Question
Asked 20th Apr, 2014

Can anyone answer my questions on interaction between alkoxy groups of the silanol molecules with the OH- groups of the substrate?

My questions relate to the biochemistry and related clinical outcomes.
1) What sort of bond is there between the Si of the silanol group and O- atoms of the substrate? Is it a covalent siloxane bond much like the ones observed in SiO4? Sorry I'm not a chemistry major and this is as close as I understand from the Lung & Matinlinna (2012) paper.
2) If the substrate surface has not been silanised (e.g. w/o tribochemical activation), are there always OH- groups for the silanol group to bond with?
3) Where would the weakness of the bond be?
4) Is this bond subject to age- & moisture- related degradation notwithstanding the effect water-related ageing on resin bonding?
5) Is this bond durable?
6) Has the mechanism of phosphate bonding to ZrO2 been elucidated? If so, I would be grateful for some literature or schematics.
Thank you in advance.

All Answers (1)

You will find detailed information on zirconia and phosphates in chromatographic literature (see Peter Carr's work). Zirconia surface has lots of Lewis acid sites so it has great affinity for fluoride and phosphate ions. However, the bonding is not durable. Phosphate on zirconia can be easily washed off by NaOH.
Silanes make a covalent linkage, through the siloxane bond Si-O-Si, with surface hydroxyls on the silica surface (or hydroxyl bearing surface). The best reference for silanes is "Silane Coupling Agents" by Plueddemann. One can make general remarks. The biggest enemy of Si-O-Si bond is water, strong acids and bases which lead to the cleavage of the bond. Si-O-Si usually cleaves slowly is purely aqueous medium. Unfortunately, there is no general answer to the stability of the siloxane bonds. Some silane bonded surfaces are very durable (>1000 hours) and some leach out in hours depending on many many factors.
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