Solvent effect on distribution of phenyl groups for C<Subscript>6</Subscript>H<Subscript>5</Subscript>SiO<Subscript>3/2</Subscript>–SiO<Subscript>2</Subscript> coatings prepared on polycarbonate substrate

Phenyltriethoxysilane (PhTES) and tetraethoxysilane (TEOS) coatings [xPhTES·(100 − x)TEOS (mol%)] (x = 0–80) were prepared using methanol (Film A) or 1-propanol (Film B) as a solvent on polycarbonate (PC) substrate, and the effect of alcohol solvents on both the adhesion and distribution of phenyl groups were studied. The alcohol evaporation rates for Films A and B were monitored by using quartz crystal microbalance (QCM). QCM measurements revealed that the migration of phenyl group to the PC substrate side was strongly related with the alcohol solvent. Transmission fourier transform infrared measurements for these films suggest that a phase-separation between SiO₂ and PhSiO_3/2 networks occur during the alcohol evaporation.     

Preparation and evaluation of high-transparent scratch-resistant thin films on plasma treated polycarbonate substrate

New simple aqueous sol–gel procedure has been used for producing hard transparent organic–inorganic coatings on polycarbonate (PC). Sol-gel thins films were prepared by mixing Si and Al aqueous alkoxides and applied on the plasma treated PC. Tetraethyl orthosilicate (TEOS), 3-glycidoxypropyltrimethoxysilane (GPTMS) and aluminum tri sec-butoxide were used as main precursors. Before applying coatings PC were treated by Dielectric Barrier Discharge (DBD) system being conducted at atmosphere pressure. The effects of temperature, sols volume ratios and aging time on the coatings properties were scrutinized. Chemical, structural, morphological, optical and mechanical analyses of the samples were done by ATR-FTIR, EDS, XRD, FE-SEM, TEM, UV/vis spectroscopy, ellipsometry, pencil hardness and eraser scratch methods. TEM results showed well-dispersed nano-particles in the liquid sol. All of the films showed higher average transmittance (89 %) than the raw PC (86 %) that was stemmed from the lower refractive index (1.481) than raw PC (1.58). Films indicated good adhesion onto the plasma treated substrates (5B). The pencil hardness of the PC substrate (4B) improved to 3H (8 pencil grade increment) with just a single layer coating (775 nm thickness) due to the preparation of new hard structures of interlocked Si and Al atoms.     

Direct coating of quantum dots with silica shell

This paper describes a method for direct coating of fluorescent semiconductor nanoparticles with silica shell. The fluorescent semiconductor nanoparticles used were CdSe _x Te_1–x nanoparticles coated with ZnS and succeedingly surface-modified with carboxyl groups, or quantum dots (Q-dots). The Q-dots were silica-coated by performing sol–gel reaction of tetraethyl orthosilicate (TEOS) using NaOH as a catalyst in the presence of the Q-dots. Quasi-perfect Q-dots/silica core-shell particles were formed at 5.0 M H₂O and 4.0 × 10⁻⁴ M NaOH. Under these concentrations of H₂O and NaOH, the particle size of Q-dots/silica particles could be varied from 20.1 to 38.1 nm as the TEOS concentration increased from 2.5 × 10⁻⁴ to 50 × 10⁻⁴ M. The Q-dots/silica particles showed fluorescence as well as the uncoated Q-dots.     

Structure of Hybrid Silica Gels Incorporated with Hydrophobic Dye Molecules

Hybrid gels incorporated with functional organic molecules are interesting for their physical properties and microstructures as well as their potential applications. Organic-inorganic hybrid silica gels incorporated with hydrophobic organic dye were prepared by hydrolysis of phenyltriethoxysilane (PhTES) and tetraethoxysilane (TEOS) in ethanol solution containing organic dye, pyrene or rhodamine-B (RB). The structure of the gels were investigated by mean of IR absorption spectra and UV-visible absorption/fluorescence spectra. The xerogel prepared from the solution of [PhTES]/[PhTES + TEOS] < 0.3 was stable, and the incorporated dyes hardly dissolved into ethanol. Si-Ph bond increased with increasing PhTES content in the precursor solutions. The UV-visible absorption spectra of the gels incorporated with RB show increase in the amount of dimer with increasing Ph-content. The fluorescence spectra for the gels incorporated with pyrene show that the hydrophobic dye is preferentially incorporated as monomers when the amount of Ph-group in the gels increases in contrast with hydrophilic RB. It is also suggested that the hydrophobic dye is preferentially incorporated into gels as monomers when the gelation rate is low.     

Methyl modified siloxane melting gels for hydrophobic films

Hybrid melting gels were prepared by a sol–gel process, starting with a mono-substituted siloxane and a di-substituted siloxane. Methyl-modified melting gels were prepared using (a) methyltriethoxysilane (MTES) with dimethyldiethoxysilane (DMDES) and (b) methyltrimethoxysilane (MTMS) together with dimethyldimethoxysilane (DMDMS). The gels with MTES–DMDES were prepared with concentrations between 50–50 and 75–25 mol%. The gels with MTMS–DMDMS were prepared with concentrations between 50–50 and 70–30 mol%. For both systems, the consolidation temperature, after which the melting gel no longer softens, increased with an increase in the amount of the mono-substituted siloxane, increasing from 135 to 160 °C for MTES–DMDES and increasing from 145 to 170 °C for MTMS–DMDMS. Coatings formed on mica substrates were about 1 mm thick, and showed no visible cracks. The surfaces of the coatings were profiled using micro-Raman spectroscopy, which revealed that methyl groups were concentrated at the surfaces of the films. All contact angles measured with water were greater than 90°.     

Hydrolysis behavior of a precursor for bridged polysilsesquioxane 1,4-bis(triethoxysilyl)benzene: a <Superscript>29</Superscript>Si NMR study

The hydrolysis behavior of 1,4-bis(triethoxysilyl)benzene (BTB), a precursor of bridged polysilsesquioxane, was investigated with high-resolution ²⁹Si nuclear magnetic resonance (²⁹Si NMR) spectroscopy at ambient temperature in a system with BTB:ethanol:water:HCl = 1:10:x:0.8 × 10⁻⁴ (x = 3, 6 or 9). Signals due to hydrolyzed triethoxysilyl groups as well as unhydrolyzed triethoxysilyl groups [−Si(OEt)₃, −Si(OEt)₂(OH), −Si(OEt)(OH)₂ and −Si(OH)₃ (OEt = OCH₂CH₃)] formed four sub-regions based on the number of hydroxyl groups bound to a silicon atom. In addition, one silicon environment influenced the other silicon environment by an intra-molecular interaction between two silicon atoms, and each sub-region for monomeric species thus contained four signals. Based on the development of signal intensity, it is revealed that one of the two triethoxysilyl groups in BTB is hydrolyzed preferentially. Thus, when a triethoxysilyl group is hydrolyzed, the −Si(OH) _x (OEt)_3−x (x = 1, 2) groups formed undergo further hydrolysis, which is opposite to the tendency expected from the hydrolysis behavior of organotrialkoxysilanes under acidic conditions.     

Small-angle X-ray scattering from wet gels prepared from co-hydrolysis of tetraethoxysilane and vinyltriethoxysilane

Small-angle X-ray scattering was used to study the structure of wet gels prepared from co-hydrolysis of tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) in the VTES/(VTES + TEOS) molar ratio ranging from 0 to 1. The wet gels at pH = 6 behave as a mass-fractal structure with characteristic size ξ and fractal dimension D, both increasing with the amount of VTES from ξ = 6.78 nm and D = 2.25 for pure TEOS until an almost homogenous structure with ξ ~ 24.9 nm and D ~ 2.85 is obtained for the wet gel prepared with pure VTES. The mass-fractal structures are built up by small primary clusters of characteristic size between ~0.35 and ~0.85 nm, the size increasing with the quantity of VTES. These small particles of the gels are formed by a restructuring process of a few larger macromolecules in the stable sols (pH = 2) on passing from the acid to the increased-pH step of the process.     

Hydrothermal synthesis of cadmium sulfoselenide inclusion pigment

In this communication, a hydrothermal method for synthesizing cadmium sulfoselenide inclusion pigment was introduced. The general synthesis procedure was as follows: (1) the hydrothermal preparation of CdS _x Se_(1−x)-CeO₂ nanoparticles; (2) the dispersion of the CdS _x Se_(1−x)-CeO₂ nanoparticles in a prehydrolyzed TEOS; (3) the formation of a CdS _x Se_(1−x)-CeO₂-SiO₂ nano-composite by the gelation of the prehydrolyzed TEOS; (4) the inclusion of the CdS _x Se_(1−x) into the SiO₂-CeO₂ matrices by a hydrothermal treatment. The crystalline phase, thermal effect, microstructure and L*a*b* color parameters of the pigment were investigated by X-ray diffraction (XRD), a Differential Scanning Calorimeter (DSC-TG), a transmission electron microscope (TEM) and a differential colorimeter. The results showed that CdS _x Se_(1−x) could be partially stabilized to more than 1100 °C by the hydrothermally-densified CeO₂-SiO₂ glassy phase. The inclusion pigment showed a stable red color at 1100 °C, though it was not bright red.

Aqueous germanate solution,alternative sol–gel precursor for preparation of Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> diluted magnetic semiconductors

The solids content and gelation time of aqueous germanate solution were examined in this work. Samples of 5, 10 and 20 mol% Mn doped Ge were prepared by using the aqueous germanate solution as a liquid Ge precursor. No second phase such as Mn₅Ge₃ was detected in the 5 and 10 mol% Mn doped samples, implying that Mn ions were uniformly diluted into the Ge host matrix. The 5 and 10 mol% Mn-doped Ge samples exhibit room-temperature ferromagnetic behaviors that are likely originated from the RKKY (Ruderman–Kittel–Kasuya–Yosida)-like interaction between the localized Mn ions in the Ge matrix. Therefore, the aqueous germanate solution can be an alternative sol–gel precursor for preparation of the Mn _x Ge_1−x diluted magnetic semiconductors (DMSs).     

New synthesis of pure CexZr1?xO2 mixed oxides (0?≤?x?≤?1) by an epoxide sol–gel method

Pure ceria-zirconia mixed oxides Ce _x Zr_1−x O₂ with high specific surface area were synthesized with a new epoxyde driven sol–gel route and characterized by thermal analysis, X-ray diffraction studies and transmission electron microscopy. This sol–gel method is cheap and uses only a few steps. The Ce _x Zr_1−x O₂ mixed oxides were obtained in the range of 0 ≤ x ≤ 1 (except for x = 0.8) and crystallised at 350 °C after decomposition of the gels. This temperature is very low in comparison with the other methods. The studies of the influence of different synthesis parameters (concentration of the sol and decomposition temperature) allowed us to determine the conditions to obtain the best homogeneity in the gel to avoid the formation of a mixture of phases instead of mixed oxides. This approach leads to the synthesis of oxide with specific surface area above 100 m² g⁻¹. The elaboration of an ambigel could increase this value up to 195 m² g⁻¹ for x = 0.5. This sol–gel synthesis offers new perspectives for these oxides in several applications. Generally, these oxides are difficult to obtain pure in large range of composition at low-temperature and with high specific surface area by other methods.     

An investigation of dielectric resonator antenna produced from silicon (100) enhanced by strontium doped-barium zirconate films

Dip-coated Ba_1−x Sr _x ZrO₃ thick films with different Ba/Sr ratios (x = 0.0, 0.1, 0.3, 0.5, 0.7 and 0.9) were fabricated on Si (100-orient) substrate at a low temperature of 800 °C via the sol gel method. The experimental results show that dielectric resonator (DR) properties of Ba_1−x Sr _x ZrO₃ films depend on the different Ba/Sr ratios. For structural characterization, the X-ray analysis revealed that phase transformation was affected by the increase in Sr concentrations for heat treatment at 800 °C. The films were crystalline and of single phase. The thickness of one BSZ film is around 1.259 μm when measured using the field emission scanning electron microscope. The BSZ film’s surface morphology as indicated by the atomic force microscopy showed the mean grain size to be in the range of 2.56 to 94.34 μm, and the surface roughness (RMS) was recorded to be between 2.35 to 19.64 nm. The dielectric resonator (DR) properties were measured using a network analyzer. By introducing Ba_1−x Sr _x ZrO₃ (BSZ) films on the high dielectric Si (100-orient) substrate, better frequency stability was achieved i.e. within the range of 8–10 GHz. Measured results show that Si (100-orient) DRA has a 10 dB impedance bandwidth of 4.11% at 9.34 GHz and the BSZ improved this to 11.34% with x = 0.7 at 9.15 GHz. The radiation pattern was observed to be stable throughout the operating frequency and holds good potential for DR applications.     

Redistribution of cations and enhancement in magnetic properties of sol–gel synthesized Cu0.7?xCoxZn0.3Fe2O4 (0?≤?x?≤?0.5)

Cu_{0.7− x} Co _x Zn_0.3Fe₂O₄ (0 ≤ x ≤ 0.5) nanoparticles are prepared by sol–gel auto combustion method, using copper nitrate, zinc nitrate, ferric nitrate, cobalt nitrate, and citric acid as the starting materials. The process takes only a few minutes to obtain as-received Co-substituted Cu–Zn ferrite powders. X-ray diffraction (XRD), vibrational sample magnetometer and thermo gravimetric analysis are utilized in order to study the effect of variation in the Co substitution and its impact on particle size, lattice constant, density, cation distribution and magnetic properties like magnetization, coercivity, remanent magnetization, ferritization temperature and associated water content. Lattice parameter found to increase with increasing Co content, whereas X-ray density, bulk density, particle size showed decreasing trend with the Co content. Cation distribution indicates that the Co and Cu ion show preference towards octahedral [B] site, Zn occupy tetrahedral (A) site whereas Fe occupy both tetrahedral (A) and octahedral [B] site. Redistribution of cations takes place for x > 0.3. Saturation magnetization (Ms) increases from 52.99 to 79.62 emu/g (x ≤ 0.3), for x > 0.3 Ms decreases with increase in Co content x. However, coercivity, magnetocrystalline anisotropy and remanent magnetization increases with the Co²⁺ substitution.     

Effect of Zr/Ce molar ratio on the structure of powders and Zr1−x Ce x O2 coatings on quartz fiber reinforced polyimide matrix composites via sol–gel process

In this investigation, Zr_1−x Ce _x O₂ coatings were fabricated on quartz fiber reinforced polyimide matrix composites via sol–gel process at 400 °C. The phase evolution, structural and morphological characteristic of specimens were investigated by differential scanning calorimetric, Fourier transform infrared spectroscopy, powder X-ray diffraction and scanning electron microscopy. The significant phase evolution of final powders with the decreasing Zr/Ce molar ratio could be observed as follows: tetragonal (t′) → cubic + tetragonal (t′) → tetragonal (t″). BET specific surface areas of powders exhibited a decreased tendency with the increasing calcination temperature as well as the decreasing Zr/Ce molar ratio. The average crystallite size and the mean particle size increased with the elevated calcination temperature, while the particle size also increased with the increase in Ce content. The progressive addition of Ce could promote the sintering process and the densification of coating. Morphologies of coatings changed with the variation of the Zr/Ce molar ratio. The results indicate that Zr_0.75Ce_0.25O₂ coating with the Zr/Ce molar ratio of 3 is a stable uniform coating with excellent adhesion.     

Corrosion behavior of AA2024-T3 alloy treated with phosphonate-containing TEOS

Protection from corrosion of the aluminum alloy AA2024-T3 coated with a tetraethoxysilicate (TEOS)/aminotrimethyllenephosphonic acid (ATMP) film in a 0.05-mol L⁻¹ NaCl solution was evaluated using electrochemical impedance spectroscopy, scanning electron microscopy, energy disperse spectroscopy, and atomic force microscopy. The present work investigates the influence of different pretreatment procedures of the alloy surface and the ATMP concentration on the corrosion resistance of the coated samples. The undoped sol–gel coatings did not provide adequate corrosion protection. The best corrosion protection was achieved using acetic acid pretreatment and subsequent deposition of an ATMP-modified TEOS film with an optimal concentration of 5.00 × 10⁻⁴ mol L⁻¹ in the deposition bath. The acetic acid pretreatment promotes a decrease in galvanic corrosion and the surface enrichment of aluminum favoring the metalosiloxane and the metal–phosphonic bonds with increasing likely reaction sites, thus promoting the formation of a more homogeneous and compact coating with improved resistance.     

Vacuum ultraviolet irradiation on siliceous coatings on polycarbonate substrates

We studied the effect of vacuum ultraviolet (vuv) irradiation on siliceous coatings of polycarbonate (PC) substrates derived by the sol–gel method, with the aim of improving the abrasion resistance of the substrate surface. Methyltriethoxysilane with colloidal silica was used to prepare the sol solution. The sol solution was spin-coated on PC and this was followed by vuv irradiation with a Xe excimer lamp at 172 nm under N₂ atmosphere. The PC substrate with vuv irradiated coating retained its high transmittance in the visible region for about 3 or more times of scraping turns by a steel wool tester on the surface, compared with the non-irradiated or mercury lamp-irradiated coatings, which demonstrated the remarkable improvement of the abrasion resistance by the vuv irradiation. The chemical changes under the vuv irradiation were also investigated by FTIR–ATR spectroscopy, composition analysis conducted with X-ray photoelectron spectroscopy and hardness measurements. It was concluded that the vuv light irradiation resulted in degrading the Si–CH₃ bond in sol–gel derived siliceous coatings to yield hardening of the coatings. The transmittance of the coating in vuv region also increased with the Xe lamp irradiation.     

The local structure of gadolinium vanadate–tellurate glasses and glass ceramics: Te2V2O9 crystalline phase

Glasses in the system xGd₂O₃ · (100 − x)[0.7TeO₂ · 0.3V₂O₅] with 0 ≤ x ≤20 mol% have been prepared from melt quenching method. Influence of gadolinium ions on structural behavior in vanadate–tellurate glasses has been investigated using FTIR spectroscopy, X-ray diffraction (XRD), and magnetic susceptibility measurements. The structural changes have been analyzed with increasing rare earth concentration. The structural changes, as recognized by analyzing band shapes of XRD and FTIR spectra, revealed that Gd₂O₃ causes a higher extent of network polymerization as far as 20 mol%. The structure of the heat-treated glasses was found to consist mainly of the Te₂V₂O₉ crystalline phase. These vitreous systems were investigated by magnetic susceptibility measurements. From the paramagnetic susceptibility χ was calculated at different temperature and from the 1/χ(T) graph, the Curie temperature of the glass has been evaluated. Magnetic susceptibility data show the presence of small antiferromagnetic interactions between the Gd⁺³ ions.     

Physicochemical properties of non-stoichiometric oxides

One of the most important challenges with solid oxide fuel cells (SOFC) is to find cathode materials with high enough catalytic activity for the dissociation of the molecular oxygen. Oxide mixed conductors with the perovskite structure (ABO₃) and high Co content in the B site have been extensively studied to be used as cathode in SOFC. This is the second part of a review of high temperature properties of two mixed conductors systems. The first part was focused on the n = 2 Sr₃FeMO_6+δ (M = Fe, Co, Ni) Rudlesdden Popper phases, while in this paper we discuss the thermodynamic and transport properties of the perovskite solid solution Sr_1−x La _x Fe_0.2Co_0.8O_3−δ (0 ≤ x ≤ 0.4) in the temperature range 773 ≤ T ≤ 1173 K. In particular, the interest has been focused on the x = 0 sample, which exhibits large ionic conductivity values (σ_i ~1 S cm⁻¹), but suffers a structural transformation from cubic to orthorhombic symmetry because the ordering of the oxygen vacancies when the oxygen partial pressure decreases. Measurements of the oxygen chemical potential ( m_\textO2 \mu_{{{\text{O}}_{2} }} ) as function of oxygen content and temperature, coupled with high temperature X-ray diffraction data, permitted us to broaden the knowledge of the T–δ–p(O₂) phase diagram for the x = 0 sample. In addition, we have investigated the effects of the La incorporation on the stability range of the cubic phases of the Sr_1−x La _x Fe_0.2Co_0.8O_3−δ solid solution.     

Radiation effects in physical aging of binary As–S and As–Se glasses

Radiation-induced physical aging effects are studied in binary As _x S_100−x and As _x Se_100−x (30 ≤ x ≤ 42) glasses by conventional differential scanning calorimetry (DSC) method. It is shown that γ-irradiation (Co⁶⁰ source, ~3 MGy dose) of glassy As _x S_100−x caused a measurable increase in glass transition temperature and endothermic peak area in the vicinity of glass transition region, which was associated with acceleration of structural relaxation processes in these materials. In contrast to sulfide glasses, the samples of As–Se family did not exhibit any significant changes in DSC curves after γ-irradiation. The observed difference in radiation-induced physical aging between sulfides and selenides was explained by more effective destruction-polymerization transformations and possible metastable defects formation in S-based glassy network.     

Li-cycling properties of nano-crystalline (Ni1 ? xZnx)Fe2O4 (0 ≤ x ≤ 1)

Sol–gel auto-combustion method is adopted to prepare solid solutions of nano-crystalline spinel oxides, (Ni_1 − x Zn _x )Fe₂O₄ (0 ≤ x ≤ 1).The phases are characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy, selected area electron diffraction, and Brunauer–Emmett–Teller surface area. The cubic lattice parameters, calculated by Rietveld refinement of XRD data by taking in to account the cationic distribution and affinity of Zn ions to tetrahedral sites, show almost Vegard’s law behavior. Galvanostatic cycling of the heat-treated electrodes of various compositions are carried in the voltage range 0.005–3 V vs. Li at 50 mAg⁻¹ up to 50 cycles. Phases with high Zn content x ≥ 0.6 showed initial two-phase Li-intercalation in to the structure. Second-cycle discharge capacities above 1,000 mAh g⁻¹ are observed for all x. However, drastic capacity fading occurs in all cases up to 10–15 cycles. The capacity fading between 10 and 50 cycles is found to be greater than 52% for x ≤ 0.4 and for x = 0.8. For x = 0.6 and x = 1, the respective values are 40% and 18% and a capacity of 570 and 835 mAh g⁻¹ is retained after 50 cycles. Cyclic voltammetry and ex situ transmission electron microscopy data elucidate the Li-cycling mechanism involving conversion reaction and Li–Zn alloying–dealloying reactions.     

Hydrogels from diacylphosphatidylcholine

The formation of hydrogels from diacylphosphatidylcholine (PC) and water/glycerol mixtures and the properties of the gels are reported. The gels are formed when L_α phases from the PC in the solvent mixtures are cooled from T >55 °C below the Krafft temperature of the PC (T _m ∼52 °C). The glycerol can also be replaced by other co-solvents like butylenglycol. Above T _m, the PC spontaneously forms L_α phases with multilamellar vesicles that show a strong stationary birefringence. On cooling below T_m, the L_α phases jellify to transparent gels. DSC measurements of the gels show that the PC molecules undergo a phase transition into the crystalline state. This transition does not seem to be accompanied by a change of the morphological structure of the liquid L_α phase. The hydrogels also have a stationary birefringence. The vesicles in the gels have been imaged by the CryoTEM method. The hydrogels are already formed with as little as 1% of PC in the mixed solvent. The rheological properties of the gels were determined from oscillating rheological measurements. Samples with 10% of PC have a storage modulus of >10,000 Pa.