Organofunctional Silanes Research Articles

Selective surface modification of lithographic silicon oxide nanostructures by organofunctional silanes

This study investigates the controlled chemical functionalization of silicon oxide nanostructures prepared by AFM-anodization lithography of alkyl-terminated silicon. Different conditions for the growth of covalently bound mono-, multi- or submonolayers of distinctively functional silane molecules on nanostructures have been identified by AFM-height investigations. Routes for the preparation of methyl- or amino-terminated structures or silicon surfaces are presented and discussed. The formation of silane monolayers on nanoscopic silicon oxide nanostructures was found to be much more sensitive towards ambient humidity than, e.g., the silanization of larger OH-terminated silica surfaces. Amino-functionalized nanostructures have been successfully modified by the covalent binding of functional fluorescein dye molecules. Upon excitation, the dye-functionalized structures show only weak fluorescence, which may be an indication of a relatively low surface coverage of the dye molecules on length scale that is not accessible by standard AFM measurements.

An Extremely Simple and Effective Strategy to Tailor the Surface Performance of Inorganic Substrates by Two New Photochemical Reactions

This article reports on a new sequential strategy to fabricate monolayer functional organosilane films on inorganic substrate surfaces, and subsequently, to pattern them by two new photochemical reactions. (1) By using UV light (254 nm) plus dimethylformamide (DMF), a functional silane monolayer film could be fabricated quickly (within minutes) under ambient temperature. (2) The organic groups of the formed films became decomposed in a few minutes with UV irradiation coupled with a water solution of ammonium persulfate (APS). (3) When two photochemical reactions were sequentially combined, a high-quality patterned functional surface could be obtained thanks to the photomask.

Degradation of Transparent Conductive Oxides, and the Beneficial Role of Interfacial Layers

ABSTRACTThe lifetime performance and reliability of photovoltaic (PV) modules are critical factors in their successful deployment. Interfaces in thin film PV, such as that between the transparent conductive oxide (TCO) electrode and the absorber layer, are frequently an avenue for degradation; this degradation is promoted by exposure to environmental stressors such as irradiance, heat and humidity. Understanding and suppressing TCO degradation is critical to improving stability and extending the lifetime. Commercially available indium tin oxide (ITO), fluorine doped tin oxide (FTO) and aluminum doped zinc oxide (AZO) were exposed to damp heat (DH), ASTM G154 cycle 4, and modified ASTM G154 for up to 1000 hours. The TCOs’ electrical and optical properties and surface energies were determined before and after each exposure and their relative degradation classified. Data demonstrate that AZO degraded most rapidly of all the TCOs, whereas ITO and FTO degraded at lower to non-quantifiable rates. One approach to suppress degradation could be to use interfacial layers (IFLs), including organofunctional silane layers, to modify the TCO. We modified the TCO surfaces using a variety of organofunctional silanes, and determined a range of surface energies could be obtained without affecting the electrical and optical properties of the TCO. Degradation studies of TCOs with a silane layer were also conducted. We found that an inhomogeneous silane layer was able to delay the resistivity increase for ITO in DH.

Electrochemical Synthesis of Functional Organosilanes II: Direct Electrochemical Formation of Si-C Bonds

Electroreductive Si-C bond formation was used for the formation of organofunctional silanes of the general formula HMe2Si-R-Y and MeOMe2Si-R-Y (R = alkylene, arylene; Y = H, MeO, Me2N, t-BuMe2SiO). Employing constant current conditions, different organic halides R-X (R = alkylene, arylene, X = Cl, Br) were electrolyzed in the presence of Me2Si(OMe)2 and HMe2SiCl, respectively. All electrolyses were carried out in an undivided cell and with a THF/LiCl (MgCl2) electrolyte. Although both salts are suitable supporting electrolytes, the highest conductivity was obtained with a mixture of LiCl/MgCl2 = 2/1. It was shown that the reaction proceeds smoothly at current densities between 0.25 and 35 mA cm−2. Cooling of the electrolysis cell can be omitted.

Low-Temperature Processing of Titanium Oxide Nanoparticles Photoanodes for Dye-Sensitized Solar Cells

Using the low-temperature processing of different organofunctional silanes like TEOS, GPTS, and MPTS to incorporate within TiO2network, dye-sensitized solar cells (DSCs) processed at low temperatures were obtained. The UV-cured MPTS-modified layer exhibited better performance over the TEOS and GPTS, where better mechanical stable layer is achieved in addition to better interconnection between the TiO2nanoparticles. TheJ-Vcharacteristics of the DSC composed of silane-based layer showed that the improved cell performance was due to the high photocurrent density accompanied with more dye adsorption and higher charge injection from TiO2to FTO substrate resulting from the formation of an ohmic contact with the substrate. The highest conversion efficiency attained for MPTS-TiO2layer cured with UV and followed by heating at 300∘C was3.75±0.07%, which is 2.8 times better than the GPTS-based layer.

Controlled tin catalyzed hydrolysis of 3-acryloxypropyltrimethoxysilane with mono- and multi-functional mercaptans

Mechanistic investigations were initiated to further our understanding of the reaction pathways for hydrolysis and condensation of organofunctional alkoxysilanes in organic media. Previous work has shown that addition of mercaptans to solutions that contain dibutyltin dilaurate (DBTDL), which functions as a catalyst, and 3-acryloxypropyltrimethoxysilane can greatly reduce the rate of silane hydrolysis and condensation. Gas chromatography/mass spectrometry (GC/MS) hydrolysis studies were carried out to understand how mercaptan structure and concentration affected the relative hydrolysis rate of the acrylate silane in solution. Detailed nuclear magnetic resonance spectroscopy (NMR) and electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry (MS) were carried out on simple mixtures of DBTDL and select mercaptans, and with varying mercaptan concentrations, to elucidate which significant tin complexes can form. These studies showed that mercaptans readily undergo ligand exchange reactions with the labile carboxylate groups of DBTDL and that an excess of mercaptans reduced the amount of proposed active catalyst species. It was found that an excess of mercaptan functional group was necessary to prevent significant and rapid hydrolysis of the organofunctional silane in organic media. A minimum of 1:4 DBTDL carboxylate group:mercaptan functional group was required for most mercaptans examined. A tetramercaptan, pentaerythritol tetrakis(3-mercaptopropionate), was shown to be effective in deactivating the DBTDL catalyst, even at relatively low concentrations of tetramercaptan. The findings in this work provide further support for the proposed mechanism for catalyzed hydrolysis and condensation. The tin metal was determined to be predominately 4-fold coordinated in the various tin mercaptide compounds studied. Evidence for transient tin hydroxide reactive intermediates was detected using mass spectrometry, as upon the addition of water, oligomeric condensation products were observed. However, the lifetime of these reactive intermediates precluded their direct observation by either mass spectrometry or NMR. Oligomeric and cyclic tin mercaptide species were shown to form when multifunctional mercaptans were combined with DBTDL in solution.

Effects of Silanes Alone and Their Blends with HEMA on Resin–Titanium Bonding

Two organofunctional silane coupling agents alone and two silane blend systems with HEMA were evaluated in vitro as adhesion promoters for bonding bis-GMA resin to a silica-coated titanium surface. The silanes were applied onto tribochemically silica-coated titanium surfaces. Experimental bis-GMA resin stubs were applied and photo-polymerized onto titanium. The specimens were subjected to three different conditions: (1) dry storage for 24 h, (2) storage in de-ionized water at 37°C for six months and (3) alternating storage in de-ionized water at 37°C and thermocycling (6000 cycles, 5–55°C) for 6 months. Shear bond strengths of the resin to titanium were measured using a universal testing machine. Surface examination was made with a scanning electron microscope (SEM) after the bond strength test. Highest shear bond strength was obtained with 3-acryloxypropyltrimethoxysilane stored in dry condition (20.2 ± 3.2MPa), and the lowest value was obtained with 3-methacryloxypropyltrimethoxysilane (ESPE Sil) in alternating water storage and thermocycling condition (1.4 ± 0.6 MPa). The type of storage condition affected significantly the shear bond strength (p < 0.05). The shear bond strength obtained from dry storage was the highest, while the shear bond strength obtained from alternating water storage and thermocycling condition was the lowest. Interfacial failure was the main failure mode (87.2%) followed by mixed failure (9.4%) and cohesive failure (3.4%). The addition of 0.5 vol%. HEMA into silane primers did not improve the shear bond strength between the experimental resin and silica-coated titanium.

Graphite oxide as an intumescent flame retardant for polystyrene

In this work the possibility to apply graphite oxide (GO) as an intumescent flame retardant added in situ during suspension polymerization of styrene was studied. Synthesis of GO was carried out starting from natural flake graphites with different carbon content and particle size (between 45 and 500 žm). The obtained products were examined using elemental and scanning electron microscopy (SEM) analysis, Fourier transform infrared spectroscopy (FT-IR) as well as X-ray powder diffractometry (XRD). Thermal stability and expansion properties of GO were also investigated. It was stated that with an increase in particle size GO exhibited a lower degree of oxidation while the temperature of maximum decomposition rate increased. The highest expansion volume at 600 °C was observed for GO prepared from graphite with large-sized plates (300 and 500 žm). In order to prevent the dispersion of hydrophilic GO in an aqueous phase during the polymerization of styrene, GO was modified with organofunctional silane. Polystyrene with added GO (15 wt. %) reached HF-1 rating in the UL 94 horizontal burning test, however it failed to pass the required vertical flame test. The modification with melamine-formaldehyde resin (MF) resulted in an increase of GO thermal stability. Polystyrene with 15 wt. % of GO-MF additive obtained maximum ratings HF-1 and V-O in the UL 94 flame test. An attention should be paid to safe handling of GO which, although stable at ambient conditions, may undergo highly exothermic decomposition, e.g. when subjected to mechanical impact at moderately elevated temperature.

Shear bond strength between resin and zirconia with two different silane blends

Objective. To study in vitro the effect of two cross-linking silanes, bis-1,2-(triethoxysilyl)ethane and bis[3-(trimethoxysilyl)propyl]amine, blended with an organofunctional silane coupling agent, (3-acryloxypropyl)trimethoxysilane, on the shear bond strength between resin-composite cement and silicatized zirconia after dry storage and thermocycling. Materials and methods. Six tested groups of 90 samples of yttria stabilized zirconia were used for sample preparation. The surfaces of the zirconia were silica-coated. 3M ESPE Sil silane was used as a control. Solutions of (3-acryloxypropyl)trimethoxysilane with cross-linking silanes bis-1,2-(triethoxysilyl)ethane and bis[3-(trimethoxysilyl)propyl]amine were applied onto the surface of silicatized zirconia. 3M ESPE RelyX resin-composite cement was bonded onto the silicatized and silanized zirconia surface and light-cured. Three groups were tested under dry condition and the other three groups were tested for thermocycling. The shear bond strength was measured using a materials testing instrument. Group mean shear bond strengths were analysed by ANOVA at a significant level of p < 0.05. The zirconia surface composition was analysed by X-ray Photoelectron Spectroscopy. Results. The highest shear bond strength was 11.8 ± 3.5 MPa for (3-acryloxypropyl)trimethoxysilane blended with bis-1,2-(triethoxysilyl)ethane (dry storage). There was a significant difference between mean shear bond strength values for (3-acryloxypropyl)trimethoxysilane blended with two cross-linking silanes, bis-1,2-(triethoxysilyl)ethane and bis[3-(trimethoxysilyl)propyl]amine, after thermocycling (p < 3.9 × 10−8). Various surface treatments of zirconia influenced the surface roughness (p < 4.6 × 10−6). The chemical composition analysis showed there was an increase in silicon and oxygen content after sandblasting. Conclusions. The results suggest that the combination of functional (3-acryloxypropyl)trimethoxysilane with cross-linking bis[3-(trimethoxysilyl)propyl]amine showed superior hydrolytic stability than with bis-1,2-(triethoxysilyl)ethane.

Surface decoration of carbon nanosheets with amino-functionalized organosilica nanoparticles

Carbonaceous nanosheets decorated with amino-functionalized organosilica nanoparticles have been synthesized by a direct pyrolysis of betaine at 400°C in air, followed by a simple surface treatment with ([3-(2-aminoethylamino) propyl]trimethoxysilane under reflux conditions. Both pristine and organosilica modified carbon nanosheets (OMCNs), were characterized by Fourier-transform infrared (FTIR), Raman, and electron paramagnetic resonance (EPR) spectroscopies, transmission electron microscopy and thermal analysis methods. The experimental data reveal a dramatic increase in the number of radical centers on the surface of the developed OMCN hybrid. The organosilica nanoparticles, ranging in size between 3 and 15nm, are spherical and homogenously anchored on the surface of carbon nanosheets. The formation of COSi bridges between carbon sheets and the organosilica nanoparticles has been supported by FTIR and EPR. These nanoparticles are bound to the nanosheet surface together with individual functional organosilane groups at a spacing of about 4Å distance. The final hybrid is the complex nanosystem composed of 2D carbon nanosheets, spherical organosilica nanoparticles and immobilized amino organosilane molecules.

Long-Chain Organofunctional Silanes: Synthesis and Surface Derivatization

A series of organofunctional long-chain alkylfunctional silanes have been synthesized for the purpose of derivatization of micro- and nanoparticles and generation of molecular monolayers and films on the substrates. 11-bromoundecylsilane and 1, 10-disiladecane are evaluated to interact with a variety of clean hydrogenated metal and metalloid including titanium, silicon and silicon dioxide. The surface of those treated substrates has been analyzed by X-ray photoelectron spectroscopy (XPS) and reflection-absorption infrared spectroscopy (RAIRS). Our preliminary results indicate that self-assembled monolayer has been well formed on titanium metal and silicon wafer, minimally on silicon-dioxide. The discussion of experimental results is also provided.

Effects of dynamic aging (hydrolysis and condensation) behaviour of organofunctional silanes in the aqeous solution on their penetrability into the cells walls of wood

The hydrolysis and condensation (aging) dynamics of aqueous solutions of (3-glycidyloxypropyl)trimethoxysilane (GPS), vinyltrimethoxysilane (VTS), and (3-aminopropyl)trimethoxysilane (APS) and their penetrability into the cell walls of European spruce (Picea abies) wood were studied to investigate the feasibility of using silanes as a cell wall modifying agent for wood and other lignocellulosic materials. The size distribution of silane particles in aqueous solution was determined using a dynamic light scattering apparatus and increased with the aging time, but at different rates depending on the silane monomer. With increasing aging time, the treated wood exhibited decreased cell wall bulking (swelling), and the water vapour sorption behaviour was less affected by treatments when compared with unmodified wood; SEM-EDX analysis revealed that there was a reduced amount of silane in the cell walls with increased aging time. These findings demonstrate the reduced accessibility of silane to cell walls following aging.

Understanding the silylation reaction of multi-walled carbon nanotubes

Functional organosilanes were appended, in aprotic and anhydrous conditions, onto multi-walled carbon nanotubes (MWCNTs) previously submitted to three different oxidative treatments: acid, acid with subsequent thermal treatment at 400 °C and 5% O 2/N 2 treatment at 500 °C. The materials were characterised by X-ray photoelectron spectroscopy, elemental analysis, temperature programmed desorption, Fourier transform infrared spectroscopy, thermogravimetry, nitrogen adsorption isotherms at −196 °C and scanning electron microscopy. The techniques provided a correlation between the type and oxygen contents present in the oxidised MWCNTs and the silylation reaction efficiency, leading to a comprehensive overview of the reaction mechanism and materials structure/composition. The highest silylation reaction efficiencies were achieved with the aminosilane in all the oxidised materials and with mercaptosilane in the acid oxidised MWCNTs with nearly 4% Si insertion, whereas for the other organosilanes values lower than 2% were observed. The silylation mechanism was found to proceed through reaction of the alkoxy moieties from the organosilane with phenol surface groups from the MWCNTs; in the case of aminosilane for all MWCNTs and mercaptosilane in acid oxidised MWCNTs, it also occurred by reaction with the carbonyl surface groups. Furthermore, for these latter materials a polymerisation side-reaction was proposed as a parallel functionalisation pathway.

A composite coating for corrosion protection of AM60B magnesium alloy

Oxide films have been produced on AM60B magnesium alloy by micro-arc anodic oxidation in an environmentally friendly alkaline solution, with and without addition of nanoparticles (TiO2, ZrO2 and Al2O3). Because of the anodic oxide porosity, inherent in the sparking process, organo-functional silanes top coat has been applied to seal pores and cracks, and achieve an efficient protective coating system. The surface and cross-section morphology of samples were analyzed by Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS). Scratch tests were performed for evaluating the adhesion strength and scratch hardness of the anodic oxides to the AM60B substrate. The corrosion resistance of both anodic oxides and oxide/silane composite coatings was evaluated in 0.6M NaCl solution using potentiodynamic polarization tests. The addition of nanoparticles to the anodizing solution doesn't affect significantly the corrosion resistance in comparison with anodic oxides produced in nanoparticles free solutions. Conversely, the adhesion strength and scratch hardness of the anodic oxides to the substrate is quite scattered, and it is higher for the samples produced in ZrO2 and in Al2O3 rich solutions. For this reason specimens anodized in ZrO2 and Al2O3 containing solutions were chosen for silane deposition. Two silanes were used, namely octyltrimethoxysilane (OSi) and 1, 2-bis [triethoxysilyl] ethane (BTSE). The anodizing treatment carried out in oxides nanoparticles containing solutions (ZrO2 or Al2O3), followed by a silane top coat treatment performed using OSi precursor, is an interesting way, suitable for industrial applications, to synthesize adherent corrosion resistant coatings on magnesium alloy AM60B in a short process time.

Synthesis of linear and branched oligodialkylalkylhydrosiloxanes

New linear and branched oligodialkylalkylhydrosiloxanes were prepared by hydrolytic cocondensation of various functional organosilanes with diethyl(dimethyl-)dichlorosilane, ethylhydro-(methylhydro-) dichlorosilane, and trimethylchlorosilane, followed by catalytic rearrangement in the presence of an electrophilic catalyst. The products are of interest as hydrophobizing agents and starting compounds for replacement of hydrogen atoms at silicon by other substituents.

Glucose diffusivity and porosity in silica hydrogel based on organofunctional silanes

The silica hydrogels prepared at physiological conditions were characterized with respect to the glucose diffusion properties and the porosity by employing various approaches. A diffusion coefficient of glucose in silica hydrogel in the range of 2 × 10 −10 m 2 s −1 was determined by two complementary techniques based on the glucose ingress and egress, respectively. The confocal laser scanning microscopy in a time-lapse imaging mode was employed to measure the ingress of fluorescently labeled glucose analogue inside the hydrogel. In addition, a method for direct glucose release from the hydrogel was established. The simple diffusion model based on the Fickian diffusion and Ritger–Peppas theory were employed for evaluation of diffusion coefficients, respectively. The BET analysis and permeation of fluorescently labeled dextrans of various molecular weights were used to characterize the porosity of silica hydrogel. The radius of pores accessible for diffusion of dextran molecules in prepared silica hydrogel ranges between 1 and 6 nm.

Effects of Different Silane Coupling Agent Monomers on Flexural Strength of an Experimental Filled Resin Composite

The hydrolytic stability of various silane combinations and their effects on biomechanical properties and water sorption of an experimental dental composite made of bis-GMA and TEGDMA and silane-treated fillers were evaluated. Four silane coupling agents and their blends with a cross-linker silane were used as coupling agents for the 0.7-μm BaSiO3 fillers. The silanization was carried out in toluene containing 1% (v/v) of one of the four following organofunctional silane coupling agents: 3-acryloxypropyltrimethoxysilane, 3methacryloxypropyltrimethoxysilane, 3-styrylethyltrimethoxysilane and 3-isocyanatopropyltriethoxysilane. Blends of these functional silanes with 1% (v/v) of a cross-linker silane, 1,2- bis -(triethoxysilyl)ethane were also used for silanization. Composites were prepared by mixing 5.00 g Ba-glass filler with 2.00 g of a resin mixture consisting of bis-GMA (58.8 wt%) and TEGDMA (39.2 wt%) in a high-speed mixer. Threepoint bending test specimens (2.0 mm × 2.0 mm × 25.0 mm) were fabricated (n= 8) in a mould and photo-polymerized. The degree of conversion was measured with FT-IR. Biomechanical testing was carried out according to the ISO 10477 standard. Specimens were tested (flexural strength) after 30 days of water storage (37° C, distilled water). Water sorption and solubility (in wt%) were also measured on 1, 2, 3, 5, 7, 14, 21 and 30 days in water storage. Statistical analysis with ANOVA showed that the highest flexural strength was obtained when 3-acryloxypropyltrimethoxysilane + 1,2- bis -(triethoxysilyl)ethane (100.5 MPa; SD, 25.7 MPa) was used in the silanization step, and the lowest was obtained when 3isocyanatopropyltriethoxysilane + 1,2- bis-(triethoxysilyl)ethane (28.9 MPa; SD, 8.8 MPa) was used. The three-point bending strength was significantly affected by the functionality of the main silane tested (p< 0.05), but not by the addition of the cross-linker silane ( p> 0.05). The composite that had been silanized with 3-isocyanatopropyltriethoxysilane had the greatest amount of water uptake (1.75%), and the composite silanized with 3-methacryloxypropyltrimethoxysilane + 1,2- bis-(triethoxysilyl)ethane had the least (1.08%). In conclusion, selection of the functional silane monomer can be a significant factor in developing filled resin composites in dentistry.

In situ modification of cellulose paper with amino groups for catalytic applications

Amino groups were successfully introduced to cellulose paper using a silane coupling technique, through the condensation reaction between Si–OH of the organofunctional silane coupling agent and C–OH of cellulose. The as-prepared paper material, denoted amine-modified paper, had excellent handling convenience and some degree of hydrophobicity, indicating that the silane coupling treatment enhances the physical strength and the hydrophobicity of cellulose paper. In the batch process of the Knoevenagel condensation reaction, the amine-modified paper demonstrated high catalytic efficiency and reusability, suggesting that the amino groups introduced to the cellulose paper can act as an efficient base catalyst. In addition, the porous structure of the paper allowed successful use in a flow process. Thus, cellulose paper modified with amino groups is a promising material for practical use in catalytic and other applications, and the silane coupling technique has great potential to develop an array of practical new functional paper materials.

Experimental Novel Silane System in Adhesion Promotion between Dental Resin and Pretreated Titanium. Part II: Effect of Long-Term Water Storage

In this study we have assessed the effect of long-term water storage at 37oC on silane-aided adhesion promotion. Five experimental silane blends were evaluated as adhesion-promoters. First, five functional organosilane monomers (silicon esters), 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, tetrakis-(2-methacryloxyethoxy)silane and bis-[3-(triethoxysilyl)propyl]tetrasulfide, were diluted to 1% (v/v) in 95% ethanol and blended with a non-functional cross-linking silane, bis-1,2-(triethoxysilyl)ethane (1%). A commercially available pre-activated silane product was used as the control. After activation by hydrolysis, each primer blend was applied to silica-coated Ti coupons. Stubs of experimental bis-phenol-A-diglycidyldimethacrylate (bis-GMA)-based resin were bonded by photo-polymerization onto the pretreated Ti coupons. Half of the specimens were stored in deionized water for 6 months and half for 12 months. The primer containing 3-acryloxypropyltrimethoxysilane and bis-1,2-(triethoxysilyl)ethane produced significantly higher shear bond strengths than the control silane and other experimental silane primers after both periods of storage.

Nanopatterning from the Gas Phase: High Resolution Soft Lithographic Patterning of Organosilane Thin Films

A general methodology for nanopatterning organosilane thin films directly from vapor phase precursors is presented. Aminosilane line patterns with a width of approximately 200 nm in an area of 1 cm(2) were fabricated on silicon substrates by diffusion of aminosilane vapor through the open channels of PDMS stamps bonded to a substrate. The patterned thin films were characterized by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Patterns were initially formed at the three-phase boundary lines between substrate, PDMS mold, and vapor by exploiting the fact that vapors condense preferentially in geometrically restricted areas with a concave shape compared to flat surfaces. The lateral resolution of the formed patterns is about 1 order of magnitude smaller than the feature sizes of the PDMS stamp. Prolonged exposure to the precursor vapor resulted in micrometer-sized patterns with similar features and dimensions as the stamp. This methodology provides an easy and low cost parallel fabrication route of functional organosilane nanoscale patterns of arbitrary shape and composition from micrometer-size patterned stamps.