How does the silver nucleate on glass in Tollen's reagent mirroring?
I'm trying to figure out how exactly does the silver start to grow during a mirroring with Tollen's reagent. I've made two pictures to illustrate how i see the nucleation/growth process of silver on silica:
Now, as you can see, i didn't draw any chemical bonds. That's because I think that the silver adherence is due to Van Der Waals forces. Am I right to think this? If this is the case, then a place with high permanent polarisation would be better suited for the nucleation of silver.
Now, let's follow the logic. We have a greater electronegativity difference between O and Si (3.44 - 1.90 = 1.54) than between O and H (3.44 - 2.2 = 1.24).
For the upper oxygen, assuming an angle of 109 degrees, you get a total dipole moment of: 2 (1.54) cos(109/2) = 1.79
For the lower oxygen with the bonded hydrogen, assuming an angle of 120 degrees , you would get a total dipole moment of: 1.54 + 1.24 = 2.78 (please tell me if i'm wrong to assume a straight line!)
So, this would mean that you have a greater accumulation of electrons at the bottom oxygen, which would favor Van Der Waals attraction (Debye interaction, I guess, since you have a permanent dipole and an induced dipole). 969
This, in turn, would mean that it would be a better nucleation site.
NOW, i like ranting, so i'll go on. If you make a surface treatment using silane groups, I think that you promote the presence of OH groups at your silica surface, although my understanding/knowledge is hazy at this point. I do know that it makes better silver mirroring though. I made another drawing:
Following my logic, this one is wrong in many way. First of all, i drew angles on the Si - O - H bonds, which I didn't draw on my first pictures. Second, the silver is not even near the oxygen atoms, which are supposed to be the nucleation points, according to me.
I'm confused, could you please point out to me where i'm right and wrong in my logic/knowledge? Mainly: - Is there a bond forming between the silica surface and the silver or is it <PERSON> Der Waals (<PERSON>) attraction only? - Is my depiction of nucleation & growth correct (the first two pictures)? - Did I make the electronegativity maths correctly? - Is my logic of " higher total electronegativity difference, hence better nucleation site" correct? (assuming i'm right about the <PERSON> thing) - Is my depiction of silanisation correct? - Am I right to say that the higher presence of surface OH groups by silanisation mean better nucleation - If this is the case, could I do the same thing using a strong acid on my glass surface?
Thank you very much! 979