Hybrid Sol-gel Materials Research Articles

Characterization by IR spectroscopy of an hybrid sol–gel material used for photonic devices fabrication

In the last few years, ORganically MOdified Silicates [RxSi(OR)4−x] prepared by sol–gel process were particularly attractive for integrated optics fabrication. A composition based on MAPTMS (3-(trimethoxysilyl)propylmethacrylate) has already allowed the industrial fabrication of optical integrated devices. For this kind of materials, the polymerization of the organic network is typical of free radical curing. This material is the more advanced and industrialized material but the composition has some disadvantages which can complicate or prohibit specific IOC fabrication. In this work, we try to obtain waveguides with another hybrid precursor [2-(3,4-epoxycyclohexylethyltrimethoxysilane)] using cationic polymerization. The main advantage of cationic polymerization is its ability to allow spontaneous cure reaction in presence of oxygen, in contrast with radical polymerization. We choose cycloaliphatic compounds because of their well known high polymerization rates. The polymerization of the organic network of this hybrid material requires a cationic photoinitiator. High losses of light propagation at 1550nm are mainly due to the presence of OH groups originating from the sol–gel process at low temperature. Thus, improvement of the final properties of this material is correlated with the inhibition of OH group concentration. In this work, near and middle IR spectroscopy experiments show the presence of a still too high proportion of OH species in the structure. Polymerization is studied through the absorption band of the epoxy ring-opening before and after irradiation. In order to reduce the OH content, we study the effect of a post bake treatment.

Polymeric and Hybrid Materials for Electrooptical Devices: Polar Order Dynamics

The present contribution reviews some aspect of the exploitation of polymeric and hybrid solgel materials for optoelectronic devices. In particular a procedure addressed to experimentally investigate the order stability of systems containing NLO dipolar molecules will be discussed. A figure of merit, allowing the comparison among candidate systems for devices, is recognized in the RT d 33 decay time value. Its relation with glass transition temperature of a series of similar polymeric systems is reported. Moreover, a hybrid solgel system containing electro-optic active molecules is shown.

Conductive Sol-Gel Hybrid Materials for Novel Cofactor Regeneration in Biocatalysis

The electrochemical recycling of cofactors during enzymatic biocatalysis has long been acknowledged as a potentially powerful technology in fine chemical synthesis. Major obstacle for this approach is that cofactors only in the immediate vicinity of the electrode surface are productive. This problem further causes high overpotential at electrode surfaces leading to undesired side reactions producing enzymatically-inactive dimer and isomer of cofactor. So far, several attempts had been made to address these problems by focusing on surface modifications, which explored to retain the enzyme and/or cofactor close to the working electrode including electrode deposition and membranes surrounding the electrode. In this work, we demonstrate a new concept of cofactor regeneration by using ‘electronically-conductive’ sol-gel hybrid materials. When conductive hybrid gels were added to the reaction medium, we found that cofactor could be efficiently recycled throughout the whole reactor system leading to high yield of product, which was unattainable with conventional technologies.

Photo-imageable Sol–Gel Hybrid Materials for Simple Fabrication of Micro-optical Elements

Special attention has been focused on photo-imageable sol-gel hybrid (SGH) materials because of their synergetic effects, such as high photosensitivity and transparency, as well as mechanical and chemical durability resulting from the presence of polymer and silica networks in the hybrid structure. Photo-induced migration, which accompanies photopolymerization and photolocking in these materials, allows for the formation of convex micropatterns with a higher refractive index than the original film through exposure to UV radiation. Controlling the parameters affecting this photo-induced migration can permit modulation of the size and shape of such microstructures for the simple and cost-effective direct photofabrication of micro-optical elements, such as microlenses and microlens arrays.

Linear and non-linear optical properties of 2,5-disubstituted pyrroles supported by a catalyst-free SiO 2 sonogel network

The preparation and optical characterization of pyrrole based sol–gel hybrid materials generated by ultrasonic irradiation (Sonogel composites) are presented in this work. Pyrrole compounds were recently synthesized in our group by a modification of the Schulte–Reisch reaction; these molecular systems were dissolved at different concentrations in tetrahydrofuran (THF) and optimally embedded into a catalyst-free SiO 2 sonogel network. For this purpose, we exploited the novel catalyst-free (CF) sonolysis route to produce highly pure sol–gel glasses, generated via sonochemical reactions. This approach has been recently developed in our research group and has been successfully implemented to develop several hybrid composites for optical applications. By this method, homogeneous and stable solid-state hybrid samples suitable for optical characterization can be produced. The high porosity exhibited by the sonogel matrix allowed us to prepare several pyrrole doped composites with variable dopant concentration. The linear and nonlinear optical (NLO) properties of these amorphous hybrid structures were determined by absorption- and photoluminescent (PL)-spectroscopies, and by the optical third harmonic generation (THG) techniques, respectively. The implemented catalyst-free sonolysis route produced SiO 2-host networks of high chemical and optical purity, suitable for optical and photonic applications.

Double component long period waveguide grating filter in sol-gel material

An efficient, tunable Long Period Waveguide Grating (LPWG) filter based on a new hybrid sol-gel material is demonstrated. The LPWG exhibits an attenuation of -22 dB and a high temperature sensitivity of ~3.3 nm/ degrees C. At room temperature the device shows an almost polarization independent wavelength. We took the advantage of the UV-curable sol-gel materials and used soft lithography to demonstrate a simple approach of integrating two LPWG filters on the same structure. The gratings were fabricated on the top and on the bottom of the same ridge waveguide and operate at communication wavelengths of 1550 and 1310 nm, respectively.

Alkoxysilyl derivatives of polyhedral oligosilsesquioxanes containing amino and hydroxyl groups and sol-gel hybrid materials on their basis

A mixture of polyhedral oligosilsesquioxanes of the empirical formula ((HOCH 2 CH(OH)CH 2 ) 2 N(CH 2 ) 3 SiO 1.5 ) n characterized by narrow molecular-mass distributions has been syn- thesized by the hydrolytic condensation of the product resulting from the interaction of glycidol and 3-amino- propyltriethoxysilane. The said oligosilsesquioxanes have been involved in reaction with 3-isocyanatopropyl- triethoxysilane to give rise to urethane-containing alkoxysilyl derivatives of various degrees of substitution. Organo-inorganic hybrids have been prepared on their basis through the sol-gel method. The structure and properties of the products have been studied by matrix laser desorption/ionization mass spectrometry, GPC, X-ray diffraction, DSC, and thermogravimetry. It has been demonstrated that the properties of the polymer materials thus prepared may be controlled by variation of the ratio of hydroxyl and alkoxysilyl groups in oligosilsesquioxane derivatives and by incorporation of low-molecular-mass sol-gel precursors.

Using Novel Polysaccharide−Silica Hybrid Material to Construct An Amperometric Biosensor for Hydrogen Peroxide

A new type of sol-gel organic-inorganic hybrid material was developed and used for the fabrication of an amperometric hydrogen peroxide biosensor. This material was prepared from natural chitosan and recently introduced completely water-soluble precursor, tetrakis(2-hydroxyethyl) orthosilicates (THEOS), by the sol-gel process without the addition of organic solvents and catalysts. The gelation time for the sol-gel transition and dynamic rheological properties of the resultant gel matrix could be modulated by the amount of added THEOS. The structure of the hybrid gel was made up of a network and spherical particles, as confirmed by SEM observation. By electrochemical experiments, it was found that such a hybrid gel matrix could retain the native biocatalytic activity of the entrapped horseradish peroxidase and provide a fast amperometric response to hydrogen peroxide. The linear range for the determination of hydrogen peroxide was found to be from 1.0 x 10(-6) to 2.5 x 10(-4) mol/L with a detection limit of 4.0 x 10(-7) mol/L. The apparent Michaelis-Menten constant was determined to be 2.198 mmol/L. To improve the analytical characteristics of the fabricated biosensor, the effects of applied potential and pH value on the steady-state current were studied. Under the optimized experimental conditions, the fabricated biosensor was found to have good analytical performance, reproducibility, and storage stability.

Direct nanopattern of hybrid sol–gel films

We propose a direct nanopatterning process of hybrid sol–gel materials useful for photonics application. A specific organic–inorganic film based on 3-glycidoxypropyltrimethoxysilane with epoxy rings acting as silica network modifier and sensitive to radiation has been developed, with a controlled inorganic crosslinking degree and an almost total absence of organic polymerization. The film has been exposed to electron beam or X-ray synchrotron radiation. Both the interactions induce the polymerization of the organic part of the film generating its hardening after post exposure baking. The exposed material becomes insoluble determining a negative-resist like behaviour: the nanolithographic process results from the dissolution of the un-exposed areas in proper solvents. After its optimization unexpected spatial resolution of the pattern were achieved with structures below 200 nm sized, both with electron beam and X-ray lithography. The real advantages of this approach are that almost all the significant parameters for a photonic device (refractive index, light absorption and emission) can be tailored during the material synthesis and with a single lithographic step the device is ready without any further etching process, undoubtedly simplifying the photonic devices nanofabrication. A demonstration test has been performed doping the film with commercial Rhodamine 6G that after the exposure didn’t degraded its luminescence efficiency.

Optical and dielectric characteristics of photochromic hybrid sol-gel materials

Photochromic silica based organic-inorganic hybrid materials containing covalently linked cyanoazobenzene chromophores were investigated by optical and dielectric spectroscopy. These materials, obtained via sol-gel process, were deposited onto glass substrates by spin coating technique to achieve thin transparent films. To investigate photoinduced alignment, the UV-Vis absorption spectra of the sol-gel films were recorded under illumination with linearly polarized blue light. Dielectric relaxation spectroscopy revealed a variety of relaxation processes: the α-process related to the dynamic glass transition temperature located around 150°C, and an Arrhenius-type β-relaxation (activation energy 58–60 kJ/mol) that was assigned to orientational fluctuations involving the azobenzene group. The correspondence between dielectric and photochemical behavior was discussed.

Low drive voltage Fabry-Pérot étalon device tunable filters using poled hybrid sol-gel materials

Nonlinear optical chromophore coupled hybrid sol-gel materials have been synthesized and incorporated in Fabry-Pérot étalon devices (ED’s) using highly reflective distributed Bragg reflector mirrors. Étalon structures with indium tin oxide electrodes outside the ED cavity have been applied to reduce absorptive loss. Large tunability (∼0.75nm∕V), high finesse (∼235), and wide tunable range (>50nm) have been obtained. A transmitted light intensity isolation ratio of ∼35dB at ∼1550nm has been achieved at a low drive voltage of 10V. The electro-optic effect and inverse piezoelectric effect are discussed. The results indicate that such hybrid sol-gel ED’s are promising candidates for tunable filters in wavelength division multiplexing communication systems.

Durable electrochromic coatings prepared from electronically conductive poly(3HT-co-3TPP)-silica hybrid materials

In this paper, a series of organic-inorganic hybrid materials, consisting of heterocyclic conjugated poly(3-hexylthiophene), P3HT, network, and silica particles, were successfully prepared for electrochromic studies. First, the heterocyclic co-polymer of poly[3-hexylthiophene-co-N-(3-trimethoxysilylpropyl) pyrrole], P(3HT-co-3TPP), containing trimethoxysilyl functional groups in the co-polymer backbone as the sol-gel precursor were prepared by conventional oxidative polymerization. Subsequently, P(3HT-co-3TPP)-silica hybrid sol-gel materials in the form of coatings were prepared by baking the microslides and ITO-coated electrodes that had been cast with homogeneous blending solutions containing co-polymer, acid-dopant, tetraethyl orthosilicate (TEOS), and a few drops of water. The microstructures of silica particles formed in the P(3HT-co-3TPP)-silica hybrid materials were investigated by transmission electron microscopy (TEM). The as-prepared hybrid coatings had improved adhesion capability on inorganic glass substrates relative to the pure P3HT on the basis of electrochemical cyclic voltammetric studies and Scotch tape test evaluations. During potential cycling, the film color of P(3HT-co-3TPP)-silica hybrid materials and P3HT coated on ITO electrode changed from orange yellow (i.e., reduced form) to dark blue (i.e., oxidized form) as the redox reactions proceeded. Effects of the material composition of P3HT along with hybrid materials on the electrochemistry, spectroelectrochemistry, thermal stability, and electrical conductivity were also studied.

Robust free-standing nanomembranes of organic/inorganic interpenetrating networks

Hybrid sol-gel materials have been a subject of intensive research during the past decades because these nanocomposites combine the versatility of organic polymers with the superior physical properties of glass. Here, we report the synthesis, by spin coating, of hybrid interpenetrating networks in the form of free-standing nanomembrane (around 35-nm thick) with unprecedented macroscopic size and characteristics. The quasi-2D interpenetration of the organic and inorganic networks brings to these materials a unique combination of properties that are not usually compatible within the same film: macroscopic robustness and homogeneity, nanoscale thickness, mechanical strength, high flexibility and optical transparency. Interestingly, such free-standing nanofilms of macroscopic size can seal large openings, are strong enough to hold amounts of liquid 70,000 times heavier than their own weight, and are flexible enough to reversibly pass through holes 30,000 times smaller than their own size.

Sensitivity to alcohols of a planar waveguide ring resonator fabricated by a sol–gel method

A planar waveguide ring resonator was fabricated by organic–inorganic hybrid sol–gel materials; its sensitivity to ethanol vapor was experimentally investigated. It was found that dips in the transmission spectrum of the device shifted to longer wavelengths with increasing the ethanol concentration, and its sensitivity showed a linear relation with the ethanol concentration, showing a coefficient of 1.13 pm/ppm. In addition, the transmission loss of the ring resonator decreased with increasing the ethanol concentration. The measured characteristics suggest that the device may be considered as one of the candidates of alcohol vapor sensors.

Effect of baking treatment and materials composition on the properties of bulky PMMA–silica hybrid sol–gel materials with low volume shrinkage

AbstractA series of bulky PMMA–silica hybrid sol–gel materials had been successfully prepared through the conventional HCl‐catalyzed sol–gel approach with 2‐hydroxyethyl methyl methacrylate (HEMA) as coupling agent under pumping pretreatment (i.e., exhaustive vacuum evacuation). In this work, the hydroxyl groups of HEMA monomers were first cohydrolyzed with various contents of tetraethyl orthosilicate (TEOS) to afford chemical bonding for the forming silica networks by removal of solvent and byproduct of sol–gel reactions through pumping pretreatment before gelation reactions. Subsequently, the resultant viscous solution was then copolymerized with methyl methacrylate (MMA) monomers at specific feeding ratios by using benzoyl peroxide (BPO) as free‐radical initiator. Eventually, transparent bulky organic–inorganic hybrid sol–gel materials loaded with different silica content were always achieved. The obtained bulky hybrid sol–gel materials were found to be transparent, crack‐free, and of relatively low volume shrinkages even in high silica content. The as‐prepared bulky hybrid sol–gel materials were then characterized through silicon element mapping studies of energy‐dispersive X‐ray (EDX) and transmission electron microscopy (TEM). Effect of heating process at 150°C for 5 h after polymerization and material composition on the thermal properties, mechanical strength, and optical clarity of a series of bulky PMMA–silica hybrid sol–gel materials was investigated and compared by thermogravimetric analysis (TGA), thermomechanical analysis (TMA), hardness test, dynamic mechanical analysis (DMA), and UV–vis transmission spectroscopy, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1151–1159, 2006

Anticorrosively enhanced PMMA–SiO 2 hybrid coatings prepared from the sol–gel approach with MSMA as the coupling agent

A series of sol–gel derived organic–inorganic hybrid coatings consisting of organic poly(methyl methacrylate) (PMMA) and inorganic silica (SiO 2) were successfully synthesized by using 3-(Trimethoxysilyl)propyl methacrylate as a coupling agent. In this work, MSMA is first copolymerized with methyl methacrylate monomer at specific feeding ratio by using benzoyl peroxide (BPO) as initiator. Subsequently, the as-prepared copolymer (i.e., sol–gel precursor) is then cohydrolyzed with various contents of tetraethyl orthosilicate (TEOS) to afford chemical bondings to the forming silica networks, giving a series of hybrid sol–gel coatings. Transparent organic–inorganic hybrid sol–gel coatings with different contents of silica are always achieved. The as-synthesized hybrid sol–gel materials were subsequently characterized by Fourier-Transformation infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). The hybrid sol–gel coatings with low silica loading (e.g., 5 wt.%) on cold-rolled steel (CRS) coupons were found much superior in anticorrosion efficiency over those of neat PMMA based on a series of electrochemical measurements of corrosion potential, polarization resistance, corrosion current, and corrosion rate in 5 wt.% aqueous NaCl electrolyte. The enhancement of corrosion protection effect of hybrid sol–gel coatings may be due to the increase of adhesion strength of hybrid sol–gel coatings on CRS coupons relative to neat PMMA, which was further evidenced by the Scotch tape test evaluation. The increase of adhesion strength of hybrid sol–gel coatings on CRS coupons may be attributed to the formation of Fe–O–Si covalent bonds at the interface of coating/CRS system based on the FTIR–RAS (reflection absorption spectroscopy) studies. Effects of the material composition on the thermal stability, mechanical strength, wettability, and surface morphology of neat copolymer and a series of hybrid sol–gel materials, in the form of coating/film, were also studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), hardness tests, contact angle measurement, and atomic force microscopy (AFM), respectively.

Thermally stable optical characteristics of sol-gel hybrid material films

Thermo-optic (TO) coefficients for transverse-electric and transverse-magnetic polarized light (dnTE∕dT and dnTM∕dT, respectively) were measured for sol-gel-derived, new organic-inorganic hybrid materials. The absolute values of dnTE∕dT are comparable to those of dnTM∕dT, indicating low anisotropy (dnTE∕dT-dnTM∕dT) in the TO coefficients. The low anisotropy is evidenced by the very small polarization dependence of the refractive index (nTE−nTM). The high stability of these materials is consistent with a high glass transition temperature (Tg>150°C), and evidenced by an absence of hysteresis in the refractive index and in film thickness during temperature cycling between 30 and 150°C.

Photoinduced effects in hybrid sol-gel materials

Hybrid silica-based sol-gel films containing Disperse Red 1 (DR1), carbazole units (CBZ) and 2,4,7-trinitro-9-fluorenone (TNF) at different concentrations show reversible photoinduced birefringence. Polarization sensitive holographic gratings have been produced and characterized. Dichroism measurements give information on the orientation mechanisms and on the aggregation of the dye molecules. The alignment of the DR1 molecules by corona poling is verified by second harmonic generation (SHG) and a moving grating technique is used to investigate an asymmetric energy exchange in a two-beam coupling experiment, typical of photorefractive gratings.

Low adhesive force of fluorinated sol–gel hybrid materials for easy de-moulding in aUV-based nano-imprint process

A fluorinated methacryl hybrid material, with low surface tension, was used as animprinting material for easy de-moulding in a UV-based nano-imprint process.Specifically, a method to measure the adhesive force between the poly(dimethylsiloxane)(PDMS) mould and the imprinting material, using the force–distance curve ofPDMS, was suggested to represent the de-mouldability of the PDMS mould ina UV-based nano-imprint process. The fluorinated methacryl hybrid materialexhibited a low adhesive force to PDMS, as well as low surface tension, and could benano-imprinted without using an anti-sticking treatment on the PDMS mould.

Photocurable glycidoxypropyltrimethoxysilane based sol-gel hybrid materials

Abstract Hybrid sol-gel materials are promising candidates for electro/optical applications, combining the most important glass-like and polymer-like properties. Hybrid patternable materials produced by photopolymerisation processes have been mainly developed on 3-methacrloxypropyltrimethoxysilane based systems in which the polymerisable organic function is the C C bond of the methacrylic group. A new photosensitive hybrid material is described here, based on 3-glycidoxypropyltrimethoxysilane (GPTMS) and on the cationic photopolymerisation of the epoxide groups, which lead to the formation of a PEO organic interpenetrating network.