What is a typical monolayer formation time for liquid phase adsorbate on a solid surface? Let's say a solid is submerged in a solution of species with functional groups and a self-assembled monolayer is forming. What are the typical time scales for the formation of a continuous monolayer? (seconds, minutes, days..?)

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For an adsorbate in gaseous phase and high vacuum, a rough approximation on Wikipedia is ~1 sec.
Depends on concentration and other parameters. For thiols on gold, for example, a typical concentration is 1-5 mM, and formation time is 24-48 hours; "Longer assembly times tend to result in better monolayer packing." (ref)