Re: Ethanolamine vs. Ethanolamine hydrochloride for glass functionalization


I've seen some references in the literature for functionalizing glass
surfaces with amine groups using Ethanolamine hydrochloride (instead
of using silanes). The rationale being that the polymerization of
silanes on the surface into long fingers can be avoided. Since I am
not a chemist, I have a few questions

The silanes don't polymerize into "long fingers" - they glop down, but
not badly. The coating won't be a perfect monolayer, but it will be
less than 10 nm thick. The coating should be invisible. Do you need
better? I'm not sure if you're the same person I responded to a while
ago suggesting aminosilanes, but use of anhydrous toluene should help
prevent bulk polymerization. Triethoxysilanes are quite water stable
and don't significantly polymerize even in aqueous solution over a
period of hours. And yes, cure the coatings - 120C for 5 minutes will
do it.

Ethanolamine sounds like physisorption. How robust a coating do you
need? What is the application?

1) Is it equivalent to use Ethanolamine (H2NCH2CH2OH) instead of
Ethanolamine Hydrochloride (
H2NCH2CH2OH · HCl)

They are equivalent, except the hydrochloride will be strongly acidic
when dissolved. Note that glass and silica surfaces are negatively
charged down to a pH of about 2 (below this they become positively
charged). Metals are usually negatively charged down to a pH of 4-6.
Ethanolamine has a pK of 9.498, so neutralizing the ethanolamine
solution shouldn't change its ionization state.

2) How good is this functionalization work vs. Silane's?

Silane is covalent, quite permanent.


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