I have to measure the viscosity of a suspension of nanoparticles. My goal is to characterize the influence of shear rate and concentration. But I have a small amount of sample. Can you advise me on the rheometric techniques for small samples? Thank you.
Dear Prof. A.Magnin,
I am not an experimentalist, but , may be, this work is useful for you - the authors measured the viscosity in narrow gaps.
Best wishes,
Igor Popov
Li T.-D., Gao J., Szoszkeiwicz R., Landnan U., Riedo E. Structured and viscous water in subnanometer gaps.//
Phys. Rev. B. – 2007. – 75. 115415-1–115415-6.
For small amount of sample (1-2 ml), and ink in particular (your other question), I advise you to use microfluidic capillary rheometer mVROC fabricated by RheoSence (USA). This apparatus is distributed by Malvern in France and a large shear rate range can be obtained.
Regards
Patrice Estellé
I thank my colleagues for their suggestions. The use of conventional rheometry techniques used with thin gap will allow me to make measurements on samples of 2 to 5 ml. Especially with plane-plane geometry. I thank Dr. Estelle for her suggestion mVROC rheometer. Actually this microfluidic technique should allow me to measure small samples on a large shear rate range (up 10^5s^-1). Although I could not measure high concentrations but it's satisfying.
I will also go fo microfluidic rheometer. Formulaction Company might be able to propose something. You may contact them for some tests.
An alternative if you want to measure the viscosity of very small samples would be to use a light scattering technique such as the one discussed here
https://www.researchgate.net/publication/253982144_Optical_coherence_tomography_picorheology_of_biopolymer_solutions
The technique in the above paper has since been extended for measuring sheared systems:
https://www.researchgate.net/publication/51074496_Optical_coherence_tomography_velocimetry_in_controlled_shear_flow
https://www.researchgate.net/publication/265137770_Optical_Coherence_Tomography_Velocimetry_of_Colloidal_Suspensions
Article Optical coherence tomography picorheology of biopolymer solutions
Article Optical coherence tomography velocimetry in controlled shear flow
Article Optical Coherence Tomography Velocimetry of Colloidal Suspensions
I don't know how small is your sample but if it is concentrated enough, as it seems to be the case, to have a good signal, you may use a cone/plate with relatively small diameter (20mm, for instance) and a small cone angle and you need less than 0.05 ml.
If the signal is not enough you may use plate/plate, and with the same diameter and a gap of 250 micrometer, you will need less than 0.1 ml.
I would be cautious about using capillary flow and related instruments, as there is the well known effect of particle migration in shear fields that could make the sample become inhomogeneous in flow. If the colloid forces are strong enough, this would probably not happen.
Hi Albert, The preceding answers seem helpful but raise the question of how large your samples are and what shear-rate range you hope to achieve. As far as I know, no one has worked out a theory of Brownian motion that would allow one to deduce shear-rate dependence of the surrounding medium, but it might be possible to use other forcing. Do you have the resources to develop an instrument or are you looking for a quick, off-the-shelf solution? Joe
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