As i am working on liquid crystal material and till now we are using commercial samples which already had the coating. But now i need to device the cell with modified substrate for my current objective, can somebody suggest some appropriate concentration of polyimide solution or from where i can get polyimide solution for my objective of preparing cell for Liquid crystal material into order to get planner alignment.
The appropriate polyimide is normally dissolved (5 - 10% solution) in a solvent such as DMF or NMP and spun onto the substrate with a Headway (photoresist) spinner. There is then a bake stage before the plates are rubbed in the appropriate directions to make a twisted nematic structure.
Dear Dr. Kumar:
The choice of the appropriate solvent for preparation of PI solution depends on the type of polyimide (PI) Do you use Thermo-resistant (like Kapton or Upilex) or Thermoplastic PI (the latter have rather low softening temperatures and the phenylene rings are linked by bridges and/or contain kinks.
In fact ANY type of PI can be easily dissolved in alkali - completely - down to the initial monomers.
If you use thermoplastic PIs - of course you can use as solvent the so-called aprotic solvents like DMAc, DMF or NMP.
You can also try a 1:1 by weight mixture of THF and Methanol (but trhe rate of dissolution will strongly depend on the structure of your PI.
Best Regards,
Leonid
Prepare 1 to 10 wt% Poly vinyl alcohol in de ionized water,spin coat it on substrate it will give the planar anchoring
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