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Splitting of a Mercury droplet

  1. Aug 9, 2015 #1
    I recently saw a phenomenon wherein a metal droplet was stretched and stuck between two electrodes that it wet to. Upon applying electric field, the droplet split into two. ANy idea why?
  2. jcsd
  3. Aug 10, 2015 #2
    could it be heat? If you pass sufficient voltage through a wire it will heat, melt and drop; could the same apply to the viscosity of a mercury droplet?
  4. Aug 11, 2015 #3
    Repeat the experiment 20 times. Does the same thing happen every time?

    Is your question: Why did the droplet split in two rather than conducting the current?

    One wild explanation: a competition between electromigration (the electron wind) and surface tension.
    Conducting electrons impart momentum to the molecules in the droplet whenver the electrons scatter. If the droplet cross-sectional area is not uniform, you have a mechanical force on the molecules in the droplet. I would suspect electromigration in a liquid would be much faster than in a solid.
    Surface tension would still keep one portion of the droplet attached to the initial electrode after the droplet split (After the fuse blew).
  5. Aug 12, 2015 #4
    It seems like a plausible explaination. I was wondering if Continuous electrowetting would play a role here. (which sounds a lot like electromigration).
  6. Aug 12, 2015 #5
    Electrowetting and electromigration are different. Electromigration is imparting momentum to atoms from current-carrying electrons. Electrowetting is changing surface tension due to an electric field. The wiki says electrowetting is usually with Fluoropolymers - which are quite different than Mercury.
    Maybe simple joule heating and Fuse-like behavior could explain it. What was the total current in the circuit?
  7. Aug 12, 2015 #6
    Electrowetting seems like an established phenomenon in liquid metals in an electrolyte bath . (I forgot to mention that the setup was in an electrolyte bath). Are you saying that the current being carried through the circuit causes the droplet to split?
  8. Aug 12, 2015 #7
    Seems like there is quite a bit of literature out there about electrowetting.
    The Hg being in a electrolyte bath would allow faster heat transfer to the solution than the air, an indication against the hot-fuse idea.

    What is the geometry of the electrodes: are they planar surfaces much larger than the droplet? or are they small wires much smaller than the droplet?
    Surface roughness of the electrodes could also play a role.

    What is the applied potential (V)? field strength (V/cm)? Initial current (A) vs steady state current (A)?
  9. Aug 15, 2015 #8
    The forces responsible for surface tension and similar phenomenon are small compared to the interactions between the electrical current and it's own magnetic field, if the current between the electrodes is non-trivial.

    if you have two parallel wires and you run current through both in the same direction then they will be attracted by their magnetic fields. A drop of liquid metal bridging the gap between two electrodes can be thought of as a collection of many many very tiny wires in parallel. So when the current flows they are effectively all trying to squeeze together tighter. If the drop were to somehow become slightly hourglass shaped than the current will be more dense in the narrower part. Thus, the squeezing-ness will be stronger in the narrower part. You can see how this would lead to the drop of mercury pinching itself into two smaller parts.

    Obligatory YouTube link:

    Read the video description.
    Last edited: Aug 16, 2015
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