Dispersion mechanism of titanium dioxide water dispersion
For the improvement of water dispersibility of TiO2, this paper first analyzes the mechanism of water dispersibility and then confirms it by modification test. The picture below attached showed our aluminum lock nuts. Black, red, blue, purple, pink, green, silver,orange, and gold color are our popular colors. Aluminum Flange lock nuts,aluminum Flange serrated lock nuts, aluminum self-locking nuts, aluminum hex nuts etc are available. But different Sizes and colors could be customized according to your draiwngs or requirements. Both 6061-T6 aluminum lock nuts and 7075-T6 aluminum lock nuts could be offered. If you need special packing service for the nylon washers including special package boxes, it is also ok for us. Any questions or demand, please feel free to contact us. Aluminum Nut,Aluminum Blind Rivet Nut,Injection Molded Aluminum Nut,Aluminum Barrel Nut Hobby Carbon CNC Technology(Shenzhen) Limited , https://www.hobbycarbon.com
Dispersion mechanism of titanium dioxide water dispersion
1 Introduction
TiO2 is the most commonly used white pigment and is widely used in the coatings, plastics, rubber, paper, ceramics, cosmetics and textile industries. With the increasing attention to the environment, water-based environmentally friendly coatings are favored, and TiO2 as a high-quality white pigment, how to better apply to water-based coatings is the subject of today's research. Water dispersibility is an important performance index for the application of TiO2 in waterborne coatings. Its pros and cons directly affect the hiding power and other properties of the coating. For the improvement of water dispersibility of TiO2, this paper first analyzes the mechanism of water dispersibility and then confirms it by modification test.
2 theoretical basis of modification
2.1 TiO2 surface characteristics
2.1.1 Agglomeration in single phase
The primary particles obtained by calcination of TiO2 are small, have a high specific surface energy, are extremely unstable, and agglomerate rapidly at high temperatures to form metastable larger particles. For a certain amount of TiO2, the smaller the particles, the stronger the attraction between the primary particles, and the particles are more easily agglomerated.
At present, the average particle size of TiO2 measured by the instrument is mostly the particle size of the secondary particles (generally 0.2-0.4 um), and the surface energy is still high. It is easy to reduce the surface energy by agglomeration and reach a quasi-stable state. Therefore, the phenomenon of easy agglomeration of TiO2 in a single phase is a prerequisite for discussing its water dispersibility.
2.1.2 High dispersion in two phases
In the aqueous dispersion, TiO2 exhibits a high degree of dispersibility. The reason is: 1TiO2 has many hydroxyl groups on the surface, which can adsorb polar particles, so that the solid surface carries the same charge, and is dispersed by the same charge repulsion; 2 the specific surface energy of the particles is large, the surface shrinks and the surface energy is reduced. Stabilize the dispersion. It is the high dispersion of TiO2 in water that makes it widely used in waterborne coatings.
2.2 Dispersion process of TiO2 in aqueous dispersion
2.2.1 Adsorption
A large number of studies have shown that there are many polar hydroxyl groups on the surface of TiO2. If no dispersant is added in water, TiO2 will adsorb a large number of polar groups when dispersed in water. If a certain concentration of polymer dispersant is added, the polymer dispersant will adsorb. On the surface of the TiO2 particles, the thickness of the adsorbed layer is increased, and the surface characteristics are changed.
2.2.2 Electric double layer theory
By detecting the zeta potential of TiO2 in water, it was found that the anatase TiO2 has a zeta potential of about 36 mV at a pH of about 6.8, which indicates that the surface of TiO2 has a charge and is more electronegative. According to the electric double layer theory, it is reasonable to explain the dispersion process of TiO2 in water, which has certain scientific basis.
In fact, the process of dispersing TiO2 in water is a process of forming an electric double layer. When TiO2 contacts the surface of water, it is impregnated and wetted instantaneously, and its surface adsorbs an opposite charge to form an electric double layer. This electric double layer can be regarded as a particle surrounded by the same electric charge. When the Brownian motion brings the two particles close together, a repulsive force is generated between the electric charges of the same nature. When the repulsive force is greater than the van der Waals attraction, the particles are separated. The system is in a state of dispersion and stability.
3 modification test
In order to improve the hydration of TiO2 in terms of water dispersibility, it is required to be surface-treated. The most common is stabilization, which involves adding other elements to the crystal structure or modifying the surface of the particles, all of which help to change their physicochemical properties.
3.1 Purpose of modification
Introduce new groups that interact with organic matter, improve interfacial adhesion, and change the hydrophilic/hydrophobicity of the surface. The modified product should have as low a bulk density as possible and as high a hydrophobicity as possible.
3.2 Modified materials
TiO2 was prepared by the Jinan Yuxing Chemical Plant in a sulfuric acid process. The main physical and chemical properties of the TiO2 (model R-818) were tested as shown in Table 1.
3.3 Modifier selection
Among the modifiers, the most commonly used are silane, titanate, zirconate coupling agents, and fatty acids and derivatives thereof and surfactants. In this paper, a silane coupling agent previously used as an adhesive is selected as a modifier. Specific compounds are shown in Table 2.
3.4 modification method
3.4.1 Modified process
Prepare a suitable silane solution, and then mix 100 parts (parts by mass) of the TiO2 to be modified and 0.25-5.00 parts of the silane coupling agent solution in a surface modification mixer to ensure uniform and uniform surface of the TiO2. Wet. After mixing, the solvent was removed at 10 ° C and the modified powder was dried.
3.4.2 Physical and chemical properties testing
After the modification, the physical and chemical properties of TiO2 were measured, and the bulk density, water absorption, dibutyl phthalate, and paraffin oil were measured. In order to obtain dispersibility data, morphological, microstructure study and particle shape, grain morphology, single particle structure, TiO2 aggregation, and aggregation type were studied (the instrument used was a scanning electron microscope).
3.5 Modification results and discussion
The basic physical and chemical properties of the modified and unmodified TiO2 are shown in Table 3. These parameters indicate significant changes in the surface properties of the modified product.
Table 3 Physical and chemical properties of unmodified and modified TiO2
When modified with a silane coupling agent, the bulk density of the TiO2 sample slightly increased. When a silane having an octyl group or a vinyl functional group is used, the hydrophobicity of TiO2 is remarkably increased due to partial or complete loss of water wettability of the surface. When modified with n-octyltriethoxysilane (U-222), the effect on hydrophobicity is most pronounced. When 0.5 part of TiO2 is modified with 0.5 part of the compound, the water wettability of TiO2 is lost. When modified with ureidosilane, the surface group of TiO2 is partially blocked, and the hydrophobicity is only negligible. Since the amino group is present on the surface of the modified material in this case, hydrogen bonds can be formed with water molecules, resulting in less hydrophilicity on the surface.
Electron microscopic observation of unmodified TiO2 and TiO2 modified with U-222 showed that the unmodified TiO2 showed a high degree of dispersion and small particles, and a slight tendency to aggregate. When 100 parts of titanium dioxide is modified with 0.25 parts of U-222, TiO2 can be completely dispersed; and when modified with 5 parts of U-222 silane, the tendency of agglomeration of TiO2 is significantly increased.
4 Conclusion
The surface characteristics of TiO2 change with modification. The modified TiO2 obtains surfaces with different physicochemical properties through chemical and physical processing. The water dispersibility of TiO2 is improved in the modification, so that it is better used in aqueous coatings.
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