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I've read in literature that the silanization reaction is completed in a second. However, I realized an interesting thing; after one hour that my cleaned glass beads are deep coated in a silan bottle two things might happen:

1) If I take out the beads from the silan bottle and then wash them with water and then acetone, contact angle is ~102 deg and the beads are still transparent.

2) But if I take out the beads and then put them on a flat surface (in one layer) and pour some silan solution on them and let them to be dried in silan, then the contact angle is ~118 deg and glass beads are not transparent anymore (they're milky white).

Has anybody had a similar experience or know the reason of this?

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    $\begingroup$ What is in the silan solution? What is its solvent? In method 2, perhaps the solvent evaporates, leading to a coating of the glass beads not only with the chemically reactive silanization reagent, but also whatever stabilizers, emulsifiers, and who knows what else might be in there. That could explain the color and the contact angle, but without more info on the composition of your silan solution, this is just speculation. $\endgroup$ – Curt F. Jan 6 '16 at 0:58
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    $\begingroup$ You can try to measure thickness of the coating. It should by different and I suppose that the dipped layer is thicker. The molecules have more time to create smoother layer than the molecules prepared by the second approach. $\endgroup$ – Jaroslav Kotowski Jan 6 '16 at 13:21
  • $\begingroup$ @JaroslavKotowski But in both methods, first I deep coat the glass beads for 60 min which gives them enough time to be coated properly. After this stage, I either let them to be dried while they are smeary in a thin silan cover (which gives a higher CA) OR wash them instantly (gives lower CA) $\endgroup$ – Nick Jan 6 '16 at 18:08
  • $\begingroup$ @CurtF. Silan solution was Octadecyltrichlorosilane >90% and I used it without any other additives or solvents. Also, the point that you mentioned for creating a coating of whatever is in silan solution on the beads surface after drying out, is very reasonable but you think they could not be cleaned up even by acetone? $\endgroup$ – Nick Jan 6 '16 at 20:45

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