Hi all,
I have opportunity to work with Anton Paar MCR 302 rheometer with double gap system. I would like to measure low viscosity fluid between 1mPa.s to 1000mPa.s in the range of the shear rates between 0.01 to 1000 [1/s]. I tried it with the Newtonian fluid and known viscosity value, however the device failed to measure correct values. It shows me like 10-100 times above the correct one for the shear rates below 50-100 [1/s]. I understand the limitation of the device such as velocity and torque needed to archived this shear rates and viscosity. However, it shows me the measured torque around 100nNm where it can go down to 0.1nNm. Company presented data showing to measure correct viscosity around torque 1nNm. It means that I should have it as well. I have already passed through all calibration process. Any clues or suggestions how I can do it correctly?
Hi Kamil,
Using a low shear rate to measure a low viscosity sample takes the lowest torque (1 mPas x 0.01 1/s = 0.00001 Pa Stress), and so it's important that the instrument is level and that it has been recently torque mapped. Can you rerun a torque map with the double gap cell and then retry your sample? I expect that Anton Paar support can talk you through this on the phone if you've not run it before. Please note that you'll probably have to integrate the results for 60 s or so per point to get a good result even if the calibration is spot on. If the instrument cannot generate good data at this low a torque, it's probably a good idea to look for another rheology test that may give analogous data, such as a frequency sweep to low frequencies, or run the flow curve from 0.1 1/s and up and then extrapolate down to the zero shear rates. Usually samples with such a low viscosity are Newtonian anyway, so there's not much benefit to measuring to 0.01 1/s.
Best regards,
Phil
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