Hi,
When glass fibers are coated, a coupling agent such as gamma-APS is applied to the surface, and is reacted with silica surface resulting in the formation of [Glass]-Si-O-Si-[Coupling Agent] covalent bonds.
When these coated glass fibers are exposed to water environment, then these bonds are known to be cut by the action of hydrolysis (reversible reaction).
My questions are: (1) what is the rate of this hydrolysis reaction, resulting in broken bonds between glass and coupling agents, any literature available? (2) Are there any existing models that can describe the kinetics of this reaction, and if yes which ones?
Thank you very much!
Best Regards,
Andrey
Interesting Statement. Can you name some reverence?
The silane is not stable towards hydrolysis. We published as far as I know the first kinetic analyses of the siloxane formation with stoichiometric / controlled amount of water. We did not observe a back reaction. Siloxanes are like SiO2 stable.
Article Analysis of silanes and of siloxanes formation by Raman spectroscopy
For all of our investigations using siloxane layers on silicon wafer surfaces (a few hours in contact with ultrapure water) a significant amount of reversibility was not observed. The only tested way to “cut” the Si-C bond or to degrade the agent was to use strong UV-light.
It might be possible that the pretreatment of the glass surface was insufficient or that the "Agent" is degradated (UV, Bio,...), but Hydrolysis of the SiOSi bond from my opinion unlikely.
We further attempted to look into this question for a cured composite material, where the interphase and interface are fully formed and intact. The composite samples were placed in hot water for almost a year, allowing us to see a long-term behaviour. Using a mass balance approach, it seems to be possible to obtain a kinetic constant of interphase degradation in water. For all those who are interested, we have recently published an article with more details on the topic:
Would be exciting to see more research in this direction, as the sizing-rich composite interphase & interface still is the most "mysterious" composite constituent.
Article Long-Term Hydrolytic Degradation of the Sizing-Rich Composit...
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