Formation, structure, and reactivity of amino-terminated organic films on silicon substrates

Amino-functionalized organic films were prepared by self-assembling 3-aminopropyltriethoxysilane (APTES) on silicon wafers in either anhydrous toluene or phosphate-buffered saline (PBS) for varied deposition times. Fourier transform infrared spectroscopy (FTIR) and ellipsometry have shown that the structure and thickness of APTES films are governed by the deposition time and reaction solution. Deposition from an anhydrous toluene solution produces APTES films ranging from 10 to 144 A in thickness, depending on the reaction time. FTIR spectra indicate that film growth initially proceeds by adsorption of APTES to the silicon surface followed by siloxane condensation, and after an extended period of time APTES molecules accumulate on the underlying APTES film by either covalent or noncovalent interactions. In contrast, spectroscopically indistinguishable APTES films in thickness ranging from 8 to 13 A were formed when deposition was conducted in aqueous solutions. Measured water contact angles indicate that APTES films deposited in aqueous solutions are more hydrophilic compared to those prepared in toluene solutions. Fluorescence measurements revealed that APTES films prepared in toluene solutions contain more reactive surface amino groups by ca. 3 to 10 times than those prepared in aqueous solutions for the identical reaction time.     

Preparation and self-assembly of carboxylic acid-functionalized silica

A simple method for the fabrication of silica nanoparticle film based on the covalent-bonding interaction between carboxylic acid-functionalized silica nanoparticles (SiO(2)-COOH) and amino-terminated silicon wafer was developed. Prior to assembly, silica nanoparticles with an average diameter 80 nm were prepared using the St?ber method, amino-functionalized silica nanoparticles (SiO(2)-NH(2)) were prepared by a silanization with 3-aminopropyltriethoxysilane (APTES), while carboxylic acid-functionalized silica nanoparticles (SiO(2)-COOH) were prepared by a ring opening linker elongation reaction of the amine functions with succinic anhydride, at the same time, amino-terminated silicon wafer (Si-NH(2)) was obtained by self-assembling 3-aminopropyltriethoxysilane, then one layer relative close-packed carboxylic acid-functionalized silica nanoparticles (SiO(2)-COOH) was arranged on silicon wafer through amidation reaction under DCC coupling agent.     

一步可控合成二氧化硅纳米管和空心球

通过简单的溶胶凝胶法在相同体系中可控合成了新颖有序的二氧化硅纳米管和空心球,对制备二氧化硅纳米管的多种反应条件进行了系统研究。发现反应时间、溶液中水和乙醇比例、搅拌和滴加速度对形成管状结构都有着重要影响。同时,纳米管的形成机理研究表明,在醇水混合溶液中柠檬酸三铵晶体为细柱状形貌,其作为重要的结构导向剂为二氧化硅胶晶附着提供模板,从而形成管状结构,二氧化硅空心球也显示了相似的形成过程。     

Coating process regimes in particulate film production by forced-convection-assisted drag-out

Operating conditions for the deposition of monolayer and bilayer particulate coatings from aqueous 20-nm-diameter silica dispersions are identified in the context of a drag-out operation assisted by forced convection. The dry film thickness, uniformity, and morphology are assessed within an operating window parametrized by the capillary number and silica dispersion weight fraction. Three film deposition regimes with respect to the capillary number are observed: convective film deposition at low process rates, film entrainment at moderate process rates, and a thin-film transition regime at intermediate process rates. Locally ordered particulate films of variable layering thickness, including (i) a discontinuous submonolayer or (ii) a mixed submonolayer and monolayer, (iii) a mixed monolayer and bilayer, and (iv) multilayers, are dominant under convective deposition conditions. A map of morphologies is presented within the capillary number-weight fraction operating window, where monolayer and mixed monolayer-bilayer films are demonstrated in the thin-film transition regime at an intermediate dispersion weight fraction. A complementary map of the morphologies formed by the drag-out of 110 nm silica dispersions reveals a broader applicability to this type of operability diagram. These operating maps are constructed using model silica dispersions and are therefore relevant to particulate coatings of other inorganic materials.     

Amino-functionalized SBA-15 type mesoporous silica having nanostructured hexagonal platelet morphology

Amino-functionalized SBA-15 type mesoporous silicas having unique hexagonal platelet morphologies with short channels (100-300 nm) running parallel to the thickness of the nanostructured hexagonal platelet type morphologies have been directly synthesized by co-condensation of aminopropyltriethoxysilane (APTES) and sodium metasilicate as a silica source in the presence of Pluronic P123 triblock copolymer as a structure directing agent.     

Coating Multi-walled Carbon Nanotubes with Uniform Silica Shells:Independent of Surface Chemistry

A facile and general method was described to coat six types of multi-walled carbon nanotubes, functionalized by either noncovalent or covalent way, with smooth silica shells. 3-Aminopropyltriethoxysilane(APTES) and pH value play important roles in the coating process and the thickness of silica shell could be controlled by the added amount of silicon alkoxides. After the removal of multi-walled carbon nanotubes by calcination, the silica nanotubes were successfully prepared.     

Biomimetic synthesis of silica nanostructures with controllable morphologies and sizes through tuning interfacial interactions

By manipulating the interfacial interactions between the peptide templates and the silicate species derived from TEOS and APTES, a facile biomimetic method was developed for the fabrication of silica nanostructures exhibiting "string-of-beads" and fibrillar morphologies of varied sizes.     

The effects of network structure on the resistance of silane coupling agent layers to water-assisted crack growth

Silane adhesion promoters are commonly used to improve the adhesion, durability, and corrosion resistance of polymer-oxide interfaces. The current study investigates a model interface consisting of the natural oxide of(100) Si and an epoxy cured from diglycidyl ether ofbisphenol A (DGEBA) and triethylenetetraamine (TETA). The thickness of (3-glycidoxypropyl)trimethoxysilane (GPS) films placed between the two materials provided the structural variable. Five surface treatments were investigated: a bare interface, a rough monolayer film, a smooth monolayer film, a 5 nm thick film, and a 10 nm thick film. Previous neutron reflection experiments revealed large extension ratios (>2) when the 5 and 10 nm thick GPS films were exposed to deuterated nitrobenzene vapor. Despite the larger extension ratio for the 5 nm thick film, the epoxy/Si fracture energy (Gc) was equal to that of the 10 nm thick film under ambient conditions. Even the smooth monolayer exhibited the same Gc. Only when the monolayer included a significant number of agglomerates did the Gc drop to levels closer to that of the bare interface. When immersed in water at room temperature for 1 week, the threshold energy release rate (Gth) was nearly equal to Gc for the smooth monolayer, 5 nm thick film, and 10 nm thick film. While the Gth for all three films decreased with increasing water temperature, the Gth of the smooth monolayer decreased more rapidly. The bare interface was similarly sensitive to temperature; however, the Gth of the rough monolayer did not change significantly as the temperature was raised. Despite the influence of pH on hydrolysis, the Gth was insensitive to the pH of the water for all surface treatments.     

Efficient synthesis of asymmetric particles by sol-gel process

This paper presents a novel and facile method of synthesizing polymer/silica particles with controlled asymmetric morphologies. Our approach is based on the sol–gel process in which cross-linked polystyrene particles (CPS) are adopted as templates and 3-mercaptopropyltriethoxysilane is used as a single silica source. The reaction process causes silane oligomer to preferentially grow on the local surface of CPS, giving rise to polystyrene/thiol-functionalized silica composite particles with a tunable shape. It is found that the morphologies of particles can be easily tailored by changing the ratio of ethanol/water in the reaction medium. In addition, the amount of cross-linker used during the polymerization also plays a key role in the formation of various complex-shaped particles. Controlled geometries of these organic/inorganic composite particles will allow a broad range of potential applications, such as photonic crystals, Pickering emulsifier, sensors, and so on.     

Electrochemically‐Induced Deposition of Amine‐Functionalized Silica Films on Gold Electrodes and Application to Cu(II) Detection in (Hydro)Alcoholic Medium

Well‐adherent amine‐functionalized porous silica films have been deposited on gold electrodes by combining the self‐assembly technology, the sol–gel process, and the electrochemical modulation of pH at the electrode/solution interface. A partial self‐assembled monolayer of mercaptopropyl‐trimethoxysilane (MPTMS) was first formed on disposable gold electrodes from recordable CDs (Au‐CDtrodes). The so pretreated MPTMS‐Au‐CDtrodes were immersed in a stable sol solution (pH 3) containing (3‐aminopropyl)‐triethoxysilane (APTES) and tetraethoxysilane (TEOS). Polycondensation of the APTES and TEOS precursors was then achieved by applying a negative potential for a given period of time to generate a local pH increase at the electrode/solution interface and promote the deposition of the amine functionalized silica film adhering well to the electrode surface owing to the MPTMS monolayer acting somewhat as a “molecular glue”. Various parameters affecting the electrodeposition process have been studied and the film permeability to redox probes in solution was characterized by cyclic voltammetry. The amine‐functionalized silica film electrodes were then applied to the preconcentration of copper(II) species prior to their electrochemical detection by anodic stripping differential pulse voltammetry. Getting high sensitivity has however required the application of an electrochemical pre‐activation step as the majority of the organo‐functional groups were in the form of ammonium moieties (because the film was prepared from an acidic sol). This was achieved by applying a sufficiently negative potential to the electrode surface to reduce protons and increase consequently the amine‐to‐ammonium ratio within the film and, thus, the efficiency of the precocentration process. The resulting device was then optimized for copper(II) determination in hydroalcoholic medium, giving rise to a linear response in the 0.1–10 μM concentration range.     

Influence of surface hydroxylation on 3-aminopropyltriethoxysilane growth mode during chemical functionalization of GaN Surfaces: an angle-resolved X-ray photoelectron spectroscopy Study

A comparative study of the chemical functionalization of undoped, n- and p-type GaN layers grown on sapphire substrates by metal-organic chemical vapor deposition was carried out. Both types of samples were chemically functionalized with 3-aminopropyltriethoxysilane (APTES) using a well-established silane-based approach for functionalizing hydroxylated surfaces. The untreated surfaces as well as those modified by hydroxylation and APTES deposition were analyzed using angle-resolved X-ray photoelectron spectroscopy. Strong differences were found between the APTES growth modes on n- and p-GaN surfaces that can be associated with the number of available hydroxyl groups on the GaN surface of each sample. Depending on the density of surface hydroxyl groups, different mechanisms of APTES attachment to the GaN surface take place in such a way that the APTES growth mode changes from a monolayer to a multilayer growth mode when the number of surface hydroxyl groups is decreased. Specifically, a monolayer growth mode with a surface coverage of approximately 78% was found on p-GaN, whereas the formation of a dense film, approximately 3 monolayers thick, was observed on n-GaN.     

硅表面复合自组装膜的制备及其摩擦性能

采用自组装技术在单晶硅表面制备了3-氨基丙基三乙氧基硅烷(APTES)-SiO2-APTES复合膜,并对其表面的组成、结构及摩擦性能进行了表征.结果表明:复合膜表面对水的接触角约为63°,且表面平整、致密,其平均粗糙度(Ra)约为0.963nm.通过原子力显微镜(AFM)和透射电子显微镜(TEM)观察到夹层中SiO2颗粒的粒径约为20-50nm,较均匀地分布在第一层APTES膜的表面.与APTES自组装单层膜(SAMs)相比,APTES-SiO2-APTES复合膜由于纳米SiO2颗粒的引入而表现出更低的摩擦系数和更长的耐磨寿命.     

Fluorinated nanodiamond as a wet chemistry precursor for diamond coatings covalently bonded to glass surface

The chemical reaction between fluoro-nanodiamond (F-ND) powder, solubilized in o-dichlorobenzene, and a glass surface, functionalized with the silane coupling agent, 3-aminopropyltriethoxysilane (APTES), was found to proceed under heating at 130 degrees C for 24-40 h and to result in covalent bonding of F-ND particles to a glass substrate, forming a 10-40 nm thick nanocrystalline film. The observed process presents a novel and cost-effective approach to fabrication of diamond coatings on glass by using wet chemistry instead of CVD and can be extended to other materials.     

Immobilization and electrochemistry of cytochrome c on amino-functionalized mesoporous silica thin films

The immobilization and electrochemistry of cytochrome c (cyt c) on amino-functionalized mesoporous silica thin films are described. The functionalized silica films with an Im3m cubic phase structure were deposited on conducting ITO substrate by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of Pluronic F127 under acidic conditions. The high specific surface area, large pore size and functional inner surface of mesoporous silica thin films result in a high cyt c loading, and the cyt c immobilization on this silicate framework is stable. After adsorption of cyt c, the ordered cubic structure of mesoporous silica and the redox activity of immobilized cyt c are retained as demonstrated by X-ray diffraction (XRD), Transmission electron microscope (TEM) and cyclic voltammetry. The redox behavior of the cyt c/silica film-modified ITO electrode is a surface-controlled quasi-reversible process for the experimental conditions used in this work and the electron transfer rate constant is calculated is 1.33 s⁻¹. The ITO electrode modified by cyt c/silica film possesses a high stability; even cyt c retains its redox activity following immobilization for several months. Furthermore, the electrocatalytic activities of the modified ITO electrode to hydrogen peroxide and ascorbic acid have been studied. Since these behaviors are quite pronounced, the modified electrode can be used for detection of hydrogen peroxide and ascorbic acid.     

Direct synthesis and catalytic applications of ordered large pore aminopropyl-functionalized SBA-15 mesoporous materials

SBA-15 mesoporous silica has been functionalized with aminopropyl groups through a simple co-condensation approach of tetraethyl orthosilicate (TEOS) and (3-aminopropyl)triethoxysilane (APTES) using amphiphilic block copolymers under acidic conditions. The organic-modified SBA-15 materials have hexagonal crystallographic order, pore diameter up to 60 A, and the content of aminopropyl groups up to 2.3 mmol g(-1). The influences of TEOS prehydrolysis period and APTES concentration on the crystallographic order, pore size, surface area, and pore volume were examined. TEOS prehydrolysis prior to the addition of APTES was found essential to obtain well-ordered mesoporous materials with amino functionality. The amount of APTES incorporated in the silica framework increased with the APTES concentration in the synthesis gel, while the ordering of the mesoporous structure gradually decreased. Analysis with TG, IR, and solid state NMR spectra demonstrated that the aminopropyl groups incorporated in SBA-15 were not decomposed during the preparation procedure and the surfactant P123 was fully removed through ethanol extraction. The modified SBA-15 was an excellent base catalyst in Knoevenagel and Michael addition reactions.     

四氨基酞菁锌负载二氧化硅纳米粒子的合成及其对细胞毒性的研究

通过在无极核微乳液中水解乙烯基三乙氧基硅烷(TEVS)和3-氨丙基三乙氧基硅烷(APTES),制备了疏水性光敏剂-2,9,16,23-四氨基酞菁锌负载的表面带有正电荷的二氧化硅纳米粒子(SiO2@ ZnPc( NH2)4).通过透射电镜(TEM)、Zetasizer Nano-ZS粒度仪(DLS)、紫外-可见分光光度计...     

Multifunctional NO-delivery vessel derived from aminopropyl-modified mesoporous zeolites

A new strategy, releasing nitric oxide (NO) and adsorbing nitrosamines simultaneously by zeolitic materials in the digestive system, is validated in this paper. Three types of moisture-saturated molecular sieves, HZSM-5 zeolite, mesoporous zeolite, and mesoporous silica MCM-41, are used as NO-delivery vessels in mimic gastric juice after modification of γ-aminopropyltriethoxysilane (APTES). APTES modification dramatically increased the capability of zeolite and mesoporous silica in NO release in acidic solution, because more NO can be adsorbed in the composite and stored in the form of nitrite. Some composites released the NO 10 times more than their parent materials, and synchronously captured the carcinogen nitrosamines in mimic gastric juice. The influences of APTES modification on the porous structure and surface state of zeolite and mesoporous silica were investigated by XRD, N(2) adsorption, and FTIR tests, through which the mesoporous zeolite is proven to be the optimal support. With this hierarchical material a controllable APTES modification is realized in which a lot of aminopropyl groups are grafted in mesopores while the zeolitic structure is maintained, so the resulting sample exhibits a high capability in releasing NO and adsorbing nitrosamines. This investigation provides a clue for elevating the efficiency of zeolites in the application of life science.     

Macroporous thin films for planar chromatography

A procedure for the preparation of macroporous silica films suitable for planar chromatography is described. The films are produced by a low pH catalyses of alkyltrialkoxysilanes in oversaturated solution of pore forming organic compounds. A segregated three phase system yields thick films (10–60 µm) that have good adhesion to silica glass supports, uniform, mirror like surface and intercalated micron-dimension pores that permit capillarity driven elution of solvents through the film. A phase diagram demonstrating optimal operating conditions for macroporous and microporous film formation is introduced and analyzed.     

Interface-directed sol-gel: direct fabrication of the covalently attached ultraflat inorganic oxide pattern on functionalized plastics

For plastic electronics and optics, the fabrication of smooth, transparent and stable crack-free inorganic oxide films (and patterning) on flexible polymeric substrates with strong bonding strength and controllable thickness from nanometers to micrometers is a key but still remains a challenge. Among versatile inorganic oxides, silica oxide film as SiO _x is especially important because this semiconductor material could provide crucial properties in devices or serve as a base layer for further multilayer construction. In this paper, we describe a new interface-directed sol-gel method to fabricate flexible high quality silicon oxide film onto commodity plastics. The resulting crack-free silica film has strong covalent bonding with polymer substrates, homogeneous morphology with ultralow roughness, highly optical transparency, tunable thickness from nm to μm, and easy patterning ability. Such fabrication strategy relies on a novel photocatalytic oxidation reaction by photosensitive ammonium persulfate (APS), which is able to fabricate highly reactive hydroxyl monolayer surface on inert polymeric substrates. This kind of hydroxylated surface could serve as nucleation and growth sites to initiate surface sol-gel process. As a result, well-defined SiO _x film deposition (gelation) occurs, and patterned hydroxylation regions could be easily utilized to induce the formation of patterned oxide film arrays. Our strategy also excludes the requirements of clean room and vacuum devices so as to fulfill low-cost and fast fabrication demands. Two application examples from such high quality SiO _x layer onto plastics are given but should not be limited within these. One is that oxygen permeation rate of SiO _x deposited polymer film decreases 25 times than pristine polymer substrate, which is good for the potential packaging materials. The other one is that silanization monolayer, for example, 3-aminopropyltriethoxysilane (APTES), could be successfully constructed onto silica layer through classical silanization reaction, which is applicable for many potential purposes, for instance, proteins could be accordingly immobilized onto plastic support with effective signal-to-background ratio. Moreover, we further demonstrate that this interface-directed sol-gel strategy is a general method which could be successfully extended to other high quality oxide film fabrication, e.g., TiO₂.     

Reaction of N-phenyl maleimide with aminosilane monolayers

Reaction of N-phenyl maleimide (NPM) with silica surfaces modified with a self-assembled monolayer of (aminopropyl)triethoxysilane (APTES) was investigated using infrared spectroscopy (FTIR), elemental analysis, and titration assays. This reaction is of interest as a test case for using amine-maleimide coupling for immobilization of biomolecules. Addition of NPM to surface APTES residues was consistently sub-stoichiometric, with typical yields of about 75% on monolayers with a coverage of 1.15 APTES residues/nm2. Titration analysis found negligible presence of imide alkene C=C bonds in modified supports, indicating that addition of NPM to APTES proceeded via amine attack at the imide olefinic bond. FTIR measurements also revealed presence of amide bands which intensified over periods of 10 h. These observations were attributed to a slower secondary process in which APTES amines attack imide carbonyls to produce amide linkages. Stability of NPM-modified surfaces was examined under room temperature storage in pH 7 buffer up to 72 h and for 2 h exposure to buffer at temperatures up to 90 degrees C. It was found that stability was determined by robustness of APTES-silica attachment, with about 30% loss under the harshest conditions investigated.