ABSTRACTS

The following is a list of the abstracts for papers which will be presented in THE SIXTH 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.)

m.abel@surrey.ac.uk

The Use of Organo-Silanes as Primers and Within an Adhesive Formulation

The use of organofunctional silanes as primers for adhesive bonding has increased recently as a result of the potentially harmful environmental impact of the traditional pretreatment methods for this metal¹. The formation of a covalent bond via condensation between hydroxyls present at the surface of the metal and silanols of the hydrolysed silane is well documented and it now seems very likely that there is a direct correlation between covalent bond formation as evidenced by the Me-O-Si⁺ fragment in the ToF-SIMS spectrum and good durability of the adhesively bonded structure^2,3,4. We have carried out extensive work on the mode of action of the 1% GPS treatment in recent years and we will use this understanding as a basis for exploring the mode of action when an organosilane is incorporated in the formulation of an adhesive. This is probably the most promising and cost effective manner of employing them for structural adhesive bonding, but, also the least well understood. The work shown will include studies on the mode of action of these molecules when incorporated within an adhesive formulation as well as an investigation of the effect of various process parameters such as concentration, chemistry of silane, type of substrate and curing temperature.

1) R.P. Digby and S.J.Shaw, Int. J. Adhes. Adhes. 18 (1998) 261.

2 ) E.P. Pluedemann, Silane Coupling Agents (Plenum Press, New York, 1991)

3) M-L. Abel, R.P. Digby, I.W. Fletcher and J.F. Watts, Surf. Interface Anal. 29, (2000) 115.

4) N. Porrit PhD dissertation, University of Surrey, 2001.

Investigation of the Interphase Epoxy Composites

The composite interphase can significantly affect the mechanical and thermal properties of the composite. Fourier transform infrared spectroscopy has been used to investigate the interfacial chemical bonding at the interfaces of the coupling agent and epoxy matrix in glass fiber-reinforced composites.

As objects researched the glass fiber mark VMS-6, coupling agent the processing aids 80 on based -aminopropyl- triethoxysilane and epoxy matrix polyglycidyl esters of p-aminobenzoic acids (consisting 9% NH groups) without/ with curing agent 4,4¹-diaminodiphenylsulfone(DDS) selected.

The results indicate that chemical bonds are formed in the interfacial region the matrix and components of the coupling agent. It is found that from hydrogen bonds between the functional groups of molecules this epoxy matrix and corresponding donor-acceptor groups of processing aids 80 (coupling agent). The effect of the presence of an interphase of the composites was determined by mechanical analysis.

The amount of the interfacial bonding depends on the composition (epoxy resin without or with curing agent DDS). In addition experimental results also clearly show the dependence of the crosslinking process on the concentration of the coupling agent treated surface.

Hydrophobicity, Hydrophilicity and Silane Surface Modification

A problem distinct from the issue of wet adhesion and hydrolytic stability of coatings is controlling the interaction of water with a coated surface. Very often the the descriptors hydrophobic or hydrophilic are applied to coated surfaces. Although the terms hydrophobic and hydrophilic are casually used, they are usually not defined. A growing number of applications ranging from architectural coatings to aortic stents require a precise control and, therefore, precise understanding of substrate interaction with water. Silanes are playing an increasing role in controlling the interaction of water with a surface. Different than most additives, which have a limited performance range, they can achieve surface properties ranging from hydrophobic to hydrophilic. Hydrophobic interaction can lead to adhesive bonding. A the same time self-cleaning surfaces are often associated with super-hydrophobicity. The structures of new and existing silanes suitable for surface modification will be related to effects associated with hydrophobicity.

Sol-gel-coatings Filled with Doped Tin Oxide Nanoparticles for Textiles with Modified Absorption and Reflection Properties

(Abstract not yet available)

Surface Free Energy of Silicon-Based Plasma Polymer Films

Silicon-based plasma polymer films are tested as compatible interlayers for multicomponent materials, where one of the components is silicon dioxide, and wettabilty together with functional groups at the film surface are the key material characteristics for constitution of chemical bonding to another component. Vinyltriethoxysilane (VTES) and tetravinylsilane (TVS) monomers were used for deposition of thin films by plasma-enhanced chemical vapor deposition (PE CVD) technique. Introduction of oxygen-containing species at the film surfaces is known to improve wettability and thus oxygen gas was mixed in tetravinylsilane to prepare hydrogenated amorphous silicon oxycarbide (a-SiOC:H) films with vinyl groups as functional species. Plasma-polymerized VTES and TVS/O₂ films were deposited on glass and IR-transparent silicon wafers at different effective power (0.1 - 10 W) and oxygen content in the mixture (2 - 79%) using RF (13.56 MHz) pulsed plasma. The method of sessile drop was employed to characterize wettability of films and contact angles were measured using distilled water, ethylene glycol, glycerol, and methylene iodide as the probe liquids. The surface free energy, as well as the dispersive and polar components, was evaluated using the approach of Owens-Wendt geometrical mean method and Wu harmonic mean method. Van Oss, Good and Chaudhury acid-base theory enabled us to determine the Lifshitz-van der Waals and the acid-base components. Values of the surface free energy and its components were correlated with surface elemental composition and chemical structure of films analyzed by X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIR). An influence of deposition conditions on the surface free energy of plasma polymer films will be demonstrated in the study.

Advanced Electrochemical Techniques for Studying Silane Based Pretratments as Adhesion Promoters on Different Metals

A large part of aluminium products are coated with an organic layer in order to improve the corrosion resistance. Copper surfaces are also sometimes protected with an organic coating to improve the durability or the aesthetic properties. Examples of industrial applications are household appliances and heat exchanger components. For these applications it is not rare to have the industrial need to treat at the same time components made of aluminium and copper. In order to extend the service life of the organic coated copper a specific surface pre-treatment is often required. Nevertheless, probably because of the limited market of this application, no specific pretreatments for copper are industrially developed, with the exception of cleaning procedures, but simply extensions of existing pretreatments optimised for other metals (aluminium, zinc) are used. The application of silane pretreatments as adhesion promoters for organic coated metals is remarkably increasing in the last decade, because silanes offer very good performance together with high environmental compatibility. The idea is therefore to try to develop a specific multi-metal silane based pretreatment (copper, aluminium, zinc). The starting point is the existing silane products, optimising the composition and the application conditions (concentration, temperature, pH of the bath etc.) in order to develop a high performance metal pre-treatment increasing the protective properties and the adhesion of a successively applied organic coating. The deposits were analysed using FT-IR spectroscopy and optical and electron microscopic observations. A electrochemical characterisation was carried out to highlight the silane properties and to evaluate the performance of the different deposits. The electrochemical approach is based on the comparison of DC and AC techniques, mainly electrochemical impedance spectroscopy and electrochemical techniques with spatial resolution, like SVP (scanning vibrating electrode) and SKP, (Scanning Kelvin Probe), in order to better understand the properties of the pretratment both on large and small scale.

Coupling Agents in Chelating Chemicals, Printing Inks, Silicon Emulsions and Paint Adhesive Formulations

Industrial uses of sealants and adhesives have been highlighted. Sealants for cement, bricks, wood, paper and other porous substrates have bee discussed in detail. Our construction chemicals substantially improve the strength of concrete apart from making it fully waterproof. Over 30% cement could be saved by incorporating one of these chemicals in as low as 0.1% concentration of the weight of the concrete mixture. Our paper modifying products convert an ordinary paper into a currency grade paper. Stainless steel surface modifier sealants of our Company could make it fully rustproof even in the most hostile environments such as rains, saline waters, etc. 2-component PU wood flooring adhesives for varnished and virgin surfaces have been described. D-series of water-resistant as well as waterproof products have been given; especially, the role of D5 (based on cyclopentasiloxanes) and D6 (made from cyclohexasiloxanes) has been discussed in detail. Surface modifiers such as chelates as coupling agents in the manufacture of printing inks, silicon emulsions and paint and pigments have also been highlighted. Importance of surface deactivators in molding and casting industries has been emphasized. Specialty sealants based on plasticized polystyrene as well as PVAc-butaraldehyde co-polymer have also been discussed.

1) Interuniversity Microelectronics Center (IMEC), BELGIUM

2) Katholieke Universiteit Leuven, Chemistry Department, BELGIUM

How to Tune the Functionality of Magnetic Nanoparticles Using Silanes?

Ferrite magnetic nanoparticles (MNPs) were functionalized with a variety of silanes, bearing different endgroups, to render them stable with respect to aggregation and keep them highly dispersed in aqueous media. The MNPs were prepared by a thermal decomposition method, widely used for the synthesis of monodisperse nanoparticles with controllable size. This method makes use of a hydrophobic surfactant, to passivate the surface, which results in nanoparticles that are solely dispersible in non-polar solvents. For use in biological applications, these nanoparticles need to be made water-dispersible. Therefore a new procedure was developed to decorate ferrite magnetic nanoparticles with diverse functionalities, based on the exchange of the hydrophobic surface ligands with silanes bearing different endgroups. By this means, we could easily determine the impact of the chemical functionality on the nanoparticle stability and water-dispersibility. Amino-, carboxylate- and poly(ethylene glycol)-terminated silanes were found to render the MNPs highly stable and water-dispersible, due to respectively electrostatic and steric repulsion. The silane molecules were also found to form a protective layer against mild acids or alkaline environments. The ligand exchange on the nanoparticle surface was characterized using SQUID, TEM, XPS, DLS, TGA, FTIR, UV-vis and zeta potential measurements. This approach represents a generic strategy to functionalize magnetic ferrite nanoparticles that form stable solutions in aqueous media and facilitates the use of these magnetic nanoparticles in biological applications.

1) Department of Polymer Science, University of Akron, Akron, OH 44320

2) Department of Materials Science, Rensselaer Polytechnic Institute, Troy, NY 12180

Synthetic Gecko Foot-hairs from Multiwalled Carbon Nanotubes

The mechanism that allows a gecko lizard to climb any vertical surface and hang from a ceiling with one toe has attracted considerable interest and awe for over two millennia. Recent studies have discovered that the gecko's ability to defy gravity comes from its remarkable feet and toes. Each five-toed foot is covered with microscopic elastic hairs called setae. The ends of these hairs split into spatulas and this allows the Gecko to hold on to the surfaces based on intermolecular (van der Waals, (VdW)) forces between the spatulas and the surface. Similarly, the same VdW forces act between our two hands when they are held together, but in this case they do not stick to each other. The reason is that the roughness of our hands prevents them from coming close to each other at separations relevant for VdW forces. On the other hand, based on the gecko's foot anatomy, if our hands were made up of tiny elastic structures that were able to deform or bend at different length scales in accordance with the contact surface and correct for the roughness, then perhaps our hands could also adhere to the surfaces we touch. In my talk, we will present the recent advances in fabricating polymer surfaces with multiwalled carbon nanotube hairs. These structures exhibit strong nanometer-level adhesion forces that are 200 times higher than those observed for Gecko foot-hairs. This fabrication process allows the flexibility to create structures that are found in nature on the Gecko's foot and offer excellent potential for applications as dry adhesives for space, microelectronics and MEMS devices.

Durability of Silane-Modified Adhesive Bonds

(Abstract not yet available)

Improving the Corrosion Performance of Epoxy Coatings by the Modification with "Active" and "Non-Active" Silane Monomers

(abstract not yet available)

1) Department of Engineering Materials, University of Sheffield, Sheffield, S1 3JD, UK

2) European Owens-Corning, Rue de Charneux, Battice, B-4651, BELGIUM

The Concentration of Hydroxyl Groups on Glass Surfaces and Their Effect on the Structure of Silane Deposits

The work described in this paper is to investigate the concentration of hydroxyl groups on glass surfaces by contact angle goniometry (CAG). The density of hydroxyl groups was quantified by measuring the contact angle with water in octane as a function of the water pH. It has been found that a maximum contact angle appeared at the point of zero charge, which has been used to calculate the density of hydroxyl groups on boron-free E-glass and E-glass surfaces. The density of hydroxyl groups was slightly higher on boron-free E-glass surface than that on E-glass surface, which was 2.23 and 2.16 OH nm^-2 respectively. It has also been demonstrated that the surface concentration of hydroxyl groups is not only sensitive to glass formulation, but also the heat treatment history. After heating at 600 ºC, the glass surface concentration of hydroxyl groups was significantly decreased. Re-hydrolysis at humidity of 80 % also had an effect on the surface OH density. It only partially re-hydrolysed the glass surfaces. The structure of a silane deposit on differing surfaces is a function of the hydroxyl group concentration.

Kent Ridge, SINGAPORE 119260

Silane Coupling Agents for Surface-initiated Living Radical Polymerizations

(Abstract not yet available)

Plasma Silanization of Metals, Ceramics and Polymers

Plasma is an effective means to attach functional silanes to a wide variety of materials. Examples of plasma silanization are presented.

Zirconia for Corrosion Resistant Primers

The use of chromium was strongly restricted in the past years and this gave a new impulse to the study of alternative anti-corrosion treatments.

A promising route seems to be the deposition of a thin ceramic layer on the metallic surface by sol-gel process. In this paper are reviewed the most recent results of the use of zirconia primers deposited via sol-gel on 1050, 2024 and 6060 aluminum sheets as protective film for enhancing the adhesion of top-coatings.

Zirconia was prepared by different ways, dependently on the type of precursor used for sol preparation. The first attempt was performed by alkoxide route, which resulted quite critical for an industrial implementation of the method. In order to improve zirconia application, the sols were successively obtained using different oxide precursors. At this regard, stable sols were prepared using both zirconium salts in water and zirconium Nano Building Block (ZrNBBs) in organic monomer. Accordingly, several coated specimens were prepared and characterized in order to establish their behavior with respect that of samples coated with industrial primers.

AFM analysis revealed that covering and structure of the coating were uniform. XPS depth profiling allowed measuring the film thickness, which is in the nanometer range, and that chemical composition was constant through primer thickness.

Corrosion tests demonstrated that zirconia primers showed good performances comparable to chromate and fluoro-titanate layers industrially prepared.

Adhesion of Different Modified Glass Surfaces to a Model Pressure-sensitive Adhesive

Pressure sensitive adhesives (PSA) play an important role as materials in many industrial applications as well as in everyday life. The adhesive performance is depending on the properties of the solid surface that come in contact. Our study aims to investigate the adhesion of a model system based on the triblock copolymer styrene-isoprene-styrene (SIS) and a tackifier resin to various chemically modified solid surfaces. This will help to understand the effect the chemical/physical surface properties at the interface on the adhesion performance. The probe tack method apparatus allows for the recording of the force-distance curve and the microscopic observation of the debonding at the contact surface between glass probe and PSA. Different glass probe surfaces are modified using acid cleaning, base cleaning, microstructured siloxane layer, and other organic coatings. The modified surfaces are probed prior to the mechanical investigation using AFM, optical spectroscopy and ellipsometry to gather information on the surface roughness and morphology. The influence of these treatments on the confined flow behaviour of polystyrene has been shown recently [1]. The adhesion performance of these modified surfaces to our model PSA will be discussed in this work.

[1] E. Bauer, E. Maurer, T. Mehaddene, S. V. Roth, P. Müller-Buschbaum, Macromolecules 39, 5087-5094 (2006)

1) Polymertechnik/Polymerphysik; Technical University of Berlin, Fasanenstraße. 90, D-10623 Berlin, GERMANY

2) Radiation and Polymer Chemistry Lab., Institute of Nuclear Science and Technology Bangladesh Atomic Energy Commission, P. O. Box 3787, Dhaka, BANGLADESH

Role of Amino-Silane on the Mechanical Performance of the Jute-Polycarbonate Composites

The composites of jute fabrics and polycarbonate (PC) were prepared by compression molding. Jute surface was modified with two types of amino-silane coupling agent like g-aminopropyl trimethoxy silane (Z-6011) and N-(b-amino ethyl) g-aminopropyl trimethoxy silane (Z-6020) to improve the interfacial adhesion between jute and PC. The treated and untreated jute surface as well as composites were characterized by X-ray photoelectron spectroscopy (XPS), Fourier-Transform Infrared Spectroscopy (FTIR), Environmental Scanning Electron Microscopy (ESEM) and Differential Scanning Calorimetry (DSC). Between the used two coupling agent, Z-6011 exhibited the better performance.

KEY WORDS: Amino-silane, Composites, Compression Molding, Fabric.

^*Correspondence: Dr. M. Masudul Hassan , E-mail: msdhasan@yahoo.com

1) Universal Technology Corp., 1270 N. Fairfield Rd., Dayton, OH 45432-2600, USA

2) University of Dayton Research Institute, 300 College Park, Dayton, OH 45469-0168

3) Center for Nanoscale Science & Engineering, North Dakota State University, 1805 NDSU Research Park Drive, Fargo, ND 58102

4) Air Force Research Laboratory, Materials and Manufacturing Directorate, Nonmetallic Materials Division, Nonstructural Materials Branch, Coatings Research Group, Wright-Patterson AFB, OH 45433-7750

Phosphonate-Functionalized Sol-Gel Surface Treatments for Aluminum and Magnesium Alloys

The inclusion of pendant phosphonate groups in a sol-gel surface treatment can substantially improve the metal/coating interface through chemical bonding with the metal surface. The phosphonate functional group's strong chemical interaction with the surface metal oxide layer on magnesium and aluminum aerospace alloys makes phosphonate-modified sol-gels attractive materials for developing enhanced protective coatings. A commercially available phosphonate-functionalized organo-silane was used as a precursor for the series of coating materials processed by sol-gel hydrolysis and condensation reactions. The hydrophobic/hydrophilic balance and barrier properties of the coatings were varied through variations in organo-functional silanes co-condensed with the phosphonato-silane. The coatings were deposited on pure aluminum and magnesium, as well as magnesium AZ31B and aluminum 2024-T3 alloys. The corrosion protection properties were evaluated by various methods including constant immersion and electrochemical tests. The surface chemistry within the coating/substrate boundary layer was studied by X-ray photoelectron spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The improved corrosion protection properties of phosphonate-functionalized coatings were explained by the favorable combination of the barrier properties of the organo-silicate matrix along with the strong chemical bonding/adhesion of the phosphonate-groups to the metal substrate. The improvement was most pronounced on the magnesium metal samples. Potential applications of this class of materials for metal surface treatments will be discussed.

1) Department of Engineering Materials, University of Sheffield, Sheffield, S1 3JD, UK

2) European Owens-Corning, Rue de Charneux, Battice, B-4651, BELGIUM

XPS and AFM Study of the Structure of Hydrolysed Aminosilane on E-glass Surfaces

X-ray photoelectron spectroscopy (XPS) has been used to study the interaction of -aminopropyltriethoxysilane (APS) with an E-glass surface. Three components of differing hydrolytic stability and molecular structure in the APS deposit have been confirmed by the study of warm water (50 ºC) and hot water (100 ºC) extractions. Warm water extracted the APS hydrolysed monomers and the oligomers with low molecular weight. Hot water extraction was supposed to remove the loosely chemisorbed silane layer on E-glass surface. Atomic force microscope (AFM) has also been employed in this study. The differences were observed in the AFM images of APS coated E-glass fibres before and after water extractions. A topography of 'hills' or 'valleys' on APS coated E-glass fibre was changed to a topography of 'pores' or 'pits' on hot water extracted E-glass fibre. This also reflected the partial removal of the silane components after water extractions.

1) NIOM - Nordic Institute of Dental Materials, P.O.Box 70, NO-1305 Haslum, NORWAY

2) Institute of Dentistry, Department of Prosthetic Dentistry and Biomaterials Science, University of Turku, Lemminkäisenkatu 2, FI-20520 Turku, FINLAND

*corresponding author: jumatin@utu.fi, JPM@niom.no

The Effect of the Novel Silane System to the Flexural Properties of E-glass Fiber-Reinforced Composite

Objectives: The coupling properties of three functional silanes and their blends with a cross-linker silane in bonding of continuous E-glass fibres to a bis-GMA resin system was evaluated by measuring the flexural properties of the fibre reinforced composite (FRC). Such structures (e.g. crowns, bridges, root canal posts, periodontal splints) are modern dental biomaterials in clinical use.

Methods: E-glass fibres were silanized with three functional silanes: 3-meth-acryloyloxypropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, and 3-acryloyl-oxypropyltrimethoxysilane. The fibres were also silanized with a blend of the functional silanes and 1,2-bis-(triethoxysilyl)ethane. Silanized fibres were embedded into a bis-GMA (bis-phenol-A-glycidylmethacrylate) -based monomer system and photo-polymerized to form test specimens, 2 mm x 2 mm x 25 mm (n=6). The control group was FRCs with the original silanization made by the manufacturer of the fibres. The storage conditions of the specimens were: dry, 30 days and 6 months in water (37 °C). Flexural strength and modulus of the test specimen were measured. Fracture surface imaging was carried out with a scanning electron microscope.

Results: Statistical analysis, ANOVA, showed that the highest flexural strength after water storage for 6 months (399 ± 91 MPa) was obtained for the control sample (the original silanization), and the lowest flexural strength value (309 ± 138 MPa) for the specimens with 3-isocyanatopropyltriethoxysilane. After water storage of 30 days the highest flexural strength (370 ± 63 MPa) was obtained using 3-methacryloyl-oxypropyltrimethoxysilane, and the lowest (203 ± 21 MPa) for 3-isocyanato-propyltriethoxysilane + 1,2-bis-(triethoxysilyl)ethane. For dry storage conditions, the highest strength was found for the control group (465 ± 91 MPa), and the lowest value for 3-acryloyloxypropyltrimethoxysilane (387 ± 68 MPa). Two-way ANOVA showed that the means differed significantly for the storage conditions (p < 0.005), for the silane (p < 0.05) and for storage + silane (p < 0.005).

Significance: After water storage, silanization of E-glass fibres with the cross-linker silane system provided flexural properties for FRC equal to that with the original silanization of fibres.

Investigation of the Surface Effects of Sulfur and Nitrogen Containing Silanes for the Design and Production of Novel Silane Compounds used in Surface Modification

The surface effects of commercially-available sulphur and nitrogen-containing silanes were investigated. The results were used to contribute to the design of organic precursors containing thio-ethers, secondary amides and polyethylene glycols to create hydrophobic and hydrophilic regions within the same organic molecule. The precursors were manufactured and reacted with commercially-available silanes to create new silanes with novel properties for surface modification. Particular attention was paid to organic precursor/silane combinations that enabled the production of new silanes in 'one pot' reactions.

Aminosilane treated glass substrates for DNA microarrays

DNA microarrays are miniature gene-based sensors immobilized on coated glass microscope slides. The surface properties and structure of mono-, di-, and tri- aminosilane treated glass surfaces were investigated for DNA microarray applications. An optimized dip coating process was demonstrated to produce roughly silane monolayer coverage on the glass surface. The surface charge measurements indicated that aminosilanization converts the glass surface from negative to positive potentials at neutral pH values. Higher positive streaming potential was observed for tri- compared with mono- and di- amino silane treated glass surfaces. For all aminosilane treated glass samples, the high-resolution N 1s XPS spectra indicated a preferential orientation of the protonated amino-groups towards the glass surface whereas the free amino groups were protruding outward. This study aimed to obtain uniform, reproducibly thin, strongly adhering, internally cross-linked, and high positively charged aminosilane coated glass surfaces for the attachment of DNA fragments used in microarraying experiments.

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

2) Department of Chemistry, The University of Akron, Akron, OH

Solid State NMR Studies of Surface Adsorbed Molecules on Inorganic Pigments

Phosphorus-31 and Carbon-13 solid state NMR techniques were used to study the structure and dynamics of surface-adsorbed n-octylphosphonic acid (NOPA) on surface-treated inorganic pigments. The chemical shifts and the molecular mobilities of the surface-adsorbed species were observed to vary with the NOPA surface concentration, and with the nature of the inorganic pigment. The hydrophobic/lipohilic properties of these surface-treated pigments will be discussed together with the relationships between the structure and the dynamics of the chemisorbed surface species.

Cincinnati, OH 45221-0012

Novel Chromate-Free Silane-Containing Superprimer Technology

By the use of superprimer technology the chromate in the conversion coating and the primer as well as the volatile organic compounds of the primer can be eliminated. The superprimer, which is based on water-dispersed resins, cross-linkers and silanes, is applied onto the substrate directly after alkaline cleaning. Because of the organofunctional silane contained in the superprimer, its adhesion to the substrate is maintained even without a pretreatment layer. The corrosion resistance of the primer is assured by adding chromate-free corrosion-inhibiting pigments into the formulation.

In this presentation we will discuss epoxy-acrylate, novolac-polyurethane and epoxy-based systems for use in aerospace applications and automotive coatings. The corrosion protection performance of these primers was evaluated by electrochemical methods and performance tests. The reactions occurring in the superprimer dispersion have been analyzed by NMR and the resulting coatings with surface analytical techniques. The characterization methods have provided information on the formation of the coatings and the mechanism by which the coatings protect the metal substrates. It will also be shown that 2000 hours of salt spray resistance has been obtained with the primers both on aluminum and HDG steel.

The Role of Silane Coupling Agents in Metal-Protective Films

Silane coupling agents are know to improve the anti corrosion properties of many metals. Electrochemical impedance measurements show that the silanes improve the barrier properties of both neat films and silane-laced polymer coatings. This presentation focuses on the morphological characteristics and water-response of silane films determined by x-ray and neutron reflectivity. With few exception thin films of pure silanes, mixed silanes and silane-laced epoxy absorb water and swell. The effect of silane type, film thickness, substrate and curing temperature are summarized. In addition, water absorption kinetics and salt penetration are examined. Of particular interest are the properties of mixed films composed of two bridged silanes neither of which is particularly protective. The improved protective behavior is related to the impact of one of the silanes on the cure chemistry of the other.

Characterization of Hydrothermal Degradation of Organosilane Films on Silicon Wafer by Neutron Reflectivity

The hygrothermal degradations of Bis[3-(triethoxysilyl)propyl]tetrasulfide (bis-sulfur silane), bis[3-(trimethoxysilyl)propyl]amine (bis-amino silane) and the mixture of bis-sulfur and bis-amino (weight ratio 3:1) films were studied though neutron reflectivity (NR). Numerous physical and chemical factors are involved in the hygrothermal stability of silane films. Type of bridging groups, thickness of the films and the curing temperature are believed to be the key factors which determine the hygrothermal stability of silane films. By comparing the NR data of as-prepaired dry films and the re- dryed films after 10 and 24 hours' exposure to 80°C liquid water we figure out the change of the films. The different bridging groups of bis-sulfur and bis-amino have different water barrier properties which leads to different hygrothermal degradation behaviors. Bis-sulfur silane shows hydrophobic properties, bis-amino silane is hydrophilic instead. The SLD profiles indicate that bis-amino films show monotonic degradation no matter how thick the films are, whereas for bis-sulfur films, thickness is a key factor, when the thickness is below 200 Å, bis-sulfur films reconstruction; on the other hand, thicker films (above 1000 Å) are robust. Elevated curing temperature (180°C) gives improved hygrothermal stability to bis-sulfur films because bis-sulfur films become more condensed at a higher curing temperature (180°C). For mixed silane films, because of the existent of bis-amino silane, degredation takes place during 80°C water conditioning. The degradation rate is related to the crosslink density profile in the film vertical to the substrate surface. Higher crosslink density regions have lower degradation rate.

1) Department of Chemistry, University of Liverpool, UK

2) Defence Science and Technology Laboratory, Salisbury, UK

Spectroscopic Probing of Model Silane Coupling Compounds at Model Surfaces

The use of adhesive bonding in the manufacture of engineering structures can provide numerous benefits in comparison to more traditional joining techniques. Unfortunately however, a lack of confidence in the ability of bonded joints to withstand the environmental conditions typically encountered in many applications has limited their widespread use. Numerous studies have shown that the precise nature of environmentally driven failure is frequently associated with the substrate-adhesive interphase, thus showing this region to be the primary zone of weakness. Accordingly, in order to promote long-term durability, surface treatment of the substrate prior to bonding has generally been regarded as a vital component of the manufacturing process.

With aluminium alloys substantial evidence has indicated that the most durable bonds are provided by surface treatments comprising hexavalent Cr compounds. However, in recent years there has been pressure to remove such substances from bonding processes. This has resulted in attempts at developing alternative, less hazardous treatments. To this end organosilanes have been considered as the basis of alternative treatments, with some studies demonstrating at least equivalence between silanes and anodising techniques.

With glycidyl functional silanes conventional wisdom dictates that terminal glycidyl groups will be free to react with similar groups within a contacting adhesive. However little if any direct experimental evidence has been presented to confirm this view with one of the most commonly evaluated silanes, -GPS. Indeed, with some silane types, there exists considerable evidence to suggest that the organofunctional part of the molecule can interact with the substrate surface, thus minimising any potential for interaction with an adhesive material. To investigate the extent to which a molecule such as -GPS can behave in a similar way, we have employed experimental techniques such as RAIRS to probe interactions between glycidyl groups on model compounds (i.e. epoxyhexane and glycidylisopropyl ether) with model oxide surfaces.

In this paper the experimental techniques employed to probe such interactions and the results obtained are considered. The results reveal that, for both model compounds, under certain conditions, they can interact with a model substrate surface via their glycidyl groups. The extent to which this behaviour occurs with -GPS will also be discussed.

Degussa GmbH, Rheinfelden, GERMANY

VOC Free Multifunctional Organosilane Systems - A New Modular Concept for Water Borne Sol-Gel Coatings

The basic chemical reactions behind the sol-gel process, hydrolysis and condensation of alkoxysilanes, are well known. In the 1980ies hybrid sol-gel materials were developed, which opened a large variety of potential new applications. Key ingredients to this organically modified sol-gel process are organofunctional alkoxysilanes. Due to the sensitivity of alkoxysilanes against hydrolysis and condensation, solvent-free, water-borne and storage-stable sol-gel systems pose a challenge. Water borne sol-gel systems as stabilized silanol-group bearing oligosiloxanes have been commercially available since the 1990's. An important improvement of this technology is the development of a modular concept consisting of different multifunctional sol-gel systems. As of such coatings can be easily formulated which exhibit customized properties. The presented modular system comprises a basic sol-gel component, a component for pH optimization and two further components for improved weather resistance, hydro- and oleophobic surface properties. Potential applications range from easy-to-clean top coats to primer systems for anti-corrosion coatings.

Photocatalytic Titania Derived by Sol-Gel-Technique for Textile Application

(Abstract not yet available)

The Use of Supercritical CO₂ for Conducting Silane Reactions on Surfaces

(Abstract not yet available)

Surface Modification of Wood by Alkoxysilane Sol-gel Deposition to Create Anti-mold and Anti-fungal Characteristics

Hybrid inorganic/organic thin films deposited on wood substrates have been shown to lower the rate of moisture sorption of the wood. Deposition of such thin films can be accomplished by sol-gel deposition or by plasma enhanced chemical vapor deposition. This paper describes in situ sol-gel deposition of hybrid inorganic/organic thin films on wood substrates using methyltrimethoxysilane (MTMOS) as precursor and trifluoroacetic acid as catalyst. The surface chemistry of wood specimens coated with these thin films was characterized by Fourier Transform Infrared Spectroscopy (FTIR) and energy dispersive X-ray analysis (EDXA). The surface morphology was characterized by scanning electron microscopy (SEM).

The effect of the sol-gel deposited thin films on preventing mold growth and fungal colonization on wood surfaces was investigated. It was found that these thin films inhibited both growth of mixed mold spores and white rot (Trametes versicolor) and brown rot (Gloeophyllum trabeum) fungi on the wood surfaces. It is proposed that moisture resistance properties of the sol-gel thin film deposit may be the single most important contributor to the anti-mold and anti-fungal properties of the sol-gel treated wood surfaces.

Overview of Potential of Silanes to Protect Metal Against Corrosion Phenomena

(Abstract not yet available)

Characterization of Epoxy-Silane Films by Combined Scattering Techniques

Bis-silanes with the general formula of (RO)3Si(CH2)3-R'-(CH2)3Si(OR)3, where OR represents an alkoxy group and R is an organic functionality, show excellent performance as coupling agents in anti-corrosion films; Epoxy resin also has superior chemical and corrosion resistance as well as outstanding mechanical toughness. A combination of silane and epoxy is an excellent coating system with high hardness based on the mixture of epoxy (EPI- REZ™ 5003-W-55) and bis-sulfur silane (R' = S4). This one step coating provides excellent anti-corrosion protection of metals substrates. The goal of this study is to fully understand this two component system. Morphology, thickness, chemical composition, water barrier properties, response to organic solvents as well as hydrothermal degradation were investigated using x-ray and neutron reflectivity; Phase separation was studied by small angle scattering of neutron and X-ray scattering. Minority phase distribution profile was elucidated by using GISAXS.

Acknowledgment: This research is supported by SERDP.

Zinc Phosphate as an Effective Anticorrosion Pigment in Silane-based Waterborne Primers

Chromates are widely used as corrosion inhibitors and are effective both in solvent-based and waterborne metal primers. Zinc phosphate is a conventional corrosion inhibitor but is not found to be a good inhibitor in the conventional primers. However, in our study zinc phosphate makes a very effective inhibitor in the silane-based waterborne primers in the presence of silane. The study began with screening from a wide variety of inhibitors. Zinc phosphate (ZP) was found an overall best pigment for our superprimers, a series of one-step, low-VOC, and chromate-free waterborne primers. Epoxy/acrylate-based superprimer containing ~20 wt% ZP performed well on aluminum and steel alloys and novolac epoxy-based superprimer containing ~15 wt% ZP works well specifically on aluminum alloys.

The protection mechanism of zinc phosphate in the two superprimers is studied. SEM/EDS study shows expoxy/acrylate-based superprimer was found to have a stratified double layer structure, with a less-penetrable hydrophobic layer on the top and a hydrophilic layer accommodating the inhibitors underneath, while novelac epoxy-based superprimer shows a relatively uniform structure. The presence of silane was found to be critical for the adhesion and anti-corrosion performance of the primer.

Plasma Polymer Coatings in Corrosion Protection of Metallic Materials

This paper reviews recent studies conducted on plasma polymer coatings applied to metal substrates for improved corrosion protection. Low-temperature plasma polymerization is a promising pretreatment technique for metallic materials to create environmentally friendly coating systems for corrosion protection. As an ultra-thin interfacial layer, the pinhole-free plasma polymer films can be used as interface adhesion promoter to enhance the adhesion of organic coatings to metallic substrates. Recent research results clearly demonstrated that plasma interface engineered coating systems had excellent corrosion protections to various metallic materials including steels and aluminum alloys. However, knowledge on how the unique physical and chemical properties of the plasma polymer films relate to the corrosion performance of the coated metals is still lacking and is of great interest. To further understand the role of these plasma thin films in corrosion protection, the pretreatment effects of plasma treatment and plasma polymer coatings on alclad Al alloy 2024-T3 [2A] were investigated using electrochemical characterization techniques, including cyclic polarization (CP) and electrochemical impedance spectroscopy (EIS). The experimental results illustrated that, due to their thin thickness, the ultra-thin plasma polymer films without subsequent organic coatings provided very limited corrosion resistance. The main contribution of these plasma polymer films to the excellent corrosion protection of the Al alloy was laid in their enhanced water-insensitive interface adhesion, or tenacious wet adhesion, of the resulted plasma interface engineered coating systems of Al/plasma polymer/organic coatings.

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