Hi Seyede,

What you describe is dewetting of your glass surface, it typically starts from the edges and leads to contraction of the liquid phase. This is observed in case the surface tension of the liquid (from which you deposit the film) is not able to fully wet the glass, which is most crucial at the edges. Any surface requires a specific surface tension of a liquid to fully spread, this is called the 'critical surface tension for wetting'.

The fact that your solution initially wets the full surface but in time starts to de-wet seems to suggest that while casting the surface tension of your solution increases. This can be due to the fact that the compounds responsible for initially lowering the surface tension are disappearing from the solution (i.e. they precipitate to form the cast film).

There are two solutions to this problem: treat the glass or change the solution.

Glass is a strange material, it has a memory effect and remembers the last solvent it has seen. The best way to prepare glass for film casting is as follows:

1. Remove organics and dirt particles, rinse with for instance ethanol.

2. Next rinse the glass with an abundant amount of water to remove the ethanol.

3. Polish the glass with an abrasive cleaner, this 'refreshes' the surface.

4. Rinse well with water to remove the cleaner.

5. Preferably store the glass plates submerged in water, dry them by a filtered nitrogen flow shortly prior to use.

Anyway for any good experiment one would need a standardized method to clean the glass, I would recommend doing this anyway also if you decide to use option 2, changing the solution properties...

If your experiments allow for the adaptation of the casting solution, you could try to add a tiny amount of a nonionic surfactant like Tween 80 or a volatile alcohol. This will lower and maintain a constant surface tension of the solution which is now controlled more by the soluble surfactant/alcohol, than by your film-forming agents . Do not use ionic surfactants as they may bind to the glass surface and cause disruption of your casting process.

I hope this helps, good luck!!

Kind regards, Leo

Dear Leo

thank you so much for your detailed answer. I will try do do so although I am not sure about N2 since I should change placr during ny tests and in the ginall place it is not possible to do that ...

actually it is strange because in some case it does bot shrink so much in some cases ot is terrible and totally moves and in some cases it is so so as you can see in the picture from one edge it is not happened for example!

Hi Seyede,

The pictures, and your information, suggest de-wetting caused by the glass itself. I would clean a batch of glass first rigorously before trying anything else. After you cleaned the glass be sure not to touch it anymore with your bare hands, wear nitrile gloves or similar. N2 is only needed when you don't have an oven to dry, or when you can leave the plates out for some time while they dry. If you have to store dry glass plates, get some household aluminum foil and make sure the glass is only in contact with the dull side of the foil. From experience I know this is the best way to protect cleaned surfaces. NEVER store glass in plastic bags!! Glass will quickly bind the softening and finishing agents in the plastic foil; these agents are desastrous for the surface making it hydrophobic (which is what you don't want at all in this case).

Kind regards, Leo

Thank you so very much Leo I will do so this time and write here about the results.

Regards