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The nanometer dispersible liquid (Ⅳ)

The nanometer dispersible liquid (Ⅳ)

  • April 13,2020.

The nanometer dispersible liquid

- promotes the exchange of ceramic ink-jet technology of traditional inorganic pigments


2.3 Design of chemical interface modification agent

Generally there are two ways of processing slurry's surface, one is by complex interaction force such as electrostatic repulsion, stereo repulsion, volume exclusion force and other forces to form a solid or liquid surface stabilized status, its purpose is to avoid the powder aggregated again. One of the most simple way is by PH adjustment, to charge the surface of the nanometer powder, and cause electric repulsion between powders. However, nano powder due to restricted to its final product application and formula of the limit, application suit to this method is not much.

The second common method is to form the stable state between solid and solid, solid and liquid by using the stereo repulsion force. This method most often selects the polymer or monomer with high molecular weight as the dispersant. When the particle size of the slurry is micron or subnanometer, this method is quite effective.

However, when the required particle size of the slurry to be dispersed or grinded is less than 100 nanometer, if the polymer or monomer with high molecular weight is still used as the dispersant, when the powder is nano-sized, most volume in the slurry had been occupied by obstacles formed by high molecular weight polymers or monomers.

At this time the slurry is prone to the following problems:

  • The solid content is drastically reduced, generally below 35% wt;
  • As the viscosity of the slurry increases, the movement of the grinding bead in the grinding machine is adversely affected, resulting in the failure of particle size reduction.
  • Since powder is easy to aggregate, resulting in the failure of nanometer phenomenon.

In order to avoid the above problems, functional agents with lower molecular weight will be used as surface modification agents in the chemical mechanical process introduced in this article. According to the concept of solution chemistry, the functional agent formed by the chemical bond of small molecular weight will be more easily connected to the surface of the nano powder (as shown in the example in figure 7 below), the selected interface modification agent is the functional group of organic acids with low molecular weight.

Figure 7Principles and examples of the selection of interface modification agents

In principle, the selected interface modification agent has the following two functional groups: one is designed to connect to the surface of the nano powder, so that the surface of the nano powder produces a stable phase, in order to avoid the reaggregation of the powder; The design of another functional group is based on the interface (Matrix) that the nano-powder is measured and added in the future to avoid the occurrence of incompatibilities.

Since the tool used in this interface modification process is wet-dispersing nanometer grinding equipment, the interface modification agent selected should be compatible with the solvent used. Although the molecular weight of the selected interface modification agent is very small, it can still produce 2-5 nm thick films on the surface of the nano particles, which is enough to produce a stereo barrier and support the stability of the nano particles.

It is believed that the interface modification agent customized according to the above principles can meet the following requirements

  • The solid content can be greatly increased to over 35 ~ 45 %
  • Particle size can be reduced to the primary particle size of powder (e.g., about 10 nm)
  • The viscosity of slurry will not increases rapidly with the influence of particle size downscaling
  • The powder will not easily generate the phenomenon of reaggregation

2.4 Examples of application

As shown in figure 8, nanometer zirconium oxide powder, primary particle size is less than 10 nm, the one on the left is the nano zirconia has not been prior to the modification, due to the aggregated phenomenon of powder, still cannot be applied to the processing of the posterior segment. The one on the right is the powder modified throught chemical mechanical modification, 90% of the powder particle has less than 30 nm. The modified nano-zirconia powder can easily be added to some coatings to increase surface hardness and refraction.

I. zirconia (ZrO2) under an electron microscope, as shown on the left before modification

II. Zirconia (ZrO2) under electron microscope, photo on the right is after modification

III. The samples below are 40% zirconia. Samples after 1, 2, 3, 4, 5, 6 and 7 times of grinding and dispersing .

Figure 8ZrO2 under electron microscopy (TEM), the left one is before modification, and the right one is after modification.

Another example is the application of nano-sized silicon dioxide, which has been extensively added to traditional coatings to increase the film surface strength without affecting the original light penetration.

In addition to the low price, silicon dioxide is readily compatible with most organic polymers. As can be seen from the following figure 9, the particle size distribution of colloidal silica is D90 < 12 nm. However, appropriate interface modification should be made before adding to the coating, to avoid the reaggregation after adding, thus affecting the penetration rate.

Figure 9: Particle size distribution of Colloidal silica D90 < 12 nm

From the following figure 10, we can understand the relationship between the penetration rate and the use of different interface modification agents and silica colloids with different particle sizes. In principle, the smaller the transmission coefficient is, the greater the penetration rate will be. When the transmission coefficient is > 100, it is completely opaque.

It can be seen from the figure that the hardness of the coating can be improved without affecting its penetration rate as long as the appropriate interface modification agent is selected and silicon dioxide is modified and added to the coating. However, when incompatible solvents are added to the coating for the same interface modification agent, the effect may be reversed. For example, the theory of FIG.10 shows that when 100 nm colloidal silical is added to the coating with butylacetate as solvent, the penetration rate of the coating decreases.

Figure 10: The relationship between the penetration rate and the additional of nano-sillica in coatings.

In principle, the higher the value of γ, the lower the light penetration rate

3 - Conclusion

With the government vigorously advocating and promoting the technology and application of nanotechnology, how to meet the requirement of nanoscale materials will be one of the important factors affecting the maturity and growth of nanotechnology.

How to find a good dispersing and nano grinding equipment to overcome the potential technical bottleneck in the development of traditional grinding machines to mass production of nano materials will be an important issue.

The author has article which introduced the new generation of peg type nanometer grinding machine PHE SuperMaxFlow® +H has obtained a invention patent from the Chinese Patent Office. The nanometer grinding bead mill not only can solve the traditional grinding machine to enlarge the problems, but also can increase the grinding efficiency more greatly in production, in quality aspects at the same time also can achieve the request of the nano materials. The model has been widely used in the key core new materials field in China and other countries in the world.

(To be continued)

© Copyright: 2020 PUHLER (Guangdong)Smart Nano Technology Co.,Ltd. All Rights Reserved.

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