Viscoelastic characterization of TEOS sols in three different solvents when DBTL is used as polycondensation catalyst

The gelation process of TEOS sols in three different solvents using di-n-butyltin dilaurate (DBTL) as polycondensation catalyst has been investigated. Sol compositions were similar to those employed in the field of stone consolidation for the conservation of historical buildings. Three different systems were studied: TEOS in ethanol (S-EtOH) which was tested to explain gelation in protic solvents; TEOS in a mixture of methylethylketone/acetone (S-MA) to represent aprotic solvents; and TEOS in a blend of MEK/ethanol (S-ME) for comparison of a system with properties intermediate between protic and aprotic solvents. The gelation process was studied by measuring the viscoelastic behavior near the gelation point (GP). A scaling exponent (Δ) was determined for the elastic modulus, G(ω)′ and the viscous modulus, G′′(ω), which both follow the same power law, ω^Δ, at GP. The fractal dimension, df, was calculated from the scaling exponent, Δ, for each TEOS-DBTL system. For each type of solvent studied, values of Δ from 0.34 to 0.53 with df of 1.9–2.2 were obtained. The results suggest that DBTL leads to a TEOS polycondensation mechanism similar to that observed for a base-catalyst system. However, the change in df suggests that there is a significant effect of the solvent on aggregation mechanisms of the gelation process. A diffusion limited cluster–cluster aggregation mechanism (DLCCA) was observed when ethanol was used as protic solvent, while a reaction limited cluster–cluster aggregation mechanism (RLCCA) was observed for MEK/acetone (aprotic solvent).     

New nanomaterials for consolidating stone

A novel sol-gel synthesis, in which a surfactant acts to make the pore size of the gel network more coarse and uniform, is shown to provide an effective alternative for the consolidation of stone. The new mesoporous silica avoids the main inconvenience of current commercial consolidants, which is their tendency to crack inside the pores of the stone. Since the cracking of xerogels is a well-known drawback of the sol-gel process, the synthesis presented here can be extended to other applications. Finally, preliminary studies of the effectiveness of the novel surfactant-templated sol in consolidating a typical biocalcareous stone are also discussed.     

A New Sol-Gel Derived Optical Fiber Sensor for High Acidity Measurements: Application in Nuclear Fuel Reprocessing

Nuclear fuel reprocessing requires high acidity levels that should be accurately and rapidly controlled in order to optimize extraction yields and process efficiency. A new optical fiber sensor based on a sol-gel film doped with an acid-sensitive indicator has been developed to improve remote and on-line monitoring.The organic molecule was physically incorporated in an acid-catalyzed sol-gel matrix and coated onto the core of a denuded optical fiber. The sensor response was evaluated in synthetic solutions of nitric acid, concentrations ranging from 1 to 10 mol · l^–1. Changes in absorption properties and response characteristics of the sensor, when compared to the indicator in solution, have been discussed. Analytical performances of the sensor, i.e. sensitivity, response time, reversibility and repeatability are very encouraging for the on-line analysis. Viability of the sensor for process measurements depends on the stability which might be improved by a strict control of the sensitive film porosity.     

Formation of zein spheres by evaporation-induced self-assembly

Zein is an amphiphilic protein capable of self-assembly into microspheres. Zein microspheres may form by evaporation-induced self-assembly (EISA) of zein solutions in ethanol/water. The formation of microspheres is of particular interest for the development of delivery systems. Zein solutions in ethanol/water 75?% (v/v) were slowly evaporated to promote self-assembly of microspheres. The ethanol content of the solvent decreased during EISA changing solvent polarity which induced self-assembly of zein particles. The growth of zein spheres was modeled from the hydrophobic and hydrophilic contributions to the interfacial free energy (R ²?=?0.92). The good fit indicated that during EISA zein microspheres increased in size due to hydrophobic interactions between zein molecules. The model may allow the prediction of evaporation time and thus control over microsphere size.     

Detection of NADH and ethanol at a graphite electrode modified with titania sol-gel/Meldola’s Blue/MWCNT/Nafion nanocomposite film

For electrocatalytic determination of NADH, a graphite electrode modified with titania sol-gel/Meldola’s Blue/MWCNT/Nafion nanocomposite was proposed. The composition of the matrix film was optimised in terms of the content of carbon nanotubes and Nafion. Incorporation of a redox mediator, Meldola’s Blue, into the nanocomposite film enabled electrocatalytic determination of NADH at a low potential, −50 mV. For determination of ethanol, alcohol dehydrogenase (ADH) was immobilized into the matrix layer. Experimental conditions affecting the biosensor response were examined, including enzyme loading, temperature of measurement and pH of background electrolyte. Assessments of the analytical characteristics of the biosensor were performed with respect to sensitivity, limit of detection, operational stability, repeatability and reproducibility. The proposed biosensor showed electrocatalytic activity toward oxidation of ethanol with sensitivity of 2.24 μA L mmol⁻¹, linear range from 0.05 to 1.1 mmol L⁻¹, and limit of detection of 25 μmol L⁻¹. The apparent Michaelis-Menten constant was 1.24 mmol L⁻¹, indicating a high biological affinity of ADH/titania sol-gel/Meldola’s Blue/MWCNT/Nafion electrode for ethanol. The developed biosensor was tested in determinations of ethanol content in alcoholic beverages.     

Thin films of functionalized amorphous silica for immunosensors application

Within the framework of the development of an optical immunosensor, the sol-gel process has been used to prepare a thin film of amorphous silica, deposited by spin coating on a gold-coated glass slide, and possessing chemically active functional groups (SH, NH₂...). After activation of the sol-gel film in aqueous buffers by a bifunctional coupling agent, biological molecules such as antibodies could be covalently bonded on or inside the sol-gel film. Therefore, the behavior in aqueous solutions of the functionalized silica thin films has been analysed by Surface Plasmon Resonance (SPR) and guided wave propagation. Results show a modification of the thickness and of the refractive index of the silica film. Pore size range has been deduced by the infiltration of different molecular weight dextran molecules diluted in water into the sol-gel material. Immunosassays have demonstrated biological activity of antibodies which are covalently linked to or entraped in the sol-gel film.     

Influences of Solvent on Properties of TiO<Subscript>2</Subscript> Porous Films Prepared by a Sol-Gel Method from the System Containing PEG

Ethanol, n-butanol, mixed ethanol/terpineol and ethanol/1-decanol were used as the solvents to prepare porous TiO₂ films by the sol-gel method from the system containing tetrabutylorthotitanate as starting material and PEG as a template. The comparison of effects of the four solvents on the porous structure, film thickness, crystallization behavior from amorphous to anatase and optical properties of the resultant TiO₂ porous films are discussed. The maximum thickness of the film prepared by one-run dip-coating reaches over 1.17 μm when 1-decanol is used as the solvent. The mechanism for formation of the porous structure is interpreted based on the phase separation and self-assembly of PEG in the sol systems.     

Steady-state γ-radiolysis of aqueous methyl ethyl ketone (2-butanone) under postulated nuclear reactor accident conditions

The steady-state γ-radiolysis of aqueous solutions containing 1×10⁻³ mol dm⁻³ methyl ethyl ketone (MEK) has been studied at a dose rate of 0.12 Gy s⁻¹, 25°C and an initial pH of 10. Experiments were conducted in air-, Ar- or N₂O-purged aqueous solutions, or in Ar-purged solutions with added tert-butanol. MEK, its radiolytic products, and the change in pH resulting from MEK decomposition were analysed as a function of time (or total absorbed dose). The main initial step for the radiolytic decomposition of MEK is the H abstraction from MEK by OH, produced by γ-radiolysis of water, to form MEK radical. In the absence of O, the main decay path of the MEK radical appears to be dimerization to , -dimethyl-2,5-hexanedione. In the presence of oxygen, the MEK radical reacts primarily with O to form the MEK peroxyl radical. This radical ultimately results in a series of progressively smaller oxidation products. The formation of organic acids, and eventually CO₂, reduces the pH of the solution. This paper presents the experimental data and proposes the MEK decay kinetics and mechanism.     

Atomistic Modeling of Silica Based Sol-Gel Processes

Density Functional Theory is used to study water, methanol, ethanol, TMOS, and TEOS molecules and the most important silica clusters participating in sol-gel processes. Calculated bond lengths, bond angles and electric dipole moments compare well with experimental data. The energy of these molecules is reported and used to discuss the energetics of the hydrolysis and condensation reactions. Molecular Dynamics is employed to simulate liquid water, methanol, ethanol, TMOS, TEOS and experimental sol-gel solutions. Calculated densities and enthalpies of vaporisation compare well with experimental data. Preliminary results are presented for MD simulations of sol-gel solutions.     

Influence of the Deposition Parameters on the Characteristics of Aerosol-Gel Deposited Thin Films

The aerosol-gel process is a thin film deposition process based on the sol-gel polymerisation of a liquid film deposited from an ultrasonically sprayed aerosol. This process offers an attractive alternative for the deposition of sol-gel thin films. The effects of the aerosol deposition route on the film characteristics have been investigated with regard to sol-gel chemistry. TEOS solutions have been studied by viscosimetry and FTIR spectroscopy using an ATR device. Silica xerogel coatings have been studied by transmission FTIR and optical microscopy. Film morphology and uniformity depend closely on the aerosol deposition conditions. The film growth is controlled by a droplet coalescence surface phenomenon.     

Miscibilities of methanol and ethanol with dodecylammonium chloride in the adsorbed film and micelle

The surface tension of the aqueous solutions of methanol– dodecylammonium chloride (DAC) and ethanol–DAC mixtures has been measured as a function of the total molality of the mixture m^ and the mole fraction of DAC X^₂ in the mixture at 298.15?K under atmospheric pressure. The compositions of the adsorbed film at 50, 40, and 30?mN?m^-1, and that of the micelle at the critical micelle concentration (CMC) have been evaluated by applying the thermodynamic equations derived previously and shown in the form of phase diagrams of adsorption and micelle formation. It has been found that (i) methanol is hardly miscible in M28.8nthe adsorbed film and micelle, and (ii) ethanol molecules are very slightly incorporated into adsorbed film of DAC at high-surface tension and into the micelle, although hardly miscible in the adsorbed film at low-surface tension. By comparing the corresponding phase diagrams of ethanol-2- (octylsulfinyl)ethanol (OSE) mixture, furthermore, it has been shown that there exists a difference in the miscibility of ethanol between DAC and OSE.     

Modification of micro-cantilever sensors with sol-gels to enhance performance and immobilize chemically selective phases

A chemical sensor based on the deflection of a surface modified silicon micro-cantilever is presented. A thin film of sol-gel was applied to one side of the micro-cantilever surface using a spin coating procedure. The sensor has been shown to give different responses to vapor phase analytes of varying chemical composition, as well as to varying concentrations of a given analyte. Ethanol, a highly polar molecule, exhibits a strong affinity for the polar sol-gel coating resulting in a large response; pentane, a non-polar hydrocarbon, shows very little response. The sol-gel coating has also been shown to function as a backbone for the immobilization of chemically selective phases on the cantilever surface. Reaction of the sol-gel film with chlorotriethoxysilane and subsequent capping of the remaining reactive surface silanols with hexamethyldisilizane increases the non-polar nature of the film. This results in an increase in the response of the sensor to non-polar analytes. The effects of film thickness and cantilever structure thickness on response were also investigated.     

Study of the acid hydrolysis of (3-methacryloxypropyl)trimethoxysilane by capillary electrophoresis-ion-trap mass spectrometry

The sol-gel method is a widely used technique for the synthesis of various functional coating films. Alkoxysilanes such as (3-methacryloxypropyl)trimethoxysilane (MEMO) are largely used as precursors for inorganic-organic hybrid sol-gel materials. Indeed, these compounds can form complex network, through hydrolysis and condensation reactions. The latter have to be perfectly controlled to obtain the required properties. In such a context, we have studied the potentialities of capillary electrophoresis-ion-trap mass spectrometry (CE-MS) coupling to resolve both separation and characterization of the synthesized compounds as a function of the hydrolysis time. The study of acid hydrolysis of MEMO was carried out as an example. After optimization of the running electrolyte in capillary zone electrophoresis (CZE) with UV detection, we characterized the synthesized compounds in CE-MS by using positive detection mode. The obtained resolution in CZE-UV was not entirely satisfactory because of the very closed charge/mass ratio of formed solute but also because of the interaction between the solutes and the capillary walls. Nevertheless, several oligomers were characterized in CE-MS. The absence of detection with regard to oligomers that possess higher molecular masses than octamer is discussed in this work.     

Immobilization of acetylcholinesterase on screen-printed electrodes: comparative study between three immobilization methods and applications to the detection of organophosphorus insecticides

The analytical performance of three acetylcholinesterase (AChE) screen-printed biosensors designed for the detection of pesticides are evaluated. Bioencapsulation of the enzyme in a sol-gel composite and immobilization by metal-chelate affinity were compared with the entrapment of the enzyme in a photopolymerisable polymer. A very low amount of enzyme ranging between 0.8 and 1.2 mIU was immobilized on the electrode surface in each approach. The sensors exhibited a storage stability of over 6 months when the enzyme was encapsulated in a polymer film. Pesticide concentrations in the range of 10⁻⁸ to 10⁻⁹ M paraoxon, dichlorvos and chlorpyrifos ethyl oxon could be detected according to each configuration by following an incubation time of 20 min.     

MFI zeolite as adsorbent for selective recovery of hydrocarbons from ABE fermentation broths

1-Butanol and butyric acid are two interesting compounds that may be produced by acetone, butanol, and ethanol fermentation using e.g. Clostridium acetobutylicum. The main drawback, restricting the commercialization potential of this process, is the toxicity of butanol for the cell culture resulting in low concentrations of this compound in the broth. To make this process economically viable, an efficient recovery process has to be developed. In this work, a hydrophobic MFI type zeolite with high silica to alumina ratio was evaluated as adsorbent for the recovery of butanol and butyric acid from model solutions. Dual component adsorption experiments revealed that both butanol and butyric acid showed a high affinity for the hydrophobic MFI zeolite when adsorbed from aqueous model solutions. Multicomponent adsorption experiments using model solutions, mimicking real fermentation broths, revealed that the adsorbent was very selective to the target compounds. Further, the adsorption of butyric and acetic acid was found to be pH dependent with high adsorption below, and low adsorption above, the respective pKa values of the acids. Thermal desorption of butanol from MFI type zeolite was also studied and a suitable desorption temperature was identified.     

Phospholipid black foam films: dynamic contact angles and gas permeability of DMPC bilayer films

The behavior of bilayer Newton Black Films (NBF) from aqueous dispersions of dimyristoylphosphatidylcholine (DMPC) have been studied in dynamic conditions. The dynamic contact angles θ and the gas permeability coefficient K have been measured using the diminishing bubble method. Two different solutions have been used: (i) DMPC vesicle suspension in water obtained through sonication and (ii) DMPC dissolved in ethanol plus water mixed solvent. Both solutions contain 0.1 M NaCl. The behavior of the dynamic contact angles is very different for NBF from the two types of solutions. In the case (i) the initially constant θ(t) sharply increase after approximately 2 h of the spontaneous diminishing of the bubble, they follow the gas pressure variation in the cell and depend on the film area. On the contrary in case (ii) the θ(t) values are almost constant during the spontaneous diminishing of the bubble as well as during the gas pressure variation in the cell and they do not depend on the film area. The gas permeability coefficient is larger in case (ii). The results are discussed in connection with the thickness and structure of the NBF from the two types of solutions, taking into account the solubility (or insolubility) and the hydration of the adsorption layers of the DMPC molecules.     

聚苯胺对新型杂化透明导电薄膜制备和性能的影响

以聚苯胺和掺锑的氧化锡作为主要原料, 采用溶胶-凝胶法制备了新型有机-无机杂化透明导电薄膜. 薄膜的可见光透过率为85%以上, 电导率达到10⁰～10¹ S•cm^－1. 研究了聚苯胺含量的变化对浸涂液粘度、薄膜结构、光透过率、电导率的影响. 随着聚苯胺引入量的增加, 薄膜的电导率、可见光透过率均有所增大. 浸涂液的粘度可在长达25天的时间内保持稳定, 很适于浸涂工艺. 扫描电镜照片显示, 薄膜比较致密、均匀, 厚度为250 nm左右.     

Elaboration at 80°C of SiO2 Layers Deposited by Aerosol-Gel Process

The aerosol-gel process is a thin film deposition technique based on the sol-gel polymerization of a liquid film deposited from an ultrasonically sprayed aerosol. SiO2 layers have been deposited by aerosol-gel process from TEOS solutions prepared using a two-step procedure. After a post-treatment at 80°C, the layers have a remarkable abrasion resistance and a high refractive index. In this paper, the chemical mechanisms involved in the formation of SiO2 layers at low temperature are studied by FTIR spectroscopy and related to the processing conditions.     

Potentiometric determination of potassium ferricyanide

A rapid and accurate electrometric method for the determination of potassium ferricyanide solutions has been investigated. It consists in titrating ferricyanide solutions potentiometrically against standard AgNO₃, using a silver indicator electrode in conjunction with a saturated calomel electrode connected by a KNO₃ bridge. Either of the reagents may be used as the titrant. A marked change in e.m.f is observed at thc end-point corresponding to the formation and precipitation of Ag³[Fe(CN)₆]. The curves have a regular form, a pronounced maximum in dE/dV occurs at the end-point and the results are very accurate and reproducible. The reaction, though simple, affords a quantitative method for the determination of ferricyanide or silver. The effect of neutral salts and ethanol on the accuracy of the end-point has been studied.     

A sol-gel route for the development of rare-earth aluminum borate nanopowders and transparent thin films

A new sol-gel route was applied to obtain Y_0.9Er_0.1Al₃(BO₃)₄ crystalline powders and amorphous thin films by using Al(acac)₃, B(OPrⁱ)₃, Y(NO₃)₃·6H₂O, and Er(NO₃)₃·5H₂O as starting materials dissolved in propionic acid and ethyl alcohol mixtures. Our study shows that propionic acid acts as good chelant agent for yttrium and erbium ions while ethyl alcohol allows to dissolve Al(acac)₃. This process makes the resulting sols very stable to obtain homogeneous gels and transparent amorphous thin films. In addition, the propionic acid prevents the sol precipitation, making easy porous- and crack-free thin film depositions. Chemical reactions involved in the complexation were discussed. As-prepared powders and films are amorphous and present a good thermal stability due to their high glass transition (746 °C) and crystallization temperatures (830 °C). This new sol-gel route showed to be adequate to obtain dense and crack-free thin films free of organic and hydroxyl groups that can be considered as promising materials to be used in integrated optical systems.