FRIDAY FEATURE: Nanoparticle ER Fluids

FRIDAY FEATURE

1. What is the benefit of using nanoparticles in ER fluids?

Since most ER particles used before were micro-size particles which encountered a big problem is the sedimentation issue due to density mismatching between solid phase and liquid, therefore, the ER effect will decrease after some operation period.

In addition, it is thought from dipole-dipole interaction configuration that the ER effect is strongly related to the gaps among the particles (distance between two particles), therefore, the particle with smaller size should have even closer contact under an external electric field, especially under very high potential.

We also tried many samples and found that the wetting between the particles and liquid is also very crucial influencing on the ER effect. Of course, the nanoparticles have good wetting characteristics.

2. What properties/structures are needed for rheological materials?

Usually, the materials should be dielectric (nonconducting) solid mixed with nonconducting liquid (usually silicone oil or hydrocarbon oil). In our experience, the material with high conductivity shows very high current density which will lead to the broken of ER fluid and also require huge amount of current source (high voltage power supply usually can provide small current). The structures are very important for obtaining high quality ER fluid, column or fiber-like structure of suspension is preferred, rather than fractal-like structure which can be seen when the particle¡¯s conductivity is higher enough.

3. Do mechanical forces cause rheological changes?

Yes, the mechanical forces can result in the change of rheological property. Since the columns are aligned between electrodes where an external electric field is applied, when sharing one electrode (or a plate of a viscometer), the ER effect can be seen to decrease due to perpendicular movement of electrode to the electric field induced column, thus the column can¡¯t be firmly attached among the two electrode.

However, other mechanical force has no any effect to the ER effect.

Here is my homepage where you can find some additional information regarding ER suspension.

Weijia Wen

http://physics.ust.hk/phwen

Hong Kong University of Science and Technology

Interview by nanoposts.com.