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Definition

Colloid is a dispresion of small particles of one material in another.

Definition 2 (Wikipedia)

A colloidal system consists of two separate phases: a dispersed phase (or internal phase) and a continuous phase (or dispersion medium) in which the colloid is dispersed. A colloidal system may be solid, liquid, or gas.

I am trying to answer problem 2:

Question

"Colloidal particles: What are colloidal systems, give an example, what happens to colloidal particles in a liquid medium. How to stabilize colloidal systems in a liquid medium."

My lecture slides mention this about gel: "a continuous network extending throughout the sample formed by association of colloidal particles or molecules in a liquid", "formed in concentrated polymer solutions" and "formed by association of sol-gel particles". Next lecture slides is about "liquid crystals", now I am confused -- not sure whether gel or "liquid crystals" is something to look here.

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...I think I solved this but I feel it can be useful for future random walkers and do not hesitate to comment whether I have misunderstood something or there is something to add about my trial, is it right? –  user911 May 22 '12 at 3:14
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1 Answer

up vote 2 down vote accepted

"Colloidal particles: What are colloidal systems, give an example,--"

Milk, bear foam, paste, blood, ---

"what happens to colloidal particles in a liquid medium."

I understand the q as solid in liquid so a gel. Examples about gel are "agar, gelatin, jelly and opal" according to my lecture slides. The electrostatic forces are in some sort of middle phase: not enough to repulse into liquid form but not strong enough to form liquid either.

"How to stabilize colloidal systems in a liquid medium."

Wikipedia about stability (here)

"The stability of a colloidal system is the capability of the system to remain as it is. Stability is hindered by aggregation and by sedimentation phenomena, that determine phase separation."

Now different things to consider are:

  • Electrostatic stabilization

"In a stable colloid, mass of a dispersed phase is so low that its buoyancy or kinetic energy is too weak to overcome the electrostatic repulsion between charged layers of the dispersing phase."

  • steric stabilization

"particles in polymers which prevents the particle to get close in the range of attractive forces."

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