What are colloids?
The colloids (system, suspension or colloidal dispersion) are systems composed of two phases (continuous and dispersed / fluid) usually dispersed in solid and liquid particles respectively.
Characteristics of colloids
Colloids and suspensions
Its composition includes particles of various sizes that may have intermediate properties between the solution and the suspension, which usually sediment in a state of rest.
They differ from the chemical suspensions by the size of the particles, they can be visible to the naked eye (the chemists do not), and they can be separated at rest.
Colloidal particles have a very large area / mass ratio , with high adsorption capacity (accumulation of a substance in a certain interfacial surface that forms a liquid or gaseous film on the surface of a body), through Van der Waals forces and interatomic bonds .
They have a migration of charged particles within an electric field, adsorbing surface ions (positive or negative), although the system itself is electrically neutral.
They present dialysis (movement of molecules and ions through porous membranes), which makes it possible to purify the system by eliminating ions and molecules through dialytic, animal, or cellophane membranes.
Colloidal systems are heterogeneous, with particles of one or more components and multiple in both phases, and varying sizes from 10-2000 Å or less (in the dispersing phase).
They have a Tyndall effect, that is to say: a light beam becomes visible when crossing a colloidal system, by the multidirectional dispersion of the light .
The particles move disorderly in the middle, by the collision of molecules with each other and with the medium, which can prevent them from settling and sedimentation.
Types of colloids
Their types are:
- Emulsion : colloidal dispersion of one liquid in another, stirring the mixture or using a mill.
- Sun : by electrolyte action or elevation of the temperature, causing coagulation or precipitation. They can be lyophobic and lyophilic.
- Aerosol : systems with particles subdivided and dispersed in a gas.
- Gel : higher viscosity.
- Foam : liquid or gaseous dispersing phase, and gas dispersed phase.
Examples according to their type
Some examples are:
- Emulsion: milk, mayonnaise, butter
- Sun: Painting, milk of magnesia
- Aerosol: clouds
- Gel: Jelly, gummies (sweets), gelatins
- Foam: whipped cream
Examples according to their composition
Gas continuous phase:
- Gas dispersed phase: it is not possible
- Liquid FD: fog, mist
- Solid FD: smoke, ambient dust
Continuous liquid phase:
- FD gas: shaving foam, milk cream
- Liquid FD: mayonnaise, creams
- Solid FD: paints, inks
Solid continuous phase:
- FD gas: pumice stone, meringue
- Liquid FD: gelatin
- Solid FD: ruby crystals