Hello!

to my opinion it depends more on the silane that you want to use, rather than on the substrate or on the surface. For glass both methods are fine, but some silanes give better adsorption by vapour phase and other by liquid phase deposition.

I would suggest to have a look in literature which method is mostly used for the silane you want to use.

I hope I could be of help for you.

Samantha

Depends on the purpose. Octadeclyltrichlorosilane from toluene works well for us, but that requires liquid phase deposition. That gives more homogeneous films and high contact angles. It also presupposes that the pores are much smaller than the molecules. It is important to ensue that the beads are completely dry when immersed

During my tenure with the Alberta Research Council, Canada, my lab. technologist used organo-silines to make porous glass membranes hydrophobic. He used a method he learned in a Technological Institute, the result was perfect at room temperatures. GOOGLE in Key words, you will get information on the subject.

Sorry, that I can not provide you with more details.

Gas phase silanization works pretty well for OTS. The liquid phase gives better results in term of surface coverage but with the gas phase you don't need carcinogenic solvent! For industrial processes and your health is much better!

Solvent coating if possible. Indeed you can well use vapor phase grafting which is a more rapid method, but the way your beads are packed and therefore exposed to the silane vapor which has to go through all beads will determine the efficiency and homogeneity of grafting. These potential problems are overcome by the solvent coating where each bead including the pores is well exposed to silane molecules (even at high volume fraction of beads), especially under agitation (gentle), ensuring a homogeneous and efficient coating of the beads. And for hydrophobic silanization, standard molecules like OTS, HTS and even shorter chain DTS are fine and well soluble in "non especially hazardous" organic solvents like cychlohexane, chloroforme...or a mixture of these.

Hope this will help you.

According to my experience, liquid phase deposition can lead to more homogeneous coatings on glass beads surface and the solvents used are usually non-toxic, an extra bonus.

It will depend on whether you use a mono-functional or di-/tri-functional silane and how dry your silica and solvent is (see Mark Rutland's comment above). If you can live with lowish contact angles then vapour phase trimethylchlorosilane (TMS) is convenient as the dimers formed when there's a little water around can be readily removed under vacuum/mild heating. While coverage and smoothness is good for TMS, it's a poor cousin next to OTS. My vote for a good, hydrophobic layer is OTS but you'll have to spend a little effort getting the solvent and beads dry before treating. Also, subsequent washing with dry solvent, drying and heating above 120C for 24 hours will collapse any silicate networks that may be formed when trace water polymerises this tri-functional silane.

Thank you all.

I reviewed the literature and saw that there are really a lot of different silanes, resulting in choosing the best one to get as possible as high hydrophobicity and surface roughness is difficult. In different articles, some researches say liquid phase is better because there is no full coverage as some of you said. However, some others prefer liquid phase is better than vapor phase in terms of number of thiol. Therefore I really wonder how to decide which silane chemicals is best my system whlich is basicaly focused on increasing surface roughness and hydrophobicity. For example, Mark Rutland, how did you select Octadeclyltrichlorosilane? because there are a lot of different alkyl silanes that are effective in terms of hydrophobicity. Why is Octadeclyltrichlorosilane?

BTW, I am still indecisive on which silane and silanization method will be fine on my porous glasses.

Thanks for your valuable comments.

Any silane with more than an octyl chain will be hydrophobic, but to be sure C10-C12. Chain fluidity maybe something you want in your system (less than C16 will be fluid at room temperature). If you want a really hydrophobic system (oleophobic actually) then C8-perfluoronated chains or longer will be good. Roughness will probably be more of a function of the natural roughness of your substrate. (I'm not following your comment about thiols). If you want really rough (and fluffy) hydrophobic surfaces then you could titrate in small amounts of water to the liquid phase mixture at the end of the reaction. It sounds like form you description your looking for super-hydrophobic surfaces.

Both liquid phase and vapor phase should work well if you know what you are doing. You do not need in my experience go to C10 silanes to obtain a hydrophobic layer, C4-C6 will work quite well (you will get more liquid crystallinity from C10 and up). Note that effective porosity might change due to self assembly (silanization) too.

If you need more information- these are available resources in SLC, UT: There are 2 professors in UoU at Chemistry department, who should be an experts in self-assembly reactions (on on self-assembly on TiO (Andrew Barton(?)), which should be relevant to your question), one professor in UtahStar building. Sorry I did not remember any name, but you can find these. I can also recommend you Leonard Woichek from Physics Department. You are welcome to contact me too: [email protected]

Good and friendly reply, Vova, molodets !

Please let me know about a simple method for silanization of lab glassware.