Hydrophobic silica aerogels prepared via rapid supercritical extraction

Hydrophobic silica aerogels have been prepared using the rapid supercritical extraction (RSCE) technique. The RSCE technique is a one-step methanol supercritical extraction method for producing aerogel monoliths in 3 to 8 h. Standard aerogels were prepared from a tetramethoxysilane (TMOS) recipe with a molar ratio of TMOS:MeOH:H₂O:NH₄OH of 1.0:12.0:4.0:7.4 × 10⁻³. Hydrophobic aerogels were prepared using the same recipe except the TMOS was replaced with a mixture of TMOS and one of the following organosilane co-precursors: methytrimethoxysilane (MTMS), ethyltrimethoxysilane (ETMS), or propyltrimeth-oxysilane (PTMS). Results show that, by increasing the amount of catalyst and increasing gelation time, monolithic aerogels can be prepared out of volume mixtures including up to 75% MTMS, 50% ETMS or 50% PTMS in 7.5–15 h. As the amount of co-precursor is increased the aerogels become more hydrophobic (sessile tests with water droplets yield contact angles up to 155°) and less transparent (transmission through a 12.2-mm thick sample decreases from 83 to 50% at 800 nm). The skeletal and bulk density decrease and the surface area increases (550–760 m²/g) when TMOS is substituted with increasing amounts of MTMS. The amount of co-precursor does not affect the thermal conductivity. SEM imaging shows significant differences in the nanostructure for the most hydrophobic surfaces.     

Spectroscopic study of TMOS–TMSM–MMA gels: Previously identification of the networks inside the hybrid material

A 3-(trimethoxy-silyl)propyl methacrylate (TMSM)–methylmethacrylate (MMA)–tetramethyl-orthosilicate (TMOS) hybrid glass, has been prepared using a sol–gel process. In order to study the influence of each of the inorganic matrices, the gels obtained from TMOS and TMSM have been studied separately, the hybrid compound, they have been investigated using Raman spectroscopic, FT-IR and NMR techniques. The networks formed in both TMOS and TMSM gels have been identified. Upon condensation of TMOS a tridimensional array including defect was formed, that results in a certain discontinuity of the material. Nevertheless, the characteristics of this structure have that of molten quartz (glassy silica). By contrast, room temperature condensation of TMSM gave rise to several structurally different species in suspension in the gel. The species have been identified. The insertion of TMSM in an organic network modified its degree of periodicity. The integration of TMOS into a silica network occurred through the formation of rings which link together various silica blocks originated from TMOS. Interpretation of Raman diffusion data shows that the glass still contains non-condensed silanol groups and that low molecular weight cyclic, caged polysilsesquioxanes are formed from condensed TMSM. No organic–inorganic phase separation has been observed. The organic part of the glass has been investigated by Raman Spectroscopy from a microscopic point of view. It has helped understand the competition between condensation and polymerization, and it has been shown that polymerization was not fully completed. This has been confirmed by DSC. Raman spectra have also shown that the inorganic network was mainly three-dimensional. NMR studies confirmed that condensation occurred several times on the active SiO bonds.     

Sol–gel silica hybrid biomaterials for application in biodegradation of toxic compounds

The purpose of the present work is the sol–gel synthesis, structure characterization and potential application of hybrid biomaterials based on silica precursor (MTES) and natural polymers such as gelatin or pectin. The structure formation in the biomaterials was investigated by XRD, FTIR, BET and AFM. The results showed that all studied hybrid biomaterials have an amorphous structure. The FT-IR spectra of the obtained materials with MTES showed chemical bonds at 2,975, 1,255, 880 and 690 cm⁻¹ due to the presence of Si–O–R (CH₃ and C₂H₅) and Si–C bonds. In the samples synthesized with TEOS the inorganic and organic components interact by hydrogen bonding, Van der Waals or electrostatic forces. Surface area of investigated samples decreases with increasing of the natural polymers content. The structure evolution was studied by AFM and roughness analysis. Depending on the chemical composition a different design and size of particles and their aggregates on the surface structure were established. The hybrid biomaterials were used for immobilization of bacterial cells and applied in the biodegradation of the toxic compound 4-chlorobutyronitrile, possible constituent of waste water effluents in a laboratory glass bioreactor. Optimization of the process at different temperatures was carried out.     

NMR Study of Intercalates and Grafted Organic Derivatives of H2La2Ti3O10

The protonated perovskite-like titanate H₂La₂Ti₃O₁₀ has been used to produce organic-inorganic hybrids with simple organic molecules: methylamine, methanol, monoethanolamine, and n-butylamine. The optimal pathways for the preparation of such hybrids are summarized. Solid-state NMR, combined with thermal analysis, Raman, and IR spectroscopy, has been applied to determine the bonding type in the obtained organic-inorganic hybrids. It has been found that, in the methanolic hybrid, the organic residues are covalently bound to the inorganic matrix. In contrast, in the methylamine and n-butylamine hybrids, the organic molecules are intercalated into the inorganic matrix in cationic forms. The structure of the monoethanolamine hybrid is composite and includes both the covalently bound and intercalated organic species.     

Synthesis of poly(diallyl phthalate) and silica gel polymer hybrids utilizing π–π interactions

We report here the synthesis of homogeneous polymer hybrids of poly(diallyl phthalate) (PDAP) and silica by utilizing π–π interactions. Use of arylalkoxysilanes such as phenyltrimethoxysilane (PhTMOS), phenethyltrimethoxysilane (PhenethylTMOS) and mesityltrimethoxysilane (MesTMOS) as sources for inorganic phases resulted in optically transparent PDAP-silica polymer hybrids in a wide range of organic and inorganic content ratios. On the other hand, alkoxysilanes such as tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMOS) and i-butyltrimethoxysilane (iBuTMOS) resulted in phase separated, turbid solids. A mixture of tetramethoxysilane (TMOS) and PhTMOS was also studied for the synthesis of PDAP-silica gel polymer hybrids to control the cross-linking density in the inorganic phase. Homogeneity was found to be improved with an increase in PhTMOS content. These homogeneous PDAP polymer hybrids were found to have high thermal stability which wasachieved by nano-scale dispersion of PDAP in silica through extensiveinterface interactions. The homogeneity of the polymer hybrids was confirmed by SEM and TEM, which demonstrate a nanometer level integration of the organic polymer and the inorganic phase.     

Effect of Inorganic Components on Thermal Stability of Methylsiloxane-Based Inorganic/Orgnaic Hybrids

The thermal decomposition behavior of methylsiloxane-based inorganic/organic hybrids containing an inorganic component derived from metal alkoxides such as Si(OCH₃)₄, Al(O^sC₄H₉)₃, Ti(OⁱC₃H₇)₄ and Nb(OC₂H₅)₅ was investigated by means of thermogravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The decomposition temperature of methyl groups in methylsiloxane-based inorganic/organic hybrids containing an inorganic component derived from metal alkoxides was higher than that in the methylsiloxane-based inorganic/organic hybrid prepared from only CH₃Si(OC₂H₅)₃. In particular, when incorporating Nb and Ti inorganic components, methyl groups in methylsiloxane-based inorganic/organic hybrids decomposed at about 100 and 200^∘C higher temperatures, respectively, than those in the methylsiloxane-based inorganic/organic hybrid prepared from only CH₃Si(OC₂H₅)₃. The incorporation of an inorganic component other than siloxane into methylsiloxane-based inorganic/organic hybrids was found to thermally stabilize the methyl groups of methylsiloxane networks.     

Processing and Properties of Inorganic-Organic Hybrids Containing Various Inorganic Components

Inorganic-organic hybrids containing various inorganic components have been synthesized from silanol-terminated polydimethylsiloxane (PDMS) and three different inorganic components: Al(O-sec-C4H9)3, Ti(OC2H5)4 and Ta(OC2H5)5. The hybrids obtained were transparent and flexible. Dynamic mechanical measurements and stress-strain experiments were carried out in order to study the effect of inorganic component on the properties of the Metal-O-PDMS hybrids. The storage modulus at around room temperature increased in the order Al-O-PDMS, Ti-O-PDMS, Ta-O-PDMS hybrids, indicating that the three-dimensional network structure became denser in this order. The tensile strength increased in the order Al-O-PDMS, Ta-O-PDMS, Ti-O-PDMS hybrids. The difference in tensile strength is considered to be related to the strength of the interaction between the inorganic component and PDMS. The elongation at failure also depended on the inorganic component. Ti-O-PDMS hybrid exhibited the largest elongation of all the samples (more than 200%).     

Preparation and Characterization of the Hybrids Containing Silica Nanoparticles by Sol-Gel Crosslinking Process

The organic/inorganic hybrid nanomaterials containing silica nanoparticles are synthesized by sol-gel crosslinking process. The tetraethoxysilane (TEOS) and γ-aminopropyltriethoxylsilane as coupling agents are used as a precursor. The 2,4,6-tri [(2-epihydrin-3-bimethyl-ammonium)propyl]-1,3,5-triazine chloride (Tri-EBAC) as crosslinking agent is used to form covalent bonds among the inorganic nanoparticles. The chemical and morphological structures of the organic/inorganic hybrid are characterized with FTIR spectra, ²⁹Si-NMR, x-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and atomic force microscope (AFM). The results show that the organic/inorganic hybrid forms covalent bond between the inorganic nanoparticle and Tri-EBAC. The network organic/inorganic hybrid can form good film with even nanometer particles. The network organic/inorganic hybrids nanomaterial not only exhibits the thermal properties of inorganic compounds, but also exhibits the thermal properties of organic polymer.     

Organic–inorganic hybrid materials. I. Characterization and degradation of poly(imide–silica) hybrids

Poly(imide–silica) hybrid materials with covalent bonds were prepared by (3-aminopropyl)methyldiethoxysilane (APrMDEOS) terminated amic acid, water, and tetramethoxysilane (TMOS) via a sol–gel technique. Infrared (IR), ²⁹Si and ¹³C CP/MAS nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis (TGA) were used to study hybrids containing various proportions of TMOS and hydrolysis ratios. The microstructure and chain mobility of hybrids were investigated by proton spin–spin relaxation T₂ measurements. The apparent activation energy E_a for degradation of hybrids in air was studied by the van Krevelen method. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2275–2284, 1999     

Solid Acid-Base Control of Inorganic/Organic Hybrids by Inorganic Components for Molecule-Selectivity

Solid acid-base properties of methylsiloxane-based inorganic/organic hybrids were controlled by incorporation of inorganic components other than Si into methylsiloxane networks. The effect of different inorganic components on the solid acid-base properties was estimated by first-principles calculations based on density functional theory (DFT). The deprotonation tends to occur in the order Si < Al < Nb inorganic components, suggesting that the acidity increases in the same order. Methylsiloxane-based hybrids with solid acid-base properties were also synthesized by incorporating inorganic components derived from metal alkoxides. Hammett indicators revealed that the solid acidity increased in the order Si < Al < Nb inorganic components, which was consistent with the results of first-principles calculations. Preliminary experiments revealed that the methylsiloxane-based hybrids also provided a solid basic nature by containing Ca and Y inorganic components derived from metal alkoxides. The acidic hybrids were found to have Brønsted acid sites from the FT-IR experiments of adsorbed pyridine on the hybrids.     

高折射率有机/无机纳米杂化透明膜层材料的制备与性质研究

采用溶胶-凝胶法,将钛酸酯和硅烷偶联剂(KH-560)进行共水解,经涂膜、固化,制备了一系列含有无机二氧化钛纳米相的无机/有机杂化膜层材料,通过不同方法对杂化膜层的微结构、光学、机械和热性质进行了表征.结果表明,所得到的有机/无机纳米复合膜层,在可见光范围内的透过率均在90%以上,同时具有较好的耐热性和较高的折射率(nd=1.47~1.73),并且膜层与基材的附着性好,铅笔硬度达到4~5H.     

Polyimide–Silica Gel Hybrids Containing Metal Salts: Preparation via the Sol–Gel Reaction

A facile preparation of polyimide–silica gel hybrids by the simultaneous in-situ formation of polyimides during the hydrolysis–condensation of tetramethoxysilane (TMOS) is reported here. The hydrolysis and condensation of TMOS was carried out in a solution of DMAc containing 5% LiCl, CaCl₂ or ZnCl₂ and the seven-membered cyclic polyimide intermediate. The seven-membered cyclic intermediates, precursors of polyimides, were derived from the low-temperature polycondensation of dianhydrides [benzophenonetetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA), and 4,4-bis(hexafluoroisopropylidene)phthalic dianhydride (6FDA)] and di-isocyanates [isophorone di-isocyanate (IPDI), toluene di-isocyanate (TDI), hexamethylene di-isocyanate (HDI) and 4,4′-diphenylmethane di-isocyanate (MDI)]. These intermediates could readily be converted to the corresponding polyimides. Films were cast from the resulting mixtures and the solvent was gradually evaporated at 130 °C to result in the formation of clear, transparent, pale yellow or amber-colored hybrid films in which the salts were dispersed at the molecular level. Pyrolysis of polyimide–silica gel hybrids at 600 °C gave mesoporous silica. Silica gel obtained from hybrids HPI-8 (containing no salt) and HPI-11 (containing ZnCl₂) had a pore radius (BJH method) of 2.9 nm, while that from hybrid HPI-9 (containing LiCl) had a pore radius of 11.4 nm. The surface areas (BET method) obtained were 203 m² g⁻¹, 19 m² g⁻¹ and 285 m² g⁻¹, while the pore volumes were 0.373 cm³ g⁻¹, 0.158 cm³ g⁻¹ and 0.387 cm³ g⁻¹, respectively, for samples obtained from hybrids HPI-8, HPI-9 and HPI-11. © 1997 by John Wiley & Sons, Ltd.     

纳米TiO2介孔薄膜的模板组装制备研究

以TiCl₄为无机前驱体、三嵌段高分子共聚物EO₂₀PO₇₀EO₂₀为模板剂，在非水条件下制备了有序的锐钛矿TiO₂纳米晶介孔薄膜。通过热重-差热（TG-DTA）分析、X射线衍射（XRD）分析、原子力显微观察（AFM）及N₂吸附-脱附等测试对样品进行了表征。结果表明，薄膜具有均一的大介孔孔径（～10 nm），其BET比表面积为150 m²·g^-1，薄膜较宽的无机壁厚显著提高了介孔结构的热稳定性。通过红外（IR）光谱分析考察了溶胶-凝胶过程中发生的物理化学变化。在对薄膜表面形貌进行AFM观察的基础上初步探讨了嵌段共聚物EO₂₀PO₇₀EO₂₀对薄膜孔结构形成的导向机理。     

Thermal stability and degradation kinetics of novel organic/inorganic epoxy hybrid containing nitrogen/silicon/phosphorus by sol-gel method

Hybrids containing silicon, phosphorous and nitrogen were prepared by the sol-gel method and compared with pure epoxy. The silicon, phosphorous and nitrogen components were successfully incorporated into the networks of polymer. Thermogravimetric analysis (TGA) was used for rapid evaluation of the thermal stability of different materials. The integral procedure decomposition temperature (IPDT) has been correlated the volatile parts of polymeric materials and used for estimating the inherent thermal stability of polymeric materials. The IPDT of pure epoxy was 464 °C and the IPDTs of hybrids were higher than that of pure epoxy. The thermal stability of hybrids increased with the contents of inorganic components. The inorganic components can improve the thermal stability of pure epoxy.Two methods have been used to study the degradation of hybrids containing silicon, phosphorous and nitrogen hybrid during thermal analysis. These investigated methods are Kissenger, Ozawa's methods. The activation energies (E_a) were obtained from these methods and compared. It is found that the values of E_a for modified epoxy hybrids are higher than that of pure epoxy. The hybrids of high activation energy possess high thermal stability.     

Rational synthesis of covalently bonded organic-inorganic hybrids

Hybrid materials based on covalently linked inorganic polyoxometalates (POMs) and organic species containing a delocalized pi system have drawn increasing attention. These hybrids, traditionally prepared by cluster assembly approaches that lack predictability and controllability, can now be synthesized through common organic reactions by using organically functionalized POM clusters as building blocks. This minireview highlights some of the most recent advances on a particular type of hybrids where the organic and inorganic components are connected by an imido linkage.     

Structural models for homogeneous organic-inorganic hybrid materials: Simulations of small-angle X-ray scattering profiles

Two morphological models have been proposed to describe small-angle x-ray scattering from organic-inorganic composite (OIC) materials. The first model invokes the idea of a liquid-like arrangement among noninterpenetrating fractal clusters, and the second employs an empirical correlation function that would be expected for a bicontinuous two-phase (B2P) picture with the inorganic portion exhibiting fractal characteristics. Simulated scattering profiles have been generated for direct comparison with experimental data. The samples studied were a triethoxysilane-endcapped bisphenol A epoxide resin (EAS) reacted in the presence of tetraethoxysilane (TEOS) under slightly basic conditions, and a random trimethoxysilane-functionalized copolymer of poly(methyl methacrylate) (MMA-TMS) with added tetramethoxysilane (TMOS), reacted in an acidic medium. Each morphology model qualitatively simulates the broad scattering maximum and limiting high-angle slope commonly seen in SAXS profiles. It is concluded that the inorganic phase in the EAS hybrid exhibits particle-like characteristics at length scales less than approximately 250 Å, and the organic and inorganic components are bicontinuous at larger distances. The MMATMS composite is better described by bicontinuous organic and inorganic phases with a periodic fluctuation of about 40 Å. The scattering maximum arises either from the mean separation of particles or a dominant wavelength in a concentration fluctuation, similar to that observed for spinodal decomposition. In either case, the SAXS peak position is related to the distance between junction points of the crosslinked organic polymer. © 1995 John Wiley & Sons, Inc.     

Abrasion resistant inorganic/organic coating materials prepared by the sol-gel method

Novel abrasion resistant coating materials prepared by the sol-gel method have been developed and applied on the polymeric substrates bisphenol-A polycarbonate and diallyl diglycol carbonate resin (CR-39). These coatings are inorganic/organic hybrid network materials synthesized from 3-isocyanatopropyltriethoxysilane functionalized organics and metal alkoxide. The organic components are 3,3-iminobispropylamine (IMPA), resorcinol (RSOL), diethylenetriamine (DETA), poly(ethyleneimine) (PEI), glycerol and a series of diols. The metal alkoxides are tetraethoxysilane (TEOS) and tetramethoxysilane (TMOS). These materials are spin coated onto bisphenol-A polycarbonate and CR-39 sheets and thermally cured to obtain a transparent coating of a few microns in thickness. Following the curing, the abrasion resistance is measured and compared with an uncoated control. It was found that the abrasion resistance of inorganic/organic hybrid coatings in the neat form or containing metal alkoxide can be very effective to improve the abrasion resistance of polymeric substrates. The adhesion tests show that the adhesion between coating and substrate can be greatly improved by treating the polymeric substrate surface with a primer solution of isopropanol containing 3-aminopropyltriethoxysilane (3-APS). The interaction between 3-APS and the polycarbonate surface was investigated by a molecular dynamics simulation. The results strongly suggest that the hydrogen bonding between the amino group of the 3-APS and ester group in the polycarbonate backbone are sufficiently strong to influence the orientation of the primer molecules. The abrasion resistance of these new coating systems is discussed in light of the structure of the organic components. All of these results show that these coating materials have excellent abrasion resistance and have potential applications as coating materials for lenses and other polymeric products.     

Monitoring of the Viability of Cells Immobilized by Sol-Gel Process

Three different types of cells, Pseudomonas fluorescens HK44, Saccharomyces cerevisiae strain SP4 and plant cells Nicotiana tabacum L. BY-2, were immobilized by entrapment in tetramethoxysilane prepolymer (TMOS) gel or in composite gel containing prepolymer TMOS and alginate in various ratios. Their growth and viability were monitored by bioluminescence and 2-D fluorescence spectra, which are fast and do not need the dissolution of a matrix. The resulting biocomposite gels were obtained by gelation of the mixtures of TMOS prep. or TMOS/alginate sols and the particular cells in proper media on glass supports to provide films ～1 mm thick. The effect of the following parameters on the growth and viability of the cells was studied: (a) the composition of the biocomposites, (b) the preparation conditions of TMOS and (c) the conditions of the procedure of entrapment. All three types of cells were tested in TMOS gel and the composite TMOS/alginate = 1:1 (v/v). The sensitivity of the cells to the changes of conditions increased in the sequence: P. fluorescence HK44 < S. cerevisiae strain SP4 < N. tabacum L. BY-2. Cell viability decreased with the increasing content of Si in biocomposites. The entrapment into alginate–silica composites resulted in the leakage of microbial and yeast cells. However, it had positive effects on the growth and metabolic activity of plant cells.     

Preparation and characters of hyperbranched polyester‐based organic‐inorganic hybrid material compared with linear polyester

To compare the properties of hyperbranched polymers with linear oligomers for preparing organic‐inorganic hybrids, hyperbranched aliphatic polyester (Boltorn^TM H20) and linear polyester hexa‐acrylate (EB830) were selected as organic components for preparing UV‐curable transparent hybrid materials using 3‐(trimethoxysilyl) propylmethacrylate as a coupling agent via a sol‐gel process. The prehydrolyzed product of tetraethoxysilane was used as an inorganic component. The effects of inorganic content on the morphologies, thermal behaviors, photopolymerizaiton kinetics and mechanical properties of the hybrids were investigated. The results show that for hyperbranched polyester‐based hybrids, the organic phase shows much better compatibility with inorganic phase even at high inorganic component content due to its special spheral shape and plenty of functional end groups, compared with linear EB830‐based hybrids. Copyright © 2004 John Wiley & Sons, Ltd.     

线型脲醛树脂的半结晶模板化作用

酸性条件下硅溶胶体系中尿素和甲醛聚合反应会产生脲醛树脂-氧化硅杂化沉淀. 沉淀的质量随有机组分比例的增加而增加, 当尿素和甲醛物质的量比≥1.0时生成沉淀的量为恒定最大值. 红外分析表明杂化材料在3348, 1635, 1572和784 cm^－1处产生了可被归结为线型结构(—[NHCONHCH₂]_n—)的特征吸收. XRD分析表明这种线型分子可形成氢键(C＝O…H—N)导向型的半结晶. 微分热重和XRD结果证明结晶物种在290 ℃完全分解. SEM表征显示半结晶杂化沉淀以三维网络结构为特征, 具有层状结晶的各向异性, 其初级粒子即使在室温下干燥也容易开裂. 随着反应时间的延长、酸性的增加或无机组分量的相对增加杂化粒子变得更加致密. 液氮吸附结果证明沉淀焙烧后所得氧化硅材料的结构具有层状孔结构性质, 其比表面积、孔尺寸和孔体积可以达到510 m²/g, 14.3 nm和1.68 cm³/g. 改变反应体系的酸性和反应组分配比等条件可以方便地控制杂化材料的结构.