You may use plasticizers, but the risk is modifying the surface properties that you want to measure. You can also use a convective drying in a not completely dry atmosphere, to allow a slow drying and thereby minimizing the defects. But a non-uniform surface can also be investigated. There are some contact angle measurement systems wich allow the deposition of extremely small droplets, at the level of microlitres. In these conditions, you can always find an area of the material for which the surface can be considered as locally flat.

Alain

this link might help 

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0CDoQFjAC&url=http%3A%2F%2Fwww.google.com%2Fpatents%2FWO2013131079A1%3Fcl%3Den&ei=5e9qVI_DAc2hugTdoYCoCg&usg=AFQjCNFSFhpJ4dTY5kUdjXyYk6DwziYMlQ&sig2=GTd2H0aLyf2QYmZ9PcMV0g&bvm=bv.79908130,d.c2E

Dear Colleague, using a suitable cross-linker can help you to overcome this problem. If you will give more information about casting, then it will be more easy  to explain this problem. Please tell one thing  how are you drying your films? Drying of films at high temperature might lead to shrinkage. 

To Alain Celzard,Thankx sir for valuable information, actually we dont have such sophisticated instrument, bt still looking for the same. 

To, Shakeel Ahmed, Sir, m drying the films at room temp, in vacuum oven overnight, as vacuum applied, even very slowly, air bubbles formed causing non-uniform surface.

Add plasticizer such as glycerol or propylene glycol.

I have used both glycerol & PEG as plasticizer, but still as soon as I remove the film from glass after neutralization, it persists shrinking........I need more suggestions.

Well, I think you need to reconsider the preparation in-terms of polymer concentration, amount of added plastciser (we try several values to choose the best), solvent employed (are you using water+HCl +ethanol)

I found that best drying for film preparation is room temperature. 

I am drying at room temperature sir, also using the the well reported solvent conc. of 2% acetic acid solution, now attempting different conc. of plasticizer..

Can you think of using chitosan oligomer salts which are water soluble instead of using raw chitosn which require acetic acid to dissove it.

Actually Sir, my aim is to enhance the hydrophilicity of chitosan & nw m getting the expected results of contact angle by directly putting breaked petridish containing film over sample sample holder, Also, by air drying film by attaching it to plate in reverse direction of shrinkage, m getting flat film, hope it will repeat. Thank you!

Hallo everybody,

I have the same problem, the chitosan samples shrink and wave during the drying, I have one question about the concetration of glycerol? I am working with 2% chitosan solutions,

regards

Monika

Dear Monika,

Better you deal with 2% glacial acetic acid directly & dry sample with slow evaporation under compressed conditions later.

Dear Sarang,

thanks for your response,!!!

regards

Monika