Stober silica nanoparticles

C.A.R. Costa, C.A.P. Leite, F. Galembeck, Size dependence of stober silica nanoparticle microchemistry. The Journal of Physical Chemistry B 107 (2003) 4747-4755. 

Size, volume fraction, and nucleation of Stober silica nanoparticles. /. Colloid Interface ScL, 266 (2), 346-358. 

Green, D.L., Jayasundara, S., Lam, Y.F., and Harris, M.T. (2003) Chemical reaction kinetics leading to the first Stober silica nanoparticles NMR and SAXS investigation. J. Non-Cryst Solids, 315, 166-179. 

G. Tolnai, A. Agod, M. Kabai-Faix, A. L. Kovacs, J. J. Ramsden, and Z. Horvolgyi, Evidence for secondary minimum flocculation of Stober silica nanoparticles at the air-water interface Film balance investigations and computer simulations, /. Phys. Chem. B, 107,11109, 2003. 

Fluorescent silica nanoparticles, called FloDots, were created by Yao et al. (2006) by two synthetic routes. Hydrophilic particles were produced using a reverse micro-emulsion process, wherein detergent micelles formed in a water-in-oil system form discrete nanodroplets in which the silica particles are formed. The addition of water-soluble fluorescent dyes resulted in the entrapment of dye molecules in the silica nanoparticle. In an alternative method, dye molecules were entrapped in silica using the Stober process, which typically results in hydrophobic particles. Either process resulted in luminescent particles that then can be surface modified with... 

Generally, two common methods, the Stober method and the reverse microemulsion method are used for synthesis of silica nanoparticles. As derivatives of a sol-gel process, both methods involve hydrolysis of a silicon alkoxide precursor to form a hydroxysilicate followed by polycondensation of the hydroxysilicate to form a silica nanoparticle [44]. 

The Stober method is also known as a sol-gel method [44, 45], It was named after Stober who first reported the sol-gel synthesis of colloid silica particles in 1968 [45]. In a typical Stober method, silicon alkoxide precursors such as tetramethylorthosili-cate (TMOS) and tetraethylorthosihcate (TEOS), are hydrolyzed in a mixture of water and ethanol. This hydrolysis can be catalyzed by either an acid or a base. In sol-gel processes, an acidic catalyst is preferred to prepare gel structure and a basic catalyst is widely used to synthesize discrete silica nanoparticles. Usually ammonium hydroxide is used as the catalyst in a Stober synthesis. With vigorous stirring, condensation of hydrolyzed monomers is carried out for a certain reaction time period. The resultant silica particles have a nanometer to micrometer size range. 

The Stober method can be used to form core-shell silica nanoparticles when a presynthesized core is suspended in a water-alcohol mixture. The core can be a silica nanoparticle or other types of nanomaterials [46, 47]. If the core is a silica nanoparticle, before adding silicon alkoxide precursors, the hydroxysilicates hydrolyzed from precursors condense by the hydroxide groups on the surface of the silica cores to form additional layers. If the core is a colloid, surface modification of the core might be necessary. For example, a gold colloid core was modified by poly (vinylpyrrolidone) prior to a silica layer coating [46]. 

The size of silica nanoparticles affects their physical, chemical, electronic, and optical properties. Proper size of silica nanoparticles is crucial for design of silica-based nanomaterials. In Stober methods, the size of silica nanoparticles is adjusted by changing the type of organic solvent, the amount of silicon alkoxide, and the... 

Figure 11.1 TEM images of silica nanoparticles of different sizes (a) 20 nm, (b) 50 nm, (c) 200 nm, (d) 290 nm, prepared with the Stober method [scale bar at the comer of (d) corresponds to 300 nm].

Silica nanoparticles are commonly prepared by polymerization of appropriate precursors such as silicates, silicon alkoxides, or chlorides (Fig. 11.2).2 Besides the industrial methods, which rely mainly on condensation of sodium silicate in water induced by sodium removal through ion exchange, three different synthetic methods are currently used in research labs to prepare silica nanoparticles loaded with organic molecules. In the first method, proposed by Kolbe in 1956s and developed by Stober and coworkers in the late 1960s,6 the particles are formed via hydrolysis and... 

A recent example of how silica nanoparticles prepared by the Stober method can be used as supports was the work of Gao et al., who derivatized a silica nanoparticle first with APTMS and then with acryloyl chloride to form reactive vinyl groups.74 A polymer shell with sites imprinted with the template, TNT, was then formed around the silica nanoparticle using conventional acrylic organic polymerization procedures. The capacity and binding kinetics were shown to be significantly better than traditional imprinted particles.74... 

Segmented gas-liquid (Taylor) flow was used for particle synthesis within the liquid slugs. Tetraethylorthosilicate in ethanol was hydrolyzed by a solution of ammonia, water and ethanol (Stober synthesis) [329]. The resulting silicic acid monomer Si (OH)4 is then converted by polycondensation to colloidal monodisperse silica nanoparticles. These particles have industrial application, for example, in pigments, catalysts, sensors, health care, antireflective coatings and chromatography. 

Dense silica nanoparticles have received considerable attention since monodisperse colloidal silica spheres, obtained liom aimnoniacal TEOS solution, were reported in the late 1960s by Stober et aL [1]. These dense particles, more often being monodispersed with controlled particle size, a well-defined morphology, and a surface with silanol groups by which they could be functionalized, are used for a variety of commercial applications including colmants, fillers and pigments. 

The main advantage is the simphcity of the reaction system, as well as the preservation of the irutial morphology/texture of the sohd. In general, only a slight decrease in the specific surface area is observed. Starting materials for this type of synthesis typically are commercially available amorphous and mesostructured sihcas such as MCM-41, SBA-15, or SBA-16 [34], silica nanoparticles (e.g., Stober spheres) [35], or magnetite-sihca particles [36],... 

Figure 5.17 Schematic synthesis of silica nanoparticles by the Stober method (top) and via reverse-phase microemulsion (bottom). The scale bars represent 1000 nm and 500 nm, respectively. Adapted from ref. 51 with permission from the Royal Society of Chemistry.

First, cores of silica nanoparticles are fabricated as described by Stober et alP in which tetraethyl orthosilicate is reduced in NH4OH in ethanol. Next, the silica surface is aminated by reaction with aminopropyltriethoxysilane in ethanol. Gold shells are then grown using the method of Duff et Briefly, small gold colloid (1-3 nm) is adsorbed onto the animated silica nanoparticle... 

Fig. 7 Stober synthesis of dye coated silica nanoparticles (DCSNs)...

Fig. 9 Van Blaaderen modification of the Stober method for the synthesis of dye doped silica nanoparticles...

The photophysical properties of dye molecule in DDSNs can also be tuned by exploiting plasmonic effects, that is by growing the silica nanoparticle around a metal core. Experimentally, such sophisticated structures are achieved by carrying out the Stober synthesis in the presence of preformed metal nanoparticles stabilized... 

Monolayers of nanoparticles at liquid-fluid interfaces have attracted considerable attention over several decades [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17]. Among others, the examinations focused on thin-layer preparation [10, 18, 19, 20, 21, 22, 23], emulsion stabilisation [15, 24] and particle characterisations [25, 26, 27]. The Stober silica (synthesised by controlled hydrolysis of tetraethylorthosilicate in ethanol in the presence of ammonia and water) [28] has many advantageous properties for model investigations. The nearly spherical particles show a narrow size distribution and are compact above a certain particle size (around 20 nm diameter) [29]. The particles, on the one hand, show partial wettability and, on the other hand, form a weakly cohesive two-dimensional dispersion at the water-air interface [10, 14]. All that makes them suitable to determine the total repulsive interparticle energies in a film balance by measuring the effective surface tension of the monoparticulate layer [30, 31, 32, 33, 34, 35, 36]. 

Keywords Scanning-angle reflectometry Reflectance of inhomogeneous layers Layer of silica nanoparticles Stober silica... 

The silica nanoparticles of about 40-nm diameter were produced by the Stober method [9] from ethanol, ammonium hydroxide and tetraethyl orthosilicate. One kind of sample was used as formed, (hydrophiUc sample), the other was surface-treated by trimethyl-silyl-A,A-dimethylcarbamate, in order to render the particles hydrophobic. The samples were used from the alcosols. The solid content of the sols was determined from the amount of solid residuum after evaporating the solvent at 80 °C. The diameter of the particles was determined from the transmission electron microscope (TEM) image of layers transferred on Formvar-coated grids. Details of sample preparation and characterization have been described in previous papers [10, 11]. 

In our laboratory, we have recently conducted gelation studies of silica nanopardcles in microgravity during the STS-95 space shuttle mission (28). Stable silica nanoparticle dispersions may be form either by polymerization of silicic acids in an aqueous system or through hydrolysis and condensation of silicon alkoxides (the sol-gel or Stober route). Comparison of small-angle x-ray scattering (SAXS) measurements of Ludox, a commercial aqueous silicate with acid- and base-catalyzed alkoxides shows that only aqueous silicate sols are uniform, whereas alkoxides generate fractal particles. As Brinker and Scherer point out (29), these results illustrate that sols derived from aqueous silicates are... 

The production of polyacrylamide nanoparticles is based on a water-in-oil (W/0) microemulsion technique 40). The silica nanoparticles are prepared by a modified Stober method (75). The ormosil nanoplatform is prepared by a two-step method based on sol-gel process 24,41). The poly decylmethacrylate nanoplatform is prepared by emulsion polymerization 27,42). Encapsulation of drugs or nanocrystals into nanoparticles was made by adding these components to the reaction mixture at the beginning of, or during, the synthesis. Covalent... 

Inorganic silica nanoparticles have been prepared using both the Stober method [44] and reverse microemulsion [45]. With the Stober method, submicron-sized TEOS nanoparticles can be obtained, and the synthetic mixtures typically contain ethanol, ammonium hydroxide and water. Although the method is simple and... 

With amorphous silica having been employed in industry for many years, the methods for its synthesis and its properties-including its toxicity-have been well documented. However, as the dimension of amorphous silica moves down to the nanometer level, not only have some of the properties of silica materials changed, but different synthetic methods have also been developed for the preparation of suitable sizes of silica nanoparticles [28-30, 59]. Currently, the most common methods used to create silica nanoparticles are the Stober method and the water-in-oil (w/o) microemulsion method (also known as reverse microemulsion) [6-9, 28-30, 56, 58, 59, 63, 64, 70, 71, 75, 78, 82]. Moreover, on the basis of the very narrow size-distribution of the products, the w/o microemulsion method is the preferred approach (Figure 7.1). 

The Stober method, which was developed in 1968, is a simple and convenient method for producing silica nanoparticles, in which a mixture of water and alcohol (e.g. methanol, ethanol, propanol) is employed as a hydrolysis reaction medium [59]. The hydrolysis of tetraethylorthosilicate (TEOS) leads to the formation of silica nanoparticles, with ammonia being used to catalyze the hydrolysis. The resultant... 

Rossi, L.M., Shi, L, Quina, F.H. and Rosenzweig, Z. (2005) Stober synthesis of monodispersed luminescent silica nanoparticles for bioanalytical assays. Langmuir, 21, 4277-80. 

Efficient intracellular delivery of the anticancer drug camptothecin (CPT) by hollow silica/titania nanoparticles has been reported [114]. Monodispersed hollow nanoparticles (about 50 nm) were prepared by titania coating of Stober silica particles followed by silica dissolution and redeposition in an ammonia solution (Figure 11.13). Surface modification of these particles with an antibody herceptm, a... 

The success of DNP-NMR for mesoporous materials could be attributed to the large surface area of these samples that favors interaction between the radicals and the surface sites, and thus their detection. But what about powdered samples with much less specific surface area (<100 m g ) A study on microcrystalline organic solids has been published [27]. The surface of silica nanoparticles prepared by the Stober process and functionalized with aminopropylsilane groups was also studied by the authors of this chapter. The idea was to see whether DNP MAS-NMR could help in the detection of the T units (R—SiOs) grafted on the surface of silica composed of Q units. This is a really important issue for the characterization of functionalized particles. 

Improvements in the impact resistance of hybrid sol-gel silica coatings have been obtained after modifying the surface of silica nanoparticles obtained by the Stober method [74] with 3-methacryloxypropyltrimethoxysilane (3-MPS). The reaction of the —OH groups with —O—CH3 groups leads to organic surface modification (Figure 39.4). 

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