colloid

Chemistry

2022

We explain what a colloid is, the types of colloids and their main characteristics. Also, its importance and multiple examples.

The phases of the colloids do not tend to separate.

What is a colloid?

In physical Y chemistry Colloids, colloidal systems, or colloidal suspensions are a type of mixture, generally composed of a fluid or continuous phase (liquid or gaseous) and another dispersed (generally solid) in very small and very fine particles (with a diameter of between 10-9 and 10-5 m), which cannot be seen by the simple view.

The latter distinguishes them from chemical suspensions, as well as the fact that when resting for a long time the phases of a suspension tend to separate, but not those of a colloid.

The word colloid comes from the Greek word kolas, which means "that can stick", which refers directly to the tendency of colloids to form clots and to adhere to other substances. Therefore, they can alter the properties of other substances with which they come into contact, that is, they are potentially polluting.

It could be said that colloids are somewhere in between solutions and suspensions.

Types of colloids

The phases that form a colloid cannot be seen with the naked eye.

Colloids are classified depending on the proportion of their respective phases, according to the scheme: dispersed phase in continuous phase:

  • Colloids liquid (dispersed phase) in gas (continuous phase). They form liquid aerosols, such as fog, mist, or mist.
  • Colloids solid (disperse phase) in gas (continuous phase). They form solid aerosols, such as smoke from a fire, dust in the air, or the volcanic ash in the atmosphere.
  • Colloids gas (dispersed phase) in liquid (continuous phase). They form foams, like that of beer or shaving foam.
  • Liquid colloids (dispersed phase) in liquid (continuous phase). Form emulsions, such as milk, mayonnaise, or body creams cosmetic.
  • Solid colloids (dispersed phase) in liquid (continuous phase). They form suns (singular: "sun", for example, blood is a sun), like the paintings or Chinese ink.
  • Colloids gas (dispersed phase) in solid (continuous phase). They form solid foams, such as meringue or aerogels, or pumice.
  • Liquid colloids (dispersed phase) in solid (continuous phase). They form gels, like gelatin, cheese, or jelly bean.
  • Solid colloids (dispersed phase) in solid (continuous phase). They form solid suns, like ruby ​​crystals.

Characteristics of colloids

The phases that form a colloid cannot be filtered.
  • Colloids are inhomogeneous systems in which there is a significant difference between the size of the phases.
  • Colloids are not filterable, that is, their phases cannot be separated mechanically.
  • They have viscosity, that is, internal resistance to movement, depending on how much attraction there is between its phases.
  • They are excellent adsorbents since they have Van der Waals forces and free atomic bonds, capable of capturing other substances and retaining them.
  • Colloids make it possible to make the beams of light, in what is known as the Tyndall effect (it consists in that a beam of light, which is not necessarily visible, becomes visible after passing through a colloidal system).
  • The particles of a colloid show “Brownian” movement, that is, its particles move randomly in front of a ray of sunlight and cannot form sediments.
  • Colloids are usually electrically neutral.

Importance of colloids

Colloids have numerous applications in the medical and engineering fields, making them an important branch of study in physicochemistry. Of special attention are the properties acoustic, optical and electrical colloids, as they could be the basis for obtaining newer and more modern materials.

Examples of colloids

The paints themselves are colloids, and so are aerosols.

Some examples of colloidal systems are:

  • The dust that floats in the air. When we clean an old room, the same that we can see when a ray of light enters through the window.
  • Aerosols. With those who paint graffiti they are drops of paint sprayed on a fixed base.
  • The blood. It is a colloidal system of protein, cells and substances that give it its thickness or lightness.
  • Gelatin. Made with animal cartilage, it forms a gel to certain temperatures.
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