constant thickness is still no precise enough =(  im working in the nano structuring field,  so sometimes we want layer that are 10nm thick with a variation or less than 1 nm and sometimes i need a 300 micron layer with 10 microns varion. You can imagine 10 microns or 1 nm is a huge difference when it comes to techniques, and that all depends on the overall required thickness. Never the less i have some suggestions for you.

If you have access to money and lithographic equipment, then you can try using the ordyl dry film resist from elga europe. Its a foil, that can be structured by uv lithography, but thus allows structuring in the 10 micron range which means your active area would be very constant. In addition, the layer has a thickness of 55 microns and can be stacked as much as required. So you can make your boundries and just use a sharp edged blade to create your layer by doctor blading.

If that is too expansive or just impossible, then you should really either try to improove your scotch tape technique, or use some other kind of foil. Finding the right foil with the correct thickness and viscosity might take awile, but then its easy to cut it in the correct way on a cutting board (that is a thick board with lines on it). Maybe you can even remove the foil after doctor blading a layer, clean it, and reuse it for another substrate, so your active areas match perfectly. Again, this will require the right material.

To get the layer smoother (more constant thickness) try changing your recipe, maybe add a solvent like acetone to get your paste more fluidic, that your settle some roughness of the layer, but of course you cant use to much, that needs some experimenting.

I hope that helps

Im working with TiO2 pastes for mesoporous electrodes, and im doctorblading, but i still think its difficult to answer your question. First of all, how are you dooing it right now? We can't help you optimizing a procedure we don't know. And secondly, what thickness and what areasize are you thinking about. What particle size are you using?

Doctor blading is not a precise technique and results can be difficult to reproduce.  Can you adapt your material to a spin-casting technique?

yeah, you may need to rephrase your question, are you trying to find out how to get a constant thickness and active area?

If so, getting constant thickness is very difficult especially with manual doctor blading even if it is the same person who keeps doing it all the time, it still varies. Thus, I do not know how to do this unless you want to try spin  casting.With this method and with practice or from literature, you can know what speed gives what thickness.

For constant active area,  it seems to me that you could use a scotch tape to limit the area and use the same dimensions each time or do you mean something else?

Thanks all for your answers

I use TiO2 P25 as a starting material (1 gm), 2 ml water, 30 μL acetylacetone, and 30 μL triton X-100. I need to make a constant active area 1 cm^2 and with constant thickness. I  used to use adhesive tape to get the requited area by putting the substrate on a patterened paper, but the area varies from one electrode to another and the thickness also.

constant thickness is still no precise enough =(  im working in the nano structuring field,  so sometimes we want layer that are 10nm thick with a variation or less than 1 nm and sometimes i need a 300 micron layer with 10 microns varion. You can imagine 10 microns or 1 nm is a huge difference when it comes to techniques, and that all depends on the overall required thickness. Never the less i have some suggestions for you.

If you have access to money and lithographic equipment, then you can try using the ordyl dry film resist from elga europe. Its a foil, that can be structured by uv lithography, but thus allows structuring in the 10 micron range which means your active area would be very constant. In addition, the layer has a thickness of 55 microns and can be stacked as much as required. So you can make your boundries and just use a sharp edged blade to create your layer by doctor blading.

If that is too expansive or just impossible, then you should really either try to improove your scotch tape technique, or use some other kind of foil. Finding the right foil with the correct thickness and viscosity might take awile, but then its easy to cut it in the correct way on a cutting board (that is a thick board with lines on it). Maybe you can even remove the foil after doctor blading a layer, clean it, and reuse it for another substrate, so your active areas match perfectly. Again, this will require the right material.

To get the layer smoother (more constant thickness) try changing your recipe, maybe add a solvent like acetone to get your paste more fluidic, that your settle some roughness of the layer, but of course you cant use to much, that needs some experimenting.

I hope that helps

You can obtain constant area by masking the substrate by Kapton tape.