Why Do Heavier Particles Float in a Colloidal System?

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Discussion Overview

The discussion revolves around the behavior of heavier particles in a colloidal system, specifically why silica particles, which are denser than the liquid (2M hydrobromic acid), float when styrofoam is added to the mixture. The inquiry seeks to understand the underlying mechanisms at play in this phenomenon.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant describes an experiment involving silica particles in 2M hydrobromic acid and notes that adding styrofoam causes the silica to float rather than sediment.
  • Another participant requests clarification on the experimental setup, including the identity of the liquid and the denser material, and seeks to understand the interaction between styrofoam and silica.
  • A later reply suggests that the silica may bond with the styrofoam, resulting in a compound with a lower density than the acid, which could explain the observed floating behavior.
  • One participant expresses doubt about their understanding but acknowledges the explanation provided by another participant.

Areas of Agreement / Disagreement

The discussion includes multiple viewpoints, with some participants proposing explanations for the observed behavior while others seek further clarification. No consensus is reached on the exact mechanisms involved.

Contextual Notes

Participants have not fully resolved the assumptions regarding the interactions between the materials involved, and the specific conditions under which the observations were made remain unclear.

fifi olu
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Hi,

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.
 
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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 ?

Dave
 
davenn said:
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 ?

Dave
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.

fifi
 
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, ...
 
https://www.physicsforums.com/threads/denser-material-floats.772393/reply?quote=4861154hank you very much M Quack. I thought as much; I just doubted myself.
 

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