Stober silica particles preparation

Szekeres et al. (2003) prepared monolayers of Stober silica particles on the surface of water and deposited onto glass substrates by the Langmuir-Blodgett method. Prior to film formatiou the surface of the silica particles was methoxylated by washing with methanol at room temperature. This reaction... 

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... 

Interestingly, it was found that gold particles were not produced with monodisperse amorphous Si02 particles prepared by the method of Stober et al. [26]. Flence, silica... 

The use of silica particles in bioapplications began with the publication by Stober et al. in 1968 on the preparation of monodisperse nanoparticles and microparticles from a silica alkoxide monomer (e.g., tetraethyl orthosilicate or TEOS). Subsequently, in the 1970s, silane modification techniques provided silica surface treatments that eliminated the nonspecific binding potential of raw silica for biomolecules (Regnier and Noel, 1976). Derivatization of silica with hydrophilic, hydroxylic silane compounds thoroughly passivated the surface and made possible the use of both porous and nonporous silica particles in all areas of bioapplications (Schiel et al., 2006). 

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. 

In 1956 Gerhard Kolbe (1) published the first results that showed that spherical silica particles could be precipitated from tetraethoxysilane in alcohol solutions when ammonia was present as the catalyzing base. Several years later, in 1968, StOber, Fink, and Bohn (2) continued in this research area and published the frequently cited original article for the preparation of monodispersed silica particles form alkoxide solutions. StOber et al. improved the precipitation process and described the formation of exceptionally monodispersed silica particles. The final particle size could be controlled over a wide range from about 50 nm to 1 1/2 p,m. Variations of the particle size could be achieved by different means, e.g., temperature, water and ammonia concentration, type of alcohol (solvent), TEOS (tetraethoxysilane) concentration, or mixing conditions. 

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... 

Last names (e.g. Stober used as abbreviation for method of preparation of silica particles from tetraethoxysilane), etc. 

Stober et al. (15) developed a method of preparing remarkably uniform silica particles with sizes ranging from 50 nm to >1 pm in diameter. Their recipe involves hydrolyzing silicon alkoxides in aqueous alcoholic solutions containing ammonia. The resulting solids are amorphous and are 11-15% porous. We chose to use the hydrolysis and condensation of tetraethylor-thosilicate, TEOS, in ethanol as a model precipitation reaction to study parameters leading to uniformity. 

An elegant method proposed by Stober et al. [61] for the preparation of monodisperse spherical silica particles with controlled size comprises the hydrolysis and condensation of aUcoxysilanes in mixtures of ammonia, water, and a lower alcohol. The reactions involved can be represented by ... 

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]. 

The sol-gel process - either aqueous or nonaqueous - is one of the most important processes for the preparation of oxidic nanopartides. For silica particles, the sol-gel-based Stober process is definitely the most used wet chemical preparation route. Particularly, the mild reaction conditions combined with the excellent control over nanopartides properties malce it a universal method for the production of colloids for various applications. In recent years, the metal oxide routes have also become more and more sophisticated. Another reason for the attractiveness of the preparation route is the activity of the derived particles toward surface functionalization. Such modified particles can be easily incorporated into polymer matrices to obtain nanocomposites with extraordinary properties. 

Several reports have shown that hollow silica particles can be prepared by hydrolysis and polycondensation of tetraalkoxysilane in the presence of aggregates of polymers such as polyamines [5], polylysine [6], poly(acrylic acid) (PAA) [7], and poly(JV-isoprop)dacrylamide) [8]. Although this method often results in broad particle size distributions (100 nm to several micrometers), relatively fine control of the size (in the range of 25-400 nm) and shell thickness was achieved with PAA [7]. The synthesis route involves (i) the formation of spherical aggregates of PAA in an ethanol solution, (ii) the formation of silica particles from tetraethoxy-silane (TEOS) by the modified Stober method [9], and (iii) subsequent removal of PAA by washing. 

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. 

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... 

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