Whether it has been treated or not, silica has good thixotropy in many systems. Of course, nanoscale is also required to have a significant effect, and micron-sized silicon micropowder is much worse. Even white carbon black can observe similar thixotropy itself (I am not sure if this is thixotropy): the silane-treated white carbon black is shaken, and the white carbon black is like water. After a while, the white carbon black seems to form a mass, then shakes, and immediately has the same water mobility. This process can be repeated. Here, when the white carbon black is shaken, high-voltage static electricity is generated, and the powder has a good fluidity (I think that it is not caused by a decrease in the frictional force after the silane treatment, although it is also a factor), and the time of agglomeration occurs. Depends on the time that static electricity is derived. When the white carbon black is added to other powders in a small amount, the fluidity is improved, and it is also related to the static electricity generated by the friction of the white carbon black, and especially after the treatment, the hydrophobic white carbon black is more effective.
The treated silica, which does not have a structured structure for silicone rubber, still has good thixotropy and is even better used in non-polar coating systems. Therefore, it is foreseeable that the factor causing the thixotropy of silica should be van der Waals force. Of course, the hydrogen bond will not be ineffective, because the untreated hydrophilic white carbon black seems to be more thixotropy when it is well dispersed. Strong. Therefore, I think it is a comprehensive result, but it is based on Van der Waals power.

I don't think that the thixotropy of silica is the result of supramolecularity. The supramolecular thixotropic agent is the kind of block, such as polyurethane, which is usually used as a thickener. Silica does not appear to be blocky, but the technology is developed. It is not impossible to make white carbon black into a block structure, but the problem is that silica does not require a block structure and has good thixotropy.

Since the hydrogen bond strength far exceeds the van der Waals force, there seems to be a contradiction. Why is thixotropy based on Van der Waals? In fact, it can be understood that only a few nanometers of fumed silica will not exist in a separate way, but in agglomerated manner, or that silica itself has been structured, it can be understood that hydrogen bonds are built on The reunion of the white carbon black, of course, just because of solid limitations, the agglomeration can only reach a certain level, into the micron level. When the rubber is refined, the agglomerated particles are broken up, and a large amount of silicic hydroxyl groups are exposed, which creates a very favorable condition for structuring. However, it should be noted that uncoupling agglomeration is not only a mechanical force, but also silicon. Glue also has an important contribution ------Compared with non-silicone polymers.

However, even if the maximum shearing force is applied and the affinity of the silicone raw rubber is utilized, in view of the large specific surface area of the nano-silica, a large amount of silicon-hydroxyl is strongly hydrogen-bonded, and is dispersed to a single particle, almost It is impossible.

At this point, based on the understanding of the agglomeration of nano-powders, and then look back at the structuring, is there a new understanding of the following phenomena?
1. The structuring progresses slowly with time. It is likely that the agglomerated powder slowly exposes more silanol groups, giving the impression that the anti-structurant such as hydroxy silicone oil has lost its effect.
2. Although more silicic hydroxyl groups are exposed, the hydrogen bonding between the white carbon blacks is stronger, and the raw rubber or additives are not enough to disperse the white carbon black more effectively (so it is not more transparent after structuring, even The decrease in transparency) can be seen as a small “turning around” in the surface of the agglomerated silica.
3, the next step to get a conclusion, on-site treatment (usually with the addition of silazane), it is difficult to eliminate the silicon hydroxy group, it is also understandable, professional silica treatment, it may not be able to deal with the place, purely consider processing The agent bond energy is obviously insufficient.

Looking back and touching the degeneration, it can be understood as a kind of role of van der Waals force between the white carbon black. Of course, the role of hydrogen bonding cannot be ruled out. Therefore, as long as the external force is not large, the system can flow. Infinitely reversible, builds quickly, and works in non-silicon systems.