Silane Chain Research Articles

A Novel Strategy To Obtain a Hyaluronan Monolayer on Solid Substrates

The aim of this study was to find a novel simple method to obtain polysaccharide ultrathin layers on solid substrates to investigate the interaction between the surface and the biological environment. A Hyaluronan (Hyal) monolayer with a well-defined chemistry was obtained by exploiting the capability of organosilanes to spontaneously adhere onto glass surfaces. A silane alkylic chain was conjugated with Hyal, and the derivatized polysaccharide was allowed to spontaneously adhere onto a glass surface. The elemental analysis of the modified polysaccharide demonstrated that one out of five disaccharide units was conjugated with the alkyl silane chain, corresponding to a substitution degree of the carboxylate groups of approximately 20%. The film of the modified polysaccharide was characterized by means of X-ray photoelectron spectroscopy (XPS), water contact angle, and atomic force microscopy (AFM) measurements. XPS analysis demonstrated that we obtained a Hyal layer with a thickness of about 2.0 nm corresponding to a Hyal monolayer. The Hyal-coated surfaces appeared to be rather smooth and highly hydrophilic and showed significant resistance to nonspecific cell adhesion.

Dual-Surface-Modified Reverse-Selective Membranes

The reverse selectivity of inorganic membranes can be enhanced by surface modification using long hydrocarbon chain silanes. Improvements in n-C4H10 selectivity of Vycor porous glass over N2 and CH4 were obtained by sequentially modifying it with a C18 monochlorosilane (OCS) followed by a C18 trichlorosilane (ODS). The membranes were tested for pure and mixed gases at different feed pressures. The dual-modified membranes have higher ideal, or pure-gas, selectivities than membranes modified using OCS alone. The n-C4H10/N2 and n-C4H10/CH4 ideal selectivities for the dual-modified membrane were 88 and 35, respectively, as compared to values of 13 and 7, respectively, for the OCS-modified membrane. Adsorption experiments showed an increase in the relative adsorption of n-C4H10 over N2 and CH4 after dual surface modification of Vycor glass. Nuclear magnetic resonance, X-ray photoelectron spectroscopy, and thermogravimetric analysis techniques were used to confirm the presence of silanes on the surface of the substrates. A high flux of n-butane was measured for a dual-modified membrane fabricated using a 5 nm pore diameter γ-alumina ultrafilter substrate. The mixed-gas n-butane permeance for this membrane was 2 × 10-4 cm3(STP) cm-2 cm Hg-1 s-1 (6.7 × 10-8 mol m-2 s-1 Pa-1).

Proton Conductive Composite Materials Using Functionalized and Crosslinkable VDF/CFTE Fluoropolymers and Proton Conductive Inorganics

The synthesis of crosslinkable P(VDF-CTFE) copolymer with controllable structure, molecular weight and terminal and side chain silane groups was developed. The chemistry of the synthesis was centered on a specifically designed functional borane initiator containing silane groups. Polymer electrolyte composite membranes were fabricated by dispersion of additive particles in the polymer solution and film casting, followed by thermocompression, which allowed for formation of crosslinking sites in 3-D polymer network. Two types of membranes were investigated: P(VDF-CTFE)/Nafion/Inorganic and P(VDF-CTFE) with incorporated sulfonated units. Different types of inorganic proton conductors were synthesized and tested in P(VDF-CTFE)/Nafion/Inorganic membranes. The highest conductivity was obtained using H3OZr2(PO4)3 particles. Optimization of the P(VDF-CTFE)/Nafion/H3OZr2(PO4)3 membrane composition allowed to substantially increase the membrane conductivity. Two avenues were explored to add sulfonic acid groups to P(VDF-CTFE) to obtain a desirable membrane conductivity without an addition of Nafion: introduction of sulfonated silicon dioxide and sulfonated SPETMS.

Study of self-assembled triethoxysilane thin films made by casting neat reagents in ambient atmosphere

We studied four trialkoxysilane thin films, fabricated via self-assembly by casting neat silane reagents onto hydrophilic SiO x /Si substrates in the ambient. This drop-casting method is simple, yet rarely studied for the production of silane self-assembled monolayers (SAMs). Various ex-situ techniques were utilized to systematically characterize the growth process: Ellipsometry measurements can monitor the evolution of film thickness with silanization time; water droplet contact angle measurements reveal the wettability; the change of surface morphology was followed by Atomic Force Microscopy; the chemical identity of the films was verified by Infrared–Visible Sum Frequency Generation spectroscopy. We show that the shorter carbon chain (propyl-) or branched (2-(diphenylphosphino)ethyl-) silane SAMs exhibit poor ordering. In contrast, longer carbon chain (octadecyl and decyl) silanes form relatively ordered monolayers. The growth of the latter two cases shows Langmuir-like kinetics and a transition process from lying-down to standing-up geometry with increasing coverage.

Effect of silane chain length on the mechanical properties of silane-treated glass beads-filled PVC

The surface treatment of glass beads, chosen as model filler, with silane coupling agent with multilayer coverage was carried out. The treated beads were incorporated with poly(vinyl chloride), chosen as a typical ductile polymer. The effects of the organic functional group of silane and silane chain length on the mechanical properties of the filled composite were investigated. For this purpose, silanes having aminopropyl or methacryloxypropyl group as organic functional group with dialkoxy structure were used. The silane chain length on the bead surface varied from one to nine times the amount required for monolayer coverage. The yield stress was higher in the order of aminopropyl silane-treated > methacryloxypropyl silane-treated > untreated beads-filled systems. However, the elongation at break had a quite opposite order. The effect of silane chain length appeared only in the methacryloxypropyl silane-treated system. The yield stress increased slightly, whereas the elongation at break decreased with the increase of silane chain length. In the case of short silane length, the yield stress could be improved without decreasing of the elongation at break.

Bright luminescence from silane substituted and bridged silicon nanoclusters

Time-dependent density functional theory (TDDFT) calculations show that silicon nanoclusters (Si-NC) capped by linear silane groups have large oscillator strengths of the same magnitude as reported in recent experimental studies. We propose a mechanism where linear silanes attached to the Si-NC surface affect the optical properties enhancing the oscillator strengths and thereby accounting for the bright luminescence observed in the blue region of the visible spectrum. The anisotropic emission seen experimentally can also be explained by the presence of the silane groups on the cluster surface. The excitation energies are found to be only slightly affected by the silanes, whereas the oscillator strengths increase with the length of the silane chain and are significantly larger than obtained for unsubstituted Si-NCs. In TDDFT studies of Si-NC dimers interconnected by a linear silane bridge, we obtained large oscillator strengths indicating that such structures could be useful light sources for optical devices.

Influence of the pore structure on the properties of silica based reversed phase packings for LC

This paper describes the preparation and investigation of new, highly loaded, monomeric, silica based, reversed phase C18 and C30 packings. The influence of pore structure and endcapping on the properties of C18 and C30 packings is described. Using hydrothermal procedures, silicas with predictable pore size (9.3-25.5 nm) and surface area have been prepared. Silylation with long chain silanes substantially alters the pore structure of the silica: pore size and pore volume decrease. A new parameter, the volumetric surface coverage [mm3 x m(-2)] has been introduced. This parameter--calculated from on-column measured porosity data--indicates the pore volume portion occupied by the hydrocarbon chains. Endcapping does not significantly change the pore structure of the bonded phases. The reduced retentions (reduced with respect to unit area: [k/m2])--a good measure for comparing the retention behaviour of packings with different surface areas--are similar for most of the phases, demonstrating good accessibility of the pores for the solutes. Slightly lower retentions were found on the endcapped than on the non-endcapped phases for probes with dense pi-electron system (e.g. polyaromatic hydrocarbons) demonstrating the contribution of silanophilic interactions to the retention. The phases had been successfully used for various demanding separations, e.g. for the separation of flavonoids, carotenoids, resveratrol, and tocopherol isomers, fullerenes, and anions.

Influence of silane coupling agents on the interlaminar and thermal properties of woven glass fabric/nylon 6 composites

In this study, the influence of silane coupling agents, featuring different organo-functional groups on the interlaminar and thermal properties of woven glass fabric-reinforced nylon 6 composites, has been by means of shortbeam shear tests, dynamic mechanical analysis, scanning electron microscopy, and thermogravimetric analysis. The results indicate that the fiber-matrix interfacial characteristics obtained using the different analytical methods agree well with each other. The interlaminar shear strengths (ILSS) of glass fabric/nylon 6 composites sized with various silane coupling agents are significantly improved in comparison with that of the composite sized commercially. ILSS of the composites increases in the order: Z-6076 with chloropropyl groups in the silanes >Z-6030 with methacrylate groups >Z-6020 with diamine groups; this trend is similar to that of results found in an earlier study of interfacial shear strength. The dynamic mechanical properties, the fracture surface observations, and the thermal stability also support the interfacial results. The improvement of the interfacial properties may be ascribed to the different chemical reactivities of the reactive amino end groups of nylon 6 and the organo-functional groups located at the ends of the silane chains, which results from the increased chemical reactivity in order chloropropyl >methacrylate >diamine.

Structure and orientation of vacuum-evaporated poly(di-methyl silane) film

We have succeeded in obtaining the primitive translation vectors of the sub-cell of poly(di-methyl silane) [Si(CH 3) 2] n crystal. The crystal structure of poly(di-methyl silane) has been clarified by comparing the experimental X-ray diffraction pattern with that of theoretical pattern. The crystal has a monoclinic unit cell (sub-cell) with a =0.745 nm, b=0.724 nm, c=0.389 nm and γ=67.1°. Although poly(di-methyl silane) is the most fundamental polysilane, it is not solved in organic solvents at room temperature. Therefore, the poly(di-methyl silane) thin film has been prepared by a vacuum evaporation technique. In this paper, poly(di-methyl silane) thin films are prepared using new vacuum evaporation system, and the orientation of poly(di-methyl silane) chain has been examined as a function of vacuum pressure as well as substrate temperature during the evaporation. As a result, it is found that the orientation of poly(di-methyl silane) chain is strongly affected not only by the pressure but also by the substrate temperature during the deposition.

Conductive surface via graft polymerization of aniline on a modified glass surface

A functionalization with an aniline monolayer of a modified glass surface, followed by the surface grafting of polyaniline (PANI) was used to prepare a conductive surface. A bromopropylsilane monolayer was first generated by reacting a hydroxylated surface with 3-bromopropyltrichlorosilane under an inert atmosphere. This layer was functionalized by its reaction with aniline, which substituted the bromide atoms of the silane chain. Further, the tethered aniline molecules were used as active sites for the graft polymerization of PANI on the surface. The composition and microstructure of the PANI-grafted glass surfaces were examined by X-ray photoelectron spectroscopy (XPS), and ultra-violet (UV) spectroscopy, as well as by contact angle measurements. The surface conductivity of the modified glass surface-grafted with PANI was of the order of 10 S/cm, hence, larger than the usual value (∼1 S/cm) of the bulk PANI.

Design of mesoporous aluminosilicates supported (1 R,2 S)-(−)-ephedrine: evidence for the main factors influencing catalytic activity in the enantioselective alkylation of benzaldehyde with diethylzinc

(−)-Ephedrine, used as a model β-amino alcohol, was covalently anchored on mesoporous micelle templated aluminosilicates (Al-MTS) through nucleophilic substitution of halogenoalkyl(aryl)silane chains previously grafted on the surface. The covalent grafting was performed either by silylation (method a) or by surface sol–gel (method b). The latter method provided higher loading. However, the higher loading lowers the resulting mesoporous volume. The coupling alkyl halide moiety was then substituted with (1 R,2 S)-(−)-ephedrine. Used as chiral auxiliaries in the heterogeneous enantioselective catalysis of the alkylation of benzaldehyde by diethylzinc, these materials showed properties which depend mainly on the grafting method. The best results (activity, enantioselectivity) were obtained with catalysts prepared from supports featuring high initial pore diameter. The effect of the regular porosity on the efficiency and enantioselectivity was shown. Dilution of catalytic sites by alkyl groups and rigidification of the linker were also studied.

Silica surface modification using different aliphatic chain length silane coupling agents and their effects on silica agglomerate size and processability

Silica surface was treated with various aliphatic chain length silane coupling agents and compounded in EPDM using an internal mixer, and their agglomerate sizes, viscosity, and extrudate swell were investigated. The treated silica compounds showed smaller agglomerate size, lower viscosity, and lower swell reduction compared to untreated silica compound after equivalent mixing times. Short chain silane treated silica compound exhibited smallest agglomerate size. Silane acted as dispersing agents and processing aids in silica/EPDM compounds.

The use of surface preparations and fillers in the promotion of cohesive failure of EA 946/aluminum bondlines

A model amine cured structural epoxy adhesive (EA 946) that tends to fail interfacially when bonded to aluminum adherends when tested in mode I fracture, is the subject of this manuscript. Two methods of promoting cohesive failure were investigated, surface modification and adhesive filler formulation. In the former, a new metasilicate/silane surface treatment was applied to 7075 aluminum. This treatment significantly improved the zero time bond fracture toughness and durability of adhesive bondlines. The effect of silane chain length and processing time lines on joint mode fracture toughness were also examined. In the second part of the study the filler composition was changed from M5 to TS-720 Cab-O-Sil. This had a significant effect on the failure mode. It was shown that TS-720 produced a significant increase in cohesive failure compared to M5 Cab-O-Sil. Electron micrographs suggest that failure was nucleated at the interface between the epoxy and the particles of TS-720. The presence of silane adhesion promoters on the M5 Cab-O-Sil was thought to preclude this failure mechanism in the M5 formulations. A non-linear viscoelastic model and biaxial constitutive modeling showed that the volume increase for the TS-720 formulation was approximately three times that of the M5 formulation.

Adhesion Mechanisms of Silane Adhesion Promoters in Microelectronic Packaging

ABSTRACTSilane adhesion promoters are seeing increasing use in microelectronic packaging applications. For example, they are currently used to adhere the passivating polymer overlayer to oxide. In this paper, we present detailed studies of silane adhesion promoters on the silicon oxide surface. Two common promoters (aminopropyltriethoxysilane and vinyltriethoxysilane) as well as non-functional silanes are investigated. It was found that without a functional end group, long carbon chain silanes can severely degrade adhesion, resulting in interfaces weaker than if no silane is used. Several spin coat solution formulations are used in depositing these films. The resulting surface coverage is examined and quantified using XPS, and the adhesion behavior of various promoter films is tested in sandwich structures using a fracture mechanics approach. Finally, spin-coat solution concentration, surface coverage, and interface fracture energy are compared for the amine functional promoter.

Monolayer Damage in XPS Measurements As Evaluated by Independent Methods

The damage caused to amphiphilic n-alkane monolayers under XPS measurement conditions was assessed in a combined XPS-FTIR study supplemented by additional AFM imaging and contact angle measurements. Nine different self-assembled monolayer/substrate systems were examined, comprising a long chain silane (C18, OTS), a short chain silane (C1, MTS), a functional (COOH-terminated) long chain silane (C18, NTSox), a long chain carboxylic acid (C20, AA), and four different solid substrates (silicon, quartz, glass, and ZnSe). Significant differences were observed in the behavior of the various examined monolayer systems under identical X-ray irradiation conditions. These are interpreted in terms of effects associated with the specific mode of layer-to-surface and intralayer coupling, the size of the monolayer hydrocarbon core, and the presence of radiation-sensitive functional groups in the layer. All these factors and their influence on the degradation path followed by a particular monolayer upon exposure to the X-rays were found to be interrelated, giving rise to a variety of possible damage patterns, including an unexpected overall stabilization effect initiated by the preferential rapid loss of a labile top functional group (NTSox). XPS is shown to be insufficient as a tool for the evaluation of the radiation-induced damage in such ultrathin films, because of its insensitivity to loss of hydrogen and to structural transformations that occur without a net loss of carbon from the surface. Independent methods of surface analysis (mainly FTIR), applied in conjunction with XPS, provide a more comprehensive picture of the induced damage, thus permitting a realistic interpretation of the XPS experimental data as well as the design of improved data acquisition procedures. This could also assist in the tailoring of monolayers with predetermined degradability, for specific purposes. Finally, results of combined AFM-XPS-FTIR-contact angle measurements suggest the possible formation of a “diamond-like” surface film upon extensive X-ray irradiation of an OTS/Si monolayer.

Spatial orientation of highly ordered self-assembled silane monolayers on glass surfaces

The orientation behaviour of self-assembled silane monolayers deposited onto glass surfaces was investigated by conoscopic microscopy. Conoscopy is a suitable tool for characterizing the orientation behaviour of nanoscaled layers on such silane-modified glass surfaces. Compared with other methods, for instance X-ray reflection, infrared spectroscopy, X-ray photoelectron spectroscopy, and ellipsometry, it is possible to determine the tilt angle (φ) as well as the azimuthal direction (Φ) of the molecules in the chemisorbed silane layer. Even at low tilt angles different azimuthal angles were found. Reverse φ's were detectable for a close-packed octadecyltrichlorosilane (OTS) layer with a near-perpendicular chain orientation (φ 6° to 2°, Φ 0° and 180°). A random azimuthal distribution was found at tilt angles exceeding 10°. Examples are given for selected silane layers prepared from different solvents and solvent mixtures depending on the silane concentration and composition. The tilt angles of the liquid crystal molecules determined by conoscopy on glass were comparable to the tilt angles of the silane chains on silicon determined from ellipsometric measurements.

Evidence for a Unique Chain Organization in Long Chain Silane Monolayers Deposited on Two Widely Different Solid Substrates

We address the longstanding issue of substrate effects in alkylsiloxane monolayer self-assembly. With proper substrate prehydration, we observe formation of identical quality, compact, quasi-crystalline monolayers on oxidized silicon and gold substrates with widely different chemical character, the former capable of covalent bonding to the adsorbed molecules via silanol groups and the latter devoid of reactive surface sites. Infrared spectroscopy, ellipsometry, and wetting measurements show identical average film structures consisting of highly extended chains tilted at 10 (±2)° with significant end-gauche defect content. This observed substrate independence is consistent with our previous hypothesis that substrate-bound water promotes the decoupling of the organic film from the underlying solid surface.

Patching in reversed-phase high-performance liquid chromatographic materials studied by solid-state NMR spectrometry

The distribution of silane chains over the silica gel surface in reversed-phase high-performance liquid Chromatographic (RP-HPLC) phases was investigated with special attention being paid to surface homogeneity: there might be areas with high coverage and areas with low coverage of silane chains, hence clustering or patching of the silane chains can occur. Two RP phases were studied before and after well conditioned ageing, together with four silylated silica gels, serving as models. Two solid-state NMR techniques, namely 1 H- 29Si dipolar dephasing 29Si cross-polarization magic angle spinning NMR and 13C spin-lattice relaxation in the rotating frame, were used. For the four model compounds with varying degrees of coverage only differences in the NMR time constants were observed between the maximally covered phase and the three less densely covered silica gels. This proves that silane chains on an RP phase with maximum coverage are restricted in their mobilities with respect to the less densely packed materials. For the two non-aged RP phases the silane chains are probably homogeneously distributed over the silica gel surface. Further, the non-aged RP phases were compared with their counterparts, aged under well defined experimental conditions. After ageing, no differences were found between the original and the aged phases, now indicating however, that patching had developed upon ageing.

An Oxynitride ISFET Modified for Working in a Differential Mode for pH Detection

In this study, we have shown that it is possible to deposit a silicon oxynitride membrane on silica ISFETs by plasma enhanced chemical vapor deposition (PECVD) and to develop a solid‐state device for pH detection which works in a differential mode. Silicon technology using a new encapsulation technique and a new geometry of the ISFETs is described. The PECVD oxynitride membrane is deposited without damaging the structure. A nernstian stable pH response is obtained: between pH 2 and 8.3 and it is only slightly affected by the concentration of Na+ ions. Moreover, this silicon oxynitride membrane can be grafted with a long alkyl chain silane in order to make a REFET with a sensitivity of between pH 3.3 and 8.1. The pH response of the solid‐state device obtained is from pH 2 to 8.

On the charge storage and decay mechanism in silicon dioxide electrets

A mechanism for both the storage and the decay of charge in a charged silicon dioxide layer is proposed. The oxide layer needs neutral electron traps to obtain stable trapped negative charge, after having been charged, resulting in an electret that can be applied in microphones. The deprotonization of the silanol groups, followed by charge injection, results in an electrochemical reaction with immobile SiO/sup -/ as one of the reaction products. Decay of the stable charge thus obtained can occur by the clustering of water molecules at inner silanol groups, resulting in a conductive hydrogen bonded network, which eventually leads to the discharge of the electret. Measurement results are presented, showing a considerable decrease in surface conductivity, after having grafted the SiO/sub 2/ surface, resulting in covalently bonded, relatively long octadecyl silane chains.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>