Thermal stability of proton-conducting silicophosphate materials formed by sol-gel method

Russian Journal of Electrochemistry - This work estimated ionic conductivity and studied thermal stability of proton-conducting xerogel materials and films formed from sol-gel system based on...     

Nonlinear optical materials by the sol-gel method

The sol-gel method, because of the use of homogeneous liquid solutions and the ability to form gels at room temperature, is uniquely suited for the preparation of many nonlinear optical (NLO) materials, especially films. The preparations of NLO crystalline solids, such as ferroelectrics, oxide glasses, and amorphous ferroelectrics, are described. The preparation of NLO nanocomposites can be made by a number of approaches. These include the mixing of optically active organics into the sol-gel liquid solution, the impregnation of organics into the interconnecting pores of a stabilized oxide gel, and the direct chemical bonding of optically active organics and inorganics to form new hybrid NLO nanocomposites.     

Abrasion resistant inorganic/organic coating materials prepared by the sol-gel method

Novel abrasion resistant coating materials prepared by the sol-gel method have been developed and applied on the polymeric substrates bisphenol-A polycarbonate and diallyl diglycol carbonate resin (CR-39). These coatings are inorganic/organic hybrid network materials synthesized from 3-isocyanatopropyltriethoxysilane functionalized organics and metal alkoxide. The organic components are 3,3-iminobispropylamine (IMPA), resorcinol (RSOL), diethylenetriamine (DETA), poly(ethyleneimine) (PEI), glycerol and a series of diols. The metal alkoxides are tetraethoxysilane (TEOS) and tetramethoxysilane (TMOS). These materials are spin coated onto bisphenol-A polycarbonate and CR-39 sheets and thermally cured to obtain a transparent coating of a few microns in thickness. Following the curing, the abrasion resistance is measured and compared with an uncoated control. It was found that the abrasion resistance of inorganic/organic hybrid coatings in the neat form or containing metal alkoxide can be very effective to improve the abrasion resistance of polymeric substrates. The adhesion tests show that the adhesion between coating and substrate can be greatly improved by treating the polymeric substrate surface with a primer solution of isopropanol containing 3-aminopropyltriethoxysilane (3-APS). The interaction between 3-APS and the polycarbonate surface was investigated by a molecular dynamics simulation. The results strongly suggest that the hydrogen bonding between the amino group of the 3-APS and ester group in the polycarbonate backbone are sufficiently strong to influence the orientation of the primer molecules. The abrasion resistance of these new coating systems is discussed in light of the structure of the organic components. All of these results show that these coating materials have excellent abrasion resistance and have potential applications as coating materials for lenses and other polymeric products.     

Electrochemistry of proton-conducting ceramic materials and cells

Journal of Solid State Electrochemistry -     

Properties and applications of proteins encapsulated within sol-gel derived materials

The last decade has seen a revolution in the area of sol-gel-derived materials since the demonstration that these materials can be used to encapsulate biological species such as enzymes, antibodies and other proteins in a functional state. The interactions between the biomolecule and the inorganic, organic or hybrid nanocomposite material determines the degree to which the biomolecule retains its native properties, and such interactions can be tuned to provide optimised biomaterials that are suitable for a variety of applications. Typical applications of sol-gel derived biomaterials include selective coatings for optical and electrochemical biosensors, stationary phases for affinity chromatography, immunoadsorbent and solid-phase extraction materials, controlled release agents, solid-phase biosynthesis, and unique matrices for biophysical studies. Through careful selection of precursors and additives, these materials can be designed for specific applications, and can produce useful, robust devices with good analytical parameters of merit. Indeed, current advances in the development of nanocomposite and mesostructured materials suggest that major improvements in bioimmobilisation are on the horizon, and should result in substantial improvements in bioanalytical devices over the next decade.     

Heteropolyacid-encapsulated self-assembled materials for anhydrous proton-conducting electrolytes

The composite material of heteropolyacid (12-phosphotungstic acid; PWA) and polystyrene sulfonic acid (PSS) construct the PWA-encapsulated material by the self-assembly of -SO3H onto the PWA surface; as a result, the fast proton transfer occurred at the interface between the PWA and -SO3H, and the encapsulated material indicated the high anhydrous proton conductivity of 1 x 10(-2) S cm(-1) at 180 degrees C. These anhydrous proton-conducting materials without the existence of water molecules are quite different from customary ion-exchange membrane, such as Nafion, and may have advantages as an electrolyte membrane for polymer electrolyte membrane fuel cells operating at intermediate temperatures under anhydrous conditions but also for electrochemical devices including electrochromic displays, chemical sensors, and others.     

Photothermal and photocatalytic processes on TiO2 based materials prepared by sol-gel method

In the present work, Fe³⁺ doped TiO₂ coatings on glass substrates were prepared by dip-coating from a sol-gel solution. The influence of the dopant concentration on the structure, optical, photocatalytic and photothermal properties of the films was studied. The results obtained have shown a strong correlation between the catalytic properties and the amount of iron dopant and the temperature of the thermal treatment.     

Auto-organisation of hybrid organic-inorganic materials prepared by sol-gel process

Silica-based hybrid organic-inorganic materials prepared by sol-gel chemistry exhibit chemical and physical properties revealing their anisotropic organisation. Besides the opportunities that this phenomenon opens for the preparation of new materials, it also provides arguments to the chemist looking for a better comprehension and control of the organisation of solids.     

Preparation and properties of luminous materials of CaSiO3: Pb, Mn by sol-gel method

The luminous materials of CaSiO₃: Pb, Mn were synthesized by sol-gel method and ultrasound technology. The properties of the phosphors were characterized by luminescence spectrum, differential thermal analysis and thermal gravimetry analysis (DTA-TG), X-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR) and transmission electron microscopy (TEM). The effects of factors such as the synthetic material compositions, ultrasound time and annealed temperature on phosphorescent brightness of sample were studied and the optimum synthetic conditions were determined. The results show that, compared with the sample made by the high temperature solid-state reaction, the luminescent intensity of the CaSiO₃: Pb, Mn sample increased by about 200% and the mean diameter of particles of the sample decreased by about 300 nm. __________ Translated from Chemical Research and Application, 2007, 19(2): 140–144 [译自: 化学研究与应用]     

Application of functional coatings by sol-gel method

Nippon Sheet Glass Co. has developed many sol-gel derived products during the last decade. In this paper, the history of the production development, the details of the products and the production process for automotive windows using sol-gel thin-film coatings are introduced. These sol-gel thin-film coatings include UV absorbing, hydrophobic, low reflective and solar control coatings.     

Synthesis of mixed cerium-zirconium oxides by the sol-gel method

Mixed oxides CeO₂ ZrO₂ with the Ce/Zr molar ratios varying in a wide range were synthesized by the sol gel method. The phase composition of the resulting particles was determined. The specific surface area of the mixed oxide calcined at various temperatures was found.     

Synthesis of halide glasses by reactive processing of sol-gel materials

This paper aims to introduce fluoride materials, their conventional processing and how sol-gel processing can be used both to simplify processing and to improve properties. A multistep process incorporating sol-gel synthesis and reactive treatment is used to prepare a monolithic ZBLA fluoride glass. The first step is synthesis of a porous, monolithic, atomically homogeneous hydrous oxide gel containing zirconium, barium, lanthanum, aluminum and possibly sodium as components (ZBLA or ZBLAN). The second step is a relatively low-temperature reactive treatment of the gel with a fluorinating agent to achieve a porous fluoride glass. Subsequently, the gel is viscous sintered to a dense glass. The present status and future challenges in the preparation of optical-quality fluoride glasses via this method will be presented.     

A fast convenient method to prepare hybrid sol-gel materials with low volume-shrinkages

We present a simple and fast method for the synthesis of polyacrylates-silica hybrid materials with significantly low volume shrinkages through the sol-gel reactions of tetraethyl orthosilicate and 2-hydroxyethyl methacrylate along with the free-radical polymerization of the acrylate monomer. The volume shrinkage from the processible sol to the final product was about 6–20% for the hybrid materials having the silica contents up to about 50 wt-%. As a result of the low shrinkage, crack-free, transparent and monolithic hybrid materials of relatively large sizes can be prepared within a short period of 6 to 12 hours. The formation of covalent bonding between the organic and the silica components in the hybrid materials was demonstrated. Thermal stability of the polyacrylate component in the hybrid materials were found to be higher than that of the bulk polymer. Other vinyl polymers such as poly(methyl methacrylate) and polyacrylonitrile have also been incorporated into the inorganic silica sol-gel matrix by using this method.     

Polyacrylate/silica nanocomposite materials prepared by sol-gel process

Polyacrylate/silica nanocomposite was prepared by sol-gel process via in situ emulsion polymerization. The influence of the synthetic conditions, such as the ratio of different monomers and the contents of tetraethoxysilane (TEOS), γ-methacryloxypropyltrimethoxysilane (Z-6030), diethanolamine (DAM) and ammonium persulfate (APS) on the physical mechanical properties of polyacrylate/silica nanocomposite was investigated in details. Dynamics Laser Scattering (DLS) indicated that the average diameter of the polyacrylate/silica latex particles (177 nm) was bigger than that of the pure polyacrylate latex particles (105.3 nm), but the ζ potential of polyacrylate/silica was decreased respectively in contrast to that of the polyacrylate. Differential Scanning Calorimeters (DSC) analysis confirmed that the glass transition temperature of polyacrylate/nano-SiO₂ (T_g = −24 °C) was higher than that of polyacrylate (T_g = −36 °C). UV analysis showed that the UV absorbency of polyacrylate/silica was improved evidently in contrast to that of polyacrylate.     

Extraordinarily water permeable sol-gel formed nanocomposite nanofibrous membranes

Electrospun nanofibrous membranes (ENMs) are considered as a state of the art in water filtration technology mainly owing to their high interconnected porosity and tunable pore size assumed to offer a very high permeability also selectivity. However, the extremely high surface area makes the ENMs prone to mechanical breakdown and lack of wettability lowering the filtration efficiency. Hence, any attempt to enhance both the mechanical properties and hydrophilicity of the ENMs is highly recommended. In the current study, the structural and transport properties of polyethersulfone (PES) ENMs were modified through incorporation of titania (TiO(2)) nanoparticles via a sol-gel approach. Presence of titania precursor increased the conductivity of the electrospun solution thereby optimized the structural features of the electrospun mat in terms of formation of very thin beadless nanofibers, a higher porosity and smaller pore size. Moreover, a significant rise in mechanical properties, thermal stability and switching from a highly hydrophobic membrane to a superhydrophilic one occur simultaneously. The combination of a more optimum porosity, very high mechanical properties and hydrophilicity leads to a significantly higher water permeability in the TiO(2)/PES ENMs encouraging us to propose it as a water filtration membrane with longer life span and lower energy consumption.     

Silica reinforcement of epoxidized natural rubber by the sol-gel method

The sol-gel technique was employed to prepare silica-reinforced vulcanizates using tetraethylorthosilicate (TEOS) and epoxidized natural rubber (ENR). The rubber was first precured with 3-aminopropyltriethoxysilane (APS) by heat pressing at 180°C for a range of cure time. The resultant rubber sheets or vulcanizates were swelled in TEOS, and subsequently subjected to a sol-gel reaction in butylamine aqueous solution. Hydrolysis and condensation of the TEOS resulted in the formation of silica particles in the rubber network yielding silica-contained vulcanizates. Silica content as high as 28% and TEOS-to-silica conversion of over 60% were observed. When prepared under certain reaction conditions, the sol-gel vulcanizates obtained were more rigid and stronger than a typical sulfur-cured ENR vulcanizate that contained comparable amount of silica. Comparative stress-strain and dynamic mechanical property analysis suggest that chemicals bond are formed between the silica particles and the rubber network in the ENR-APS-sol-gel vulcanizate. Thus, the in situ silica reinforcement of ENR was successfully established.On leave from School of Industrial Technology, University Sains Malaysia, Minden, 11800, Penang, Malaysia.     

Synthesis of ZrB2 nanoparticles by sol-gel method

Zirconium diboride (ZrB₂) nanoparticles were synthesized by sol-gel method using zirconium n-propoxide (Zr(OPr)₄), boric acid (H₃BO₃), and sucrose (C₁₂H₂₂O₁₁). Additionally, acetylacetone (acac) was used as chemical modifier in a neutral condition to stabilize Zr(OPr)₄ which hydrolyzes easily. Here, C₁₂H₂₂O₁₁ was used since it can be completely decomposed to carbon. Thus, carbon might be accounted precisely for the carbothermal reduction reaction. A single phase ZrB₂ without residual ZrO₂ was obtained with a molar ratio of B/Zr = 2.3 for the starting materials at 1,550 °C and the average grain size of ZrB₂ nanoparticles was ca. 50 nm. The photomicrograph revealed a spherical round shape morphology of the ZrB₂ nanoparticles with an uniform size distribution. On the other hand, in the case of either B/Zr (mol.) = 2.0 or pyrolyzing temperature below 1,550 °C for B/Zr (mol.) = 2.3, there existed both m-ZrO₂ and t-ZrO₂ phases besides ZrB₂.     

Properties of proton-conducting Nafion-type membranes with Nanometer-thick polyaniline surface layers

The study is directed to the improving of proton-conducting Nafion-type membranes for using in fuel cells with direct oxidation of liquid fuels. Nanometer-thick layer of polyaniline (in its conducting emerald-dine form) was deposited onto the membrane surface by in situ polymerization. The structure of the polyaniline layer is studied, as well as the properties of thus modified membranes (electronic and proton conduction, permeability for methanol, thermal stability). A method of platinum catalyst deposition onto the Nafion-modifying polyaniline layer is developed.     

Cathode materials for lithium ion batteries prepared by sol-gel methods

Improving the preparation technology and electrochemical performance of cathode materials for lithium ion batteries is a current major focus of research and development in the areas of materials, power sources and chemistry. Sol-gel methods are promising candidates to prepare cathode materials owing to their evident advantages over traditional methods. In this paper, the latest progress on the preparation of cathode materials such as lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, vanadium oxides and other compounds by sol-gel methods is reviewed, and further directions are pointed out. The prepared products provide better electrochemical performance, including reversible capacity, cycling behavior and rate capability in comparison with those from traditional solid-state reactions. The main reasons are due to the following several factors: homogeneous mixing at the atomic or molecular level, lower synthesis temperature, shorter heating time, better crystallinity, uniform particle distribution and smaller particle size at the nanometer level. As a result, the structural stability of the cathode materials and lithium intercalation and deintercalation behavior are much improved. These methods can also be used to prepare novel types of cathode materials such as nanowires of LiCoO₂ and nanotubes of V₂O₅, which cannot be easily obtained by traditional methods. With further development and application of sol-gel methods, better and new cathode materials will become available and the advance of lithium ion batteries will be greatly promoted.