The thickness of a non-spreadable liquid between two surfaces There's this question I've come to when doing my research when working on polymer brushes; what I'm looking for is to find my reaction mixture thickness between two plates. So the setup is as follows: My bottom plate, with initiator on it. Then I put a drop of my reaction mixture on it which does not spread. Lastly, I put the top plate and the drop fills the gap between two plates and forms a film. I know how much the top plate weighs and the surface tension of drop and two plates, how can I calculate the film thickness between two plates?
Here's my thought processes:

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*Should I look at the problem unsteady or steady? When thought of steady, I tried to equalize hydrodynamic pressure and weight of top plate but that did not match for the data of a paper working close to my work. They don't mention how they calculated their thickness.


*Can I think of it simplistically? Like I know the volume of the drop that I put, I know the surface of the plate, then divide the volume by surface to get film thickness?
 A: I would absolutely apply the $\mathrm{estimated~thickness}=\frac{\mathrm{calibrated~volume}}{\mathrm{observed~surface~area}}$ approach, and I'd do a sanity check on this result with a series of experiments with calibrated polystyrene beads (e.g., from Sigma-Aldrich), which are very useful for obtaining precise film thicknesses.
You need only a few beads if the adjacent plates are stiff; serially dilute the very concentrated stock solution and add to your liquid. With replicate batches, increase the bead diameter successively from well below the estimated thickness. The surface area should stay constant until the bead diameter reaches and then exceeds the natural spreading thickness, at which point the observed surface area will begin to decrease because the comparatively rigid beads prevent the plates from being drawn closer together. Know what I mean?
This low-tech approach can be easier than trying to measure the thickness using, say, optical profilometry or spectrometry, especially if such tools aren't readily available to you.
