Organic-inorganic Hybrid Sol-gel Materials Research Articles

Amino-Alcohol Organic-Inorganic Hybrid Sol-Gel Materials Based on an Epoxy Bicyclic Silane: Synthesis and Characterization.

Organic-inorganic hybrids (OIHs) are a type of material that can be obtained using the sol-gel process and has the advantages of organic and inorganic moieties in a single material. Polyetheramines have been widely used in the preparation of this type of material, particularly in combination with epoxy-based alkoxysilanes. Nevertheless, epoxyciclohexylethyltrimethoxysilane (ECHETMS) is a promising alkoxysilane with an epoxy terminal group that is quite unexplored. In this work, four novel OIH materials were synthesized using the sol-gel method. The OIHs were based on Jeffamines® of different molecular weights (D-230, D-400, ED-600, and ED-900), together with ECHETMS. The materials were characterized using multinuclear solid state NMR, FTIR, BET, UV/Vis spectroscopy, EIS, and TGA. The influence of the Jeffamine molecular weight and the suitability of these materials to act as a supporting matrix for heteroaromatic probes were assessed and discussed. The materials show interesting properties in order to be applied in a wide range of sensing applications.

Organic-inorganic hybrid sol–gel membranes for pH sensing in highly alkaline environment

This work reports the synthesis of organic–inorganic hybrid (OIH) membranes for potential optical fibre sensors (OFS) functionalisation for pH monitoring of concrete and reinforced concrete structures (RCS). As precursors, 3-glycidyloxypropyltrimethoxysilane and Jeffamine® THF-170 were used. The OIH sol–gel materials were doped with phenolphthalein (phph) for pH sensing proposes and cetyl trimethyl ammonium bromide as surfactant.OIH membranes with pH sensing ability properties were successfully obtained. The dielectric properties of the resultant membranes were determined by electrochemical impedance spectroscopy. The logarithm of resistance obtained was 10.19 Ω cm2 for the undoped matrix and, 7.06 Ω cm2 for the doped one with phph. The results obtained in simulated concrete pore solutions, for the OIH produced, showed to be promising for application in fresh concrete. The transmittance of the synthesized OIH materials decreased after the doping with phph. The matrix showed intrinsic fluorescence and doping it only led to small deviations in the wavelength of the peak of maximum emission. Regarding thermal analysis, no significant changes were obtained on the thermal profile of the doped and undoped OIH membranes. The pH variation was detected by the OIH membrane colour change. Stability studies regarding the release of phph from the OIH matrix led to a mean dissolution time equal to 75.4 (±0.02) hours, indicating that the proposed system reveals long-term stability.

Sol-Gel Coating Membranes for Optical Fiber Sensors for Concrete Structures Monitoring

The use of advanced sensing devices for concrete and reinforced concrete structures (RCS) is considered a rational approach for the assessment of repair options and scheduling of inspection and maintenance strategies. The immediate benefits are cost reduction and a reliable prevention of unpredictable events. The use of optical fiber sensors (OFS) for such purposes has increased considerably in the last few years due to their intrinsic advantages. In most of the OFS, the chemical transducer consists of immobilized chemical reagents placed in the sensing region of the optical sensor by direct deposition or by encapsulation in a polymeric matrix. The choice of the support matrix impacts directly on the performance of the OFS. In the last two decades, the development of OFS functionalized with organic–inorganic hybrid (OIH) sol–gel membranes have been reported. Sol–gel route is considered a simple method that offers several advantages when compared to traditional synthesis processes, allowing to obtain versatile materials with unique chemical and physical properties, and is particularly valuable in the design of OIH materials. This review will provide an update of the current state-of-the-art of the OFS based on OIH sol-gel materials for concrete and RCS since 2016 until mid-2021. The main achievements in the synthesis of OIH membranes for deposition on OFS will be discussed. The challenges and future directions in this field will also be considered, as well as the main limitations of OFS for RCS monitoring.

Synthesis, Optical and Electrical Characterization of Amino-alcohol Based Sol-gel Hybrid Materials.

This manuscript describes the synthesis and characterization of five new organic–inorganic hybrid (OIH) sol-gel materials that were obtained from a functionalized siloxane 3-glycidoxypropyltrimethoxysilane (GPTMS) by the reaction with the new Jeffamine®, namely three different diamines, i.e., EDR-148, RFD-270, and THF-170, a secondary diamine, i.e., SD-2001, and a triamine, i.e., T-403. The OIH sol-gel materials were characterized by UV-visible absorption spectrophotometry, steady-state photoluminescence spectroscopy, and electrochemical impedance spectroscopy. The reported OIH sol-gel materials showed that, with the exception of the samples prepared with Jeffamine® SD-2001, the transmittance values ranged between 61% and 79%. Regarding the capacitance data, the values reported changed between 0.008 and 0.013 nF cm−2. Due to their optical and electrical properties these new OIH materials show promising properties for applications as support films in an optical sensor area such as fiber sensor devices. Studies to assess the chemical stability of the OIH materials in contact with cement pastes after 7, 14, and 28 days were also performed. The samples prepared with THF–170 and GPTMS, when compared to the samples prepared with RFD-270 and T-403, exhibited improved behavior in the cement paste (alkaline environment), showing promising properties for application as support film in optical fiber sensors in the civil engineering field.

Solution-Processed Flexible Gas Barrier Films for Organic Field-Effect Transistors

The solution-processed gas barrier film was fabricated and used for organic field-effect transistors (OFETs). Organic-inorganic hybrid sol-gel materials and cyclic transparent optical polymer (CYTOP) were used as the bottom and top layers of the barrier films, respectively, to effectively protect against gas permeation through the barrier films. The organic-inorganic hybrid material includes sol-gel precursors and amphiphilic polymers. The conventional sol-gel precursors form siloxane bonds by sol-gel reaction and form densely-packed rigid part in thin films. The alkoxysilane-functionalized amphiphilic polymer in the sol-gel precursor solutions has two hydrophobic segments and a hydrophilic segment. The amphiphilic polymer with reactive alkoxysilane groups at both ends of the hydrophobic segments can be involved in the sol-gel reaction, and they can act as surfactants to surround the conventional precursors stabilizing the nanoparticles formed by the hydrolytic condensation reaction of precursors. The amphiphilic polymer also provides flexibility for hybrid sol-gel thin films. CYTOP was used to introduce hydrophobicity on top of the organic-inorganic hybrid thin films. The barrier films containing the organic-inorganic hybrid and hydrophobic CYTOP layers were applied to OFETs and exhibited notable gas barrier properties, high transparency, and flexibility. The encapsulated OFETs with 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) as an organic semiconductor showed a slight decrease in hole mobility from 0.13 to 0.11 cm2 V-1 s-1, while the OFETs without barrier films showed a mobility decrease from 0.11 to 0.03 cm2 V-1 s-1.

Recyclable solid-phase biocatalyst with improved stability by sol–gel entrapment of β-d-galactosidase

β-d-Galactosidase from Kluyveromyces lactis was for the first time immobilized by entrapment in hybrid organic-inorganic sol–gel materials with microporous structure, obtained from alkoxy silanes and alkyl substituted alkoxy silanes, in different combinations. The immobilization matrix was tailored by fine tuning of several parameters, such as: nature of alkyl group of silane precursors, molar ratio of silane precursors, nature of additives, protein concentration. Unlike other enzymes, β-d-galactosidase showed the best catalytic activity at low alkyl group content in the sol–gel matrix, at a molar ratio of 7:1 between the tetraalkoxysilane alkyl-trialkoxysilane precursor. The immobilized enzyme demonstrated enhanced storage, pH and thermal stability compared to the soluble enzyme. The composite sol–gel materials were characterized by transmission electron microscopy, scanning electron microscopy, fluorescence confocal microscopy, and porosity measurement. The biocatalyst was successfully reused in five reaction cycles, maintaining more than 60% of the initial activity.

Sensing Performance of a Refractometric Optical Sensor Platform Based on Multimode Interference Couplers

This paper focuses on characterization of the sensing performance of a refractometric sensing platform based on multimode interference couplers (MMICs). Platform fabrication exploited a low-cost process using photocurable organic-inorganic hybrid sol-gel materials which were structured to form optical waveguides by direct UV laser writing. The sensing principle is based upon the high sensitivity of the optical field distribution formed in the MMIC toward changes in the refractive index of its environment. Simulations demonstrated the importance of correctly specifying the length of the MMIC section and illustrated that longer platforms are more sensitive due to a greater shift in self-image position. To characterize sensing performance, a porous sol-gel humidity sensing enrichment layer was coated on the MMIC. Relative humidity was detected by the system with a resolution of 0.097%. Refractive index resolution of the platform was determined to be ~ 2 × 10-6 RIU , which is an analyte-independent value and illustrates the generic nature of this platform. As such, this platform has immense potential for future applications as a label-free and real-time biosensor platform.

Photoregulated uptake and release of drug by an organic–inorganic hybrid sol–gel material

A photo-responsive molecularly imprinted sol–gel organic-inorganic hybrid material prepared by covalent imprinting of the template-functional monomer complex formed between 4,4′-dihydroxylazobenzene and ibuprofen was developed to explore the photo-regulated uptake and release of drug by a silicate-based smart molecularly imprinted materials. After imprinting, the template molecules (ibuprofen) were removed via hydrolysis in acid, and accurate cavities were left, which could be used as the receptor recognition sites for ibuprofen. The new organic–inorganic hybrid material shows specific affinity to ibuprofen and reversible uptake and release of ibuprofen upon alternate irradiation at 365 and 440 nm, respectively. The favorable binding strength of the imprinted receptor sites in the molecularly imprinted polymer (MIP) for ibuprofen is found to be 2.28 × 103 M−1. Density of receptor sites in the MIP material was 4.0 µmol/g—MIP.

Interferential lithography of Bragg gratings on hybrid organic–inorganic sol–gel materials

In this work we report on the application of laser interference lithography (LIL) to create periodic features on a photosensitive hybrid organic inorganic (HOI) sol–gel material based on 3-glycidoxypropyltrimethoxysilane (GPTMS).To better understand the mechanisms behind the grating formation and optimize the overall process, the chemical changes produced by the laser exposure have been investigated by FTIR spectroscopy. The effects of the development step on the hybrid sol–gel network have been also discussed, trying to explain the origin of the selective dissolution of the unexposed area.High quality gratings with lines down to 250nm have been realized by LIL, in the Lloyd’s mirror configuration, and their morphological characterization has been performed by AFM and SEM.The generation of profiles with controlled sinusoidal features on HOI sol–gel materials could be exploited in different applications such as the realization of plasmonic crystals for sensing applications or as master molds for nanoimprinting lithography.

Two step modification of poly(vinyl alcohol) by UV radiation with 2-hydroxy ethyl methacrylate and sol–gel process for the application of polymer electrolyte membrane

Two step modification of poly(vinyl alcohol) (PVA) by UV radiation and sol–gel process was used to prepare the modified PVA membranes. From the first step modification of PVA by UV radiation with 2-hydroxy ethyl methacrylate (HEMA) monomer, the poly(2-hydroxy ethyl methacrylate) (PHEMA) modified poly(vinyl alcohol), PVAHEMA, was obtained and characterized by Fourier transfer infrared spectra (FTIR) and optical polarizing microscopy for the chemical compositions and morphology. With the second step modification of sol–gel process, the organic–inorganic hybrid sol–gel material, PVAHEMA–SiO 2, was prepared. Both of the modified PVA, (PVAHEMA and PVAHEMA–SiO 2), were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetry analysis (TGA). To prepare the alkaline solid polymer electrolyte, the various PVAHEMA and PVAHEMA–SiO 2 membranes were immersed in 40 wt% KOH solution to form the KOH containing polymer electrolyte membranes. And then their performances were conducted with ac impedance spectroscopy to evaluate the ionic conductivity through the membranes. At room temperature, the ionic conductivity increased from 0.044 to 0.073 S/cm for the PVAHEMA membrane; whereas the ionic conductivity was about 0.11 S/cm for the PVAHEMA–SiO 2 membranes. Compared to other reports in references, our hybrid sol–gel membrane is a highly ionic conducting alkaline solid polymer electrolytes membrane.

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.

Hybrid Organic-Inorganic Sol-Gel Materials Based on Epoxy-Amine Systems

Understanding the synthesis-structure-properties relationship of hybrid organic-inorganic materials is an important and fundamental task to develop a new generation of highly performing systems for the new needs of nanotechnologies. This issue is, also, important to improve the properties of hybrids when used in applications where nanoscale control is not a fundamental request. In this article, a short overview of epoxy amine sol-gel hybrids is reported. The synthesis of these materials has a large flexibility to allow the fabrication of a wide group of hybrids with different structures and properties, whose applications are ranging from non-linear optics to adhesive and protective coatings.

High sensitive SiO2/TiO2 hybrid sol-gel material for fabrication of 3 dimensional continuous surface relief diffractive optical elements by electron-beam lithography

A negative-tone sensitive SiO2/TiO2 organic-inorganic hybrid sol-gel material was synthesized and characterized for fabrication of multilevel micro-optical elements by direct electron-beam lithography. The exposure was carried out by an in-house modified electron-beam writing system using LEO SEM-982 with Elphy Quantum exposure beam-blanking control system at 25keV. The hybrid Sol-Gel material demonstrated a superb sensitivity for doses between 0.22microC/cm2 and 0.33microC/cm2.