With the growing environmental problems, traditional solvent-based coatings are gradually being replaced by some environmentally friendly coatings, water-based coatings, especially for the development of water-based coatings for wood, the demand for silica matting agent is also increasing. Although traditional matting agents can matte water-based coatings, there are many drawbacks. The viscosity of aqueous coating systems is low, so the matting agent is required to have as little effect on the system as possible, i.e., the amount of silica absorbed by the oil is as small as possible, and must also be conducive to dispersion in the aqueous system.
The total interface charge of a spherical particle.
This is actually the electric potential obtained by Coulomb’s law. VR can be obtained by the following formula:
Vx=Q*/[e(2a+h)](2-20) It can be seen from this formula that Vk is the value calculated by Coulomb’s law for two particles with Q charge. In the limit case of non-aqueous system K-0, there is amide wax structure no diffusion double layer. Generally, the existence of the electrical double layer obscures Coulomb’s law.
In the non-aqueous system, V-VR+VA, compared with the water system, the degree of V attenuation is small, so the non-aqueous system has the following characteristics:
① VR decays slowly to a distance, so the change of VA does not have much effect on V.
②a. Not big, V.x is small
For example, in a non-aqueous carbon black dispersion system, when; =30mV, a=0.6pm,
Vmax~10kT; when y=30mV, a=0.2pm, Vmax~3kT. In these two cases, agglomeration of carbon black can be observed, and the particle size becomes a~1jm. This is because the carbon black has a small particle size and a low energy barrier Vmx x.
Sato et al. studied the relationship between impurity flocculation and test potential in non-aqueous pigment dispersions. He believes that it is difficult for pigments with the same symbol to agglomerate. When different symbols are used, both inorganic pigments are difficult to agglomerate. When inorganic and organic pigments are mixed, agglomeration will occur, and when both are organic pigments, agglomeration will also occur.
The role of charge on dispersion and aggregation in aqueous dispersion systems is greater than that in non-aqueous systems. In the non-aqueous system, when the particle concentration is low, the charge effect has a certain effect. However, when the particle concentration is high, the electric double layer will overlap and play a role; the electric potential drops, and the charge effect is not as obvious as that of the adsorption layer at this time.
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