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How To Modify The Surface Of Nano Silica?

wallpapers Industry 2020-07-14

Nano silica has small particle size, large specific surface area, excellent biocompatibility, and has the advantages of surface interface effect, little size effect, quantum size effect of nanomaterials, and is widely used.

However, there are a large number of active hydroxyl groups on the surface of nano-silica, which is highly hydrophilic, making it very easy to form agglomerates or secondary aggregation, which is not conducive to its dispersion in the material, thereby affecting the structure and performance of the material. Therefore, it is necessary to modify surface of the nano-silica to ensure its stable storage and improve its dispersion in the polymer matrix.

There are many methods for surface modification of nano-silica, mainly divided into two categories of physical change and chemical modification.

1. Physical modification of nano-silica

The physical modification of nano-silica mainly attracts the modifier to the surface of nano-silica through physical effects such as adsorption and coating and changes its surface properties to achieve the purpose of reducing agglomeration and increasing dispersion stability.

The physical modifiers of nano-silica mainly include surfactants, metal oxides and polymers.

The physical modification of the surface of the nano-silica can produce a variety of coating structure materials, which can meet the needs of different applications. However, because it merely adsorbs or coats the nano-silica particles by van der Waals force, electrostatic force, etc., the interaction force between the organic phase and the inorganic step is weak. When the system environment such as temperature, pH, pressure and other conditions change At this time, apparent phase separation may occur.

2. Chemical modification of nano-silica

The chemical modification of nano-silica is mainly to use a large number of hydroxyl groups on the surface of nano-silica to react with the modifier to reduce the number of hydroxyl groups, change the hydrophilicity and hydrophobicity of the particle surface, and introduce different groups as needed to expand the nanometer Application range of silica.

(1) Coupling agent modification method

Among the commonly used coupling agent modification methods of nano-silica, the silane coupling agent is most widely used, and it can be condensed with the hydroxyl group on the surface of nano-silica to form a silicon-oxygen bond.

When a coupling agent is used to modify the surface of the nano-silica, the coupling agent needs to be hydrolyzed before it can react with the nano-silica. The hydrolysate will undergo self-condensation, hindering the reaction of the hydrolysate with the hydroxyl groups on the surface of the silica, to a certain extent, reduce the coupling efficiency, and make the surface modification of the nano-silica incomplete.

(2) Alcohol ester modification method

Alcohol ester method is to use fatty alcohol to react with the hydroxyl group on the surface of nano-silica under the condition of high temperature and high pressure to achieve the purpose of changing the wettability of silica surface.

Compared with the silane coupling agent method, the advantage of the alcohol ester method is that the modifier fatty alcohol has a lower price, it is easy to synthesize, and the structure is easy to control. However, the modification effect is affected by the length of the alkyl chain of the alcohol, and it needs to be carried out under high temperature and high pressure, which requires high reaction conditions.

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Tag: Nano Silica