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Denser material floats

  1. Sep 22, 2014 #1

    Sorry for double posting but I wasn't sure of the right thread.

    I am working with a colloidal system in which the particles are heavier than liquid. However when I add styrofoam to the system, the particles float. I can't seem to understand why the heavier particles float instead of sediment. Please help.
    Thank you.
  2. jcsd
  3. Sep 22, 2014 #2


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    hi there
    welcome to PF :)

    you need to explain/clarify your experiment a bit more

    what is the liquid ?
    what is the denser material?
    However when I add styrofoam to the system, the particles float <---- what do you mean by this ?

  4. Sep 23, 2014 #3
    Hi Dave, thank you very much for your response.

    the liquid is 2M hydrobromic acid (density: 1.49g/cm3)
    the denser material is silica (density: 2.65g/cm3)
    the sililca is dispersed in the acid. but when I add styrofoam balls to the mixture, the dispersion separates into 'acid at the bottom' and 'styrofoam with silica at the top'.

    thank you again.

  5. Sep 23, 2014 #4
    I guess you answered your own question: Styrofoam with silica

    The silica must bond with the styrofoam, and the resulting compound particles have a smaller density than the acid. Note that in soft condensed matter the bond can be "soft", such as electrostatic, ...
  6. Sep 24, 2014 #5
    thank you very much M Quack. I thought as much; I just doubted myself.
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