Topographical observation of silane-treated inorganic surface using atomic force microscopy

The topography of the silane-treated layer on an inorganic surface was observed using an atomic force microscope. For this purpose, the cleaved mica plate was treated with some silane coupling agent at varying conditions. The silanes having aminopropyl or methacryloxypropyl group as organofunctional groups with di- or trialkoxyl structures were used. Three different solvents for silane solution — 2-propanol, 2-propanol/water mixture and water — were used. The pH of the aqueous solution was controlled. As a result, the most suitable solvent and pH in order to obtain smooth silane layer was clarified. The solubility of silane molecules in the solution, the wettability of silane molecule onto inorganic surface, and prevention of the mutual condensation of silane molecules in the solution were found to be important parameters for this purpose.     

Tensile properties of styrene-butadiene rubber/silica composites with mercapto functional silane coupling agents: influences of loading method and alkoxy group number

The influences of alkoxy group number and loading method of silane coupling agents on the mechanical properties of a styrene-butadiene rubber/silica composite were investigated. Mercapto functional silane coupling agents with dialkoxy and trialkoxy structures were used. The pre-treatment method and the integral blend method were compared. Both the fracture stress and modulus at 200% strain were higher in the pre-treatment than in the integral blend for dialkoxy type composites. However, they were higher in the integral blend than in the pre-treatment for trialkoxy-type composites. The interaction between the silane chains on the silica surface and the rubber molecular chains at the interfacial region was estimated by ¹H pulse nuclear magnetic resonance spectroscopy using an unvulcanized silica/rubber mixture. It was found that the binding of rubber molecular chains by the silane chains was higher in the pre-treatment system for dialkoxy-type composites, whereas it was higher in the integral blend for trialkoxy-type composites. The reason is proposed as follows: in the pre-treatment for dialkoxy type, a linear silane chain formed in the case of multi-layer coverage. The silane chain entangled with the rubber chain in the interfacial region and improved the reinforcement effect. For the trialkoxy type, a network structure formed using the pre-treatment method, lowering the amount of entanglement. However, in the integral blend for trialkoxy type, the formation of the silane network and the entanglement progressed simultaneously during the preparation process. A well-entangled interfacial region was formed.     

Ultraviolet Spectroscopic Study of the Cellulose Functionalization with Silanes

The reaction of a cellulosic material (Whatman no. 42 filter paper) with two silanes was studied by Diffuse Reflectance Ultraviolet-Visible Spectroscopy and Diffuse Reflectance Fourier Transform Infrared Spectroscopy. The silanes were 3-aminopropyltriethoxysilane (APS) and methyltrimethoxysilane (MS), a silane with a non-reactive organofunctional group. The use of organic peroxides was required in order to achieve an efficient cellulose modification with the silanes. The Diffuse Reflectance UV-VIS Spectroscopy can provide valuable information about the mechanism of the reactions between silanes and cellulose. The reaction between APS and cellulose involves not only the silanol groups of the silane, but also the amino groups. The spectra of APS-trealed celluloses show an absorption band at 325 nm. This band was assigned to imines produced in the reaction of the amino groups of APS with the cellulose. This absorption band increased when APS-treated cellulose was cured at 120°C. The amino groups attached to the cellulose dissappeared in this process     

AFM Observation of a Mica Surface Treated with Silane Coupling Agent Having a Mercapto Group

The topography of mica surface after treatment with silane coupling agent having a mercapto group was studied using an atomic force microscope. The cleaved mica plate was used as a model inorganic surface. The effect of treatment condition on the topography of the mica surface was investigated. Agglomerates consisting of self-condensed silane molecules were observed on the surface. However, their amount and size were smaller than those for silanes having other organo-functional groups such as amino, methacryloxy and vinyl groups. Aqueous and water/2-propanol mixture solutions gave a smoother surface as compared with a 2-propanol solution. There was no significant influence discernable from di- and trialkoxy structures. The aqueous solution of silane coupling agent having a mercapto group showed an acidic pH. This was the reason why the smoother silane-treated layer was formed by the silane with the mercapto group than by those with other organic functional groups, because the silanol group generated by hydrolysis is stable in an acidic pH.     

Interfacial reinforcement in composites with PPT aramid fiber modified by network-intercalation method

—A novel surface treatment for poly(p-phenylene telephthalamide) (PPTA) fiber is performed with silanes and urethane binder that are usually used as sizes for glass fiber treatment. The PPTA used for the surface treatment is modified by a spinning process to make the gaps between PPTA crystallites open. In this treatment, supercritical carbon dioxide fluid method is used to impregnate the sizing molecules into open gaps in PPTA fiber. After the impregnation, the fiber is heated at 100–170°C to make the gaps close and turn open-gapped fiber to the normal type of PPTA modified with sizes. The interfacial shear strength of fiber to epoxy resin is measured by microdroplet method. The modified PPTA improves the interfacial shear strength by ca. 67% to the interfacial shear strength given by normal PPTA without treatment. Those improvements are 33% without heating, 18% with only silanes, and 12% with only urethane instead of the mixture of silane and urethane. In addition, the fiber strength shows no remarkable decrease after the treatment.     

Effect of surface treatment of nanoclay on the mechanical properties of epoxy/glass fiber/clay nanocomposites

A new method of silane treatment of nanoclays is reported where in the clay is nanodispersed in hydrolyzed silanes. The surface functionalization of Cloisite^® 15A nanoclay has been carried out using two different silane coupling agents: 3-aminopropyltriethoxy silane and 3-glycidyloxypropyltrimethoxy silane using varied amounts of silane coupling agents, e.g. 10, 50, 200, and 400 wt% of clay. The surface modification of Cloisite^® 15A has been confirmed by Fourier transform infrared spectroscopy. The modified clays were then dispersed in epoxy resin, and glass fiber-reinforced epoxy clay laminates were manufactured using vacuum bagging technique. The fiber-reinforced epoxy clay nanocomposites containing silane modified clays have been characterized using small angle X-ray scattering, transmission electron spectroscopy and differential scanning calorimetry. The results indicate that the silane treatment of nanoclay aided the exfoliation of nanoclay and also led to an increase in mechanical properties. The optimized amount of silane coupling agents was 200 wt%. The nanocomposites containing clay modified in 200 wt% of silanes exhibited an exfoliated morphology, improved tensile strength, flexural modulus, and flexural strength. The improved interfacial bonding between silane modified nanoclays and epoxy matrix was also evident from significant increase in elongation at break.     

Surface treatment of CaCO3 with a mixture of amino- and mercapto-functional silane coupling agents and tensile properties of the rubber composites

In order to reinforce the composite consisting of isoprene rubber (IR) and calcium carbonate (CaCO₃) particles, the surface treatment of CaCO₃ particles with a mixture of amino- and mercapto-functional silane coupling agents was investigated. The quantity of chemisorbed silanes in treated CaCO₃ measured using thermogravimetry was greater for amino- than for mercapto-silane and for the tri- than for the dialkoxy structure. Second, the molecular mobility of polycondensate of the mixtures with the trialkoxy structure measured using ¹H pulse nuclear magnetic resonance had the least molecular mobility, i.e., formed the highest density network. The greater values of stress at 500% strain, fracture stress, and elongation at break were determined for the treatment with amino- and mercapto-functional silanes having a trialkoxy structure from the stress-strain curves of composite. The mixture treatment with dialkoxy structure and with amino- or mercapto-functional silane only did not improve the mechanical properties sufficiently. Interactions between the amino group and the CaCO₃ surface, covalent bonding between the mercapto group and the IR, and high density network formation of trialkoxy silane were important for improving the mechanical properties of the composite.     

Investigation of aminotrimethoxysilanes and organic acids functionalized surface interactions: Theoretical and atomic force microscopy studies

Silane compounds provide many applications in biotechnology field. Chemically adsorbed silanes with reactive terminal groups are used for fabrication of functional material, which can serve as a model substrate for fundamental studies of different surface interactions or as a platform for further chemical reactions.In this work, silane compounds with amine groups were the area of interest. The studies were focused on investigation of amine group interaction with different acid groups. The interactions were probed using atomic force microscope operating in force spectroscopy mode. An atomic force microscope gold tip, functionalized with thiol compounds, served as acid-terminated surface. Interactions at interfaces between the silane self-assembled monolayer (SAM) and the thiol SAM were measured in liquid environment. The results of the measurements were set against the theoretical studies performed by AM1d and PM5 semi-empirical methods. Moreover, prior to chemical force spectroscopy measurements the silane films coverage quality was studied as well. Fourier transform infrared (FTIR) spectrometer and atomic force microscope served as control equipment.     

Moisture effects on improved hydrolysis reaction for TESPT and TESPD-silica compounds

The moisture(55 wt%)-treated silica compounds, bis(triethoxysilylpropyl)disulfide (TESPD)/silica/carbon black (CB)/SBR and bis(triethoxysilylpropyl)tetrasulfide (TESPT)/silica/CB/SBR, have been processed in a batch mixer and they are investigated with respect to the alcohol residue level in silane, the processability, the vulcanization characteristics, and the mechanical properties. The alcohol level is low at the moisture treated compounds. The TESPD compounds show lower alcohol level than the TESPT ones on moisture treated and untreated compounds. The probe temperatures of the moisture treated compounds are lower than the drop temperature, while those of the untreated compounds are higher than the drop ones, respectively. The vulcanization properties of the compounds are changed by the moisture treatment and this improves the physical properties of the compounds. The moisture treatment on silica surface increases the hydrolysis reaction of the alkoxy silane and the hydrolyzed silane improved the coupling reaction with the hydroxyl group on silica surface during reactive batch processing. It also reduces the rate of temperature rise during batch mixing due to the latent heat of the moisture and the endothermic reaction between silica and silane. At the vulcanization stage, it seems to further increase the coupling reaction between silica and silane. The steric hindrance theory of an alkoxy silane (TESPT) has to be reconsidered with a large amount of moisture treated silica/TESPD/CB/S-SBR compound system.     

Novel Jute/Polycardanol Biocomposites: Effect of Fiber Surface Treatment on Their Properties

In the present study, novel biocomposites with chopped jute fibers and thermosetting polycardanol were prepared using compression molding technique for the first time. Prior to biocomposite fabrication, jute fiber bundles were surface-treated at various concentrations using 3-glycidoxypropyltrimethoxy silane (GPS) and 3-aminopropyltriethoxy silane (APS), respectively. The interfacial shear strength, flexural properties and thermal properties of jute/polycardanol biocomposites reinforced with untreated and silane-treated jute fibers were investigated by means of single fiber microbonding test, three-point flexural test, dynamic mechanical analysis, thermogravimetric analysis and thermomechanical analysis. Both GPS and APS treatments played a role in improving the interfacial adhesion, reflecting that the organofunctional groups located at the end of silane coupling agents may contribute to linking between jute fibers and a polycardanol resin. As a result, it gave rise to increased interfacial shear strength of the biocomposites. Such interfacial improvement also led to increasing the flexural strength and modulus, storage modulus, thermal stability and thermomechanical stability.     

Fixation of silane coupling agents to glass fiber in silane treatment process

Fixation of silane coupling agents to glass fiber was quantitatively determined using pyrolysis-GC/FT-IR to explore the formation of chemical-bonded and physisorbed silanes. The silane coupling agent used was N-phenyl-1-aminopropyltrimethoxysilane (AnPS). In silane treatment, E-glass fiber was dipped into acetic acid solution containing AnPS and was cured under different temperature and time. The fixation of silane was obtained by determining the amount of AnPS at the glass surface after and before washing the treated fiber with methanol. The silane fixation increased with decrease in the silane concentration, but it fell significantly below a lower silane concentration. The change of fixation in curing temperature gave an optimum temperature for the fixing. The dependence of curing time on the fixing ratio showed that the fixation was depressed below the curing temperature of 100°C. These results suggested that more than a specific amount of AnPS deposit on glass fiber was necessary to form silane networks fixed to glass fiber through siloxane bonds. The networks formation was interpreted in terms of the competitive reaction of the silanol group of silane to hydroxyl of glass fiber and to other silane molecules.     

Interfacial Properties of Phosphate Glass Fiber/Poly(caprolactone) System Measured Using the Single Fiber Fragmentation Test

Phosphate glass fiber of the composition 20Na₂O–24MgO–16CaO–40P₂O₅ was produced using an in-house fiber drawing rig. The interfacial properties of the phosphate glass fiber/poly(caprolactone) (PCL) system were measured using the single fiber fragmentation test (SFFT). The system was calibrated using E-glass fibers and polypropylene system. This gave an interfacial shear strength (IFSS) of 4.1 MPa, which agrees well with other published data. The IFSS for the unsized (as drawn) phosphate glass fiber/PCL system was found to be 1.75 MPa. Fibers treated with 3-aminopropyl-triethoxy silane (APS) showed an IFSS of 3.82 MPa. X-ray photoelectron spectroscopic (XPS) analysis of unsized and silane sized fibers established the presence of silane on the fiber surface. Degradation tests of the silane treated fiber/PCL samples were carried out in deionised water at 37°C and it was found that the IFSS values decreased over time. Four others silanes were also investigated but APS gave the highest IFSS values.     

An IETS study of a silane coupling agent; the interaction of 3-(trimethoxysilyl)propanethiol with aluminium oxide and silver surfaces

The inelastic electron tunnelling spectrum of a silane coupling agent, 3-(trimethoxysilyl)propanethiol, is presented. Approximately monolayer quantities of this silane are present on the barrier oxide of an aluminium-aluminium oxide-metal tunnelling junction, in which the counter electrode is either lead or silver. It is deduced from the IETS spectra that the alkoxy groups of this silane condense with the surface hydroxyl groups. No interaction with the lead is observed but the silver layer clearly reacts with the thiol group of the silane molecule, since the thiol stretching vibration is absent in the spectra, and probably forms the corresponding silver thiolate. The influence of this reaction on the conformation of the bound silane is discussed.     

Preparation of superhydrophobic membranes by electrospinning of fluorinated silane functionalized poly(vinylidene fluoride)

Fluorinated silane functionalized poly(vinylidene fluoride) (PVDF) is synthesized by graft polymerization of 3-trimethoxylpropyl methylacrylate with PVDF followed by coupling of fluorinated silanes. Flat membrane prepared using this functionalized PVDF has a water contact angle of 140°. Superhydrophobic PVDF membrane with a contact angle larger than 150° is prepared by the electrospinning of the fluorinated silane functionalized PVDF. The morphologies of the membranes are characterized using scanning electron microscopy. The surface composition of the membranes is analyzed using FTIR and the contact angles and water drops on the surface of the membrane are measured using video microscopy.     

表面活性剂对气-液界面纳米颗粒吸附规律的影响

通过测定及分析纳米颗粒和表面活性剂-纳米颗粒复配体系在自由吸附过程与动态收缩过程中表面张力的变化,总结了纳米颗粒在气-液界面的吸附排布规律以及表面活性剂对其吸附规律的影响.实验结果表明,自由吸附过程中,随矿化度增加、阳离子活性剂浓度增加,平衡表面张力降低,这与颗粒吸附密度增加及颗粒润湿性改变有关.浓度低于临界胶束浓度(CMC)时,阳离子活性剂体系与混合体系的表面张力差异证明了阳离子活性剂可以通过静电作用吸附于纳米颗粒表面,进而部分溶解于水相;而阴离子活性剂与纳米颗粒相互作用力较弱,对表面张力影响较小.纳米颗粒体系在液滴收缩过程中,表面张力从自由吸附平衡态进一步降低大约9 m N/m,说明自由吸附过程中纳米颗粒不能达到紧密排布;同时表面张力呈现为缓慢降低、快速降低和达到平衡三部分,表面压缩模量可达70 m N/m,满足了液膜Gibbs稳定准则,这将有助于提高泡沫或者乳液稳定性.纳米颗粒-表面活性剂体系在液滴收缩过程中表面张力降低值随活性剂浓度增加而减小;表面压缩模量由高到低依次为:纳米颗粒>阳离子活性剂-纳米颗粒>阴离子-纳米颗粒>表面活性剂.     

Field desorption mass spectroscopic analysis of silane coupling agents hydrolyzed in solution

Aqueous solutions of silane coupling agents used for surface treatment of glass fiber were analyzed using gas chromatography (GC), gel permeation chromatography (GPC), and field desorption mass spectrometry (FD-MS). N-Phenyl-3-aminopropyltrimethoxysilane (AnPS) and 3-aminopropyltriethoxysilane (APS) used were hydrolyzed and condensed in water-ethanol solution. FD-MS analysis was found to be suitable for the evaluation of polymerization of silanes in the process of hydrolysis and condensation in the aqueous solution. FD-MS analysis gave the molecular weight of each silane condensate to evaluate the respective molecular structure.     

The influence of filler modification on its aggregation and dispersion behaviour in silica/PBT composite

In this work, highly dispersed silica is obtained using a precipitation technique from emulsion medium. The selected emulsifier, applied in the process, allows production of silica with almost ideally spherical particles. To examine the tendency to aggregation, the silica powder is treated with commercially available silane coupling agents: 3-mercaptopropyltrimethoxysilane (A-189), N-2-(aminoethyl)-3-aminopropyltrimethoxy silane (A-1120) and 3-methacryloxypropyltrimethoxysilane (A-174). The silica microstructure is characterised by scanning electron microscopy (SEM). Size distribution of primary particles, aggregates and agglomerates structures is determined using dynamic light scattering (DLS) method. Surface treatment of silica generally enhances powder dispersibility. The pristine spherical silica and silica modified with silanes are introduced to poly(butylene terphthalate) (PBT). Dispersion of nanosize precipitated silica particles in PBT matrix is studied by SEM technique. For the visualisation of silica particles covered by polymer layer, the composite fracture surfaces are etched by air-plasma. The agglomerates of untreated silica are not efficiently destroyed during the extrusion process, whereas surface treatment by selected silanes leads to a significant reduction of agglomerate number. However, a large number of small, strongly bonded aggregates still occupied the composite structure.     

Theoretical Study of Photoabsorption Spectra near Si 2p Edges of Silanes： to Determine Orientations of Adsorbed Silanes

In the frame work of quantum defect theory, photoabsorption spectra near Si 219 edges of silane have been studied. When silanes are adsorbed on a physical surface and excited by polarized x-ray photons, relative intensities of the spectra will be different from that of free molecules. Such features can be used to determine orientations of adsorbed silanes based on selection rules.     

Numerical simulation of silane decomposition in an RF plasma

A model of silane decomposition in a radio-frequency argon plasma is constructed. The concentrations of SiH₄ decomposition products, as well as products of synthesis (higher silanes), are calculated. The role of metastable argon atoms in the formation of SiH₃ radicals and the higher silanes is analyzed.     

Interfacial modification of silica surfaces through γ-isocyanatopropyl triethoxy silane-amine coupling reactions

The development of robust, cost-effective methods to modify surfaces and interfaces without the specialized synthesis of unique coupling agents could provide readily accessible routes to optimize and tailor interfacial properties. We demonstrate that γ-isocyanatopropyl triethoxysilane (ISO) provides a convenient route to functionalize silica surfaces through coupling reactions with readily available reagents. ISO coupling agents layers (CALs) can be prepared from toluene with triethylamine (TEA), but the coupling reaction of an amine to the ISO CAL does not proceed. We use near edge X-ray absorption fine structure (NEXAFS), time-of-flight secondary ion mass spectrometry (TOF-SIMS) and sessile drop contact angle to demonstrate the isocyanate layer is not degraded under coupling conditions. Access to silanes with chemical functionality is possible with ISO by performing the coupling reaction in solution and then depositing the product onto the surface. Two model CAL surfaces are prepared to demonstrate the ease and robust nature of this procedure. The surfaces prepared using this method are the ISO reacted with octadecylamine to produce a hydrocarbon surface of similar quality to octadecyl trichlorosilane (OTS) CALs and with 9-aminofluorene (AFL), an aromatic amine functionality whose silane is otherwise unavailable commercially.