Hello!
I am investigating the extrudability of our bio-ink through rheology. Previously, I used a parallel plate to acquire the shear rate of the sample after which I tried an actual extrudability test with a 3D printing machine for viscoelastic material. I find it trivial at first to acquire the data with a parallel plate knowing that the pneumatic piston pushing the ink through the cartridge is closely conical in shape.
Would there be any significant difference at all if I choose to test it with a conical upper plate? We only have one rheometer at this moment so as much as possible I would not want to waste time.
I'd be glad to hear your thoughts on this. Thank you in advance!
Hello John Mc Guiller Daarol Calma ,
the shape of the geometry determines the shear field inside your sample and thus can influence your results. However, the suitability of different geometries is influenced by your material and rheological test.
If you want to measure something as a master curve (frequency dependent mechanical moduli in the mecahnical linear regime), you can use both in most of the cases.
If you do strain dependent experiments or experiments in the mecahnical nonlinear regime, they may be affected by the geometry. In the parallel plate case, you have a strain gradient towards the center, where you have no strain at all. Thus, the sample is less affected towards the center, which influences the data of your rheological experiment.
Additionally, some samples may require one geometry or the other. If your ink includes some particles, as an example, there could be issues if the particle size is too close to the gap, which you need to ensure the homogeneous shear field.
Dear John Mc Guiller Daarol Calma,
in your case you may obtain an adequate accuracy using both methods.
Hello Matthias Heck
Thanks for the insight. I was also able to review the modules of the rheometer and you are right about the dependency on use based on the sample material. Now, I need to establish the gap between the plates as it was mentioned on the modules that it should be 3x the size of the largest particle of the sample.
Hello Serge V. Shil’ko
Thank you for sharing your info. I'd like to know more about the impact of the distance between the plates for testing. I hope you can share some techniques regarding this. Thanks!
I agree with your estimation of the appropriate gap as a three characteristic size of particles.
- Hello John Mc Guiller Daarol Calma
The goal is to mimic the shear or extensional rate of the process on the rheometer at similar temperature and conditions ideally. In the case of your sample, it is being pushed through a conical orifice, so would be increasing in shear and extension rate, as it approaches the opening. We could estimate the highest shear rate with Pouiselle’s equation, where shear rate through a tube is 4Q/Pi.r^3. Where Q is the volumetric flow rate and r is internal radius of the orifice. As mentioned above, you can effectively use either a cone or a plate to generate these shears on a rheometer. I hope this helps!
Phil
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