Silanization is the covering of a surface with organofunctional alkoxysilane molecules. Mineral components like

glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...

and

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

oxide surfaces can all be silanized, because they contain

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydro ...

groups which attack and displace the

alkoxy In chemistry, the alkoxy group is an alkyl group which is singularly bonded to oxygen; thus . The range of alkoxy groups is vast, the simplest being methoxy (). An ethoxy group () is found in the organic compound ethyl phenyl ether (, also ...

groups on the silane thus forming a

covalent A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...

-Si-O-Si- bond. The goal of silanization is to form bonds across the interface between mineral components and organic components present in paints, adhesives, etc. Silanization (or siliconization) of glassware increases its hydrophobicity and is used in cell culturing to reduce adherence of cells to flask walls. Aside from clear applications in coatings and material science, the silanization process is also used in biomedical fields to anchor DNA to substrates.

Properties

Organofunctional alkoxysilane molecules have both organic and inorganic properties. Silanized surfaces are usually hydrophobic, but the surface properties can be adjusted by varying the side chains of the silane compound. Many common silane compounds have alkyl groups (containing only carbon and hydrogen) which are more nonpolar than the

(-OH) groups on the untreated surface, creating a hydrophobic surface. Once the surface has been functionalized, further reactions can be performed to graft molecules with properties such as

hydrophilicity A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press. In contrast, hydrophobes are no ...

hydrophobicity In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, t ...

, self cleaning,

photocatalytic In chemistry, photocatalysis is the acceleration of a photoreaction in the presence of a catalyst. In catalyzed photolysis, light is absorbed by an adsorbed substrate. In photogenerated catalysis, the photocatalytic activity depends on the abi ...

, and more onto the substrate.

Mechanism

Silanization begins with activating the desired material to expose surface hydroxyl (-OH) groups. The activated substrate, or material, is then placed in a silane solution to react; often, chlorosilanes are used due to their extreme reactivity. The silane is linked to the oxygen in the hydroxyl group, producing hydrochloric acid and a stable Si-O bond. This reaction occurs spontaneously and no catalyst is needed.

Organofunctional alkoxysilanes

The alkoxy groups usually used are the

methoxy In organic chemistry, a methoxy group is the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula . On a benzene ring, the Hammett equation classifies a methoxy substituent at the ''para'' position a ...

(-OCH₃) and the ethoxy (-OCH₂CH₃) groups. The organofunctional alkoxysilanes are classified according to their organic functions:

Aminosilanes

The organic function is a primary or secondary

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen Hydrogen is the chemical element wi ...

: *

APTES (3-Aminopropyl)triethoxysilane (APTES) is an aminosilane frequently used in the process of silanization, the functionalization of surfaces with alkoxysilane molecules. It can also be used for covalent attaching of organic films to metal oxides s ...

(3-aminopropyl)-triethoxysilane CAS# 919-30-2 APTES

* APDEMS (3-aminopropyl)-diethoxy-methylsilane * APDMES (3-aminopropyl)-dimethyl-ethoxysilane * APTMS (3-aminopropyl)-trimethoxysilane CAS# 13822-56-5

Glycidoxysilanes

The organic function is an

epoxide In organic chemistry, an epoxide is a cyclic ether () with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale ...

: * GPMES (3-glycidoxypropyl)-dimethyl-ethoxysilane

Mercaptosilanes

The organic function is a

thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...

: * MPTMS (3-mercaptopropyl)-trimethoxysilane * MPDMS (3-mercaptopropyl)-methyl-dimethoxysilane

References

{{Reflist Silicon