Silica Hybrid Films Research Articles

Highly Fluorescent Mesostructured Films that consist of Oligo(phenylenevinylene)–Silica Hybrid Frameworks

AbstractHighly fluorescent and visible‐light‐responsive mesostructured organosilica films are successfully obtained by acidic sol–gel polycondensation of oligo(phenylenevinylene) (OPV)‐bridged organosilane and tetraethoxysilane precursors in the presence of a template surfactant. The OPV‐bridged organosilane precursors with different lateral alkoxy substituents, hexyloxy and 2‐ethylhexyloxy, and no substituent, are synthesized by Rh‐catalyzed silylation of corresponding aromatic iodides. From the organosilane precursors, three kinds of mesostructured OPV–silica hybrid films are prepared by spin‐casting using evaporation‐induced self‐assembly. UV‐vis absorption and fluorescence behavior of the OPV–silica hybrid films show that the optical properties and intermolecular interactions of the OPV moieties embedded within the organosilica frameworks strongly depend on the lateral alkoxy substituents in the precursors. The hexyloxy and 2‐ethylhexyloxy substituents prevent aggregation of the OPV units in the organosilica frameworks; this result leads to high fluorescence quantum yields of 0.48–0.61 and 0.63–0.66, respectively, while non‐substitution leads to lower fluorescence quantum yields of 0.25–0.34. Fluorescence decay profiles of the organosilica hybrid films also confirm a suppression of the aggregation of OPV moieties by the lateral substituents. These mesostructured organosilica films with significant optical properties in the visible‐light region are promising as a new class of phosphor materials.

Electrochemical epinephrine sensor using artificial receptor synthesized by sol–gel process

An artificial adrenergic receptor was fabricated with molecular imprinting silica. Epinephrine (EP) was imprinted in the organic–inorganic hybrid silica film through π–π interaction from phenyltrimethoxysilane (PTMOS). The epinephrine-imprinted film was spin coated on an indium tin oxide (ITO) glass. The affinity of epinephrine to the imprinted film was determined by the oxidation current of epinephrine. The epinephrine-imprinted film showed a good selectivity toward epinephrine. Epinephrine and isoproterenol (IPT) which have two more methyl group on amino-N had comparable current responses, 79.9% and 75.3%, respectively. Negatively charged analytes including 3,4-dihydroxy- l -phenylalanine, 3,4-dihydroxyhydrocinnamic acid, and ascorbic acid had current responses lower than 47%. The mechanism of facilitated transport by fixed-site carriers was suitable to explain the current enhancement by the imprinted film. Binding sites of epinephrine-imprinted film were believed to function as the fixed site carriers for the facilitated transport. The occupation of binding sites by 2-phenethylamine which structurally resembles epinephrine decreased the current at high epinephrine concentration.

Stable Photochromism and Controllable Reduction Properties of Surfactant-Encapsulated Polyoxometalate/Silica Hybrid Films

In this paper, we present a novel strategy for fabricating polyoxometalate (POM)-based photochromic silica hybrid films. To combine metal nanoparticles (NPs) into the POMs embedded silica matrix, furthermore, we realized the controllable in situ synthesis of metal NPs in the film by utilizing the reduction property of POMs existing in the reduced state. Through electrostatic encapsulation with hydroxyl-terminated surfactants, the POMs with good redox property can be covalently grafted onto a silica matrix by means of a sol-gel approach, and stable silica sol-gel thin films containing surfactant-encapsulated POMs can be obtained. The functional hybrid film exhibits both the transparent and easily processible properties of silica matrix and the stable and reversible photochromism of POMs. In addition, well-dispersed POMs in a hydrophobic microenvironment within the hybrid film can be used as reductants for the in situ synthesis of metal NPs. More significantly, the size and location of NPs can be tuned by controlling the adsorption time of metal ions and mask blocking the surface. The hybrid film containing both POMs and metal NPs with patterned morphology can be obtained, which has potential applications in optical display, memory, catalysis, microelectronic devices and antibacterial materials.

ERDA of Ni–Al 2O 3/SiO 2 solar thermal selective absorbers

Thin film materials for the use in solar thermal absorbers have been investigated using time-of-flight energy elastic recoil detection analysis (ERDA). The ERDA measurements proved to be very efficient in detecting the elemental depth composition of a selective solar absorber. The three-layer absorber is composed of an 80% nickel–20% alumina film at the base, a 40% nickel–60% alumina layer in the middle and finally an AR film of silica or hybrid-silica film at the top. The difference between solution volume percent and actual volume percent could be investigated when studying individual nickel–alumina films with varying ratios coated on glass substrates. The result showed that there was a maximum difference of 3% between the calculated solution volume percent and the actual volume percentages in the solid films. The ERDA measurements also indicate that about 15% of the nickel found in the nickel–alumina composite films is bound in the form of NiO.

Microstructure and Properties of Polyimide /Monodispersed Colloidal Silica Hybrid Films Prepared by Sol–Gel Process

In this study, the polyimide-silica hybrid thin films, 6FDA-6FpDA-4ABA/SiO2 (FS0-FS50) were prepared from the 12nm colloidal silica and polyimide bearing acid endgroups. During the preparation, without any additional coupling agents or chelating ligands were used. The strong interactions between carboxylic acid coordinating with silica were believed to prevent the macrophase separation. TGA analysis showed that the thermal decomposition temperatures (Td) incresased with increasing the silica content. UV-VIS spectra showed that the cutoff wavelength of prepared hybrid films could be tunable through the silica content. The n&k analysis showed that the refractive index (n) of PS hybrid films were in the range of 1.575-1.479, which could be controlled by the silica content. The extinction coefficients (k) are almost zero in the wavelength range of 300–900 nm, indicating the prepared hybrid films have an excellent optical transparency in the UV and visible region. TEM images showed that the particle size of silica in the hybrid thin films could be effectively controlled. The results of SEM and AFM showed that all the prepared hybrid films have a good planarity. It demonstrated that the prepared polyimide-silica hybrid thin films have an excellent film formability and planarity.

Tuning pore size and hydrophobicity of macroporous hybrid silica films with high optical transmittance by a non-template route

Macroporous silica films with methyl groups grafted on their surface were prepared from polymethylhydrosiloxane (PMHS) and tetraethylorthosilicate (TEOS) without templates. Compared to the conventional template syntheses, this approach has several advantages. First, it avoids the removal of templates, which is sometimes an environmentally unfriendly procedure. Second, it does not require a post-synthesis grafting to form the hybrid structures with methyl groups on the silica surface. Third, the pore size and hydrophobicity (expressed by the water contact angle) of the film can be tuned readily. By adjusting the amount of PMHS used in the synthesis and introducing hexamethyldisilazane (HMDS) we can tune the pore size in a wide range from 50 nm to 500 nm. The hydrophobicity increases substantially as the pore size decreases. Evidently, the reaction mechanism of this synthesis is different from the conventional template synthesis. A tentative mechanism is proposed: the hydrogen gas released from PMHS results in the formation of the macropores in the films. With excellent hydrophobicity, optical transmittance and thermal stability, the obtained silica films have potential applications in the semiconductor industry.

Linear and nonlinear optical properties of covalently bound C.I. Disperse Red 1 chromophore/silica hybrid film

The third-order nonlinearity of an organic–inorganic hybrid silica film covalently doped and dispersed with C.I. Disperse Red 1 was studied using the Z-scan technique. The micropores in the sol–gel derived silica matrix were smaller than the dye ligand which led to dye aggregation. A nonlinear refractive index of −3.4 × 10 −9 esu and a nonlinear susceptibility of 5.9 × 10 −10 esu were recorded at 1064 nm. The large blue shift of the absorption band due to dye aggregation resulted in an enhanced two-photon absorption. The observed nonlinearity is attributable to both two-photon absorption resonance and the refraction change induced by the enlarged π-delocalization conjugation between the dye and the silica matrix.

Conductive hybrid film from polyaniline and polyurethane–silica

In order to improve the mechanical performance and water resistance of water-borne conducting polyaniline film, conducting polyaniline/polyurethane–silica hybrid film was prepared in aqueous solution employing silanol-terminated polyurethane and methyltriethoxysilane as sol–gel precursors. The hybrid film showed surface resistivity of 108Ω even though the conducting polyaniline loading was only 10wt% (or 1.5wt% of polyaniline), and the mechanical performance as well as water resistance was significantly improved, making it suitable for antistatic application. Therefore, a practical route to water-borne processing of conducting polyaniline is disclosed.

Microscopic Structure of Separately Accommodated Porphyrins and Viologens in Mesoporous Silica and Titania Nanosheet Hybrid Films

The microscopic structures of two nano-structured inorganic films, one based on titania nanosheets (TNS) and the other on mesoporous silica (MPS), were investigated. The clear stacking structure of the TNS and MPS films were observed by the XRD, SEM, and TEM analyses. The selective adsorption of the porphyrin derivatives into the MPS nano-cavities and viologens into the TNS nano-layers was also investigated by absorption and energy-dispersive spectroscopy (EDS).

Four-Channel QCA Using Mesoporous Silica Films for Gas Sensing Applications

A four-channel quartz crystal microbalance array (QCA) coated with silica hybrid films is tested as a gas sensor to identify and quantify target analytes. Plasma calcined mesoporous silica films have been used to form hybrids for gas sensing applications. Silica hybrids are obtained by incorporating various receptor molecules in the porous network through physiosorption and/or chemical bonding between the silica matrix and receptor molecules. Field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, secondary ion mass spectroscopy, and nitrogen adsorption analysis are used to characterize the obtained films. The frequency interference between the individual quartz crystal microbalance in the QCA has been eliminated by appropriate positioning of the electrodes. It is concluded that the sensitivity and selectivity of the four-channel QCA could be enhanced by depositing plasma calcined mesoporous hybrids on the electrodes

Co-immobilization of glucose oxidase and hexokinase on silicate hybrid sol–gel membrane for glucose and ATP detections

The co-immobilization of glucose oxidase (GOD) and hexokinase/glucose-6-phosphate dehydrogenase (HEX) in the silica hybrid sol-gel film for development of amperometric biosensors was investigated. The silica hybrid film fabricated by hydrolysis of the mixture of tetraethyl orthosilicate and 3-(trimethoxysiyl)propyl methacrylate possessed a three-dimension vesicle structure and good uniformity and conformability, and was ready for enzyme immobilization. The electrochemical and spectroscopic measurements showed that the silica hybrid sol-gel provided excellent matrice for the enzyme immobilization and that the immobilized enzyme retained its bioactivity effectively. The immobilized GOD could catalyze the oxidation of glucose, which could be used to determine glucose at +1.0 V without help of any mediator. The competition between GOD and HEX for the substrate glucose involving ATP as a co-substrate led to a decrease of the glucose response, which allowed us to develop an ATP sensor with a good stability. The fabricated silica hybrid sol-gel matrice offered a stage for further study of immobilization and electrochemistry of proteins.

Coarsening of Ag nanoparticles in SiO2–PEO hybrid film matrix by UV light

Ag nanoparticle incorporated inorganic–organic hybrid silica films were prepared from sols derived from tetraethyl orthosilicate–3-(glycidoxypropyl)-trimethoxysilane–silver nitrate following a sol–gel dip-coating method. Hydrolysis–condensation of alkoxy groups and polymerization of epoxy groups formed Si–O–Si (SiO2) and polyethylene oxide (PEO) networks respectively. A nominal composition of the film of 2.3 equivalent mol% Ag–74.4 mol% SiO2–23.3 mol% PEO was maintained. The precipitation of Ag nanoparticles was observed when the film was cured at 60–90 °C. UV treatment (5.3–31.8 J cm−2) causes coarsening of the Ag nanoparticles inside the hybrid SiO2–PEO film matrix. A single surface plasmon (SP) band due to Ag nanoparticles has been observed at 419 nm when the film was cured at 90 °C and UV treated with an energy of 5.3 J cm−2. This SP band is gradually divided into three peaks upon increasing the UV treatment energy up to 31.8 J cm−2. TEM study confirms the coarsening of small Ag nanoparticles of 3–4 nm in size, leading to the formation of spheroidal, elongated and fractal type small aggregates of Ag nanoparticles of size range ∼19–53 nm. The splitting of the Ag–SP band is found to be consistent with the shape of the Ag nanoparticles as observed by TEM.

Synthesis and cryogenic properties of polyimide–silica hybrid films by sol–gel process

Polyimide–silica hybrid films were prepared from tetraethoxysilane (TEOS) and polyamic acid (PAA) via sol–gel process in the solution of N,N-dimethylacetamide (DMAc). The cryogenic mechanical and electrical properties of polyimide–silica hybrid films were studied taking into account the effects of silica content. The results indicated that the cryogenic modulus increased with the increase of silica content while the tensile strength and failure strain had a maximum value at proper silica contents. Moreover, the tensile strength and modulus of the hybrid films at cryogenic temperature (77K) were obviously higher than those at room temperature, while the failure strain of the hybrid films was much lower at cryogenic temperature (77K) than that at room temperature. The mean electrical breakdown strength of the hybrid films was shown to range from 151 to 225kV/mm at cryogenic temperature (77K).

Polyimide–silica hybrid films made from polyamic acids containing phenolic hydroxyl groups

AbstractA diamine and polyamic acid containing phenolic hydroxyl group was synthesized. A series of polyimide/silica hybrid films with strong interacton between organic and inorgamic components was prepared via sol–gel reaction. The morphology of the hybrid films was investigated by scanning electron microscopy and atomic force microscopy. The thermal stability and mechanical properties of the films were detected. The results indicated that the introduction of phenolic hydroxyl groups remarkably attributed to the improvement of tensile strength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1198–1202, 2004

Synthesis and properties of new polyimide–silica hybrid films through both intrachain and interchain bonding

In this study, the new polymer–silica hybrid materials were prepared based on the organo-soluble polyimides of 4,4′-hexafluoroisopropylidenediphthalic anhydride (6FDA) and four diamines. 3-Aminopropyl trimethoxysilane (APrTEOS) and γ-glycidyloxypropyltrimethoxysilanes (GOTMS) were used to increase the intrachain chemical bonding and interchain hydrogen bonding between the polyimide and silica moieties, respectively. The chemical interaction would significantly affect the morphologies and properties of the prepared films. Highly homogeneous hybrid thin films were obtained according to the studies of atomic force microscopy and TEM. The silica size observed by the TEM picture was smaller than 5 nm. The thermal properties of the organo-soluble polyimides were significantly enhanced by hybridizing only 6.30–7.99 wt% of silica. The intrachain chemical bonding could effectively enhance the coefficient of thermal expansion in comparison with the interchain interaction. Low dielectric constants in the range of 2.85–3.73 were obtained for the prepared hybrid films. The refractive indices of the prepared materials could be tuned through the polyimide structure or the silica content. The optical losses of the planar waveguides based on the prepared polyimides and their hybrids at 1310 nm were in the range of 0.5–2.7 dB/cm, which were mostly due to the higher harmonics of the aromatic C–H vibration and the extrinsic loss. The prepared polyimide–silica hybrid materials could have potential applications for microelectronics or optical communications.

New polyimide–silica organic–inorganic hybrids

AbstractA series of polyimide–silica hybrid films with silica contents up to 30 wt % were successfully prepared by the sol‐gel reaction of tetraethoxysiliane in the presence of poly(amic acid) containing pendent hydroxyl groups. The films were yellow and transparent when the silica content was less than 11 wt %. The chemical structure of the films was characterized by Fourier transform infrared spectroscopy, and the morphology of the films was investigated by scanning electronic microscopy and atomic force microscopy. Thermogravimetric analysis, differential scanning calorimetry, and stress–strain tests were used to measure the performance of the films. The results indicate that the glass‐transition temperatures and decomposition temperatures of the hybrid films increased with increasing silica content, whereas the tensile strength had a maximum with the variety of silica contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2210–2214, 2003

Synthesis and characterization of organic–inorganic hybrid thin films from poly(acrylic) and monodispersed colloidal silica

Hybrid thin films containing nano-sized inorganic domain were synthesized from poly(acrylic) and monodispersed colloidal silica with coupling agent. The 3-(trimethoxysilyl)propyl methacrylate (MSMA) was bonded with colloidal silica first, and then polymerized with acrylic monomer to form a precursor solution. Then, the precursor was spin coated and cured to form the hybrid films. The silica content in the hybrid thin films was varied from 0 to 50 wt%. The experimental results showed that the coverage area of silica particle by the MSMA decreased with increasing silica content and resulted in the aggregation of silica particle in the hybrid films. Thus, the silica domain in the hybrid films was varied from 20 to 35 nm by the different mole ratios of MSMA to silica. The results of scanning electron microscope, transmission electron microscope, and elemental analysis support the above results. The prepared hybrid films from the crosslinked acrylic polymer moiety showed much better film uniformity, thermal stability and mechanical properties than the poly(methyl methacrylate) (PMMA) based hybrid materials. Large pin-holes were found in the PMMA–silica hybrid films probably due to the significant difference on thermal properties between the two moieties or the evaporation of solvent. The refractive index decreased linearly with increasing the silica fraction in the hybrid films. Excellent optical transparence was obtained in the prepared hybrid films. These results show that the hybrid thin films have potential applications as passive films for optical devices.

Patterning and optical properties rhodamine B-doped organic–inorganic silica films fabricated by sol–gel soft lithography

Rhodamine B (RB)-doped organic–inorganic silica films and their patterning were fabricated by a sol–gel process combined with a soft lithography. The resulted film samples were characterized by atomic force microscope (AFM), optical microscope and UV/Vis absorption and photoluminescence excitation and emission spectra. The effects of the concentration of the RB dye and heat treatment temperature on the optical properties of the hybrid silica films have been studied. Four kinds of patterning structures with film line widths of 5, 10, 20 and 50 μm have been obtained by micromolding in capillaries by a soft lithography technique. The RB-doped hybrid silica films present a red color, with an excitation and emission bands around 564 and 585 nm, respectively. With increasing the RB concentration, the emission intensity of the RB-doped hybrid silica films increases and the emission maximum presents a red shift. The emission intensity of the films decreases with increasing the heat treatment temperatures.

Synthesis and Optical Properties of Polyimide-Silica Hybrid Thin Films

In this study, two series of the polyimide−silica hybrid optical thin films, PMDA−ODA/SiO2 and 6FDA−ODA/SiO2, were synthesized using an in situ sol−gel reaction combined with spin coating and multistep curing. The hybrid thin films were prepared by the aminoalkoxysilane-capped poly(amic acid)s and tetramethoxysilane (TMOS) as the precursors. Highly transparent hybrid thin films were obtained at a silica content as high as 54.9 wt %. The FE-SEM study suggests the nanosize domain of the silica moieties in the hybrid thin films. The AFM study demonstrates that the hybrid thin films have excellent planarity. The prepared hybrid thin films show good thermal stability. The refractive indices of the prepared hybrid thin films decrease linearly with increasing silica content while the Abbe number of the hybrid thin films shows the opposite trend. The birefringence of the prepared polyimide−silica hybrid thin films is reduced by incorporating the silica moiety. Optical planar waveguides were prepared from the prepared hybrid thin films using a thermal oxide as the cladding layer. The optical losses of these planar waveguides at 1310 nm are in the range of 0.5−1.9 dB/cm, which are due to the higher harmonics of the aromatic C−H vibration, the O−H vibration, and the extrinsic loss. The optical losses of the prepared polyimide−silica hybrid films are lower than their parent polyimdes and thus have potential applications in optical devices.

Photocurrent generation of poly(titanyloxo-phthalocyanine)s and silica hybrid film

Photoelectric properties of poly(titanyloxo-phthalocyanine) bound silica hybrid film were investigated. The solution for the silica hybrid film consists of soluble poly(titanyloxo-phthalocyanine) (PTiOPc) and a sol solution prepared from the hydrolysis of r-glycidoxypropyl-trimethoxysilane and methyl trimethoxysilane. PTiOPc–silica hybrid films were prepared from the above solution by sol–gel process, to give transparent film. The film showed pencil hardness of 3-H when coated on a glass substrate. The PTiOPc–silica hybrid films coated on an ITO glass showed photocurrent higher than 4 μA/cm 2, upon excitation with a visible light under an external potential of 0.6 V (versus Ag/AgCl). The photoconductivity was not much affected by the bridging group between the phthalocyanine ring, but linearly dependent on the content of PTiOPc up to 40 wt.%.