I think you will have difficulty doing this in aqueous solution because once you hydrolyze the Si-OMe bonds, you will get cross-linking in solution and then you will drop globules of polymerized silanes onto your surface. So if you want to have a nice layer you want the reaction with the -OH groups on the surface to dominate over reactions in the liquid phase. When you use a dry solvent (such as ethanol) with just a little bit of water perhaps you get the dominant reaction being on the surface first.

Do You want to form Langmuir, or Langmuir-Blodget films? I suggest You to use a kind of surfactant to encourage the silanes self-ordereing.

Or You can use a kind of template, for example anodic alumina.

I would say Langmuir film although strictly speaking it is an organic silane with a PEG moiety. It's solubility is suggested in water. In principle, I would just like a single layer.

Do you have any article or reference for this type of surfactant approach

It depends on silyl group, if you have monoalcoxysilyl group you can get it.

The molecule is a trimethoxy silane, which I understand needs to hydrolyse first to its tri-hydroxy form in order to be more efficient.

Definitely, in case of trimethoxysilane the mission is impossible.

You should consider the possibility of getting monomethoxydimethylsilane.

As soon as you have silatrane or trihydroxysilyl derivative the formation of polymeric forms will take place. Actually, alumina forms less stable bonds with silane than siloxane bond itself.

Interesting, thank you Pavel. Sadly I think the mono-form of the product is not available commercially, nor a mono-chloro which would work also I believe.

I think you will have difficulty doing this in aqueous solution because once you hydrolyze the Si-OMe bonds, you will get cross-linking in solution and then you will drop globules of polymerized silanes onto your surface. So if you want to have a nice layer you want the reaction with the -OH groups on the surface to dominate over reactions in the liquid phase. When you use a dry solvent (such as ethanol) with just a little bit of water perhaps you get the dominant reaction being on the surface first.

Thank you Robert. Sadly for our application we cannot or should avoid the use of organic solvents since the glass is within a microfluidic channel of PDMS and ex-situ formation on the glass prevents/hinders the subsequent binding of PDMS to the glass.

Can you run an ethanol-based silanization (with a trace of water) within the channel? This has worked well for us, although we almost certainly functionalize the PDMS surfaces in addition to the glass.

I will have to look at a few fab steps before and after to come up with a right scheme. However, one way is: 1) Pass the oxidizing solution through the channel (H2O2, or something else) 2) Dry well with air 3) Pass the chlorosilane functionalized molecule in gas phase (not the trimethoxy).

Although, for the ease of fabrication, I would try to still use ethanolic solution with trace water with increase conc of trimethoxy silane so as to reduce the surface reaction to the order of seconds.

Parijat: chlorosilane is not available and gas phase is thus not an option. But thank you nevertheless.

Nathaniel: Yes, this is possible and probably not a disadvantage for our purpose. I will give it a try

Gas phase slianziation is often done also with methoxy-silanes (I'm not sure how dense is the monolayer) especailly for binding of bio-molecules. Generally, there is a huge experience with silanes in industry as primers. They might use water, though the result would probably not be a perfect monolayer (do you really need a perfect monolayer?) It is true that water opens the methoxy-silane bond and thus leads to polymerization. However, huge amount of water would also break the polymerization bond, and thus 100% water solutions might work reasonably.

Dear Mark,

gas phase is very promising even using methoxysilanes (e.g. styrylethyltrimethoxysilane in tow –color…). It is even possible using ethoxysilanes. Especially than differences have to be expected which are dependent on the pre-treatment (‘slow moving’ drops). Acid and humidity as demonstrated in the siloxane publication.

Article Analysis of silanes and of siloxanes formation by Raman spectroscopy

Article Statistical contact angle analyses: 'Slow moving' drops on i...

Article A two-color fluorogenic carbene complex for tagging olefins ...

see the sections on application and water-borne silanes in: http://www.gelest.com/themencode-pdf-viewer/?file=http://www.gelest.com/wp-content/uploads/Goods-PDF-brochures-couplingagents.pdf