Why Do Heavier Particles Float in a Colloidal System?

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In summary, the conversation is about a colloidal system where the particles are heavier than the liquid, but when styrofoam is added, the particles float instead of sinking. The experiment involves 2M hydrobromic acid and silica dispersed in the acid. The addition of styrofoam causes the dispersion to separate, with the acid at the bottom and the styrofoam-silica compound at the top. It is suggested that the silica bonds with the styrofoam, causing the resulting compound particles to have a lower density than the acid.
  • #1
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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  • #2
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
 
  • #3
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
 
  • #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, ...
 
  • #5
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.
 

1. Why do heavier particles float in a colloidal system?

The phenomenon of heavier particles floating in a colloidal system can be explained by the principle of buoyancy. Buoyancy is the upward force exerted by a fluid on an object immersed in it. In a colloidal system, the particles are dispersed throughout the fluid and are surrounded by a layer of fluid molecules. This layer of fluid molecules is known as the solvation layer. The solvation layer reduces the density of the particles, making them less dense than the surrounding fluid. As a result, the particles experience a net upward force, causing them to float.

2. Does the size of the particles affect their ability to float in a colloidal system?

Yes, the size of the particles does affect their ability to float. In general, smaller particles tend to float more easily in a colloidal system compared to larger particles. This is because smaller particles have a larger surface area to volume ratio, which means they have a larger solvation layer and are more buoyant. However, the density of the particles also plays a role, as denser particles may still sink even if they are smaller in size.

3. How does the concentration of particles in a colloidal system affect their ability to float?

The concentration of particles in a colloidal system can affect their ability to float in two ways. Firstly, a higher concentration of particles means a higher number of particles in a given volume of fluid. This can increase the chances of particles colliding with each other, which can lead to the formation of larger aggregates that may sink. Secondly, a higher concentration of particles can also lead to a higher density of the colloidal system, making it more difficult for particles to float.

4. Can the temperature of the system impact the buoyancy of particles in a colloidal system?

Yes, the temperature of the system can have an impact on the buoyancy of particles in a colloidal system. As the temperature increases, the solvation layer around the particles becomes thinner, reducing their buoyancy. This is because at higher temperatures, the thermal energy of the fluid molecules increases, causing them to move faster and reducing their ability to form a solvation layer around the particles.

5. Are there any practical applications of heavier particles floating in a colloidal system?

Yes, there are several practical applications of this phenomenon. One example is in the food industry, where heavier particles can be used to create emulsions or suspensions that are more stable and have a longer shelf life. This is because the floating of heavier particles helps to prevent settling and separation of the particles in the colloidal system. Another application is in water purification, where heavier particles can be used to remove impurities and contaminants from water through flotation processes.

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