ABSTRACTS

The following is a list of the abstracts for papers which will be presented in THE FIFTH INTERNATIONAL SYMPOSIUM ON SILANES AND OTHER COUPLING AGENTS. The listing is alphabetical by presenting author. This list is updated continually to add abstracts as they become available and to make appropriate corrections. This list may be conveniently searched by using the editor provided with most popular browsers (e.g. Microsoft Explorer, Netscape, ... etc.)

Silanes and Surface and Adhesion Properties of Mold Compounds in Semiconductor Packaging

Semiconductor industry is heading for lead (Pb)-free electronics. For this the soldering conditions demand a higher reflow temperature (260 °C). This has a ripple effect in the packaging industry and mold compound manufacturers are expected to offer green materials that can withstand higher reflow temperatures. Typical mold compounds offered as green materials are composed of specialized epoxy resins, flexible hardeners along with halogen-free flame-retardants and combinations of spherical fused silica fillers as well as a suite of adhesion promoters and flexibilizers.

This presentation will consist of an overview of the adhesion properties of mold compounds on various metallic surfaces and the effect of various additives such as adhesion promoters and silanes on final application of these compounds as packaging materials.

An Ultra-Flexible, Chromate-Free, Low-VOC, Silane-based Finishing and Coating System for Corrosion Protection of Aluminum Alloys

The capability of silanes to replace chromate in pretreatments and primer systems has been firmly established by our research group. This presentation provides an overview about the role of silanes in a two-component (silane and water-based resin) coating system for corrosion protection of aluminum alloys. The coating system consists of a two-component primer (AV5 silane, a 5:1 mixture of bis-trimethoxysilylpropyl amine and vinyltriacetoxysilane, and epoxy resin) and a two-component topcoat system (bis-sulfur silane and polyurethane resin). The coating is a low-VOC, chromate-free, highly flexible, environmentally-benign system with protective performance comparable to that of commercial chromate-containing primers. This coating system does not require the use of conversion coatings on metals. Nanoparticles, inhibitors and other additives can be incorporated in order to further improve the mechanical properties of the coating. Various corrosion tests and characterization techniques have been employed to illustrate the corrosion protection properties of the coating system on metals such as aluminum alloys. Standard ASTM tests such as tape adhesion test, pencil hardness test, bend test, DI water immersion were also employed. Some results of these tests are presented.

Influence of Glass Fiber Sizing on the Mechanical Behavior of Composite Materials: Investigation in the Low and High Strain Domains

An investigation was made on the influence of glass fiber sizing on the mechanical behavior of model GFRP composites processed by filament winding. Various sizings were used in the fabrication process in order to control interfacial properties between the fibers and the epoxy matrix: aminosilanes coupling agents, commercial epoxy sizings, sizings with high epoxy functionality, rubbery coatings.

A first set of characterizations was performed at low strain in the viscoelastic domain, using transverse tension-compression loading conditions. In this configuration, it has been shown that the viscoelastic behavior is manly governed by the morphology of the material (i.e., the volume fraction and the 2 D arrangement of fibers in the transverse plan) for all model composites. However, the nature of the sizing seems to play a indirect role on the opening of the fiber bundles during impregnation process.

In a second step, the model composites were characterized in transverse tension until rupture occurs. In these conditions, the ultimate stress and strain were found to be highly dependant on the surface treatment of glass fibers. The most reactive sizings (epoxy with high functionality) provided the highest ultimate properties. A complementary finite element modeling showed that the transverse strain of the material is governed by the strength of the fiber/matrix interface.

Last, model composites were subjected to accelerated ageing tests in (72 hours in boiling water), and characterized by 3 point bending in order to assess the residual interlaminar shear strength. It was found that highly reactive sizings limit the drop in the interfacial properties and may therefore increase the material durability.

1) Department of Chemical Engineering, King Mongkut's Institute of Technology Ladkrabang , Chalongkrung Road, Ladkrabang, Bangkok 10520, Thailand

Fracture Behavior and Toughness of a Silane Coupled, Polystyrene-Aluminum Interface

Fracture toughness of joints made from a glassy, high molecular weight polystyrene block bonded to chromic-sulfuric acid etched or phosphoric acid anodized aluminum are investigated. The fracture tests are performed with a 90° peel apparatus under "dry" ambient laboratory conditions and "wet" conditions created by submerging the apparatus in a temperature controlled water bath. The bond strengths are controlled using various concentrations of styrl silane coupling agent added directly into the styrene monomer solution that polymerizes against the aluminum. Ellipsometric measurements on smooth silicon surfaces verify that the thickness of bound polymer is controlled by the silane to polystyrene mole ratio.

X-ray photoelectron spectroscopy (XPS) analysis of the fractured surfaces indicates that the fracture is near interfacial between the aluminum and polystyrene surfaces. At slower crack propagation velocities under "wet" conditions, the fracture energy is lower and the locus of fracture is almost at the aluminum surface. Under the dry condition or at fast crack propagation velocities under wet conditions, the fracture energy is higher and the locus of fracture moves closer to the bulk polystyrene. At high crack propagation velocities (above 0.1 mm/sec), both the wet and dry fracture toughness as a function of bound polymer thickness on acid etched aluminum joints resemble quite closely the fracture toughness literature results obtained by fracturing pairs of fused, immiscible glassy polymers. Reasons for this similarity are discussed.

1) Laboratoire de Technologie des Composites et Polymères (LTC), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, SWITZERLAND.

2) Tetra Pak (Suisse) SA, Plasma Technology, C.P. 32, CH-1680, Romont, SWITZERLAND.

Influence of the Amino-organosilane/SiO_x Interphase on the Barrier and Mechanical Performance of Nanocomposites

Thin, flexible and transparent oxide films, which act as a barrier to oxygen and water vapour for plastic substrates have emerged in recent years in the fields of food packaging, medical device and opto-electronic applications. The objective of this study is to develop novel coatings with combined increase in oxygen barrier performance and in toughness, based on SiO_x coatings modified with multifunctional organo-silane polymers of controlled polarity and reactivity. The SiO_x coatings were deposited by plasma enhanced chemical vapour deposition (PECVD) from hexamethyldisiloxane vapour (HMDSO) on a semi-crystalline polymers such as poly(ethylene terephtalate) (PET). Since the behaviour of such systems depends on the interfacial structure between the organic and the oxide phases, the formation mechanism of the amino-silane/SiO_x interphase was determined in a first step. It was observed that the concomitant silane chemical sorption and oxide dissolution that follows the application of liquid amino-silane leads to the formation of an organo-metallic complex (chelate), as was explored in previous work [1]. As soon as the chelate concentration is higher than the solubility product, these species crystallize as sharp needles. The resulting oxygen permeability and cohesive properties of the nanocomposite barrier coating were investigated in a second step by means of permeation experiments on pre-stretched films and tensile tests carried out in-situ a scanning electron microscope [2], respectively. As in the case of glass fibers, the silane, whatever its pH, heals superficial defects, and leads to a decrease of the SiO_x permeability. Most interestingly, in the case of basic silane layer, and in contrary to the quasi-neutral silane, such high-barrier films survive extreme mechanical stress.

[1] J. Bouchet and A. A. Roche, J. Adhesion, 78, 1603 (2002).

[2] G. Rochat, Y. Leterrier, J.-A. E. Manson and P. Fayet. Thin Solid Films, 437, 1-2, 204 (2003).

1) Deutsches Textilforschungszentrum Nord-West e.V., Adlerstrasse 1, D-47798 Krefeld, GERMANY

2) Sensient Imaging Technologies, Sensient Straße 3, D-06766 Wolfen, GERMANY

3) Im Mühlengrund 25, D-06188 Plößnitz, GERMANY

4) Technische Universität Berlin, Fachbereich Technische Chemie, Strasse des 17. Juni 124-128, D-10623 Berlin, GERMANY

Incorporation of the Macrocyclic Ligand Cucurbit[6]uril into a Siloxane Matrix

Cucurbit[6]uril is a macrocyclic ligand with a rigid structure. The hydrophobic cavity is accessible by two portals each formed by six carbonyl groups, see Figure 1.

As a result cucurbit[6]uril is able to form complexes with cations or positively charged molecules via ion-dipole interactions. However nonpolar molecules can be complexed inside the cavity too. Dye molecules form solid cucurbituril complexes. Unfortunately this reaction can not be used for the removal of dyes and other organic pollutants from aqueous solution due to the extreme fine crystals formed. To overcome this problem a silica gel matrix is built by sa sol-gel process in the presence of cucurbituril. The pore sizes, volumina and the inner surface of the composite are influenced by variation of the sol-gel process. The presence of cucurbit[6] during the sol-gel process has an influence upon the silicon framework formed. The resulting composite with incorporated cucurbit[6]uril is characterized by means of physical methods and through adsorption experiments.

Surface Functionalisation of Textile Fibers with Reactive Silicon Compounds

Surface functionalization of textiles using reactive silicon compounds offers wide chances for textile finishing. Direct treatment of cellulosic materials with fluorinated trialkoxysilanes being covalently bound to the fibre imparts stong water repellancy.

Another perspective is offered by the sol-gel technique. Using this technique it is possible to form thin ceramic or partly ceramic coatings at moderate temperatures. The precursors for the materials used in the sol-gel processes are silicon- or other metalalkoxides bearing further functional groups like epoxy-, amine- or acrylic parts. These molecules condense (gelate) because of the rising concentration when the solvent evaporates. During the drying process usually transparent films are formed. Via the sol-gel process (inlcluding some modifiers) it is possible to create flexible inorganic/organic hybrid polymer coatings at moderate temperatures. Network formation can be done by polymerization by uv-radiation or similar radical induced processes when appropriate groups are present in the sol mixture.

These finishes can used for example for creating durable hydrophobic properties, for enhancing abrasion resistance or being barrier layers against chemical attack. The coatings can additionally be functionalized in a wide range. The sols offer the possibility of incorporating micro- or nanosized particles as metal oxides or colloidal metals or as molecular dispersed compounds. By filling the hybrid polymers with Al₂O₃, the scratch resistance of the modified surfaces can be increased, filling the sols with Fe₂O₃ leads to coatings with magnetic properties. Matrices filled with ZnO selectively absorb uv-radiation.. Furthermore it is possible to dye by incorporating dyestuff in the coatings, whereby colourations with high colour fastnesses are achieved. Such a strategy offers the chance of a obtaining a single dyeing recipe for all kind of fabrics.

1) Surfactant Technology Department, IIQAB-CSIC, c/Jordi Girona 18-26, 08034 Barcelona (Spain)

2) Optical and Applied Physics Department, UB, 08034 Barcelona (Spain)

Effect of the Post-application of Polysiloxanes on Plasma Treated Wool Fabrics

Low temperature plasma (LTP) (glow discharge) treated wool knitted fabrics reach good shrink-resistance properties, even at very short treatment times (Erra 1999; Molina 2002b), with a treatment considered as an emerging technique for its environmental friendliness and economical viability (Bureau 2003).

However, fabrics treated with glow discharge show harsh und unpleasant handle, not acceptable by the consumer. Such problem has not yet been solved, and preliminary studies of our group revealed that the post-application of certain softeners to the plasma treated wool fabric, although conferring good handle, reverted in high shrinkage values.

Up to now, the chemical, wettability and topographic modifications of the wool surface, as well as the shrink-resist and dyeability properties induced on the wool surface by an oxidative LTP have been deeply studied. However, the shrink-resistance changes promoted by the softener application on wool treated with LTP as well as on the possible reasons involved in it have been scarcely investigated.

The present work focuses on the post-aplication of various functional polisiloxane softeners with different modification degrees on wool fabrics treated with water vapour plasma. The handle of the fabrics subjective, shrink-resistance and whiteness degree have been studied by conventional textile methods. Furthermore, the changes in hydrophilicity have been recorded through drop test and contact angle techniques; surface chemistry has been studied by and surface topography by Scanning Electron Microscopy (SEM). The relationship between the different results is the key to understanding the variations in handle and shrink resistance of the wool fabrics.

Bureau, E. I. (2003). IPPC Reference Document on Best Available Techniques for the Textile Industry. Seville, European Comission, Directorate General JRC: 624.

Erra, P., Molina, R., Jocic, D., Julia, M.R., Cuesta, A., Tascon, J.M.D. (1999). Shrinkage Properties of Wool Treated with Low Temperature Plasma and Chitosan Biopolymer. Textile Res. J. 69: 811-815.

Molina, R., Jovancic, P., Comelles, F., Bertran, E., Erra, P. (2002b). Shrink-resistance and wetting properties of keratin fibres treated by glow discharge. J. Adhesion Sci. Technol. 16: 1469-1485.

Glass substrates modified with organosilanes for biological applications

DNA micro-arrays have numerous applications in DNA sequencing, mutation detection, and pathogen identification. When bound to solid substrates, DNA must still be accessible and retain the ability to hybridize with its complementary strand. One technology to produce DNA micro-arrays involves the printing of DNA molecule probes onto a silanized glass substrate as micro-spots and exposing them to a solution of fluorescently labeled samples of DNA targets. One objective of this work is to simply model the interface interactions between DNA and glass slides modified with organosilanes.

The functionalization of glass consists of chemically bonding organosilanes to the glass surface. Two functionalizations are considered. The glass is functionalized with 3-aminopropyltriethoxysilane (APS) or 3-glycidoxypropyltrimethoxysilane (Glymo). DNA behaves as a polyacid in aqueous solutions, over a wide range of pH. A glass substrate treated with aminopropyltriethoxysilane (APS) is positively or negatively charged, depending on the pH. Modeling of the surface charge of the APS treated glass has been developed from results of wetting experiments performed at various pH. A good correlation between experimental data of DNA retention at various pH and the variation of the surface charge of the APS treated glass is obtained. The epoxy (Glymo) functionalized slides are used for the covalent immobilization of unmodified and amino-modified oligonucleotides to the glass substrate. As shown in this paper, the two functionalized glass substrates have different surface properties according to their surface functionalization.

Electrodeposition of Bis-silanes for Pretreatment of Aluminum Alloys

Silane coatings have proved to be an outstanding, environment-friendly corrosion protection treatment for metal substrates. Various coating methods such as dip coating, spin coating, spray coating have been adopted to coat the surface with silane. Electrodeposition of silanes has been found to give films with significant performance advantage over other traditional techniques. In this work, electrodeposited coatings of a solvent-based nonfunctional aromatic bis-silane on aluminum alloys (AA6111 and AA2024) were obtained at different voltages. The coatings were evaluated using various characterization techniques such as Electrochemical Impedance Spectroscopy, DC polarization and Salt Spray exposure to quantify the resistance of the coated metal against corrosion. Based on these results, the best operating voltage was identified for this silane. The performance of this optimized coating was compared with that of dip-coated panels of the same silane using the aforementioned characterization techniques. AFM studies of the silane films obtained by these techniques revealed the uniformity of the electrodeposited film. The adhesion offered by these pretreatments to standard military primer coat was tested by the topcoat adhesion test (ASTM D 3359).

Metal Nanoclusters Catalyzed Transformations of Silanes and Polysiloxanes

(Abstract not yet available)

Tailored Organosilanes for Functional Immobilisation of Biomolecules

Attachment of biomolecules to solid surfaces constitutes an important issue in modern biotechnology (bioactive magnetic carriers, microchips etc.). The attachment process involves previous activation of the substrate with chemistries that permit a stable fixation of the molecule to the surface.

SAMs of organosilanes have been widely used for these purposes as silica surfaces in different variants (silica gel, glass slides, silicon wafers, quartz substrates…) are frequently used in these applications. However, commercial organosilanes of general formula X(CH₂)_nSi(OR')₃ show limited performance as coupling agents for complex biomolecules (eg. proteins) as they do not address issues like the conformation or the orientation of the immobilised specie in order to maximize its functional activity.

In this context, our group aims to design and synthesize multifunctional Y-shaped organosilanes with an optimised structure for the attachment of biomolecules. An initial screening of protein-surface interactions based on adsorption studies of model proteins onto silica substrates modified with different commercial organosilanes has been first accomplished. The results of this test have determined the chemical nature of an "ideal" bicomponent surface for protein immobilisation. Based on these results, the synthesis of our key-molecule has been attempted and its performance in protein immobilisation assays has been tested.

Photosensitive Silanes for Chemical Lithography

Immobilisation of molecules or mesoscale objects onto surfaces is a demanding subject with current applications in a variety of important technologies, eg. multifunctional biosensors for diagnosis and high-throughput screening or miniaturized electronic and photonic devices. New developments in these fields depend heavily on the selectivity and efficiency of the adsorption of particular targets onto predetermined sites of a previously chemically patterned surface. In this context, different surface patterning methods have been developed over the years, most of them based on a sequence of multiple photoresist lithography steps and surface activation using organosilanes.

Photosensitive surface modification agents offer an interesting alternative to multistep patterning processes. These can be organosilanes possessing reactive head-groups in a caged form and which can be activated (deprotected) upon irradiation with a suitable wavelength and intensity. Since the lithographic (photosensitive group) and the surface activation (head-group) tools are contained in the same molecule, a single surface modification process renders a ready-made substrate which, after masked irradiation, generates a lateral chemical pattern as a consequence of the light activated cleavage of the photosensitive group in the illuminated areas.

Complex and hierarchical chemical patterns (with a higher number of discrete reactive features on the substrate) can also be achieved by this method if the surface is modified by coadsorption of two (or more) silanes that carry different protecting groups and which can be selectively removed in successive irradiation processes using different wavelengths (orthogonality).

In this presentation, the synthesis of different orthogonal photoactivable silanes (Nitroveratryl and 3,5-dimethoxybenzoin derivatives) and their use as surface modification and micropatterning agents will be described. The application of these molecules to the site-selective immobilisation of colloidal particles and biomolecules onto planar substrates will be demonstrated.

Modeling and Practice of Ethanol-devolatilization of Silica-Silane Rubber Compounds in an Internal Mixer

During mixing of a rubber compound containing silica and silane, the mixer is not only used for the dispersion of the filler and other ingredients, but also for a chemical reaction. These two functionalities of the mixer result in opposite processing requirements: A good dispersion is reached by high shearing forces, increasing the compound temperature. The silanization is not depending on high shearing forces; it is positively influenced by high temperatures, but with an increasing risk of pre-scorch. Another drawback is the fact, that the equilibrium between the ethanol concentration in the vapor phase in the void space of the mixing chamber and the ethanol concentration in the rubber phase is limiting the reaction rate of the silanization. Devolatilization of the compound is a crucial factor for the efficiency of the silanization reaction.

A model for ethanol-devolatilization of a rubber compound in an internal mixer is developed, including a chemical reaction replenishing the volatile component during the devolatilization process. The model is based on the penetration theory, with the main contribution to the devolatilization being the mass transfer. It is compared with experimental data, resulting in the conclusion that the situation in the internal mixer can best be described by mass transport between the surface layer of the rubber phase and the vapor phase.

Infrared-Visible Sum Frequency Generation Spectroscopy to Probe Hidden Polymer Interfaces

(abstract not yet available)

The New High Speed Technology: -silanes

The majority of organofunctional silanes which have been used since decades as coupling agents, adhesion promoters and crosslinkers in plastics, coatings, sealants and adhesives possess one common structural element: silicon moiety and functional organic group are separated by a propylene spacer. Chemists call them therefore -silanes. Although already known for a long time only recently another class of organofunctional silanes was launched in the market on commercial scale: products with only a methylene spacer, so called -silanes. -Silanes perform basically in the same applications and the same way as the established -silanes, however, with the significant difference that their reactivity at the silicon moiety is dramatically higher compared to -silanes.This higher reactivity opens up new and exciting applications for -silanes. As crosslinkers in coatings mechanical and chemical properties can be achieved which were never possible with -silanes. New formulations of high performance sealants and adhesives are accessible. Processes like in filler treatment are accelerated thus reducing cycle times and costs. And last but not least environment, health and safety problems can be lowered or even eliminated as realized e.g. with Isocyanate-free Polyurethane chemistry. This paper gives an overview on the technologies of manufacturing -silanes and their use and performance in the various typical fields of applications.

Effect of Moisture on Epoxy Metal Interfaces

First, how water penetrates into epoxy adhesive layer is examined using single and multilayered bonded samples. The experimental result confirms that water is firstly absorbed from the edge surface(s) exposed to moisture containing atmosphere. Then, it diffuses through the adhesive layer according to the Fickian diffusion theory. Water absorption through the interface between metallic substrate and adhesive is not significant even if it is weak due to no surface treatment. However, water always reduces the interfacial strength and easily causes the interfacial failure at the weak interface while still cohesive failure occurs at the strong interface due to the appropriate surface treatment. In general, the fracture toughness of epoxy adhesive joints decreases with decreasing the loading rate under Mode I loading while the fracture toughness of bulk epoxy increases with decreasing the loading rate. Such time dependent properties of epoxy adhesive joints can well be explained due to water absorption in conjunction with the residual stress in the adhesive layer. At an extremely dry condition, the similar tendency in the relationship between fracture toughness and loading rate is obtained even in the case of adhesive joints after the residual stress in the adhesive layer has been well released.

Glass Strengthening by Organosilanes Water-based Coating

The general trend in glassware is for lighter products, resulting in thinner, and mechanically weaker, walls. In this work, an hybrid organic/inorganic strengthening coating made of a mixture of an epoxysilane and an aminosilane is deposited on glass by sol gel processing in aqueous media. Dynamic light scattering, IR spectroscopy and NMR were used to characterize the condensation reactions in the solution. Interaction between the two silanes does occur. This is best evidenced by the fact that the growth mode of the aggregates is dramatically modified as the ratio between the two silanes changes. RAIR (Reflectance Absorption Infra Red), was used to follow chemical reaction during film formation, showing that both epoxy amine reaction and silanol condensation are complete after thermal treatment. Mechanical properties of the film were characterised by nanoindentation and Double Cantiver Beam. It is shown that the highly crosslinked film has a high elastic modulus and is very cohesive and is also well adherent, due to silanol coupling on glass. Four points bending test on preindented glass samples shows a 75% strengthening. Possible strengthening mechanisms are discussed.

Molecular Control of Interface Chemistry by Atomic Layer Deposition (ALD), Building Aminoalkoxysilane Monolayers on Porous Silica

In our study, a gas-solid reaction technique (atomic layer deposition, ALD) is used to manufacture high-density and conformal aminofunctional molecular layers on a high-surface area silica. The precursors are aminoalkoxysilanes (e.g., H₂N(CH₂)₃Si(OEt)₃, H₂N(CH₂)₃SiMe(OEt)₂, H₂N(CH₂)₃SiMe₂OMe_, H₂N(CH₂)₂NH(CH₂)₃Si(OMe)₃) that can be evaporated without decomposition in a low vacuum. Alkoxysilanes provide strong covalent bonding via siloxane groups with the silica surface.

The self-limiting reaction sequence (i.e., the reaction cycle) does not typically result in monolayer deposition per cycle. Depending upon the size of the reactant, the attached ligands, and saturation exposure, the reaction of a precursor produces most often a submonolayer per cycle. Hence, multiple cycles are commonly required to deposit a single monolayer. In our case, multiple aminoalkoxy/water cycles are needed to produce a super-high density amino surface.

The effect of the reaction/hydrolysis temperature, precursor molecule and the number of ALD reaction/hydrolysis cycles on the surface composition of materials are elucidated by elemental analysis, DRIFT, the solid state ¹³C and ²⁹Si spectroscopy, and molecular modeling. The basic scientific understanding of interface phenomena between inorganic and organic materials will create a solid foundation in this new branch of ALD processing.

Our research also widens the applications of ALD to novel areas: e.g., chromatography, homogeneous functional surfaces for homogeneous catalysts, sensors and combinatory chemistry of small molecules, surface selective passivation and tribology in MEMS.

^†European Owens-Corning, Rue de charneux, Battice, B-4651, BELGIUM

The Differential Adsorption of Silanes from Solution onto Model E-Glass Surfaces Using High Resolution XPS

Single and mixed organosilanes are often used in commercial sizing to provide universal application of the fibres and promote the adhesion between glass fibre surfaces and the resin in a glass fibre reinforcing polymer composite. Mixed silanes can introduce different chemical properties to glass surfaces. This is fundamental to the optimisation of functional silanes for industrial applications. However, the inclusion of mixed silanes provides potential complications since the additional reactions between the silanes can modify the selective adsorption process and change the efficiency of the adhesion. In this work, -aminopropyltriethoxysilane (APS) and -glycidoxypropyltrimethoxysilane (GPS) were adsorbed from aqueous solutions of a range of solution concentration. High resolution X-ray photoelectron spectroscopy (XPS) was employed to characterize the silanes coated onto model E-glass surfaces. The selective adsorption of silanes was studied by fitting Si 2p_1/2 and Si 2p_3/2 peaks with components for SiO₄ and CSiO₃ environments.

^*To whom correspondence should be addressed. E-mail: f.r.jones@sheffield.ac.uk

Functional Polymer-Si and Polymer-SiO₂ Hybrids via Surface-Initiated Living Radical Polymerization

Linear, branched and arborescent fluoropolymer-Si hybrids were prepared via surface-initiated atom transfer radical polymerization (ATRP) from the 4-vinylbenzyl chloride (VBC) inimer and the ClSO₃H-modified VBC that were immobilized on the hydrogen-terminated Si(100), or Si-H surfaces. The simple approach of UV-induced coupling of VBC with the Si-H surface provided a stable, Si-C bonded monolayer of 'monofunctional' ATRP initiators (the Si-VBC surface). The aromatic rings of the Si-VBC surface were then sulfonated by ClSO₃H to introduce the sulfonyl chloride (-SO₂Cl) groups and to give rise to a monolayer of 'bifunctional' ATRP initiators. The halogen-terminated Si(100) or Si(111) (Si(100)-X or Si(111)-X, X=Cl, Br) surfaces can also be shown to be effective initiators for the preparation of well-defined polymer-Si hybrids via surface-initiated ATRP. Polymer-Si hybrids, prepared via surface-initiated ATRP of pentafluorostyrene, sodium 4-styrenesulfonate, poly(ethylene glycol) monomethacrylate, and (2-dimethylamino)ethyl methacrylate from Si-X surfaces, have been prepared. Finally, it will be shown that chlorinated SiO₂ surfaces of glass and Si(100) wafer are, too, effective macroinitiators for surface-initiated ATRP. Well-defined polymer-glass and polymer-Si(100) hybrids, consisting of covalently tethered polymer brushes on SiO₂ surfaces of the substrates through robust Si-C bonds, have been prepared directly via surface-initiated ATRP from the SiO₂-Cl surfaces. In addition to glass substrates and oxide-covered silicon wafers, the technique can be readily extended to the modification of a wide range of SiO₂ surfaces, such as silica surfaces.

Self-Assembled Monolayers of Omega-Functional Alkylsilanes: A Platform for

Understanding Cellular Adhesion at the Molecular Level

(abstract not yet available)

^†European Owens-Corning, Rue de charneux, Battice, B-4651, Belgium

The Interaction of Amino and Glycidyl Silanes with E-glass Surfaces

Despite research on the interaction of silanes with various substrates over many decades, there is still some uncertainty over the contribution of the glass modifiers on the nature of the deposit. Both -aminopropyltriethoxysilane (APS) with the nitrogen atom and -glycidoxypropyltrimethoxysilane (GPS) without a diagnostic element were involved in this work. A detailed study of the nature of the deposits using surface analysis and contact angle measurements has been undertaken. X-ray photoelectron spectroscopy (XPS) results provided the quantitative elemental composition and the different bonding environments of atoms. The involvement of the glass modifies in the silane deposit has been studied systematically. The paper will report how the variables in the coating procedure and the initial surface chemistry affect the structure of the deposit.

^*To whom correspondence should be addressed. E-mail: f.r.jones@sheffield.ac.uk

1) Stanford Genome Technology Center, 855 California Ave., Palo Alto, CA 94304

2) 4^th State Inc., 1260 Elmer Street, Belmont, CA 94002

Plasma Enhanced Deposition of Silane Coupling Agents for Biological Applications

Miniaturized devices are essential to advance our understanding in biology and medicine since it can reduce the amount of precious sample as well as cost of reagents by orders of magnitude. However the surface-to-volume ratio increases exponentially with miniaturization. Thus, control of the surface properties of such devices becomes increasingly important as the dimensions are reduced. Whereas known methods for liquid-phase deposition of silanes works well in current devices it will restrict future applications and novel deposition techniques are desired.

We here present the use of plasma-enhanced chemical vapor deposition (PE-CVD) of silanes for biological applications. Particular attention will be paid to experimental parameters and the structural characterization of such surfaces using X-ray photoelectron spectroscopy (XPS), contact angle measurements and AFM. The reactivity and specificity towards bio-molecules will be demonstrated by fluorescence microscopy scanning.

1) Leibniz-Institute of Polymer Research Dresden, Hohe Straße 6, D-01069 Dresden, GERMANY

2) Anton Paar GmbH, Anton-Paar-Straße 20, A-8054 Graz, AUSTRIA

Characterization of the Interaction between Silanes and Solid Surfaces by the Streaming Potential Method

Silanes are frequently used as coupling agents in different kinds of composite materials. The activity of the silanes is influenced by other components contained in the composite system, the surrounding medium, the storage conditions of reinforcing materials, and the processing conditions of the final products.

Electrokinetic investigations reflect very sensitively any changes in the chemical and physical properties at the solid/liquid interface. According to Jacobasch [1], it is even possible to distinguish between dissociation and adsorption processes that occur at the solid surface. Electrokinetic studies enable the characterization of functional groups in the outermost surface layer and the effectiveness of the used coupling agent. Streaming potential measurements are especially suited for studying such changes of surface chemistry at macroscopic solids with different size and shape.

In this contribution we show the influence of the basic material, of storage conditions, of other components in the sizing mixture, and of the used matrix material on the efficiency of silanes.

We will discuss the activity of silane coupling for reinforcing fibres and powders and describe the application of the streaming potential method for their surface characterization.

[1] H.-J. Jacobasch, Prog. Org. Coat. 17 (1989) 115-133

1) University of Turku, Institute of Dentistry, Department of Prosthetic Dentistry and Biomaterials Science, FI-20520 Turku, FINLAND

2) University of Groningen, Faculty of Medical Sciences,

Department of Dentistry and Oral Hygiene, NL-9713 AV Groningen,

THE NETHERLANDS

Silane Chemistry and its Applications in Dentistry

Dental restorative and prosthetic materials in the oral cavity are subject to stress in the hostile conditions of the mouth, viz. impact and fatigue forces due to mastication forces or trauma, oral dysfunctions, bacteria and yeast flora, temperature changes, saliva, and pH changes. High bond strength between restorative materials and dental tissues is essential for durable restorations. Treatment of the restoration surfaces in order to increase its critical surface energy is defined as surface conditioning. Two approaches are generally employed in dentistry: physico-chemical and (pure) chemical conditioning. Certain chemical primers may be chemically reactive towards the bonding agent and the use of a particular surface priming technique may also introduce micromechanical features into the substrate (e.g. acid etching of dental enamel or other non-dental surfaces). Trialkoxy silanes are a large group of hybrid inorganic-organic compounds that contain silicon atoms bonded directly to carbon atoms. They are well known wetting agents that promote adhesion between bond dissimilar materials together.

In dental materials research, silanes are used either as a surface modification agent for dental resin composite filler or as a coupling agent for adhering resin composites to conditioned ceramics, metals, or other resin composites. 3-Methacryloxypropyltrimethoxysilane (MPS) has been intensively screened and evaluated, initially with reinforcing glass fibers. MPS was early concluded to have adhesion-enhancing properties for attaching porcelain teeth to acrylic denture resin. The first results of silane treatment (i.e. silanization) were encouraging. However, the sensitivity of siloxane bonding to humidity and working conditions became understood. Many other trialkoxysilanes have been studied and developed during the last few years in the field of dental materials research that might aid prolonging the service life of dental restorations.

Some Rare Silane Coupling Agents and their Novel Dental Applications

1) University of Turku, Institute of Dentistry, Department of Prosthetic Dentistry and Biomaterials Research, FI-20520 Turku, FINLAND

2) University of Groningen, Faculty of Medical Sciences,

Department of Dentistry and Oral Hygiene, NL-9713 AV Groningen,

THE NETHERLANDS

Trialkoxy silane esters, well known coupling agents, are used to enhance adhesion between inorganic matrix and organic materials. They are widely used in several industrial fields. In dental resin composite materials, silica and glass filler particles are coupled with e.g. vinyltriethoxysilane to the polymeric matrix. In intra-oral and extra-oral repair of composite, ceramic, noble and base metal alloy appliances, amalgam, and titanium surfaces, they are typically silica-coated. An activated 3-methacryloxypropyltrimethoxy-silane, MPS, is then applied and a resin composite is light-polymerized onto it. Silanes form a siloxane film that is known to be susceptible to oral conditions for humidity, saliva, blood, bacteria, masticatory forces etc. There are no reported silane studies with some trialkoxysilanes, viz. some aminosilanes, isocyanatosilanes, or acrylatesilane, which might be promising future coupling agents under optimal conditions in dentistry.

In this study, silica-coated titanium surfaces has been silanized, then a Bis-GMA or dendrimer-based experimental resins has been light-cured onto them. The shear bond strength after aging process has been tested mechanically. Commercial dental silanes have been compared with experimental, laboratory-made trialkoxysilanes. Some rare trialkoxysilanes has been allowed to form the siloxane layer with silica-coated titanium. Different aminosilanes has been allowed to react with a polished titanium surface, and silanized at different temperatures. These tree aminosiloxane films showed differences in their texture and surface energy. Acrylate- and isocyanatosilane both showed surprisingly high shear bond strength compared to MPS, and the resin de-bonding failure was mainly cohesive according to scanning electron microscope analysis. Some siloxane film thickness simulations on Si wafer suggested approximately 5-10 nm thin siloxane films for dilute (0.5…1.0 vol-%) experimental silane solutions according to ellipsometric measurements. Drying time (reaction time) of a commercial silane on silica-coated metal surface in clinical conditions proved to be able to be less than the (by manufacturer) recommended 5 min time.

Silanes on Glass Fibre Surfaces

Glass fibres are often used to reinforce polymer resins. Silanes oligomerize on contact with surface moisture resident on E-glass fibers. A close study using XPS, SEM, TGA and DRIFT has revealed that significant changes occur with very small changes in the application procedure. It is important to be able to control E-glass fiber orientation in various polymerisable monomers preferably by using silane coupling agents. Therefore, we have examined the development and characterisation of surface treatments for glass fibres in high performance composites.

The silane coupling agents used in composites manufacture are usually trialkoxysilanes, RSi(OR')3. Such alkoxysilanes are applied from dilute aqueous solutions, partial hydrolysates, or organic solvents (generally an alcohol), and most have undergone initial hydrolysation and oligomerisation prior to interacting with the chosen substrate. Such silanes interact with glass surfaces, initially through hydrogen bonding to the surface hydroxyl groups, with subsequent condensation reactions generating siloxane structures. The Nanomaterials Group at Flinders University have shown that siloxane oligomers bearing the required functional groups may, in fact, produce better sizes for composite manufacture, than conventional silane coupling agents. Glass fibres can and do adsorb a host of agents and reagents. A close study using XPS, SEM, Streaming Potential, AFM and DRIFT has revealed that significant details of the glass surface can be spectroscopically evaluated and analysed.

Siloxane polymers bearing a variety of different functional groups are found to attach to E-glass fibres as effectively as any commercial silane coupling agent. The strength of the interaction between these polymers and the glass surface varies depending on both the nature of the functional group and the application method employed. DRIFT and XPS data establish the adsorption of such siloxanes onto the glass surface, and the strength of these interactions is indicated by the extent of removal of the adsorbed species when washed with a range of organic solvents.

Dewetting Suppression of Polystyrene Thin Films on Surfaces Modified with Aminofunctional Organosilanes

Aminofunctional organosilanes, such as 3-amino-propyltriethoxylsilane (APTES), have been utilized widely as adhesion promoters. APTES was also found to have the ability to prevent polymer thin films from separating, or dewetting, from substrates. Since APTES contains the active terminal -NH₂ group, which can interact with the multiple active head groups and the substrate, the APTES molecules likely link together and form multi-layered networks when grafted to a substrate. The multi-layered networks could form large enough loops for the polymer chains to slide into and create entanglement/interlocking, thus enhancing the adhesion or stability of the polymer films upon subjecting them to a separation force. This hypothesis was verified by dewetting studies of thin films of polystyrenes, having molecular weights above and below the entanglement molecular weight, from APTES surfaces after each thin film/APTES combination was subjected to different treatments. The adhesion enhancement was observed when polystyrene thin films placed on the APTES surface were allowed to cure in vacuum and at an evaluated temperature (~ 80°C). The stronger enhancement was found for polystyrene having the molecular weight higher than its entanglement weight. The results suggested that the curing was necessary for APTES to form multi-layered networks, which interlocked/entangled with polymer chains to enhance the adhesion.

Performance of Silanes in Protecting Metals from Corrosion: Effect of Substrate Cleaning

The degree of cleanliness and the chemical nature of the metal surface determine the wettability and adhesion of silanes to metal surfaces. Cleaning studies were conducted on Al 2024-T3 alloy to investigate this correlation. The alloy was subjected to various cleaning protocols using combinations of alkaline and acidic cleaners. The cleaned panels were then dip-coated with a water-based silane mixture and cured. Contact angle measurement, salt water immersion and characterization techniques such as DC polarization, RAIR and XPS confirm the strong dependence of the silane performance on the substrate chemistry. In this paper we will provide a mechanism for this dependence.

1) Interuniversity Microelectronics Center (IMEC), Belgium

2) Katholieke Universiteit Leuven, Chemistry department, Belgium

3) Surface specialties UCB, Belgium

Silane Monolayers for Functional Nano-bio Interfaces

The increasing miniaturisation of microelectronics based biosensors and biochips and the demand for higher sensor sensitivity and specificity put severe demands on the process and methodology of interfacing biomolecules with surfaces. More specifically, controlled thin film structures have to be created which allow the bio-receptor elements to be arranged and addressed in a reproducible, stable and controlled manner. Addressing these issues, novel surface chemistries based on functional alkylsilanes were developed for the construction of protein repellent surfaces and well-defined bio-interfaces.

For the creation of immunosensor interfaces, novel pre-activated silane compounds were compared to commercially available alkylsilanes, bearing aldehyde, cyano, epoxy or amino groups for their antibody immobilisation and specific recognition of the desired analyte. In addition the non-specific adsorption of serum species on these surfaces was also investigated. Protein repellent surfaces were created by the deposition of various poly(ethyleneglycol)-containing alkyltrichlorosilanes. The protein repellency of the former was assessed using normal human serum and its four most abundant proteins and was found to be dependent on the PEG chain length.The developed silane interfaces could further be used to functionalise magnetic nanoparticles with biological moieties for biosensing based on the detection of magnetic markers.The designed nano-bio interfaces can be used for a variety of applications, e.g. biosensors, chip-based diagnostic assays and biomaterials used for implants and tissue engineering.The interfacing of oxide based microelectronic devices with biological components requires methods for assembling biomolecules on their surfaces in a controlled manner. Examples include biosensors, chip-based diagnostic assays and biomaterials used for implants and tissue engineering.

1) A. A. Parker Consulting & Product Development; Newtown, PA.

2) JCH Consulting; Red Hook, NY.

Comparative Studies of Hydrophobic Surface Treatments for TiO₂: n-Octylphosphonic Acid vs. n-Octyltriethoxysilane

Hydrophobic titanium dioxide powders were prepared with n-octylphosphonic acid (NOPA) and n-octyltriethoxysilane (NOS) surface treatments. In both cases, complete hydrophobicity was achieved at surface treatment concentrations ranging from about 5 to 15 moles/m². Higher surface concentrations of NOS had little to no effect on hydrophobicity. However, higher concentrations of NOPA led to an unexpected reduction in hydrophobicity, and to an increase in hydrophilicity. By contrast, the lipophilic characteristics of the NOS and NOPA surface treated powders were improved at all surface treatment concentrations. Phosphorous-31 solid state NMR studies of the hydrophobic NOPA treated powders revealed the presence of chemisorbed NOPA, where the chemical shift values of the surface adsorbed species were significantly different from those of the neat compound. Analogous studies of a hydrophilic NOPA treated powder revealed the additional presence of a neat NOPA component, suggesting that the excess surface treatment forms a physically adsorbed layer that overlays the chemisorbed surface species. These findings indicate that the transition from a hydrophobic powder to a hydrophilic powder occurs when the NOPA surface concentration exceeds the available concentration of surface adsorption sites.

1) Stanford Genome Technology Center, 855 California Ave., Palo Alto, CA 94304

2) 4^th State Inc., 1260 Elmer Street, Belmont, CA 94002

Plasma Enhanced Deposition of Silane Coupling Agents for Biological Applications

Miniaturized devices are essential to advance our understanding in biology and medicine as they have advantages, particularly in reducing the amount of sample as well as cost of reagents by orders of magnitude. However the surface-to-volume ratio increases exponentially with miniaturization. Thus, control of the surface properties in such devices becomes increasingly important as the dimensions are reduced. Traditional silanization methods restrict future applications and novel deposition techniques are desired.

In this study, we present the use of plasma-enhanced chemical vapor deposition (PE-CVD) of silanes for biological applications. Particular attention will be paid to experimental parameters and the structural characterization of such surfaces using X-ray photoelectron spectroscopy (XPS), contact angle measurements and AFM. The reactivity and specificity towards bio-molecules will be demonstrated by fluorescent techniques.

Glycoxysilanes and Their Use to Reduce Volatile Organic Compound Emissions

Organofunctional glycoxysilanes were found to be effective coupling agents, adhesion promoters and crosslinking agents that reduce emissions of volatile organic compounds into the environment. These silanes are mixtures of cyclic and oligomeric compounds that form when the hydroxyl groups of the glycol react with the same or two different silyl groups. During use, these glycoxysilanes reacted with moisture to generate glycols. The effects of the glycoxysilane structure on reactivity, volatility and end-use performance were determined for various applications. The reactivity of the cyclic glycoxysilane component was determined by monitoring the acid-catalyzed hydrolysis in aqueous acetone solution at 22 °C. Application data are presented to demonstrate the ultility of these silanes.

1) Federal Mogul Corporation, Sealing Systems

2) Dept of Chemical Engineering and Materials Science, Wayne State University

Thermal Characterization on the Interaction of Adhesives and Rubber

In the automotive industry today, adhesives are widely used for rubber to metal bonding; to make flexible, tough, and durable bonds that can withstand harsh service conditions. At Federal Mogul Sealing Systems, we source our polymers used in rubber compounds and the adhesives used for rubber to metal bonding from various suppliers who more than often do not collaborate in their technical developments. The polymer suppliers consider their cure chemistries to be proprietary while the adhesive suppliers consider their products to be unique. Because of this lack of collaboration, there is very little information available in the published domain regarding matching adhesive technologies to polymer cure chemistries.

The intent of the current work is to study the reaction chemistry and kinetics of adhesive to rubber interaction. We have selected one particular adhesive - elastomer combination. Characterization and analytical work is done to establish correlation between the two systems from a chemistry standpoint. Selected cure reactions that are expected to occur between the two systems are monitored.

This work shows that the particular approach can provide meaningful insight to not only reaction chemistries that have never been monitored in the past, but also the kinetics aspects involved. We plan to extend this work to study other polymer/adhesive systems in the future.

Are Silane Films Water Barriers?

Certain bridged silanes impart excellent corrosion resistance on many metals. Electrochemical impedance measurements imply that the corrosion protection is due to water-barrier properties of the silanes. We used neutron reflectivity to investigate the penetration of water through spin-coated amine-bridged and sulfur-bridged bis-silane films. The results show that heavy water (D₂O) penetrates bis-amino silane films as well as films formulated from mixtures of bis-amino and bis-sulfur silanes up to substrate-silane interface. For Al substrate, water even penetrates into oxide layer. Only neat bis-sulfur films on Al substrate show some evidence of water barrier properties in the form of a gradient in water concentration.

The results imply that either the anti-corrosion behavior of silanes is a property of thick films only, or the mechanism of protection is not due to water-barrier properties of the bulk silanes. These issues are under investigation using films up to one-micrometer using synchrotron-based x-ray reflectivity and neutron reflectivity.

Deutsches Textilforschungszentrum Nord-West e.V., Adlerstr.1, 47798 Krefeld, GERMANY

Surface Photografting of Unsaturated Alkoxysilanes onto Polyolefins with Excimer-UV-lamps

Photochemically induced surface modifications of polyolefins with different unsaturated alkoxysilanes were carried out using excimer-UV-lamps emitting nearly monochromatic light. KrCl*-excimer-lamps emit UV-light of a wavelength of 222 nm. Polyolefins are transparent for this radiation, so the UV-light shines through the material. Surface-grafting can be carried out, irradiating unsaturated reagents as e.g. vinyltrimethoxysilane (VIME), vinyltriethoxysilane (VIET) or methacryloxypropyltrimethoxysilane (METHA) through polyethylene or polypropylene films. The combination of monochromatic lamps, transparent substrates and highly absorbing reagents allows to limit the photoreaction to the interface between polymer and monomer mainly. The results show that this approach offers far-reaching possibilities to perform photografting reactions without the need of inert atmospheres or thin liquid films to guarantee sufficient intensity of UV-radiation at the interface, therefore the technical effort for the surface graftings is comparably low.

Results for polyolefine films treated with unsaturated alkoxysilanes as well as treated with sols of the prehydrolysed unsaturated alkoxysilanes are presented. Exemplarily it is demonstrated that the modifications lead to polyolefins that can be dip coated with metal oxide sols or coated with simple technical polyurethane coatings guaranteeing a high adhesion to the substrate.

A Novel, Low-VOC, Chromate-free, One-Step, Silane-Based Primer System for Corrosion Protection

Corrosion of aerospace metals and alloys is currently mitigated by using a 2-step chromate-based technology. Cr[VI] has, however, been identified as carcinogenic and toxic by the US Environmental Protection Agency. Also, the Volatile Organic Compound (VOC) content of primers used in the coating Industry is coming under strict regulation by the various occupational safety and environmental agencies. The paint industry needs a low-VOC, chromate-free alternative to replace existing 2-step chromate-based systems. We will report here on a series of one-step organic primers obtained by combining resins such as epoxies, acrylates, or polyurethanes with organofunctional silanes. These primers are low-VOC and chromate-free. In this paper we will present some formulations which have been successfully tested for corrosion performance using standard tests such as the ASTM-B117 salt spray test, electrochemical impedance spectroscopy, DI water contact angle measurements, ASTM D 3363 (pencil hardness test), ASTM D 4752 (MEK double rub test), and ASTM D 3359 (topcoat adhesion tests). Some results of these tests are reported. FTIR-ATR and ²⁹Si NMR analysis were performed in attempts to characterize the chemistry of the systems.

Optimised Silane Treatments for Aluminium Alloys

(Abstract not yet available)

Improved Water-based Silane Pretreatment for HDG Substrates

Bis-silane pretreatments have proved to be environmentally benign, non-toxic and competent replacements for chromates, as pre-treatments for corrosion protection of metallic substrates. So far the best performances have been shown by solvent based silanes, having high VOC. Amongst the water-based silanes, AV5, a 5:1 mixture of bis-[trimethoxysilylpropyl] amine (A1170) and vinyltriacetoxysilane, has shown great promise for aluminum based alloys. However, its performance in case of more susceptible substrates like hot dip galvanized steels (HDG) and cold-rolled steels is below par. The aim of this work was to improve the suitability of AV5, as a pretreatment for hot dip galvanized steel. The aforementioned silane mixture was modified with an additive for cross-linking and toughening, and a corrosion inhibitor for self-healing. The concentration levels were optimized for the best performance after testing formulations with all the nine possible combinations of factor levels. EIS, DCP

and salt water immersion were the performance tests utilised for this screening. The efficacy of inhibitive action was confirmed using the scratch cell test. The chemical nature of the the improved system vis-a-vis the base silane system (AV5) was investigated using IR spectroscopy.

1) Chemical and Materials Engineering Department, University of Cincinnati, Cincinnati, OH 45221-0012, USA

2) Department of Chemistry, Oklahoma State University, Stillwater OK 74078, USA

Integral Epoxy Resin-silane Primer System for Hot-dip Galvanized Steel

The corrosion resistance of an environmentally friendly integral resin-silane primer coating system on hot-dip galvanized steel was investigated. The coating formulation is a mixture of hydrolyzed and non-hydrolyzed silanes incorporated into a commercial epoxy resin-curing agent system. Salt spray analysis indicated that the coating exhibits good corrosion resistance. Additionally, this unique coating system exhibited good adhesion to the zinc substrate, eliminating the need for use of a conversion coating.

Infrared spectroscopy and ¹³C NMR were used for determining the chemistry involved in the integral epoxy resin-silane coating system. These results indicate that the epoxy resin is primarily cured using the incorporated curing agent. The silanes were not found to react significantly with the epoxy resin. The non-hydrolyzed silanes are expected to hydrolyze slowly by ambient moisture following the initial curing.

1) USDA Forest Service, Forest Products Laboratory

One Gifford Pinchot Drive, Madison,WI 53726-2398

2) NIST, Building and Fire Research Laboratory

100 Bureau Dr., MS 8615, Gaithersburg, MD 20899-8615

Sol-gel Deposition of Inorganic Alkoxides on Wood Surfaces

Hybrid inorganic/organic polysiloxane networks deposited on wood substrates have been shown to lower the rates of moisture sorption by the wood. Deposition of such networks can be accomplished by cold plasma chemical vapor deposition or by sol-gel deposition processes. Using hexamethyldisiloxane as a precursor, water-repellent polysiloxane thin films were deposited on wood substrates by cold plasma chemical vapor deposition process. This paper focuses on sol-gel deposition of hydrophobic polysiloxane networks on wood substrates by using mixtures of alkoxysilanes and other inorganic alkoxides as precursors.

Investigation of the surface chemistry and morphology of wood specimens coated with these polysiloxane networks by means of x-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier Transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDXA), atomic force microscopy (AFM), and laser scanning confocal microscopy (LSCM), indicated that the sol-gel process results in deposition of polysiloxane networks that are bonded to the wood substrate by polycondensation with surface hydroxyl groups. The surface hydroxyl groups involved in the bonding appear to be located predominantly on the cellulose component of the wood substrate.

Potential of Silane Coupling Agents to Replace Chromate Metal Pretreatments

It has been amply demonstrated by our group in recent years that thin films of organofunctional silanes can be used as pretreatments of metals for paint adhesion and corrosion control in painted and unpainted state. Silanes have now become potential candidates for the replacement of chromate pretreatments in several metal-finishing industries. In this presentation an overview will be presented of applications where silanes have been demonstrated to work effectively. The mechanism of corrosion protection by silanes is also addressed. In order to further enhance the performance of silane films, they can be modified by certain additives such as inhibitors, nanoparticles, fibers, and organic resins. Example of such additions will be shown. Especially the use of water-based organic resins in combination with silanes will be highlighted, such mixtures that have the potential to develop into an entirely novel class of self-priming coatings. Such 'superprimers' are attractive as they are VOC-free, chromate-free, can cure at room temperature and, most importantly, do not require a conversion coating on the metal. A wide range of compositions consisting of silanes, resin systems and nanoparticles are possible and some specific ones will be discussed. Their performance can match that of a chromate conversion coating and a commercial chromate-containing primer combined if the superprimer is loaded with a new chromate-free pigment system developed in our laboratories. It consists of water-soluble inhibitors that have been converted into slow-release systems by encapsulating the inhibitor particles by a thin organic film deposited by a plasma polymerization process. Results obtained with the complete system on aluminum alloys, hot-dip galvanized steel and cold-rolled steel will be presented and discussed.

31077 Toulouse Cedex 4, FRANCE

Local Chemical Vapor Deposition of Silane for Combining Top down

And Bottom up Approaches

Bottom up techniques, such as self assembling of molecules and particles are efficient emerging technologies to obtain highly ordered structures and divers chemical functionality. In the other hand, top down approach allows an accurate placement of patterns but suffers from a low accuracy in the nanometer range.

The technique proposed here is a combination of bottom up and top down approaches to define chemically functionalised area at the exact place needed. It consist in four steps : cleaning and preparation of silica surface, pattern definition by e-beam or nanoimprint lithography in a resist layer, silane (octadecyltrimetoxysilane) chemical vapor deposition (CVD) and resist lift-off.

Height of the deposited layer is monitored by AFM, surface energy by contact angle measurement and chemical nature of the layer by Raman spectroscopy. All this characterizations allows to optimize and control the deposition process. CVD deposition leads to a silane layer of high quality, compared to wet techniques, avoiding the formation of aggregates and the dissolution of the resist's patterns by solvents as it happens in liquid phase deposition. The possible utilization of this chemical patterned areas for local nanoparticles deposition and self organization will also be presented.

Novel Corrosion Inhibitors for Improved Silane Systems

The role of silanes as coupling agents has been widely approved by the academics and the industry. Our research group has pioneered the use of organofunctional silanes as pretreatments to the modern day paint systems by enhancing their adhesion and corrosion protection properties. In case of damage to the coating, silane films inherently lack self-healing properties to protect the exposed surface. Thus there is a need for modification and development of more complete silane-based systems. Our work focuses on the incorporation of a combination of inhibitors into silane films in order to achieve such properties. Silane films were modified using a wide range of water-soluble inhibitors. The films were then studied and tested for their effectiveness as pretreatments. Some inhibitors were modified by plasma polymerization techniques for inducing slow-release properties. Various testing and characterization methods were employed to demonstrate the corrosion protection of the substrate over longer periods of time and to unravel the underlying mechanisms.