It depends on what you have in the casting solution. If you are using volatile solvents such as ethanol, acetone, or DCM, evaporation causes an increase in the concentration of ingredients in the casting solution. Therefore, you might have a different kinetic of coagulation. In an intense evaporation, this might change morphology and structure.  

thank u so much. I am  using NMP

Evaporation of casting solution before immersion using less volatile solvents (NMP, DMF etc.) will not show any difference if the moisture level in the air is low. If it is high these solvents will start phase inversion and will create dense top layer or top layer with different pore structures. Using volatile solvents like THF will create a dense layer irrespective of moisture level. It is advisable to  check moisture level while casting membrane.  

thanks a lot sure I will check that

Hi Tihomir,

i am using PES