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Colloids, a special type of heterogeneous mixtures, typically have two components. One is the dispersed phase (DP), which is the "solute-like" part and another one is the dispersion medium (DM), which is the "solvent-like" part. The different interactions of the DP and DM define the properties of a colloid.

My textbook has a few examples based on the different types of DP and DM, but it doesn't have any reference to a colloid where both DP and DM are gaseous. I asked my teacher about it and he told me that it was because gases can flow into each other and hence no heterogeneous mixture, and hence no colloid, of them can ever be possible.

That makes sense, but doesn't it also rules out the existence of colloids with DP and DM both being liquids? Liquids can also flow fairly easily right? Why is the science behind both of them not the same? And, WHAT exactly is the science behind both of them?

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The nature of gases is their molecules are separated while the nature of heterogenous dispersed mixtures is they are not separated. Therefore a heterogenous ( in equilibrium ) mixture of gases is an oxymoron.

Liquids are different case, forming droplets, kept by the surface tension. In contrary to gases, mutual dissolving of liquids depends on intermolecular interactions. such droplets may even have micelar nature, like n-amylalcohol in water.

Once I have tried to replace unavailable i-amylalcohol by available n-amylalcohol for extraction from water and deeply regretted it, seeing the stable emulsion. i-amylalcohol does not have such behavior, as the $\ce{(CH3)2CH^{}-}$ group is an obstacle for building such structures.

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  • $\begingroup$ If I am getting it correct, what you want to say is that liquids don't exist seperately as molecules, but as droplet like entities and that is the reason why it isn't possible for them to behave like gases while forming solutions and mixtures? $\endgroup$
    – user122625
    Commented Mar 22, 2022 at 9:43
  • $\begingroup$ Non miscible liquids form droplets. Miscible ones dissolve each other into true solutions with separated molecules, interacting all mutually by van der Waals forces and eventually forming hydrogen bonds. // Why not to read what gas and liquid mean on molecular level? All this is direct conclusion of that. $\endgroup$
    – Poutnik
    Commented Mar 22, 2022 at 13:12
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Let's take gas 1 as the dispersed phase (which is already at molecular level) which disperses evenly throughout the dispersing medium which is gas 2 (also at molecular level). Thus, the system is already homogeneous at the molecular level. So, we can consider it "solution". For e.g. The atmosphere is a solution. Take the major two gases namely nitrogen and oxygen and we can consider the atmosphere to be "oxygen dissolved into nitrogen".

For a detailed discussion, see: Name of particles in a suspension

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