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Research On Nano Silica Application And Nano Silicon Dioxide Surface Modification

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Update time : 2020-05-15 11:18:38

Nano Silicon Dioxide:

Nano silicon dioxide (also called nano-silica) is an inorganic chemical material, commonly known as white carbon black. Because it is ultra-fine nanoscale, the size range is 1-100nm, so it has many unique properties, such as optical properties against ultraviolet rays, can improve the anti-ageing, strength and chemical resistance of other materials, and it is widely used.
 

Nano-scale silica is an amorphous white powder, non-toxic, odourless, and non-polluting. The microstructure is spherical, with a quasi-particle structure of flocculent and net-like structure. The molecular formula and structural formula are SiO2, and it is insoluble in water.
 

Nano Silica Application:

The application of nano-silica is very extensive, generally, the weight is 0.5-2%, and the individual product system can be more than 10%. The key to product performance is: fully dispersed into the system. According to different systems, disperse the nano-silica in water, acetone, alcohol or other solvents in advance. For oily systems, it can be supplemented with additives for pretreatment. Mainly used in the following fields,
 

(1) Electronic packaging materials

Fully dispersing the surface-treated nano silicon oxide in the silicone modified epoxy resin encapsulant matrix can greatly shorten the curing time of the encapsulating material (2.0-2.5h), and the curing temperature can be reduced to room temperature so that the sealing performance of the device can be significantly improved and the service life of the device can be increased.
 

(2) Resin composite materials

Fully and uniformly dispersing the nano-silicon oxide particles into the resin material can comprehensively improve the performance of the resin-based material. Including A improves strength and elongation; B improves wear resistance and improves the surface finish of the material; C anti-ageing properties.
 

(3) Plastic

The use of nano silicon oxide for light transmission and small particle size can make the plastic denser. After adding silica to the polystyrene plastic film, it can improve its transparency, strength, toughness, waterproof performance and anti-ageing performance. The nano silicon oxide is used to modify the ordinary plastic polypropylene, so that its main technical indicators (water absorption, insulation resistance, residual compression deformation, flexural strength, etc.) meet or exceed the performance indicators of engineering plastic nylon 6.

(4) Paint

It can improve the coating's poor suspension stability, poor thixotropy, poor weather resistance, poor scrub resistance, etc., which greatly improves the bonding strength of the coating film and the wall, the coating film hardness increases, and the surface self-cleaning ability is also improved.
 

(5) Rubber

Silica is known as white carbon black. After adding a small amount of nano silicon oxide to ordinary rubber, the product's strength, wear-resistance and ageing resistance have reached or exceeded the high-grade rubber products and can maintain the colour for a long time. Nano-modified colour EPDM waterproof membrane, its wear resistance, tensile strength, folding resistance, anti-ageing performance are significantly improved, and the colour is bright, and the colour retention effect is excellent.
 

(6) Pigment (dye)

By adding nano silicon oxide to the surface modification treatment of organic colour (dye) material, not only the anti-ageing performance of the colour (dye) material is greatly improved, but also the indicators of brightness, hue and saturation are also improved to a certain extent, greatly broadening The grade and application scope of organic colour (dyeing) materials are shown.
 

(7) Ceramic

Replacing nano A1203 with nano SiO2 can play not only the role of nanoparticles but also the particles of the second phase, which can improve the strength, toughness, hardness and elastic modulus of ceramic materials.

The use of nano silicon oxide to composite ceramic substrates improves the compactness, toughness and finish of the substrates, and greatly reduces the sintering temperature.
 

(8) Sealant and adhesive

With the addition of nano silicon oxide, a layer of organic material is coated on the surface to form a network structure and form a silica structure, making it hydrophobic, which can inhibit colloid flow, accelerate curing speed, improve bonding effect, and increase product sealing and impermeability.
 

(9) FRP products

The grafting and bonding of nanoparticles and organic polymers can increase the toughness of the material, increase the tensile strength and impact strength, and greatly improve the heat resistance.
 

(10) Drug carrier

Using nano silicon oxide as a carrier can play a good slow-release effect.
 

(11) Cosmetics

Nano-Si02 is an inorganic component, easy to be compatible with other components of cosmetics, non-toxic, odourless, white in itself, strong in UV reflection and good instability, it will not decompose and change colour after being irradiated with UV, and it will not be combined with other components in the formula. Separate chemical reactions have laid a good foundation for the upgrading of sunscreen cosmetics.
 

(12) Antibacterial materials

Using the large specific surface area of ​​nano silicon oxide, the multi-mesopore structure on the surface, the strong adsorption capacity and the strange physical and chemical characteristics, the functional ions such as silver ions are uniformly designed into the mesopores on the surface of nano-SiOX to develop high efficiency, durability and resistance High-temperature, the broad-spectrum antibacterial nano-antibacterial powder can be widely used in bills, medical and health, chemical building materials, home appliances, functional fibres, plastic products and other industries.
 

Nano silicon oxide has small particle size, large specific surface area, good biocompatibility, and has the advantages of surface interface effect, small size effect, quantum size effect of nano materials, 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, which in turn affects the structure and performance of the material. Therefore, it is necessary to modify the surface of the nano silicon oxide to ensure its stable storage and improve its dispersion in the polymer matrix.
 

There are many methods for surface modification of nano silicon oxide, mainly divided into two categories of physical modification and chemical modification.
 

Physical modification of nano silicon dioxide

The physical modification of nano silicon dioxide mainly attracts the modifier to the surface of nano silicon dioxide 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 silicon dioxide can prepare a variety of coating structure materials, which can meet the needs of different applications. However, because it simply 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 phase is weak. When the system environment such as temperature, pH, pressure and other conditions change At this time, obvious phase separation may occur.
 

2. Chemical modification of nano silicon dioxide

The chemical modification of nano-silica is mainly to use a large number of hydroxyl groups on the surface of nano silicon dioxide to react with the modifier to reduce the number of hydroxyl groups, and change the hydrophilicity and hydrophobicity of the particle surface, expand the application range of nano silicon dioxide.
 

(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 decomposed before it can react with the nano-silica. However, 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.
 

(3) Polymer graft modification method

Grafting the polymer onto the surface of nano-silica in a specific way can effectively increase the hydrophobicity of the particles and improve their interface affinity in nano-composites. The long-chain structure of the graft polymer can produce chain entanglement with the matrix polymer, making this modification more uniform and tight. At the same time, different grafting monomers and grafting conditions can be selected according to needs, so that the modification is more diversity and controllability.
 

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