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Reaction of Organo-Silanes with Filler Surfaces
While the reaction with the filler surface is critical to the functioning of the organo- silanes, it is a very complex topic, and only an overview is possible here. The reader is referred to Rothon (2003) for a more detailed discussion.
Reaction between the alkoxysilane and filler surface hydroxyls can proceed in one of the two ways.
When the system is very dry, then direct reaction takes place:
In the more common situation, when water is present, prehydrolysis can occur, followed by condensation:
These two processes occur at different rates and respond differently to factors such as temperature and pH, and it is not clear which path is followed in most commercial processes.
This simple model ignores the fact that the silanols can react with each other as well as with the surface thus allowing cross-linking in the coating and even the formation of unbound oligomeric silane species. There is even some evidence that the oligomeric species can be beneficial to processing.
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