Nanosized silica

Arriagada, F.J., and Osseo-Asare, K. (1995) Synthesis of nanosize silica in aerosol OT reverse microemulsions./. Colloid Interface Sci. 170, 8-17. 

Arriagada FJ, Osseo-Asare K (1999) Synthesis of nanosize silica in a nonionic water-in-oil microemulsion Effects of the water/surfactant molar ratio and ammonia concentration. J Colloid Interface Sci 211 210-220... 

Arriagada FJ, Osseoasare K (1995) Synthesis of Nanosize Silica in Aerosol Ot Reverse Microemulsions. J Colloid Interface Sci 170 8-17... 

In 1968, Stober et al. (18) reported that, under basic conditions, the hydrolytic reaction of tetraethoxysilane (TEOS) in alcoholic solutions can be controlled to produce monodisperse spherical particles of amorphous silica. Details of this silicon alkoxide sol-gel process, based on homogeneous alcoholic solutions, are presented in Chapter 2.1. The first attempt to extend the alkoxide sol-gel process to microemul-sion systems was reported by Yanagi et al. in 1986 (19). Since then, additional contributions have appeared (20-53), as summarized in Table 2.2.1. In the microe-mulsion-mediated sol-gel process, the microheterogeneous nature (i.e., the polar-nonpolar character) of the microemulsion fluid phase permits the simultaneous solubilization of the relatively hydrophobic alkoxide precursor and the reactant water molecules. The alkoxide molecules encounter water molecules in the polar domains of the microemulsions, and, as illustrated schematically in Figure 2.2.1, the resulting hydrolysis and condensation reactions can lead to the formation of nanosize silica particles. 

The enzyme-containing nanosize silica particles prepared by Jain et al. (33) were characterized for their particle size (dynamic light scattering and TEM), entrapment efficiency, in vitro leaching capacity, and enzyme activity. For all three biomolecules, the entrapment efficiency was 80-90% and the entrapped molecules were found to be stable towards leaching (up to 45 days). The enzymatic activity of the entrapped molecules was lower than that of the corresponding free molecules, a result that was attributed to diffusional constraints. 

A mixture consisting of the step 1 product, bisphenol A diglycidyl dimethacrylate, ethoxylated bisphenol A dimethacrylate, triethlyene glycol dimethacrylate, bisphenol A diglycidyl dimethacrylate, and diphenyl iodonium hexafluorophosphate were thoroughly mixed with diphenyl iodonium hexafluorophosphate and then heated to 85°C for 5 minutes and mixed in a DAC 150 FV speed mixer for 1 minute at 3000 rpm. Silane-treated, nanosized silica and zirconia particle filler was added and the mixture reheated to 185°C for 5 minutes, remixed in a DAC 150 FV and an additional 1 minute at 3000 rpm, and the dental composition isolated. 

Ab initio and density functional calculations of potential energy surfaces for the ground and excited electronic states of model clusters simulating various point defects, impurities, and their combinations in nanosized silica and germania materials are reported. The accurate geometric and electronic structures of these clusters, calculated photoabsorption and photoluminescence (PL) energies, and predicted absorption and PL spectra are obtained. Our calculations reproduced the experimental excitation energy (1.9-2.0 eV)... 

Ogenko, V.M., Dubrovina. L.V., Volkov, S.V. (2005) Synthesis and structure of composites of nanosize silica particles modified with glass microspheres, Rus. Appl. Chem. 78(2), 197-199. 

Since the enthalpy difference between quartz and glass is about 9 kJ/mol, and the free energy difference somewhat less than this, a (free) energy crossover at the nanoscale is expected. If one takes the surface enthalpy of quartz as 1 J/m larger than that of amorphous silica (a conservative estimate), the enthalpy crossover will occur at a surface area of 9000 m7mol (150 m/g). This crossover at a relatively small surface area is consistent with the observation that all nanosized silica samples, both natural and synthetic, are amorphous. 

Rasmusson, M. and Wall, S., Electrostatic characterization of Al-modified, nanosized silica particles. Colloids Sutf. A, 122, 169, 1997. 

There are several reports of the unique stability of nanosize silica hydro-sols near the isoelectric point (lEP). The Canberra group experimentally discovered the existence of short-range forces that play an important role in the interaction process and must be added to those forces already accounted for by the original DLVO theory. These short-range interactions... 

Because the initial particles were quite homogeneous in size, the cores dissolved at similar rates, indicating relatively similar pore structuring in the individual gold particles [165]. After 10 minutes, the gold cores were completely dissolved, and hollow nanosized silica shells remained. 

The aim within the frame of this book is not to survey the plethora of pubH-cations devoted to surface photografting. Typical work pubhshed in recent years is compiled in Table 11.6, which demonstrates that the enhancement of hydro-philicity and wettabiUty of hydrophobic polymers and the improvement of adhesion of polymers to various substrates are still major research topics (see also [99]). Moreover, the grafting of ultrafine inorganic particles, such as nanosized silica and titania, with vinyl monomers is an attractive subject. Relevant earHer work on surface photografting has been reviewed by Yagci and Schnabel [84]. 

Muller and coworkers prepared disc-like polymer Janus particles from assembled films of the triblock copolymer SBM and, after hydrolysis of the ester groups into methacrylic acid units, used these as Pickering stabilizer in the soap-free emulsion polymerization of styrene and butyl acrylate [111]. Armes and coworkers described the synthesis of PMMA/siUca nanocomposite particles in aqueous alcoholic media using silica nanoparticles as stabilizer [112], extending this method to operate in water with a glycerol-modified silica sol [113, 114]. Sacanna showed that methacryloxypropyltrimethoxysilane [115] in the presence of nanosized silica led to spontaneous emulsification in water, which upon a two-step polymerization procedure afforded armored particles with an outer shell of PMMA [116]. Bon and coworkers demonstrated the preparation of armored hybrid polymer latex particles via emulsion polymerization of methyl methacrylate and ethyl methacrylate stabilized by unmodified silica nanoparticles (Ludox TM O) [117]. Performance of an additional conventional seeded emulsion polymerization step provided a straightforward route to more complex multilayered nanocomposite polymer colloids (see Fig. 14). 

Kim et al. electrochemically deposited PPy on a CNT/silica film substrate using a potential cycling method at room temperature. After removal of silica with hydrofluoric acid (HF), CNT/PPy composites with controlled pore size in a three-dimensional (3D) entangled structure of a CNT film were prepared as electrode materials for a pseudo-capacitor [36]. The pore size of the final CNT/PPy composite film could be controlled by changing the amount of silica in the mixed suspension of CNTs and nanosize silica. The SC of the CNT/PPy composite with 83.4 wt.% PPy was 250 F/g at a potential scan rate 10 mV/s in 1.0 mol/L KCl and it decreased by only 15% to 211 F/g at 500 mV/s. 

F. J. Arriagada and K. Osseo-Asare, Synthesis of nanosize silica in Aerosol OT reverse... 

Double-decker phthalocyanines are soluble in a narrow range of solvents and are insoluble in water, however, we have developed methods for preparing aqueous multicomponent systems based on lanthanide complexes phthalocyanines double-decker. Macromolecular stmctures (proteins, polymers), supiamolecular stmctures (micelles) and nanosized silica were used as solubilizers. 

Lan, A., Iqbal, Z., Aitouchen, A., libera, M., and Grebel, H. (2002) Growth of single-wall carbon nanotubes within an ordered array of nanosize silica spheres. Appl. Phys. Lett., 81, 433 35. 

Silica is an alternative host for lanthanide chelates. Synthesis of nanosized silica particles by well-estabhshed hydrolysis of tetraethylorthosihcate (TEOS) with ammonium hydroxide is a common route for particle preparation. The transparent inert silica material is an excellent matrix for dye-embedded nanolabels as less spectral interferences are expected from the host material. Multiple lanthanide particles have been prepared for bioanalysis. Nanoparticles have been S3Uithesized by hydrolysis of TEOS with ammonium hydroxide in a microemulsion-containing aqueous solution of N,iV,iV, N -[2,6-bis(3 -aminomethyl-l -pyrazolyl)-phenylpyri-dine]tetrakis(acetate)-Tb(in) (BPTA-Tb ) chelate. In the microemulsion, the aqueous phase containing the lanthanide chelate formed nanodroplets acting as nanoreactors for the synthesis of nanoparticles. Since the size of the nanoparticles is dependent on the size of the droplets, it can be controlled, e.g., by the t3q>e of surfactants and by adjusting the concentration of the reactants [42-46],... 

Ihe literature " describes a number of dendrimers and the closely related star-like 120-123 polysiloxanes. Ihe hyperbranched polysiloxanes are the primary example of more random structures. Although the emphasis has been on synthesis and characterization,i i modeling on hyperbranched polymers has also been carried out. Some of the most interesting species involve polysiloxane chains. Star polymers, some with nanosized silica cores, have also been synthesized.i °-i i Hyperbranched polysiloxanes have been prepared with controllable molecular weights and polydispersities,i -1 - with epoxy terminal groups some are UV-curable ° and some serve as a source of molecular silica. Hyperbranched polysiloxanes have also been used in the sol-gel preparation of polypropylene/silica nanocomposites. ... 

Liu, Y.-L. Li, S.-H., Poly(dimethylsiloxane) Star Polymers Having Nanosized Silica Cores. Macromol. Chem., Rapid Commun. 2004,25,1392-1395. 

Hitachi has developed a heat-resistant material for printed wiring boards, consisting of an epoxy polymer containing nanosized silica, evenly dispersed by means of a sol-gel reaction. At 260 °C, the nanocomposite s elasticity was said to be about ten times higher than that of epoxy, and its thermal expansion coefficient was about one-third. 

E. Matijevic, Encapsulation of nanosized silica by in-situ polymerization of tert-butyl acrylate monomer, Langmuir 2000, 16,9031 9034. 

The ion exchange capacity and the strong hydration control many properties of nanosized silica. For example, very high concentrations (up to 40% by wt) of stable... 

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