I apologize dear researcher, but it is not within my field of expertise

Hi Nikhil,

Hope the PVDF film is immersed in Silicone oil.

Breakdown field for PVDF film also depends on temperature and rate of rise of applied electric field along with film quality.

Your poling unit may have the feature to trip the supply when over current is passing during the breakdown of the sample.

Premkumar S. Thanks for the valuable reply, sir...

Our film is completely immersed in silicon oil. further, the thickness of the film being poled is around 0.15mm. How to know the breakdown field for PVDF films? We fabricated the film using the solution casting technique. Our system has the feature to trip the supply when the over current is passing during the breakdown of the sample. Can you please explain the effect of film quality on poling? Does the solution cast film further requires any processing like vacuum drying or annealing?

Nikhil Dilip Kulkarni ,

Hi

Premkumar S. Sir has already replied to your question. In addition to that, I would like to point out few things.

1. In order to know the breakdown field in contact poling(immersing metal plates sandwiched samples in silicone oil), we prepare samples in duplicates and run one of them as a dummy sample in order to check the voltage(V=A) at which breakdown is taking place. During testing, we keep the voltage lower than A for poling. Coercive electric field determination by ferroelectric hysteresis can be a guiding factor in determining voltage theoretically and then applying a similar one practically.

2. Electroding is key to a successful poling process or any other measurements thereof. The continuity has to be checked and utmost care is to be taken so that there is no electrical shorting.

3. Speaking about the film quality, it has to be uniform and standard protocols for PVDF film preparation can be followed. Thermal annealing is one of the steps although.

Thanks.

thanks Premkumar S. and Anupam Chowdhury for the valuable responses

try to prepare dense PVDF film.. there are many ways to do it.. annealing in vacuum, hot pressing, immersing the film into cold water or ice water immediately after annealing, etc. are such some processes.. These kind of treatments may increase your film quality and its breakdown strength.. However, instead of poling inside silicone oil bath, we use corona poling in this purpose.. our normal solvent casted films (without any special treatment) show almost the reported order of breakdown strength.. our film of ~ 0.04 mm thickness withstand almost 20 kV and above..

another thing what i personally noticed is:

films prepared from PVDF pellets using DMF solvent is less dense and breakdown strength is low.. But, films prepared from PVDF powder are more dense and breakdown strength is high..

Thank you for the valuable response Abhishek Sasmal

further to this, does the electrode coating matter in thermal poling. will the results be better if I thermally evaporate the electrodes on both sides of the PVDF sample?

secondly, can u give any idea how to convert the existing thermal poling setup into the corona poling?

thank you for the valuable response Premkumar S.

There is a tripping facility in the system. However, the tripping is happening at very low voltage values (at 1.5 kV) and the film is becoming burnt at the point where the electrode is pressing the film for contact purposes.

The contact poling what you are trying is also a very good technique for poling if you don't have the corona poling facility.

From my experience, I will suggest that

1. Film thickness is fine, it should be dense as said by Abhishek Sasmal because airgap leads to earlier breakdown.

2. both the surfaces of the film should have a conductive coating (may be silver paste or thermally evaporated coating)

3. Conductive coating should be such that the conductive area should be less than the whole film area. e.g. if the sample is circular, the radius of the conductive coating area must be less than the sample radius on both sides.

4. Obviously check for continuity before the poling. (it should not be conductive across the thickness)

5. After loading the sample, the voltage (field) should be increased very slowly to check the breakdown. And below that voltage, it should be poled.

6. Temperature should not be very high (less than 80 degree C as per literature) and uniform heating is needed. First, heat the Silicon oil and stir it for at least 10 min for uniform heat distribution.

7. The contact of the poling unit should not be so sharp that it may puncher due to pressure at the same point

N.B. Always applied voltage in the case of corona poling is higher as compared to contact poling.

Hi, @Nikhil Dilip Kulkarni, I have not much idea about electrodes. But I think, you need to be careful while depositing the electrodes. Electrodes must be deposited such that there occur less impregnation of electrode materials inside the PVDF film. For this purpose, preparing dense film or hot pressing is a good technique. On the other hand, electrodes must be uniformly deposited on the surface. You need to prevent any kind of leakage..

In corona poling plasma discharge is used. For this, special corona polling equipment is required. I think, normal oil bath based thermal poling system can not be converted into corona poling system.