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For silanization, I put a glass slide horizontally and pour the silan solution on it to cover the glass surface. Then I leave it for a specific time and then wash with water and acetone.

I have three questions:

  1. Is this method correct or I should necessarily deep coat the glass plate into a container of silan solution (because in the 2nd method, there are larger number of available agents than can react with glass or have better accessibility to the glass surface)?

  2. How durable is the silanized glass? i.e. after silanization, when I want to clean the glass surface from reaction products, can I rub something onto the surface to help clean it better or the treated layer of glass might be damaged? (rubbing with cleanex, etc)

  3. For getting maximum hydrophobicity, can I use Octadecyltrichlorosilane>90% directly on glass surface (for how much time?) or I should dilute it?

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Is this method correct or I should necessarily deep coat the glass plate into a container of silan solution (because in the 2nd method, there are larger number of available agents than can react with glass or have better accessibility to the glass surface)?

Your method is fine, anything method that covers the surface with solution will work.

How durable is the silanized glass? i.e. after silanization, when I want to clean the glass surface from reaction products, can I rub something onto the surface to help clean it better or the treated layer of glass might be damaged? (rubbing with cleanex, etc)

In my experience hydrophobic coatings are durable, but will wear due the the small surface thickness. My recommendation is to use rinsing only, if you can and use abrasive cleaning when you have to.

For getting maximum hydrophobicity, can I use Octadecyltrichlorosilane>90% directly on glass surface (for how much time?) or I should dilute it?

I find that hydrophobic solutions typically make very effective coatings nearly instantaneously. You can use it directly which should only require a few seconds maybe a whole minute to work. If you want to conserve octadecyltrichlorosilane you can dilute it. I have had 5% solutions also work nearly instantaneously, but if you want the most hydrophobic surface you should wait 1-5 minutes.

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  • $\begingroup$ I understood that even a shallow silan is enough AND maximum 5 min is required. 1) If I spend more time (60 min) for silanization, will I receive a higher hydrophobicity than spending just 5 min ( I need to know the APPROX. MINIMUM time that I should wait to make SURE that the solution has affected the surface COMPLETELY? 2) If I change the concentration to decrease the level of hydrophobicity (e.g. using a mixture of 1 to 10 silan in kerosene), then should I still spend the same amount of time OR a dilute solution requires more time to react even though it creates a LOWER hydrophobic surface? $\endgroup$ – Nick Dec 23 '15 at 21:26
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    $\begingroup$ The marginal gain in hydrophobic nature decreases exponentially with time. For a concentrated solution, anything past a minute won't hurt but only gives immeasurable gains. For a dilute solution even a minute is fine, you may get better results with longer time but past five minutes, the difference in properties will be a number indistinguishable from zero. $\endgroup$ – A.K. Dec 23 '15 at 21:53
  • $\begingroup$ Thanks for helpful info. First, I used only Octadecyltrichlorosilane>90% and coat one glass, and then I mixed Octa with kerosene (1 Octa+9 kerosene) too see how different hydrophobicity I will get. However, both surfaces have almost similar contact angles. Do you think that I should dilute the Octa more (e.g. using a solution of 1 to 20) or better to decrease the time (BTW, I'm trying to do both but I prefer to know what you think as well). Thanks again! $\endgroup$ – Nick Dec 23 '15 at 22:20
  • $\begingroup$ Now I get a contact angle of 108 with OctaDecylTrichloroSilan. If I deep the glass surface into H2SO4 for a few hours and then perform silanization, is it likely to get a higher contact angle? $\endgroup$ – Nick Dec 27 '15 at 2:51
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    $\begingroup$ I think you will get more consistent results. $\endgroup$ – A.K. Dec 27 '15 at 3:15

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