The novel use of organo alkoxy silane for the synthesis of organic–inorganic hybrid coatings

UV-curable, organic–inorganic hybrid coatings based on a UV-curable epoxyacrylate resin (EA) and methacryloxypropyl trimethoxysilane were prepared by the sol–gel method. 2,2′-Bis(4-β-hydroxy ethoxy) phenyl propane was modified by a coupling agent, 3-isocyanato propyl triethoxy silane, to improve the compatibility of the organic and inorganic phases. The formulations were applied onto Aluminum panels and cured by UV light to obtain a hard and clear coating with a good adhesion. The structural characterization of cured hybrid materials was performed using solid state ²⁹Si NMR spectroscopy. The real time infrared technique was used to follow the degree of double bond conversion and photopolymerization rate. The thermal properties of the coatings are improved depends on the ‘component A’ composition in hybrid mixture which was composed of methacryloxy propyl trimethoxysilane (MAPTMS) and trimethoxysilane terminated HEPA urethane (TMSHU). The char yield of pure epoxy acrylate resin was 0.7 wt% and that of 30 wt% of component A containing hybrid coating was 4.6 wt% at 900 °C in air atmosphere. The morphology of the hybrid materials was examined by scanning electron microscopy. The hybrids were nanocomposites.     

A comparative FTIR study of thermal and photo-polymerization processes in hybrid sol-gel films

Controlling the organic polymerization in organic-inorganic hybrids is a key point in the development of new materials with high homogeneity of the nanostructure. The main difficulty is related with the achievement of a simultaneous control of the organic and inorganic network formation. Thermal and photocuring represent the main routes to form the organic chains when polymerizable organic groups are present in the hybrid materials. In the present work hybrid organic-inorganic films were synthesized from 3-methacryloxypropyltrimethoxysilane (MPTMS) cohydrolyzed with tetraethylorthosilicate (TEOS) and N-[(3-trimethoxysilyl)propyl]ethylenediamine (TMESPE) or 3-(triethoxysilyl)-propylamine (TESPA). This an example of basic catalyzed hybrid material with a polymerizable methacrylate functionality whose micro-structure is modified by the amine groups. FTIR spectroscopy was used to compare the effects of thermal or photo-induced polymerization on the materials. TESPA and TMESPE showed a different catalytic effect on the condensation of the inorganic network, with TMESPE the more efficient one. The presence of a more extended silica backbone reduced the curing efficiency in TMESPE derived samples. UV curing was also very effective in catalyzing the inorganic condensation of un-reacted species still present in the film after the deposition. A photo-induced polymerization of the inorganic side was observed in the hybrid films. Thermal polymerization in TMESPE films induces the reaction between the secondary amine and CO bonds in MPTMS, this reaction is, instead, not observed in films cured by UV radiation.     

Sol-gel-derived organic-inorganic hybrid materials

Optically transparent organic-inorganic hybrid coating materials have been prepared by a sol-gel process. Four different types of the coating material produced by TWI in Cambridge, UK using the patented Vitresyn^® method, all identical in terms of the starting materials, but differing in terms of their relative proportions, have been examined. Tetraethoxysilane was used as the primary inorganic precursor and urethane acrylate was used as the source of the organic component. 3-(Trimethoxysilyl)propyl methacrylate was used as both a secondary inorganic source and a silane coupling agent to improve the compatibility of the organic and inorganic phases. The degree of chemical interaction of the organic and inorganic phases after processing was determined by ²⁹Si and ¹³C nuclear magnetic resonance and Fourier transform infrared spectroscopy. The effect of the relative amount of inorganic starting component in these hybrid materials on their thermal properties was investigated through differential scanning calorimetry and thermogravimetric analysis. Similar degrees of chemical interaction between the organic and inorganic phases were found in all four samples. T³, Q³ and Q⁴ are the main cross-linking network structures in these hybrid systems, the relative proportions of which are determined by the relative proportions of the starting materials.     

Characteristics of colored inorganic–organic hybrid materials

Inorganic–organic hybrid glasses are relatively new nanometric materials of Ormosil’s group (organic modified silicates). There co-existence, on a molecular scale, exists between inorganic structures in the form of silica-oxide network and organic structures based on carbon links. Properties of these materials are intermediate between those of inorganic glasses (hardness, chemical and thermal resistance) and organic polymers (low temperature of obtaining, elasticity of structure). The hybrid materials are compatible matrices for organic compounds such as organic dyes, laser dyes, photo-chromic compounds, etc. Inorganic–organic hybrid glasses are usually produced in the form of thin coatings on various bases using a low-temperature sol-gel process. These coatings, depending on the kind and amount of units, building their structure, show various properties: refractive index changing in a wide range, anti-static properties, anti-reflection, corrosion protection, intensive color, luminescence and others. That is why these materials found application as protective and colored covering of glass articles as well as in new technical areas. The aim of this paper is obtaining and characterizing colored inorganic–organic coatings on glass, considering both protective and colored properties. These materials have been produced from phenyltriethoxysilane (PhTES), 3-glycidoxypropyltrimethoxysilane (GPTMS), aluminium tri-sec-butylate (TBA); (PGT matrix). The structure of PGT matrix was determined using the FTIR, ²⁹Si MAS NMR and ²⁷Al MAS NMR examinations. It has been found that chemical bonds occur between structural units. The two groups of organic dyes were used for coloring the coatings. The first group consisted of ORASOL dyes, chiefly based on various metal complexes. These dyes have a wide range of commercial utilization. The second group included the organic, intensive dyes obtained in the laboratory and are inaccessible for sale. The coloring coatings were coated on flat glass using the dip-coating method. The samples were submitted for thermal treatment at temperatures of 100 and 200 °C. Investigation of chemical resistance (boiling in water for 1 h) was made for coated materials after thermal treatment at 100 °C. UV–VIS transmission of colored coatings was examined after each stage of thermal treatment and also after hydrolytic resistance examination. The quality of the coatings and their thickness were estimated by SEM observations. The obtained, inorganic–organic coatings were characterized by good chemical resistance and stability of color.     

Molecular assembly,luminescence and morphology of novel zinc/inorganic/organic nanohybrid material with covalent linkage

Polyethylene glycol (PEG) was first modified by an inorganic component of 3-(triethoxysilyl)-propyl isocyanate (TEPIC) to form the inorganic/organic polymeric functional precursor. The modified reagent with a functional group (–NHCOO–) further behaves as a bridge which can coordinate to Zn²⁺ through oxygen atom and further formed Si–O backbones after hydrolysis and polycondensation processes. Subsequently, the corresponding organic/inorganic molecular-based hybrids were assembled to behave as the structural polymeric ligands with the two components equipped with covalent bonds. Finally, ternary zinc/inorganic/organic polymeric hybrid materials with chemical bond (covalent bonds of –CO–NH– and Si–O, coordination bond of Zn–O–C) have been assembled. The resulting hybrids exhibit blue luminescence and nanometer morphology.     

Sol–gel derived organic–inorganic hybrid electrolytes for thin film electrochromic devices

Sol–gel derived, lithium ion conducting organic–inorganic hybrid electrolytes for ambient temperatures applications, have been synthesized from tetraethyl orthosilicate (TEOS), poly(ethylene oxide) (PEO), propylene carbonate (PC), propylene oxide, butyl acrylate, butyl methacrylate, ethyl acetoacetate and LiClO₄ precursors. Mass fractions of the organic additions in the gels were of ca 30 mass% for gels 0/B, F–H and 40 mass% for gel J. The colorless transparent or translucent hybrid materials obtained in this work were aged at room temperature for at least three weeks and then dried at 80 °C for 3 h. The morphology and structure of all compositions were investigated by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM/EDX), Fourier transform infrared spectroscopy and ²⁹Si MAS nuclear magnetic resonance. Amorphous nature of the hybrids was confirmed by X-ray diffraction. SEM, FTIR and NMR analysis showed structural properties and [SiO₄] tetrahedrons poly-condensation process to be strongly influenced by organic additives have been employed. Room temperature ionic conductivities of the hybrid electrolytes were in a range of 9.84 × 10⁻⁴–1.56 × 10⁻³ Ω⁻¹ cm⁻¹.     

Spectroscopic characterization of GPTMS/DETA and GPTMS/EDA hybrid polymers

Silica/epoxy hybrid polymers were synthesized from 3-glycidoxypropyltrimethoxysilane (GPTMS) by hydrolysis of the silane functional groups at a range of pHs and water contents of the reaction mixtures, followed by crosslinking by ring opening of the epoxy groups using diethylenetriamine (DETA) or ethylenediamine (EDA). The GPTMS/DETA and GPTMS/EDA hybrid polymers were formed to an extent determined by the mole ratio of active hydrogens from the diamine to epoxy rings (R_H). Structural characterization of the hybrid polymers was performed using Scanning Electron Microscopy (SEM), and Raman, and ¹³C and ²⁹Si Solid-State Nuclear Magnetic Resonance (NMR) spectroscopies. The results showed that extensive crosslinking occurred for GPTMS/DETA and GPTMS/EDA rigid, homogeneous hybrids with R_H = 1, particularly at pH 10.     

Hybrid glass-like films through sol–gel techniques

Since the time sol–gel was suggested as a nonmelting technique for the preparation of glasses, an enormous amount of work has been done, moving from the more traditional glasses to new materials. Among these, hybrid organic–inorganic materials are of particular interest, not only for the amount of the applications they may be used for, but also because of their structural characteristics: hybrids are a mix, at molecular level, of inorganic and organic moieties, where the organic ones may be simply dissolved in the matrix or behave as network former or modifier. The most recent results on the synthesis of this type of films, obtained by the author and co-workers, will be presented and discussed. In particular, the focus will be on the possibility to control the structural development by acting on the organic and inorganic polymerization separately and the challenges that this approach offers.     

WO3-based electrochromic system with hybrid organic–inorganic gel electrolytes

Thin metal oxide films for a WO₃-based symmetric electrochromic system with a nickel oxide layer as the counter electrode have been prepared by spray pyrolysis on SnO₂:F coated soda-lime float glass, at a temperature of 670–720 °C and using metal acetylacetonates as precursors. The films have been characterized for composition and morphology by scanning electron microscopy equipped with an X-ray energy dispersive analyzer (SEM/EDAX), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Electrochromic properties have been examined in the electrochemical cells of a smart window arrangement using lithium ion doped sol–gel derived organic–inorganic hybrid materials as electrolytes. Hybrids with room-temperature ionic conductivities of 10^?4–10^?3 Ω^?1 cm^?1 have been synthesized from tetraethyl orthosilicate (TEOS) with an addition of 35 mass % of organic compounds. Coloration-bleaching of WO₃ films with lithium ions from hybrid electrolytes has resulted in the desired modulating the properties in the visible and near infrared spectrum range. An XPS analysis has shown the presence of a lower oxidized tungsten oxide phase (WO_2.92) in the WO₃ film.     

Synthesis and characterization of SiO2-PEG hybrid materials

Sol-gel is a promising technique for the synthesis of organic-inorganic hybrid materials both of class I and II. In materials of class I organic molecules are physically entrapped in an inorganic matrix, while in those of class II organic and inorganic parts are connected by covalent bonds. In this paper a sol-gel procedure to obtain SiO₂-PEG hybrids of class I, in which PEG is simply mixed at the sol stage, is compared to a sol-gel procedure to obtain SiO₂-PEG hybrid materials of class II, where a particular sol-gel Si-C precursor is synthesized. XPS analyses showed the different distribution of the organic phase in the SiO₂ matrix and the bond between PEG and SiO₂ for hybrids of class II. The PEG molecule in hybrid of class II showed an enhanced thermal stability up to 350 °C. Doping with a lithium salt was performed on hybrids of class II, and the ionic conductivity was measured.     

Design of hybrid organic–inorganic materials through their structure control: The case of epoxy bearing alkoxides

Hybrid organic–inorganic materials from (3-glycidoxypropyl)methyldiethoxysilane (GPMD) and [3-(2-aminoethyl)aminopropyl]trimethoxysilane (AEAPTMS) have been synthesized. The structure of the hybrid material has been studied as a function of AEAPTMS content by a combination of vibrational and nuclear magnetic resonance spectroscopies. The amine groups in AEAPTMS have shown to be very effective epoxy curing agents and the degree of condensation inside the hybrid material can be finely tuned with the amount of AEAPTMS. Fourier transform near infrared spectroscopy coupled with 2D infrared analysis has been used to elucidate the role of amines in epoxy curing. Several reactions of the amines with the epoxies have been observed, via tertiary, secondary and primary amines. At low AEAPTMS contents the hybrid material exhibits a residual mobility of the organic species, as revealed by solid state NMR spectroscopy. This property has been evaluated comparing qualitatively the residual mobility in hybrid materials synthesized with different types of organically modified alkoxides containing epoxy functional groups.     

New route for producing crack-free xerogels: Obtaining uniform pore size

We propose an innovative strategy to obtain crack-free gels by using a surfactant as a template for the silica pores. We use a neutral surfactant – n-octylamine – which weakly interacts by hydrogen bonding with the silica precursor. This allows it to be removed by simple drying in ambient air. We investigate the effect of the surfactant in simple inorganic silica obtained from tetraethoxysilane (TEOS) and an organic–inorganic hybrid xerogel, containing TEOS and polydimethylsiloxane (PDMS), as precursors. Although both the syntheses promote the formation of a crack-free uniform mesoporous silica gel, the hybrid gel network exhibits a larger pore size than the gel containing exclusively the silica from TEOS.     

Dielectric and thermal–mechanical properties of hybrid organic–inorganic polymer systems based on isocyanate-containing oligomers

Hybrid organic–inorganic polymer systems (OIS) were obtained in reactions of the organic oligomer (macrodiisocyanate + poly(isocyanate) (MDI + PIC)) which has free isocyanate groups with inorganic oligomer – sodium silicate (SS). The structure of OIS was formed as two interpenetrated networks: an elastic network as a result of reactions MDI–SS and a rigid network PIC–SS. Depending on MDI/PIC ratio, one of the network features is prevailing as attested to by dielectric, electrical and thermal–mechanical experiments. The elastic network MDI–SS possesses high values of dielectric parameters ε′, tan δ and conductivity σ whereas for the rigid network PIC–SS the values of these characteristics are much lower and are typical for usual thermosets.     

Ag-doped antibacterial porous materials with slow release of silver ions

The inorganic–organic hybrids of polyethyleneglycol (PEG), tetraethoxysilane (TEOS) and triethylphosphate (TEP) doped by silver ions were prepared by sol–gel method. After molding and heating at 600 °C to remove organic components, porous Ag–P₂O₅–SiO₂ monoliths were obtained. Thermogravimetry (TG), differential thermal analysis (DTA), infrared spectra, ultraviolet–visible (UV–vis) spectra and pore structure of the samples were measured to show that organic components and residual water could be removed by a heat-treatment up to 600 °C and the mesopores with 6 nm pore diameter were formed. Specific surface area and pore volume of the samples were adjusted with different contents of TEP in the starting composition. Ag⁺ ions could be stably released into water at 30 °C up to 28 days. Antibacterial experiment showed that such materials treated at 600 °C could restrain Escherichia coli effectively.     

Dielectric low-k composite films based on PMMA,PVC and methylsiloxane-silica: Synthesis,characterization and electrical properties

This report describes the preparation of low-k inorganic–organic hybrid dielectric films, based on a polymethylmethacrylate–polyvinylchloride (PMMA–PVC) blend and a silica powder functionalized on the surface with methylsiloxane groups (m-SiO₂). By dispersing m-SiO₂ into a [(PMMA)_x(PVC)_y] 50/50 (x/y) wt% polymer blend, six [(PMMA)_x(PVC)_y]/(m-SiO₂)_z hybrid inorganic–organic materials were obtained, with z ranging from 0 to 38.3 wt% and x = y = (100 − z)/2. The transparent, homogeneous, crack-free films were obtained by a solvent casting process from a THF solution. The morphology, thermal stability and transitions of hybrid materials were studied by environmental scanning electron microscopy (ESEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). ESEM revealed that hybrid dielectric films are very homogeneous materials. The electrical response of the dielectric films was studied by detailed broadband dielectric spectroscopy (BDS). BDS measurements were performed at frequencies of 40 Hz to 10 MHz and a temperature range of 0–130°C. In these temperature and frequency ranges the proposed materials have a dielectric constant of <3.5 and a tan δ of <0.05. BDS also revealed molecular relaxation events in [(PMMA)_x(PVC)_y]/(m-SiO₂)_z materials as a function of temperature and sample composition. Results showed that these films with z in the range 25–35 wt% are very promising low-k dielectrics for applications in organic thin film transistor (OTFT) devices.     

Preparation and structure of organic-inorganic hybrid precursors for new type low-melting glasses

Organic-inorganic hybrid precursors for new type low-melting glasses without pollution elements such as Pb and F have been synthesized through a non-aqueous acid-base reaction process. The hybrid compounds consist of -Si-O-P- framework, in which some of the bridging oxygens of a Si tetrahedron are substituted by organic functional groups. Terminating the oxide framework by the organic functional groups lowers the network dimension. Orthophosphoric acid (H₃PO₄) and dialkyldichlorosilane (Me₂SiCl₂ and Et₂SiCl₂) were employed as starting materials. The formation of P-O-Si linkage was confirmed by IR spectra. The larger viscosity increase at higher Si concentrations is correlated to the formation of the linkage. It is proposed that an acid-base polycondensation reaction of P-OH+Si-Cl→P-O-Si+HCl↑ dominates the network formation. When dimethylsilane SiMe₂ is substituted by divalent Sn, an organic-inorganic hybrid low-melting glass in the system of SnO-Me₂SiO-P₂O₅ can be derived, the glass transition temperature of which is about 29 °C. So the present acid-base reactions provide a new process by which precursors for new type low-melting glass are synthesized.     

Lanthanide molecular-based hybrids covalently bonded with silica: Photoluminescence and control of micromorphology

The syntheses of modified 5-bromonicotinic acid by (3-aminopropyl)triethoxysilane and the preparation of their corresponding organic–inorganic molecular-based hybrid material with the two components equipped with covalent bonds are described. The organic moiety is a derivative of 5-bromonicotinic acid which is applied to coordinate to RE³⁺ and further introduced into silica matrices by Si–O bonds after hydrolysis and polycondensation processes. Judd–Ofelt theory proves that covalency increases along with increasing reciprocal energy difference between the 4fN and 4fN-15d1configurations. Ultraviolet absorption, phosphorescence and luminescence spectra were utilized to characterize the photophysical properties of the obtained hybrid material and the above spectroscopic data reveal that the triplet energy of modified 5-bromonicotinic acid matches with the emissive energy level of RE³⁺. In this way, the intramolecular energy transfer process took place within these molecular-based hybrids and strong green, red or blue emissions of RE³⁺ have been acquired. Scanning electronic microscope presents no phase separation phenomenon appear and the different crystal structures of lanthanide complex precursor molecules have influence on the microstructure and micromorphology of corresponding molecular hybrids.     

Attractive sulfonamide bridging bonds constructing lanthanide centered photoactive covalent hybrids

A new kind of sol–gel derived organic–inorganic hybrid material was prepared for the first time.In this case the organic portion of an acylamine derivation grafted by 3-aminopropyl trimethoxysilane and covalently linked together via sulfonamide linkages. Fourier transform infrared (FTIR), in ultraviolet absorption (UV) spectra and ¹H nuclear magnetic resonance (NMR) spectra were used to confirm these modifications and the X-ray diffraction (XRD) spectra were used to determine the framework. The material’s phosphorescent spectra and luminescence spectra were recorded. An efficient intramolecular energy transfer process between acylamine and lanthanide ions took place within these molecular-based hybrids. Strong green and red emissions were achieved for Tb³⁺ and Sm³⁺ ions, respectively.     

Fracture toughness evaluation of precursor-derived Si–C–N ceramics using the crack opening displacement approach

Difficulties in the fabrication of representative test specimens and in the application of suitable test procedures e.g., in the measurement of the test parameters viz., load, crack length etc., have so far limited the intrinsic fracture mechanical characterization of the precursor-derived ceramics (PDC). The present work reports the evaluation of the crack tip toughness (K_I0) of Si–C–N ceramics, using the novel crack opening displacement (COD) approach. The fully dense PDC test specimens synthesized from a poly(ureamethylvinyl)silazane precursor covered material structures ranging from partly organic amorphous to inorganic nano-crystalline states. Critically loaded cracks were achieved using either a special loading fixture or with Vickers indentation. Crack tip CODs were measured with the atomic force microscopy (AFM). Fractography of the fracture surfaces were performed using topographic, frictional and phase contrast AFM. The measured K_I0 values ranged from 0.6 to 1.2 MPa m^1/2. The net change in crack resistance was affected by the stripping of OFC-hydrogen atoms in the amorphous materials and by the segregated turbostratic graphite phase in the phase-separated materials. Nano-scale crack deflection observed even in the amorphous materials indicated the presence of structural and compositional inhomogeneities within the amorphous network.     

Mechanical and thermal properties of SiO2–PMMA monoliths

Organic–inorganic hybrid monoliths of cross-linked polymethylmethacrylate (PMMA) and silica (SiO₂) were prepared by sol–gel, using tetraethoxysilane (TEOS) and methylmethacrylate (MMA) as precursors and 3-(trimethoxysilyl) propylmethacrylate (TMSPM) to make compatible the organic and inorganic components. Two types of monoliths were prepared, H1-type using a molar ratio composition of 16:1:4 for water:TEOS:ethanol and 1:0.1:0.1 for TEOS:TMSPM:MMA and H2-type using 6.3:1:2.52 for water:TEOS:ethanol and 1:0.25:0.25 for TEOS:TMSPM:MMA. Semi-transparent monoliths were obtained in both cases after the gelation–solidification and drying processes, which took about seven days. Thermal properties of the samples were obtained by applying thermal lens spectroscopy and their mechanical properties were measured by depth sensing indentation and Vickers microhardness. FTIR spectroscopy measurements were performed to complement the characterization. We found that the hardness of the hybrid monoliths have values between those of commercial PMMA and a sol–gel SiO₂ monolith. This result is a consequence of the reinforcement produced by the SiO₂ component in the organic–inorganic hybrid matrix. The thermal diffusivity of the hybrid monoliths shows an appreciable increasing in the hybrid system with respect to the pure SiO₂ monolith. Mechanical behavior of monoliths is strong influenced by the SiO₂–PMMA ratio or changing the water:TEOS:ethanol contents.