How can one measure the surface charge for a particle

  1. Here's the thing. I want to measure the surface charge of the alginate beads synthesized in our lab. It's about 400μm in diameter. I think most people uses zetasizer to examine the zeta-potential of small particles. But I think 400μm is probably too large for this kind of equipment to measure it.

    So, are there any other kinds methods to determine the surface charge density of this particle?

    Thank you.
  2. jcsd
  3. Simon Bridge

    Simon Bridge 15,474
    Science Advisor
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    Gold Member

    Levitating them a known field? Accelerating them in a known field?
    Put a bunch of them in an enclosed volume and measure the force needed to change volume.
    Drop them at a known rate onto a conducting plate grounded through a sensitive galvenometer?
    Drop them on the plate of an electrometer?

    But the zetasizers are reported to handle sizes up to a few millimeters - have you checked with the manufacturer specifications?
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  4. You can easily measure electrophoretic mobility yourself (zetasizers do that too), and from it try to determine zeta-potential. However, the second part is more tricky. Zeta potential strongly depends on the particle surrounding and in some cases it may turn out to be very difficult if not impossible to find an appropriate model relating zeta potential and mobility. If you need to compare two particle suspensions, electrophoretic mobility may be sufficient.
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