On the nature of the processes occurring in silver doped SiO<Subscript>2</Subscript> films under heat treatment

The processes taking place on air-heating of SiO₂−Ag⁺ films and xerogels produced from the SiO₂ sols of different pH (3.7 or 9.5) were investigated. Silver nanoparticles 10–40 nm in size tolerant to oxidation at temperatures above 600 °C were found to be formed in the systems whatever the pH value of the starting sol. SiO₂ crystallization giving the cristobalite phase in the temperature range from 500 to 800 °C was shown to proceed only in the films produced from the acidic sol, while in those formed from the alkali one SiO₂ remained amorphous. A mechanism by which the formation of Ag nanoparticles and the cristobalite phase occurs in the films at the oxidative conditions is suggested.     

Precipitation-redispersion of cerium oxide nanoparticles with poly(acrylic acid): toward stable dispersions

We exploit a precipitation-redispersion mechanism for complexation of short chain polyelectrolytes with cerium oxide nanoparticles to extend their stability ranges. As synthesized, cerium oxide sols at pH 1.4 consist of monodisperse cationic nanocrystalline particles having a hydrodynamic diameter of 10 nm and a molecular weight of 400 000 g mol(-1). We show that short chain uncharged poly(acrylic acid) at low pH when added to a cerium oxide sols leads to macroscopic precipitation. As the pH is increased, the solution spontaneously redisperses into a clear solution of single particles with an anionic poly(acrylic acid) corona. The structure and dynamics of cerium oxide nanosols and their hybrid polymer-inorganic complexes in solution are investigated by static and dynamic light scattering, X-ray scattering, and chemical analysis. Quantitative analysis of the redispersed sol gives rise to an estimate of 40-50 polymer chains per particle for stable suspension. This amount represents 20% of the mass of the polymer-nanoparticle complexes. This complexation adds utility to the otherwise unstable cerium oxide dispersions by extending the range of stability of the sols in terms of pH, ionic strength, and concentration.     

Stabilization of copper nanoparticles prepared by reduction from solutions of poly(acrylic acid) complexes with Cu2+ ions and poly(ethylene glycols)

Copper sols are prepared via the reduction of copper ions with hydrazine borane in dilute aqueous solutions of mixtures of the PAA-Cu²⁺ complex and poly(ethylene glycols) of various molecular masses at PEG: PAA = 0.25 base-mol/base-mol and PAA: Cu²⁺ = 10 base-mol/mol in the pH range 4.0–7.0. The stability of sols against oxidation (dissolution) or aggregation (enlargement) of metal nanoparticles is much higher than that of sols prepared in the absence of PEG. With an increase in the initial pH or a decrease in the molecular mass of PEG, the formed copper nanoparticles are much larger (no less than 20 nm in diameter) than copper nanoparticles occurring in the sol prepared in a solution of the PAA double complex with Cu²⁺ ions and high-molecular-mass PEG at a low initial pH (3–10 nm in diameter). Copper nanoparticles in sols prepared in solutions of complexes based on the high-molecular-mass PEG do not aggregate during exposure, thereby indicating the high stability of polymer screens on their surfaces.     

Production of Titanate Microspheres by Sol-Gel and Spray-Drying

Porous titanate precursor microspheres (20–60 m in diameter), with a high sorption capacity for radioactive wastes from nuclear reprocessing plants, have been produced on a 50 kg scale by spray-drying precursor sols. Well-dispersed, stable sols were produced by hydrolyzing acetic acid modified tetraisopropyltitanate and peptizing the titania hydrolysate with acidic zirconia sol. The resulting TiO2 /ZrO2 sols were routinely concentrated to 900 g dm–3 (oxide basis) and exhibited excellent stability. These sols were subsequently mixed with dispersible alumina powder and partially aggregated by adding calcium and barium nitrate salts. The resulting sols were spray-dried to produce microspheres with controlled porosity and morphology. The properties of the spray-dried powder were very dependent upon the chemical properties of the precursor sol. In particular, hollow spheres were produced from well-dispersed sols, whereas solid spheres could be produced from partially-aggregated sols.     

The Research on the Stability of TiO2， MoO3， PEO Doped Four-member Tungstic Acid Sols

The TiO2, MoO3, PEO doped four-member tungstic acid sols were prepared for the first time. The stability of different doped content sols were investigated and optimized with rotational viscometer. The four-member doped tungstic acid sol was very stable which could be stored more than two months at room temperature. The WO3 electrochromic film prepared from this doped four-member tungstic acid sol had excellent performance and longevity of service.     

Preparation of highly stable TiO<Subscript>2</Subscript> sols and nanocrystalline TiO<Subscript>2</Subscript> films via a low temperature sol–gel route

Highly stable TiO₂ sols were prepared by adjusting the water-to-titanium molar ratio to ~4 in the process of hydrolysis and condensation of titanium isopropoxide in ethanol with HNO₃. Particularly, long-term stable TiO₂ sols were prepared without adding any chemical additives. Anatase TiO₂ nanocrystallites with sizes of 3–5 nm in diameter were uniformly dispersed in the stable sol. Crystallized TiO₂ films were successfully deposited on Si (100) using the stable sol via a dip-coating process with low temperature curing at as low as 100 °C. The synthesized TiO₂ sols and films are promising for use in flexible or dye-sensitized solar cells.     

Polymer-Metal Nanoparticle Complexes for Improving the Performance of Liquid Crystal Displays

Summary: Here we applied metal nanoparticles as a dopant of liquid crystals. Since liquid crystal molecules are self-assembled, it is not so easy to disperse metal nanoparticles in liquid crystal media. We first prepared metal nanoparticles protected by liquid crystal molecules by reduction of metal ions in the presence of liquid crystal molecules. This liquid crystal molecule-protected metal nanoparticles can be easily dispersed in liquid crystal media to fabricate liquid crystal sol containing metal nanoparticles. A simple liquid crystal molecule, 4′-pentylbiphenyl-4-carbonitrile (abbreviated as 5CB) was used in the present experiments at first. 5CB sol containing metal nanoparticles could construct novel twisted nematic liquid crystal devices (TN-LCDs), which revealed the electrooptic properties depending on the kind of metal of nanoparticles. During the experiments we discovered that 5CB-protected metal nanoparticles could move in liquid crystal media by applying the voltage. This phenomenon is inconvenient for liquid crystal displays, especially those driven by a matrix of thin-film transistors (TFTs). In order to avoid this phenomenon, we prepared polymer-protected metal nanoparticles and applied them to liquid crystal devices, which provided good performance as the devices, i.e., low driving voltage, rapid response at low temperature, and so on.     

Effects of diethanolamine on the evolution of silver/titanium dioxide sol–gel process

In order to clarify the effects of diethanolamine (DEA) in the silver (Ag)/titanium dioxide (TiO₂) sol–gel process, sols with and without DEA, and films derived from these sols were prepared. The samples were investigated by X-ray diffraction, transmission electron microscopy, electron diffraction and optical absorption spectra. The results showed that metallic Ag clusters were formed in the sol with DEA and was absent in the sol without DEA. This indicated that DEA worked not only as the stabilizer but also as the reduce agent in Ag/TiO₂ sol–gel process. After annealed, Ag metallic nanoparticles were generated in the films derived from both the sols with and without DEA. The particles in the films derived from the sol with DEA were smaller than those from the sol without DEA. This can be ascribed to the limitation of the growth of Ag cluster formed in the sol with DEA during heat treatment. Mechanisms for the formation of metallic Ag in the Ag/TiO₂ sols and films were discussed. The effects of DEA in the sols and films were studied in detail.     

The complexes of macromolecules and metal nanoparticles: pseudo-template synthesis and behavior

Metal sols composed of metal nanoparticles (1 - 10 nm in diameter) protected with polymer molecules may be regarded as dispersions of polymer-metal complexes formed due to cooperative non-covalent (e.g., hydrophobic, coulombic) interaction of polymer chains with the surface of metal nanoparticles. The sols are commonly prepared by reducing of metal ions in solutions of appropriate polymers. The interactions between macromolecules and nanoparticles are reversible. In the case of long polymer chains and minute particles, the equilibrium constant of the reaction exponentially depends on the surface area of the particle. The probability of mutual “recognition” (complex formation) of growing particle and a macromolecule rapidly increases from practically zero to practically unity in narrow interval of the particle's diameters. The recognition is followed with the shadowing of the particles and the stop of their growths. Such kind of processes was termed “pseudo-template”. In frame of the concept of pseudo-template processes can be estimated: (1) the conditions at which sol particles of desirable size can be prepared, (2) the influence of temperature, polymer concentration, nanoparticles size, and other conditions on the stability of polymer - particle complex having been prepared, and (3) the conditions at which stable sol does not exist and can not be prepared at all. The interactions between metal nanoparticles and macromolecules are highly selective regard to the structure of polymer chains. The property can be effectively used for the control the size characteristics of metal nanoparticles (in course of their formation) and the stability of metal sols. The selectivity provides high conversions in catalytic chemical modification reactions in which a macromolecule is the substrate and a component of the catalyst in the same time. As an example, the hydrolysis of lactame groups in monomer unites of poly(N-vinyl pyrrolidone) catalyzed with copper sols is discussed.     

Silica nanoparticle sols 1. Surface chemical characterization and evaluation of the foam generation (foamability)

Surface characterization and foaming studies were carried out with nine industrially manufactured, colloidal silica dispersions with particles sizes from 5-40 nm. All the silica sols produced transient foams with short decay times and the dynamic foam generation (foamability) was found to vary according to the sol type with the greatest foamability occurring for the hydrophobically modified sol and the deionized hydrophilic sol. However, it was found that improved foamability of all the sols could be achieved by changing the pH to within the region of the pH(pzc) which corresponds to the region of lowest hydrophilicity. An increase in pH (and build-up of negative charge) enhances the surface hydrophilicity and caused a decrease in foamability. In addition, for selected hydrophilic sols, it was shown that the foamability (a) increased with decrease in particle size (within the 6-40 nm range) and (b) increased with particle concentration (within the range of 1-15 wt%). Overall, it was concluded that the foamability was primary controlled by hydrophobicity (and hence by pH) and also by the particle concentration, the particle size and the degree of agglomeration.     

Preparation and controlled self-assembly of Janus magnetic nanoparticles

Janus magnetic nanoparticles (~20 nm) were prepared by grafting either polystyrene sodium sulfonate (PSSNa) or polydimethylamino ethylmethacrylate (PDMAEMA) to the exposed surfaces of negatively charged poly(acrylic acid) (PAA)-coated magnetite nanoparticles adsorbed onto positively charged silica beads. Individually dispersed Janus nanoparticles were obtained by repulsion from the beads on reversal of the silica surface charge when the solution pH was increased. Controlled aggregation of the Janus nanoparticles was observed at low pH values, with the formation of stable clusters of approximately 2-4 times the initial size of the particles. Cluster formation was reversed, and individually dispersed nanoparticles recovered, by restoring the pH to high values. At intermediate pH values, PSSNa Janus nanoparticles showed moderate clustering, while PDMAEMA Janus nanoparticles aggregated uncontrollably due to dipolar interactions. The size of the stable clusters could be controlled by increasing the molecular weight of the grafted polymer, or by decreasing the magnetic nanoparticle surface availability for grafting, both of which yielded larger cluster sizes. The addition of small amounts of PAA-coated magnetic nanoparticles to the Janus nanoparticle suspension resulted in a further increase in the final cluster size. Monte Carlo simulation results compared favorably with experimental observations and showed the formation of small, elongated clusters similar in structure to those observed in cryo-TEM images.     

Preparation of Thermostable Highly Dispersed Titanium Dioxide from Stable Hydrosols

A large set of stable nanodispersed TiO₂ hydrosols differing in particle structure and dispersion medium composition was synthesized. For highly dispersed TiO₂ samples obtained by calcination of dried sols at 500°C phase compositions, sizes of primary crystallites, and specific surface areas were found. The factors affecting thermal stability of TiO₂ nanoparticles were analyzed. The sol containing the most thermostable nanoparticles was used to produce a highly efficient catalyst for cyclohexanone ammoximation.     

Influence of Sol-Gel Synthesis Parameters on the Microstructure of Particulate Silica Xerogels

The influence of key sol-gel synthesis parameters on the pore structure of microporous silica xerogels was investigated. The silica xerogels were prepared using an acid-catalyzed aqueous sol-gel process, with tetraethoxysilane (TEOS) as the silicon-containing precursor. At high H2O : TEOS ratios, sols synthesized at pH 2–3 yielded minimum values of mean micropore diameter and micropore volume. Analysis of the resulting Type I nitrogen adsorption isotherms and the equilibrium adsorption of N(C4F9)3 indicated micropore diameters for these xerogels of less than approximately 10 Å.Xerogel micropore volumes corresponding to sols prepared at pH 3 and an H2O : TEOS ratio of r = 83 were consistent with nearly close packing of silica spheres in the xerogel. Xerogel microstructure was only weakly dependent upon H2O : TEOS ratio during sol synthesis for r > 10. Xerogel micropore volume increased rapidly with sol aging time during an initial induction period of particle formation. However, the xerogel microstructure changed only slowly with time after this initial period, suggesting potential processing advantages for the particulate sol-gel route to porous silica materials.Surface adsorption properties of the silica xerogels were investigated at ambient temperature using N2, SF6, and CO2. CO2 adsorbed most strongly, SF6 also showed measurable adsorption, and N2 adsorption was nearly zero. These results were consistent with the surface transport of CO2, and to a lesser extent SF6, observed in gas permeation studies performed through thin membrane films cast from similarly prepared silica sols.     

Preparation and characterization of TiO2 sols and their UV-cured hybrid thin films on plastic substrates

In this research, TiO₂ sols were synthesized via a sol?Cgel reaction at room temperature followed by heating under reflux. Hybrid thin films were prepared using the TiO₂ sols and dipentaerythritol hexacrylate on poly(methyl methacrylate) substrates via spin coating followed by UV-curing. The images of transmission electron microscopy (TEM) and results of dynamic light scattering (DSL) showed that some originally synthesized TiO₂ nanoparticles aggregated while many small-sized (~5?nm) TiO₂ nanoparticles still existed after reflux heating. The synthesized TiO₂ sols showed poor photocatalytic ability, which might avoid degradation of organic moieties in the hybrids. The refractive indices of the hybrid thin films were increased from 1.66 to 1.82 while the water contact angles on the thin films were increased from 70.2° to 87.7° with the increment of TiO₂ content. Increasing the heating time of the TiO₂ sol resulted in an increase in the refractive index and contact angle.     

Effects of ageing conditions and block copolymer concentration on the stability and micellization of P123-Ti<Superscript>4+</Superscript> sols prepared by the templating method

In the work reported here we studied, for the first time, the effects of ageing conditions (temperature and time) on the stability and micellization of two sets of sols with different P123 block copolymer (BC) concentrations by use of dynamic light scattering (DLS). Further, for a comparative study the aggregation/clustering behavior of pure P123 in IPA solution was also examined by DLS, and ¹H NMR, and Raman spectroscopy at room temperature. Different ageing regimes applied to the samples prepared included: (i) in-situ ageing of the sols in the sealed capillary cell of the DLS system at room temperature for 0, 1, 2, 3, 4, 5, 6, and 19 h, (ii) ageing of the sols in a Teflon-lined sealed vessel at 50, 55, 60, and 65 °C for 30 min, and (iii) isothermal ageing of the synthesized sols at 50 °C for 1, 4, 8, and 14 days. On the basis of the results obtained it is shown that both ageing time and temperature have remarkable effects on the clustering and aggregation of unimer/micelles formed in the sol system studied. Further, quantitative analysis of interparticle potential energy carried out for the prepared sol at low concentration confirmed that steric interactions play the major role among the other contributing sources of energy. This is mainly related to the presence of BC and the complex polymer structure formed by acetyl acetone (ACAC). Moreover, on the basis of the calculated stability ratio for this sol, we believe that reaction-limited cluster aggregation (RLCA) is possibly the major governing mechanism. Finally, kinetic and dynamic aspects of the micellar aggregates formed are also discussed in this paper.     

Formation and degradation of poly(D,L-lactide) nanoparticles and their potential application as controllable releasing devices

In the presence of surfactant, water-insoluble poly(D,L-lactide) (PLA) was dispersed into narrowly distributed nanoparticles stable in water via microphase inversion. The structure and degradation of such formed nanoparticles were investigated by a combination of static and dynamic laser light scattering. Our results revealed that the degradation rate increased with the temperature and pH so that the degradation could be regulated from minutes to days. Using anionic sodium dodecyl sulfate (SDS) as stabilizer resulted in a slower degradation than using cationic hexadecyltrimethylammonium bromide (HTAB). The phthalocyanine chromophores (PC) could be encapsulated inside these PLA nanoparticles. The degradation of individual PLA nanoparticles led to a controllable releasing of PC. The absorption and fluorescence studies revealed a correlation between the degradation and the releasing of PC. Our results showed that a higher PC/PLA ratio could lead to a faster degradation.     

Synthesis of zirconium diboride nano-powders by novel complex sol–gel technology at low temperature

Zirconium diboride nano-powders were synthesized by novel complex sol–gel technology at low temperature. Zirconium oxychloride as source of zirconium was complexed via adding propylene oxide that could form the stable zirconium sol by protonation and ring-opening reactions and boric acid as source of boron was dissolved effectively using glycerol that acted as complexing agent to create the boron network through forming stable coordination compound. Additionally, glycerol could be carbonized as source of carbon, which could replace the conventional carbon source additives. Then the mixed sols were gelated, dried, and exposed to 1,450 °C for 2 h with flowing argon in the furnace. High purity of ZrB₂ nano-powders with spherical shape of ca. 200 nm were synthesized via carbothermal reduction. The mechanism of two complexing agents were discussed combining with the infrared spectroscopy analysis results, and the powder characteristics were performed by using X-ray diffraction and transmission electron microscopy.     

NMP中制备TiO2溶胶及其凝胶化

溶胶-凝胶过程;NMP中制备TiO2溶胶及其凝胶化     

Solvent-stabilized oxovanadium phthalocyanine nanoparticles and their application in xerographic photoreceptors

A stable organic sol of solvent-stabilized oxovanadium phthalocynine (VOPc) nanoparticles with excellent photoconductivity was successfully prepared by ultrasonificating a prepared nanoscopic VOPc powder in1,2-dichloroethane (C(2)H(4)Cl(2)) without any additive. These solvent-stabilized VOPc nanoparticles have a size distribution from 2 to 20 nm with an average diameter of 4.6 nm. The VOPc concentration of these organic sols could be as high as 100 g/L. The nanoscopic VOPc particles were well-dispersed in an insulating polycarbonate (PC) resin, resulting in single-layered photoreceptors with high surface charge durability in the dark and excellent photoconductivity. Based on the light-assisted scanning tunneling microscopy (STM) measurements, the charge transport mechanism of these photoreceptors was ascribed to light-induced enhancement of electron tunneling through the VOPc-nanoparticle/insulator junctions.     

Stabilizer-free nanosized gold sols

The paper describes a convenient, rapid, and reproducible method for the synthesis of stable dispersions of uniform gold nanoparticles at ambient temperatures by mixing aqueous solutions of tetrachloroauric acid and iso-ascorbic acid. The influence of the experimental conditions on the size of the gold particles and the stability of the final sols was monitored by dynamic light scattering and UV-vis spectrophotometry. It was found that the size of the resulting nanoparticles is affected by the concentration and the pH of gold solution, while the stability of the electrostatically stabilized final sols is strongly dependent on the excess of reductant in the system, the ionic strength, and the temperature of the precipitation. Since the preparation process does not require the addition of a dispersing agent, the surface of the resulting gold nanoparticles can be easily functionalized to make them suitable for applications in medicine, biology, and catalysis.