics covered include: low pressure plasma surface modification of a variety of polymers using various gases; atmospheric pressure plasma treatment; improvement of stain release properties of fabrics; modification of electrostatic properties of polymers; photon-based processes for surface modification of fibers; excimer UV light treatment; excimer laser surface treatment; low-energy ion treatment; photo-grafting and photo-curing; metallization of treated polymers; chemical (wet) functionalization of polymers; adhesion of paints to thermoplastic substrates; polymer release surfaces; nanolithography in polymer films; gas barrier properties of ceramic layers on polymers; and modification of interphase layer and relevance to adhesion. This volume and its predecessors containing plentiful information should serve as a comprehensive source of latest R&D activity in the highly technologically important arena of polymer surface modification. Anyone interested a "centrally or peripherallya " in knowing or learning about the various ways to modify polymer surfaces should find this book of immense value.

Bead linkers for immobilizing nucleic acids to solid supports

Abstract: Novel compositions comprised of at least one bead conjugated to a solid support and further conjugated to at least one nucleic acid and preferred methods for making the novel compositions are described. As compared to "flat" surfaces, beads linked to a solid support provide an increased surface area for immobilization of nucleic acids. Furthermore, by selecting a bead with the desired functionality, a practitioner can select a functionalization chemistry for immobilizing nucleic acids, which is different from the chemistry of the solid support.

Chemical Modification of Lignocellulosic Materials

Abstract: Functional natural polymers - a new dimensional creativity in lignocellulosic chemistry chemical structures of cellulose, hemicelluloses and lignin reactivity and accessibility of cellulose, hemicellulose and lignins chemical modification of cellulose chemical modification of lignin chemical modification of solid wood liquefaction of wood surface modification and activation of wood chemical modification of nonwood lignocellulosics characterization of chemically modified wood weathering of chemically modified wood physical and mechanical properties of chemically modified wood viscoelastic properties of chemically modified wood biological properties of chemically modified wood.

Surface Modification of Small Particle TiO2 Colloids with Cysteine for Enhanced Photochemical Reduction: An EPR Study†

Abstract: Surface complexation of colloidal titanium dioxide nanoparticles (40−60 A) with cysteine was investigated by electron paramagnetic resonance (EPR) and infrared (diffuse reflectance infrared Fourier transform−DRIFT) spectroscopies Cysteine was found to bind strongly to the TiO2 surface, resulting in formation of new trapping sites where photogenerated electrons and holes are localized Illumination of cysteine-modified TiO2 at 77 K resulted in formation of cysteine radicals with the unpaired electron localized on the carboxyl group Upon warming to 150 K, these radicals are transformed into sulfur-centered radicals as observed by EPR spectroscopy We have demonstrated the existence of two surface Ti(III) centers on cysteine-modified TiO2 particles having different extents of tetragonal distortion of the octahedral crystal field Upon addition of lead ions, a new complex of cysteine that bridges surface titanium atoms and lead ions was detected by IR spectroscopy Illumination of lead/cysteine-modified TiO

Surface Modification and Functionalization of Polytetrafluoroethylene Films

Abstract: Argon plasma-pretreated polytetrafluoroethylene (PTFE) films were subjected to further surface modification by near-UV light-induced graft copolymerization with acrylic acid (AAc), sodium salt of styrenesulfonic acid (NaSS), and N,N-dimethylacrylamide (DMAA). The surface compositions and microstructures of the modified films were characterized by angle-resolved X-ray photoelectron spectroscopy (XPS). A stratified surface microstructure with a significantly higher substrate-to-graft chain ratio in the top surface layer than in the subsurface layer was always obtained for PTFE surface with a substantial amount of the hydrophilic graft. The stratified surface microstructure was consistent with the observed hysteresis in advancing and receding water contact angles. The graft yield increased with Ar plasma pretreatment time and monomer concentration. Covalent immobilization of trypsin on the AAc polymer-grafted PTFE films was facilitated by water-soluble carbodiimide (WSC). The effective enzyme activities incr...

Adsorption on new and modified inorganic sorbents

Abstract: Part 1 Preparation, structure and properties of new and modified inorganic sorbents: computational studies on the design of synthetic sorbents for selective adsorption of molecules, R. Vetrivel et al controlled porosity glasses (CPGs) as adsorbents, molecular sieves, ion-exchanges and support materials, A.L. Dawidowicz influence of pH of precipitation of hydroxides on the structure of co-precipitated adsorbents, V.S. Komarov colloidal silicas, S. Kondo complex carbon-mineral adsorbents - preparation, surface properties and their modification, R. Leboda and A. Dabrowski solid-phase hydrosilylation reactions with participation of modified silica surface, V.A. Tertykh and L.A. Belyakova structure and molecular organization of bonded layers of chemically modified silicas, A. Yu et al the chemical basis of surface modification technology of silica and alumina by molecular layering method, A.A. Malygin et al kinetics of organic compounds chemisorption from the gas phase on oxides surface, V.I. Bogillo functionalized polysiloxane sorbents - preparation, structure, properties and use, Yu L. Zub and R.V. Parish surface structure and molecular adsorption of apatites, T. Ishikawa surface chemistry and adsorption properties of Al13 colloids, J.Y. Bottero and J.M. Cases. Part 2 Adsorption from gaseous phase: Computer simulation of adsorption on amorphous oxide surface, V. Bakaev and W. Steele on the nature of the energetic heterogeneity of water/oxide interface in adsorption phenomena occurring at oxide surface, W. Rudzinski et al energetic heterogeneity of porous inorganic oxides - adsorption and chromatographic studies, M. Jaroniec adsorption kinetics on real surfaces, G.F. Cerofolini inverse gas chromatography in the examination of acid-base and some other properties of solid materials, A. Voekel chemical and morphological characteristics of inorganic sorbents with respect to gas adsorption, E. Papirer and H. Balard structure and properties of the films formed by organic substances on silica gel surface, investigations by inverse gas chromatography (IGC), J. Rayss the use of gas chromatography to study the adsorption from gaseous phase at the finite dilution, F.J. Lopez Garzon and M. Domingo Garcia molecular statistic and gas chromatographic study of hydrocarbons adsorption on the modified layer silicates and silica in the Henry region, Yu I. Tarasevich et al micropore filling mechanism in inorganic sorbents, K. Kaneko phase transitions in adsorbed layers, A. Patrykiejew drying of gases and liquids by activated alumina, S. Sircar et al. Part 3 Adsorption from solution: characterization of inorganic sorbents by means of adsorption at the liquid-solid interface, A. Dabrowski et al study of adsorption from solutions by chromatography, V. Ya Davydov equilibria of adsorption from solutions on the silica surface, V.A. Tertykh and V.V. Yanishpolskii adsorption from dilute solutions - some novel aspects, P. Nikitas (Part contents)

Electrochemical Deposition of Very Smooth Lithium Using Nonaqueous Electrolytes Containing HF

Abstract: X-ray photoelectron spectroscopy and scanning electron microscopy methods were used for analysis of the surface layers of lithium deposited at various current densities from propylene carbonate containing 1.0 ml/dm{sup 3} LiClO{sub 4} and various amounts of HF, to investigate the effect of HF in electrolytes on the surface reaction of lithium during electrochemical deposition. The analyses indicate that the surface state of lithium and the morphology of lithium deposits are influenced by both the concentration of HF and the electrodeposition current. The first parameter for the electrodeposition of lithium is related to the chemical reaction rate of the lithium surface with HF and second to the electrodeposition rate of lithium. These results suggest that surface modification is effective in suppressing lithium dendrite formation when the chemical reaction rate with HF is greater than the electrochemical deposition rate of lithium.

Photograft-polymer-modified microporous membranes with environment-sensitive permeabilities

Abstract: Intraporous heterogeneous modification of commercial nylon (Ny) and polypropylene (PP) microfiltration membranes, both of 0.2 μm pore size, with grafted poly(acrylic acid) (g-PAA) was accomplished by first coating the membranes with a photoinitiator, benzophenone (BP), and then UV irradiation in acrylic acid (AA) solutions in water. The degree of modification (DG) depended strongly on AA concentration (cAA) and UV time. As estimated from PAA homopolymer GPC analyses, average degrees of graft polymerization between 680 and 2200 were achieved by varying cAA between 10 and 50 g/l. PP-g-PAA and Ny-g-PAA membranes were characterized with scanning electron microscopy, revealing outer and intraporous surface coverage with g-PAA. FTIR-ATR and energy-dispersive X-ray spectroscopy data verified the chemical composition and a gradient of DG over membrane thickness, but modification also of the bottom layer. Membrane swelling and permeabilities depending on DG and pH — above and below pKgPAA — were studied. PP-g-PAA membranes were almost dimensionally stable, and with intermediate DG (around 1 mg/cm2) the ‘switch height’ of transmembrane permeability as function of pH was very high (by a factor of 100, even in 100 mM buffer). Ny-g-PAA membranes markedly changed the shape due to modification, swelling and additional pH changes; the mechanical stability — especially at DG > 1 mg/cm2 — was poor, and the permeability response to pH was less pronounced. Thus, the differences in membrane material hydrophilicity caused different modification surface selectivity, which for Ny was reduced due to sorption of BP and AA during coating and polymerization, respectively. Two different types of graftpolymer-modified microporous membranes resulted: almost ‘perfect’ pore filling for PP-g-PAA, but simultaneous matrix and pore modification for Ny-g-PAA.

Surface Modification via Chain End Segregation in Polymer Blends

Abstract: We have explored the use of chain end segregation as a means of controlling the properties of a polymer surface. Thin film blends of homopolystyrene (PS) and PS synthesized with low-energy oligotetrafluoroethylene chain ends (PS-TFE) were studied using neutron reflectivity. The fraction of PS-TFE that localizes near the surface was found to increase as a function of its concentration in the blend. Contact angle measurements indicate corresponding reductions in the surface tension due to the surface localization of the TFE chain ends. For a 10% blend of 6000 mol wt PS-TFE in 3 × 105 mol wt PS, the surface coverage of fluorocarbon ends was found to be >20%. A free energy model of the blends gives good qualitative agreement with the experimental results.

Surface‐induced mineralization: A new method for producing calcium phosphate coatings

Abstract: Calcium phosphate coatings were nucleated and grown from aqueous solution onto titanium metal substrates via surface-induced mineralization (SIM) processing techniques. This process is based on the observation that in nature organisms use biopolymers to produce ceramic composites, such as teeth, bones, and shells. The SIM process involves modification of a surface to introduce surface functionalization followed by immersion in aqueous supersaturated calcium phosphate solutions. This low-temperature process (< 100 degrees C) has advantages over conventional methods of calcium phosphate deposition in that uniform coatings are produced onto complex-shaped and/or microporous samples. Additionally, because it is a low-temperature process, control of the phase and crystallinity of the deposited material can be maintained.

Study of Grafted Silane Molecules on Silica Surface with an Atomic Force Microscope

Abstract: Atomic force microscopy is employed to study the grafting process on a silica surface of several kind of silane molecules in anhydrous and aqueous solutions: mono- and trichlorosilanes and mono- and triethoxysilanes. A systematic study of the adhesive interaction and the friction behavior is performed. With the anhydrous silane solutions, we show that only the trichlorosilane molecules are able to graft the silica surface, while with the aqueous silane solutions, except for the monoethoxysilane, the silica surface was always grafted. This study provides further support of the use of tribological properties to investigate a surface modification. We show that the influence of the tip velocity on the friction behavior is a powerful way to discriminate between the silica surface and the grafted one.

Chemical surface modification of poly(ethylene terephthalate).

Abstract: Reactions of semicrystalline poly(ethylene terephthalate) (PET) film with ester-selective reagents at the film−solution interface can be controlled to produce modified film samples containing a thin (less than ∼ 40 A) surface layer of the reagent-induced functionality. Hydrolysis of PET yields a surface mixture of alcohol and carboxylic acid groups. Reduction with lithium aluminum hydride and transesterification with ethylene glycol (glycolysis) both produce surfaces with alcohol functionality (PET−OHR and PET−OHG, respectively). Each of these modification reactions involves chain cleavage and can lead to significant sample degradation (reactive dissolution); for each modification reaction, conditions were optimized to maximize conversion and minimize degradation. The reactivity of surface alcohols (PET−OH) was assessed for samples prepared by both reduction and glycolysis, and a comparative analysis was made: the presence of benzylic alcohols in reduced samples and their absence in glycolyzed samples as...

Microstructure and mechanical properties of ternary phase polypropylene/elastomer/magnesium hydroxide fire-retardant compositions

Abstract: Fire-retardant polypropylene (PP) composites were prepared by combining this polymer with uncoated and surface treated forms of magnesium hydroxide filler and various elastomeric modifiers, with and without maleic anhydride functionalization. Mechanical properties of binary and ternary phase compositions differed significantly and are discussed in terms of their microstructures (determined principally by SEM and FTIR) and the relative interaction of the components. Impact strength, in particular, was strongly influenced by the presence of filler surface treatment and the degree of rubbery phase dispersion. FTIR showed that functionalized ethylene–propylene rubber (F-EPR) reacted with the surface of uncoated magnesium hydroxide leading to extensive rubber encapsulation and an improvement in toughness relative to unmodified EPR, which was present in the matrix only as phase dispersed droplets. However, by blending F-EPR with filler surface treated with magnesium stearate, encapsulation was inhibited and the rubber was preferentially dispersed in the PP matrix. This formulation resulted in both improved filler–matrix interaction and enhanced matrix toughening leading to a further increase in impact strength. The effects of material composition on melt flow behavior and UL94 flammability rating, are also reported. © 1996 John Wiley & Sons, Inc.

Surface modification of hydroxyapatite to introduce interfacial bonding with polyactiveTM 70/30 in a biodegradable composite

Abstract: A method was developed to improve the interfacial bonding between hydroxyapatite and a biodegradable copolymer PolyactiveTM 70/30. Hydroxyapatite was first surface modified by the polyelectrolytes polyacrylic acid or poly(ethylene-co-maleic acid) in aqueous solutions. Subsequently the surface-modified hydroxyapatite was used as filler in composites with PolyactiveTM 70/30. The strength, elongation at break and elastic modulus of the composite in aqueous environment were significantly improved by this method. Based on these experimental results, it is believed that the interface improvement is due to hydrogen bonding and/or dipole interactions formed between polyelectrolyte molecules and polyethylene glycol segments in the polymer matrix. Due to the introduction of interfacial bonding by using such method, a new biodegradable bone-bonding composite can be made.

Polysilicon surface-modification technique to reduce sticking of microstructures

Abstract: A new and simple surface-modification technique is proposed to reduce sticking of microstructures fabricated by surface micromachining. This technique realizes a very rugged surface at the polysilicon substrate, resulting in reduced sticking through a decrease of real contact area. The surface, which consists of honeycomb-shaped grain holes at the polysilicon substrate layer, is defined by a two-step dry etch without an additional masking step for photolithography or deposition of thin films. By varying the time for etching the grain holes of the polysilicon substrate, controlled surface roughness can be obtained. Test structures, including polysilicon cantilever beams of various lengths, fabricated by surface micromachining with the proposed surface modification show a doubled detachment length without sticking to the substrate.

Surface modification of polymers: Physical, chemical, mechanical and biological methods

Abstract: The principal objectives and methods of surface modification of polymers are reviewed in this paper. The techniques covered include physical, chemical, mechanical and biological methods.

Composite adhesive for optical and opto-electronic applications

Abstract: A composite adhesive for optical and opto-electronic applications contains the following: (a) transparent polymers and/or polymerisable oligomers and/or monomers suitable for use as adhesive; (b) nanoscale inorganic particles; (c) if required, compounds for the surface modification of the inorganic particles; and (c) if required, a cross-linking initiator. The composite adhesive can be used for connecting individual components of optical or opto-electronic elements and for constructing such elements.

Tailoring of thermomechanical properties of thermoplastic nanocomposites by surface modification of nanoscale silica particles

Abstract: Thermoplastic nanocomposites based on linear polymethacrylates as matrix materials and spherical silica particles as fillers have been synthesized using the in situ free radical polymerization technique of methacrylate monomers in presence of specially functionalized SiO2 nanoparticulate fillers. Uncoated monodisperse silica particles with particle sizes 100 nm and 10 nm were used as reference fillers. For surface modification, the alcoholic dispersions of the fillers were treated with appropriate amounts of methacryloxypropyltrimethoxysilane (MPTS) and acetoxypropyltrimethoxysilane (APTS). Transmission electron microscopy (TEM) was used to investigate dispersion behaviour in dependence on surface modification. Dynamic mechanical properties were measured by dynamic mechanical thermal analysis (DMTA).