Morphology and water barrier properties of organosilane films: the effect of curing temperature

The morphology of silane films and the response of these films to water vapor are studied by neutron reflectivity, X-ray reflectivity, ellipsometry, and contact angle. The systems studied include bis-[3-(triethoxysilyl)propyl]tetrasulfide (bis-sulfur) and bis-[trimethoxysilylpropyl]amine (bis-amino), as well as mixtures of these two silanes. The effect of curing temperature on water-barrier properties is determined by comparing data for films cured at 180 degrees C with existing data for films cured at 80 degrees C. Higher curing temperature leads to an increase of the crosslink density as well as chemical modification for the sulfur-containing films. For bis-amino silane films, on the other hand, the effect on the water-barrier ability is negligible. Bis-amino silane is fully hydrolyzed and condensed at the curing temperature of 80 degrees C, so further increasing cure temperature does not affect the bulk structure of the film. For bis-sulfur and mixed films, however, higher curing temperature accelerates the hydrolysis and condensation, leading to denser films with better water-barrier performance.     

Cross-condensation and particle growth in aqueous silane mixtures at low concentration

We have observed the condensation of a mixture of gamma-glycidoxypropylmethyldiethoxysilane and 3-aminopropyltriethoxysilane in dilute aqueous solutions. NMR and IR spectroscopy have allowed to follow the condensation process in the mixture, which is noticeably enhanced and proceeds faster than for each silane on its own. Cross-condensation between the two silanes was evidenced. When the hydrophilic aminosilane is in excess, the condensation, as evidenced by dynamic light scattering, proceeds toward gel formation because the oligomers formed are essentially hydrophilic. When the more hydrophobic epoxysilane is in excess, oligomer growth proceeds slowly and results in a destabilization of the solution: due to their hydrophobic character, the oligomers formed coalesce suddenly into 200-nm-diameter aggregates. Coatings deposited from such solutions with high epoxysilane content can be used to strengthen glass. We show that the progress of condensation in solution results in a wetting transition during deposition of the silane film on glass by dip coating. The production of increasingly hydrophobic oligomers as the reaction time increases results in adsorption of more hydrophobic aggregates at the surface, which eventually leads to dewetting of the film: in the absence of film, glass strengthening disappears.     

Overview: The Potential of silanes for chromate replacement in metal finishing industries

Trialkoxysilanes (or silanes) have emerged as a very promising alternative for chromates in metal finishing industries. Compared to the conventional chromating processes, the major merits of silane-based surface treatments include: eco-compliance, easy-control processing, comparable corrosion protection of metals as well as paint adhesion to a variety of topcoats. In this overview paper, we report the recent status of silane studies including results of corrosion performance tests, the mechanism of corrosion protection of metals by silanes and the themal stabilities of silane films. We also address the new fields that we are beginning to explore such as nano-structured silane films, “self-healing” silane films, and “super-primers”.     

Adsorption of organosilanes at a Zn-terminated ZnO (0001) surface: molecular dynamics study

Four different organosilanes (octyltrihydroxysilane, butyltrihydroxysilane, aminopropyltrihydroxysilane, and thiolpropyltrihydroxysilane) adsorbed at a reconstructed Zn-terminated polar ZnO (0001) surface are studied via constant temperature (298 K) molecular dynamics simulations. Both single adsorbed silane molecules as well as adsorbed silane layers are modeled, and the energy, distance, orientation, and alignment of these adsorbates are analyzed. The adsorbed silane molecules exhibit behavior depending on the chemical nature of their tail (nonpolar or polar) as well as on the silane concentration at the solid surface (single adsorption or silane layer). In contrast to the O-terminated ZnO surface studied previously, now adsorption can only occur at the vacancies of this reconstructed crystal surface, thus leading to an arched structure of the liquid phase near the crystal surface. Nevertheless, both nonpolar and polar single adsorbed silanes show a similar orientation and alignment at the surface (orthogonal in the former, parallel in the latter case) as for the O-terminated ZnO surface, although the interaction energy with the surface is considerably increased for nonpolar silanes while it is nearly unaffected for the polar ones. For adsorbed silanes within silane layers, the difference to single adsorbed silanes depends on the polarity of the tail: nonpolar silanes again show an orthogonal alignment, while polar silanes exhibit two different orientations at the solid surface-a head and a tail down configuration. This leads to two completely different but nevertheless stable orientations of these silanes at the Zn-terminated ZnO surface.     

AFM analysis of organic silane thin films for bioMEMS applications

Designing surfaces that elicit the desirable response is essential for bioMEMS (biological microelectromechanical systems) applications. To this end, we have developed two different types of silane film—hydrophobic and hydrophilic—using vinyltrichlorosilane and poly(ethylene glycol) silane, respectively. As the surface topography plays a very important role in governing protein or cell interactions, these films were characterized extensively using atomic force microscopy. All the films developed were found to have a very low root‐mean‐square roughness value (<1.3 nm). Furthermore, the topography of protein‐adsorbed silane‐modified surfaces was investigated because cell adhesion is mediated primarily by proteins. Three‐dimensional and section plots were able to differentiate the way in which protein interacts with hydrophobic and hydrophilic surfaces. Copyright © 2003 John Wiley & Sons, Ltd.     

Comparative study on the interaction of DNA with three different kinds of surfactants and the formation of multilayer films

The interactions between double-stranded DNA (dsDNA) and three different kinds of surfactants, i.e., cationic, anionic, and nonionic surfactants, were investigated by cyclic voltammetry, electrochemical impedance spectroscopy and UV-vis spectroscopy. Multilayer films composed of DNA and surfactants were prepared at gold electrode by electrostatic or hydrophobic interactions. It was found that the cationic surfactant, CTAB, can bind to DNA by electrostatic interaction, and the electron transfer resistance of CTAB-DNA complex film increases first and then decreases with CTAB concentration. The anionic surfactant, LAS, can bind to DNA but by hydrophobic interaction, and the electron transfer resistance of the complex film keeps decreasing with LAS concentration. Nonionic surfactants can also directly bind to DNA by hydrophobic interaction. All the three different kinds of surfactants can form multilayer films with DNA on the electrode surface. The chemical structure of DNA keeps unchanged during interacting with these surfactants. The binding modes of DNA with these three different kinds of surfactants were also deduced.     

Aqueous Amino Silane Modification of E-glass Surfaces

The majority of work available in the literature examines the effect of epoxy silane, gamma-aminopropyltrimethoxy silane, and methacrylate silane on E-glass surfaces. As alternatives to the most commonly used silanes, we investigated two novel silanes: gamma-ureidopropyltriethoxy silane and Nbeta(aminoethyl) gamma-aminotrimethoxy silane and additionally an amino-functional polysiloxane. The ureido silane-treated E-glass fibers demonstrated a zeta potential similar to that of the untreated E-glass fibers, which was independent of deposition solution pH over the pH range investigated. A moderately hydrophobic E-glass surface, which was silane concentration dependent, was noted as being due to condensed Si-O-Si bonds at the surface. The diamino silane demonstrated an extremely basic surface at the higher silane concentrations investigated. These outer surface layers were modified by changing the pH and the concentration of the deposition solution. The polysiloxane produced an increase in the hydrophobicity of the E-glass fiber, especially when deposited from extremely basic solutions. At the higher solution concentrations investigated, the silanes and the siloxane was initially deposited in patches and an outer surface or "skin" was formed over these patches, giving the appearance of fully coated fibers. Copyright 2001 Academic Press.     

The salivary mucin MUC5B and lactoperoxidase can be used for layer-by-layer film formation

In situ ellipsometry was used to study layer-by-layer film formation on hydrophilic and hydrophobized silica surfaces by alternating sequential adsorption of human mucin MUC5B and cationic proteins lysozyme, lactoferrin, lactoperoxidase or histatin 5, respectively. The stability of the multilayers was investigated by addition of sodium dodecyl sulfate solution (SDS). Atomic force microscopy was employed to investigate morphological structures on the surfaces during the layer-by-layer film build-up. It was clearly shown that, on both hydrophilic and hydrophobized silica, only MUC5B and lactoperoxidase showed the ability for multilayer formation, resulting in an approximately linear increase in adsorbed amount and film thickness with each deposition cycle. The net increase in amounts per cycle was larger on the hydrophilic silica. Further, MUC5B needs to be adsorbed first on the hydrophilic substrates to obtain this fast build-up behavior. Generally, addition of SDS solution showed that a large fraction of the adsorbed film could be desorbed. However, films on the hydrophobized silica were more resistant to surfactant elution. In conclusion, MUC5B-cationic protein multilayers can be formed on hydrophilic and hydrophobized silica, depending on the choice of the cationic protein as well as in which order the build-up is started on hydrophilic silica. Additionally, SDS disrupts the layer-by-layer film formed by MUC5B and lactoperoxidase.     

Application of water-soluble polymers as modifiers in electrophoretic analysis of phenols

A review of application of water-soluble cationic, anionic and nonionic polymers as pseudostationary phases in capillary electrophoresis (CE) and micellar electrokinetic capillary chromatography (MEKC) is presented. The effect of the structure of the polymers on the selectivity and efficiency of separation is discussed. A novel specially designed cationic polymer, 2,10-ionene, has been used for the separation of phenols. The polymer has hydrophilic and hydrophobic parts in its backbone. The polymer shows the best selectivity as a modifier in capillary zone electrophoresis (CZE)-mode, which allows the selective determination of both hydrophilic and hydrophobic phenols.     

Surfactant adsorption onto cellulose surfaces

The adsorption of the cationic surfactant, hexadecyl trimethyl ammonium bromide, C16TAB, onto model cellulose surfaces, prepared by Langmuir-Blodgett deposition as thin films, has been investigated by neutron reflectivity. Comparison between the adsorption of C16TAB onto hydrophilic silica, a hydrophobic cellulose surface, and a regenerated (hydrophilic) cellulose surface is made. Adsorption onto the hydrophilic silica and onto the hydrophilic cellulose surfaces is similar, and is in the form of surface aggregates. In contrast, the adsorption onto the hydrophobic cellulose surface is lower and in the form of a monolayer. The impact of the surfactant adsorption and the in situ surface regeneration on the structure of the cellulose thin films and the nature of solvent penetration into the cellulose films are also investigated. For the hydrophobic cellulose surface, intermixing between the cellulose and surfactant occurs, whereas there is little penetration of surfactant into the hydrophilic cellulose surface. Measurements show that solvent exchange between the partially hydrated cellulose film and the solution is slow on the time scale of the measurements.     

Headgroup effect on silane structures at buried polymer/silane and polymer/polymer interfaces and their relations to adhesion

Sum frequency generation (SFG) vibrational spectroscopy was used to study the effect of silane headgroups on the molecular interactions that occur between poly(ethylene terephthalate) (PET) and various epoxy silanes at the PET/silane and PET/silicone interfaces. Three different silanes were investigated: (3-glycidoxypropyl) trimethoxysilane (γ-GPS), (3-glycidoxypropyl) methyl-dimethoxysilane (γ-GPMS), and (3-glycidoxypropyl) dimethyl-methoxysilane (γ-GPDMS). These silanes share the same backbone and epoxy end group but have different headgroups. SFG was used to examine the interfaces between PET and each of these silanes, as well as silanes mixed with methylvinylsiloxanol (MVS). We also examined the interfaces between PET and uncured or cured silicone with silanes or silane-MVS mixtures. Silanes with different headgroups were found to exhibit a variety of methoxy group interfacial segregation and ordering behaviors at various interfaces. The effect of MVS was also dependent upon silane headgroup choice, and the interfacial molecular structures of silane methoxy headgroups were found to differ at PET/silane and PET/silicone interfaces. Epoxy silanes have been widely used as adhesion promoters for polymer adhesives; therefore, the molecular structures probed using SFG were correlated to adhesion testing results to understand the molecular mechanisms of silicone-polymer adhesion. Our results demonstrated that silane methoxy headgroups play important roles in adhesion at the PET/silicone interfaces. The presence of MVS can change interfacial methoxy segregation and ordering, leading to different adhesion strengths.     

Effect of the Interfacial Agents with Different Types of Hydrophilic Functional Groups on the Rheological Properties of Coal-Water Slurry

Five interfacial agents with different hydrophilic groups (DBS, SDS, SO, TX, CTAB) are used as model additives to prepare coal-water slurry (CWS). The effects of different interfacial agents on the rheological properties of CWS are systemically investigated, the microscopic aggregation behavior of coal particles in the suspensions and the zeta potentials in coal-water interface are also studied. Based on the interpretation of the results, the rheological behavior of CWS is greatly influenced by the adsorption pattern of the interfacial agents in coal-water interface. The adsorption patterns of anionic interfacial agents on coal surface are mainly influenced by the combining force between the anionic hydrophilic groups with Ca²⁺, the stronger combining force with Ca²⁺ leads to the apparent viscosity increase and heavier pseudo-plastic property of CWS. The adsorption pattern of nonionic interfacial agent on coal surface is seldom influenced by the hydrophilic polyoxyethylene chain, and the addition of nonionic interfacial agent reduces the apparent viscosity of CWS. The adsorption pattern of cationic interfacial agent on coal surface is determined by its cationic head, and the addition of cationic interfacial agent increases the apparent viscosity of CWS. The concluded adsorption models of the interfacial agents with different hydrophilic groups can be guidance for the molecular design of high-performance additives of CWS.      

Adhesive transitions in Newton black films: a computer simulation study

We report molecular dynamics simulations of Newton black films (NBFs), ultra thin films of aqueous solutions stabilized with two monolayers of ionic surfactants, sodium dodecyl sulfate. We show that at low water content conditions and areas per surfactant corresponding to experimental estimates in NBFs, homogeneous films undergo an adhesion "transition," which results in a very thin adhesive film coexisting with a thicker film. We identify the adhesive film with the equilibrium structure of the Newton black film. We provide here a direct microscopic view of the formation of these important structures, which have been observed in experimental studies of emulsions and foams. We also report a detailed investigation of the structural properties and interfacial fluctuation spectrum of the adhesive film. Our analysis relies on the definition of an "intrinsic surface," which is used to remove the averaging effect that the capillary waves have on the film properties.     

Adsorption and characterization of molecular adhesion promoter monolayers on iron surfaces under UHV conditions

To investigate the chemical modification of metal surfaces by silanes and mercaptans used as molecular adhesion promoters between metal surfaces and polymer films, the adsorption of chlorosilanes and n-propylmercaptan has been examined on iron surfaces under ultra high vacuum conditions (UHV). The adsorption of silanes directly from the vapour phase has been impossible in UHV, however, a simultaneous condensation of water and silane leads to a stable silane layer. The hydrolysis reaction is rate determining. Stable mercaptan monolayers have been obtained only on oxygen covered iron surfaces. On pure iron the mercaptan molecules have been cracked, so that methyl groups as well as sulphur atoms could be found. The characterization of the surface layers has been performed by XPS and AES.     

Characterization of siloxane films on titanium substrate derived from three aminosilanes

The aim of this investigation was to study the siloxane, ? Si? O? Si? , film formation on Ti substrate by using mono‐, bis‐ and tris‐aminosilanes. The ultimate goal was to obtain a smooth, well‐organized and stable siloxane film with suitable surface energy. Such films are expected to perform well in adhering resins to dental metal alloys when the films contain reactive functional groups. Aminosilanes were prepared as 0.5 vol.% solutions in dilute ethanol (50 vol.% ethanol in deionized water), with their natural pH of ～ 9. The substrates were silanized in two ways: silane was allowed to react at room temperature or was cured for 1 h at 110°C. The surface characterization was carried out by reflectance–absorbance Fourier transform infrared spectroscopy (RA‐FTIR), x‐ray photoelectron spectroscopy (XPS), contact angle measurement and atomic force microscopy (AFM). Siloxane film thickness measurements were not made. According to spectral analysis, all silanes indicated covalent bond formation with titanium. ?Si? O? Ti? and ?Si? O? Si? bonds were clearly seen in the spectra, suggesting that chemical retention had taken place. After curing at elevated temperature, the spectral bands seemed to be stronger than those on samples cured at room temperature. Curing of hydrolyzed silanes at elevated temperature seemed to enhance the siloxane layer formation, derived from aminosilanes, on the Ti substrate. This might have an influence on the hydrolytic stability of organosilane‐promoted adhesion between Ti and dental resins. Copyright © 2004 John Wiley & Sons, Ltd.     

Surfactant charge effects on the location, vibrational spectra, and relaxation dynamics of cyanoferrates in reverse micelles

Ultrafast infrared spectroscopy has been used to measure vibrational energy relaxation (VER) and reorientation (Tr) times for the high frequency CN stretches of potassium ferrocyanide and ferricyanide and the NO stretch of sodium nitroprusside (SNP) in several reverse micelle (RM) systems using cationic, anionic, and nonionic surfactants. The confinement effects on anion vibrational spectra and dynamics in aqueous RMs depend on the charge of the surfactant that is used to form the RMs. Spectra and VER dynamics of ferrocyanide are not significantly altered in the limited number of RMs in which it could be solubilized. The static spectra of ferricyanide suggest an environment that is most bulklike in anionic RMs and least bulklike in cationic RMs. The dynamics of ferricyanide are slower in cationic RMs and indistinguishable from the bulk in nonionic RMs. The VER dynamics and static spectra of SNP are indistinguishable from the bulk in anionic RMs, but much slower in cationic RMs. This suggests a strong surfactant-solute repulsion in the former and an attraction in the latter. Broad static spectra and probe frequency dependent dynamics are seen for SNP in nonionic RMs, indicating an inhomogeneous distribution of environments. Similar measurements were carried out for SNP in mixtures of water and a model compound containing only the hydrophilic portion of the nonionic surfactants in which RMs are not formed. The results closely resemble those observed for SNP in nonionic RMs and provide evidence that in the latter water penetrates the interface and hydrates the ethylene oxide groups before forming a water pool. The results are consistent with the explanation that Coulombic forces determine the anion location. The anions are repelled to the interior of the water pool, which has a bulklike environment in anionic RMs, and are attracted to the interface in cationic RMs, resulting in a strong interaction with the surfactant. The solute location in the nonionic RMs depends on the hydrophilic nature of the probe, with ferrocyanide and ferricyanide being more hydrophilic than SNP. These results and the dependence on surfactant charge are similar to those reported for azide.     

Co-catalyzed autoxidation of alkene in the presence of silane. The effect of the structure of silanes on the efficiency of the reaction and on the product distribution

A systematic investigation of the structural effect of silanes on the Co-catalyzed reductive oxygenation of alkene in the presence of silane (Mukaiyama-Isayama reaction) showed that the efficiency of the reaction decreases with the increase of the steric bulk of the silanes. A similar trend was observed for the metal-exchange reaction between Co(III)-alkylperoxo complex and silane, too. The peroxidation of (S)-limonene, followed by deprotection of the derived silyl peroxides, provides a mixture of the corresponding monocyclic hydroperoxide 24 and the bicyclic one 25, the ratio being a marked function of the steric bulk of silanes.     

过渡金属表面有机官能团硅烷膜的研究——镍电极表面γ-氨丙基三甲氧基硅烷膜的结构

在镍电极表面制备了γ-氨丙基三甲摒在硅烷膜并对其形成和结构进行了研究 。镍电极表面有机官能团硅烷膜的X射线光电子能谱（XPS）结果表明氮、硅等元素 在电极表面的存在，并且氨基在膜中有若干种存在方式，包括自由氨基和质子化的 氨基。通过对表面增强拉曼散射光谱（SERS）谱图的分析，发现与电极表面作用的 吸附基团硅醇羟基和氨基发生了竞争吸附，它们及其邻近基团的拉曼谱几随着电位 的负称除了相对强度发生变化以外，还发生了一定的位移，这缘于吸咐基团吸附的 量和吸附取向随电极电位发生了变化并形成的更为复杂的界面结构；氨基不同存在 方式之间也会随之发生转变，这一结果与X射线光电子能谱分析的结果相符合。原 子力显微镜（AFM）结果表明镍电极表面的有机官能团硅烷膜呈现为一种较规则的 多孔结构。     

nc-Si:H/c-Si硅异质结太阳电池中本征硅薄膜钝化层的优化

采用射频等离子体增强化学气相沉积(RF-PECVD)法在低温、低功率的条件下制备了一系列本征硅薄膜, 研究了硅烷浓度(C_S)对薄膜微结构、光电特性及表面钝化性能的影响. 将本征硅薄膜作为钝化层应用到氢化纳米晶硅/晶硅(nc-Si:H/c-Si)硅异质结(SHJ)太阳电池中, 研究了硅烷浓度和薄膜厚度对电池性能的影响. 实验发现: 随着硅烷浓度的降低, 本征硅薄膜的晶化率、氢含量、结构因子、光学带隙和光敏性等都在过渡区急剧变化; 本征硅薄膜的钝化性能由薄膜的氢含量及氢的成键方式决定. 靠近过渡区的薄膜具有较好的致密性和光敏性, 氢含量最高, 带隙态密度低, 且主要以SiH 形式成键, 对硅片表现出优异的钝化性能, 使电池的开路电压大幅提高. 但是, 当薄膜的厚度过小时, 会严重影响其钝化质量. 本实验中, 沉积本征硅薄膜的最优硅烷浓度为6% (摩尔分数), 且当薄膜厚度为~8 nm时, 所制备电池的性能最好. 实验最终获得了开路电压为672 mV, 短路电流密度为35.1 mA·cm^-2, 填充因子为0.73, 效率为17.3%的nc-Si:H/c-Si SHJ太阳电池