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How to Create a Charge Separation to Migrate Ions in Solution

  1. Dec 2, 2015 #1

    I am working in a research lab at The Ohio State University. I need to separate positively charged ions that are intramolecularly bound to negative counterions. I was hoping to use use static electricity to do this. Any suggestions on the power supply/control to do this?

  2. jcsd
  3. Dec 2, 2015 #2


    Staff: Mentor

    If you have a positive ion bound to a negative ion, don't you have a neutral particle? If so, then electric fields would do nothing by themselves.

    Might the neutral particles have a moment arm so that you could force all of them to face toward or away from a charged plate?
  4. Dec 2, 2015 #3
    This is what the system looks like from a molecular view: https://encrypted-tbn0.gstatic.com/...QTL6c4aTDiwuYyvjXk_m6yCDIEfj5_-4V5GQFY--mwdog

    Short answer: There is no ionic bond formed, just an intramolecular interaction that stabilizes the pictured structure.

    Long answer: When surfactants (surface active agents - molecules with a charged head group and greasy neutral tail) are dissolved in solution, they aggregate into structures called micelles. They orient themselves as shown in the picture to maximize the contact between the water molecules and the charged head groups. Normally, dilute surfactant solutions will only form spherical micelles - this is a balancing act between maximizing the distance between the like charged head groups - in my case, positively charged - and maximizing the the interaction between the water molecules and the surfactants. If you add oppositely charged counterions - in my case negatively charged - then they can stabilize the repulsion between the like charged head groups and thus form other structures like long wormlike threads. I am trying to control the formation and dissociation of wormlike micelles by separating the counterions from the surfactants.
  5. Dec 2, 2015 #4


    Staff: Mentor

    Interesting problem.

    The structure you showed in the picture still looks like a neutral macro particle to an external electric or magnetic field.

    But if the ions are free to migrate, you might be able attract the + to one plate and the - to another plate. But that may not achieve yor goal. It depends on what you mean by "control".

    From an external source, I don't believe you can create an electric field with features smaller in scale than molecules. By features, I mean any nonuniformity in the field.
  6. Dec 2, 2015 #5
    It has been speculated that if the micelles had a net neautral charge they would coagulate and precipitate from solution. This could be a useful property.

    The wormlike micelles (the ones that require the counter ions for stabilization) produce a viscoelastic solution while the spherical micelles produce a waterlike solution.

    Ideal case scenario would be cause the ions to migrate away from each other when an electric field is applied and for them to reassemble when there is no electric field. There has been some papers published implying this can happen, but have not explicitly attributed the property changes of the solution in the presence of an electric field to the separation of the counter ions from the micelles.

    I was wondering if maybe seperating one plate from the solution with a piece of plexiglass then applying a high enough voltage would work.
  7. Dec 2, 2015 #6


    Staff: Mentor

    That sounds like an interesting experiment. Instead of plexiglass, you could simply coat the conductors with an insulating coat.

    Rather than flat plates, a coaxial cylinders might be easier to use in a lab. Say a + outer cylinder and a - thin wire up the middle, both coated with insulators. Then swap the + and - to see if there is a difference. The field gradient will be greatest near the wire.

    I presume that you do not need high voltages. If you do, then additional safety concerns come into play.
  8. Dec 2, 2015 #7
    The current test setup is as pictured:


    I am judging whether or not this succeeds by the presence or absence of a swirl recoil: https://en.wikipedia.org/wiki/Recoil_(fluid_behavior). If there is successful separation of counterions from the surfactants then the solution should not recoil.

    My power supply goes to 50 VDC. I confirmed there was no current flow at 50 VDC. 50 VDC had no effect on the solution. Like you said, higher voltage requires more care.

    This bench scale experiment has about the same gap as what the full scale will be. Narrowing the gap is not a good option. The only thing I know of is higher voltage, but I am not sure how to do so safely and cheaply.

    Also, would AC make any difference?

    Thank you for your time so far. I am new to these forums and would appreciate any advice on how to get the most information out of them.
  9. Dec 2, 2015 #8
    I forgot to mention that the solution in the inner tube is a saturated brine solution so that it is conductive.
  10. Dec 2, 2015 #9


    Staff: Mentor

    AC power would reverse the direction of migration 50 or 60 times per second. I expect that would ruin the experiment.

    Radio frequency RF signals may or may not do something different, but that is outside my expertise. I just think about how violently microwaves shake those water molecules.
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