The Stöber process is a physical chemistry

Physical chemistry

Physical chemistry is the study of macroscopic, atomic, subatomic, and particulate phenomena in chemical systems in terms of physical laws and concepts...

 process for the generation of monodisperse

Monodisperse

A collection of objects are called monodisperse, or monosized, if they have the same size and shape when discussing particles, and the same mass when discussing polymers...

d particle

Particle

A particle is, generally, a small localized object to which can be ascribed physical properties. It may also refer to:In chemistry:* Colloidal particle, part of a one-phase system of two or more components where the particles aren't individually visible.In physics:* Subatomic particle, which may be...

s of silica. The process was discovered in 1968 by Werner Stöber et al. building on earlier work by G. Kolbe in published in 1956. The topic has since been widely researched. Tetraethyl silicate

Tetraethyl orthosilicate

Tetraethyl orthosilicate is the chemical compound with the formula Si4. Often abbreviated TEOS, this molecule consists of four ethyl groups attached to SiO44- ion, which is called orthosilicate. As an ion in solution, orthosilicate does not exist. Alternatively TEOS can be considered to be the...

 is added to an excess of water containing a low molar-mass alcohol

Alcohol

In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

 such as ethanol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

 and containing ammonia

Ammonia

Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

. The resulting solution is then stirred. The resulting silica particles have diameters between 50 and 2000 nanometers depending on type of silicate ester used, type of alcohol used and volume ratios. A particle size up to 1000 micrometres has been reported in a modified emulsion

Emulsion

An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...

 technique. The reactions taking place are hydrolysis

Hydrolysis

Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

 of the silyl ether

Silyl ether

Silyl ethers are a group of chemical compounds which contain a silicon atom covalently bonded to an alkoxy group. The general structure is R1R2R3Si−O−R4 where R4 is an alkyl group or an aryl group. Silyl ethers are usually used as protecting groups for alcohols in organic synthesis...

 to a silanol

Silanol

Silanol, also known as silyl alcohol, is a chemical with formula SiH3OH. It is the simplest silicon alcohol, and is a heavy, volatile, colorless, flammable liquid. At room temperature it is a polar liquid...

 followed by condensation reaction

Condensation reaction

A condensation reaction is a chemical reaction in which two molecules or moieties combine to form one single molecule, together with the loss of a small molecule. When this small molecule is water, it is known as a dehydration reaction; other possible small molecules lost are hydrogen chloride,...

s. The particles have been analysed by light scattering

Light scattering

Light scattering is a form of scattering in which light is the form of propagating energy which is scattered. Light scattering can be thought of as the deflection of a ray from a straight path, for example by irregularities in the propagation medium, particles, or in the interface between two media...

.

The process is believed to take place via a LaMer model (monomer addition) in which nucleation is a fast process, followed by a particle growth process without further nucleation. In an alternative model called controlled aggregation, the particles grow by aggregation of smaller particles. This model is supported by microgravity experiments and by SAXS

SAXS

Small-angle scattering is a fundamental method for structure analysis of materials, including biological materials. Small-angle scattering allows one to study the structure of a variety of objects such as solutions of biological macromolecules, nanocomposites, alloys, synthetic polymers, etc...

 analysis. Kinetics have been investigated with variation in pH.

Reported morphological variations are a PEG

Polyethylene glycol

Polyethylene glycol is a polyether compound with many applications from industrial manufacturing to medicine. It has also been known as polyethylene oxide or polyoxyethylene , depending on its molecular weight, and under the tradename Carbowax.-Available forms:PEG, PEO, or POE refers to an...

 graft and core-shell morphologies based on cyclen

Cyclen

Cyclen or 1,4,7,10-tetraazacyclododecane is a macrocycle and the aza analogue of the crown ether 12-crown-4. Derivatives of cyclen are larger cyclic polyamines but the repeating unit is always the same. Like crown ethers, cyclen compounds are capable of selectively binding cations...

, polyamines and polystyrene

Polystyrene

Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...

.

Microporous

Microporous material

A microporous material is a material containing pores with diameters less than 2 nm.Porous materials are classified into several kinds by their size. According to IUPAC notation A microporous material is a material containing pores with diameters less than 2 nm.Porous materials are...

 silica particles can be obtained through organic templating followed by calcination

Calcination

Calcination is a thermal treatment process applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction. The calcination process normally takes place at temperatures below the melting point of the product materials...

. Reported organic additives for this process are cetyltrimethylammonium bromide  and glycerol

Glycerol

Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...

 

Carbon spheres

The synthesis of carbon-based spheres has been reported in a similar process with resorcinol

Resorcinol

Resorcinol is a dihydroxy benzene. It is the 1,3-isomer of benzenediol with the formula C6H42.-Nomenclature:Benzene-1,3-diol is the name recommended by the International Union of Pure and Applied Chemistry in its 1993 Recommendations for the Nomenclature of Organic Chemistry.-Production:It is...

 and formaldehyde

Formaldehyde

Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...

.