DISPERSED PHASE: CHARACTERISTICS AND EXAMPLES - CHEMISTRY - 2024

The dispersed phase is that in a smaller proportion, discontinuous, and that is composed of aggregates of very small particles in a dispersion. Meanwhile, the most abundant and continuous phase where the colloidal particles lie is called the dispersing phase.

Dispersions are classified according to the size of the particles that form the dispersed phase, and three types of dispersions can be distinguished: coarse dispersions, colloidal solutions, and true solutions.

Source: Gabriel Bolívar

In the image above you can see a hypothetical dispersed phase of purple particles in water. As a result, a glass filled with this dispersion will not show transparency to visible light; that is, it will look the same as a purple liquid yogurt. The type of dispersions varies depending on the size of these particles.

When they are "large" (10 ^-7 m) they speak of coarse dispersions, and they can settle due to the action of gravity; colloidal solutions, if their sizes range between 10 ^-9 m and 10 ^-6 m, which makes them visible only with an ultramicroscope or electron microscope; and true solutions, if their sizes are less than 10 ^-9 m, being capable of crossing membranes.

The true solutions are, therefore, all those that are popularly known, such as vinegar or sugar water.

Characteristics of the dispersed phase

The solutions constitute a particular case of the dispersions, being these of great interest for the knowledge of the physiochemistry of the alive beings. Most biological substances, both intracellular and extracellular, are in the form of so-called dispersions.

Brownian motion and the Tyndall effect

The particles of the dispersed phase of colloidal solutions have a small size that makes their sedimentation mediated by gravity difficult. Furthermore, the particles are constantly moving in a random motion, colliding with each other which also makes it difficult for them to settle. This type of motion is known as a Brownian.

Due to the relatively large size of the dispersed phase particles, colloidal solutions have a cloudy or even opaque appearance. This is because light is scattered when it passes through the colloid, a phenomenon known as the Tyndall effect.

Heterogeneity

Colloidal systems are inhomogeneous systems, since the dispersed phase is made up of particles with a diameter between 10 ^-9 m and 10 ^-6 m. Meanwhile, the particles of the solutions are of a smaller size, generally less than 10 ^-9 µm.

Particles from the dispersed phase of colloidal solutions can pass through filter paper and clay filter. But they cannot pass through dialysis membranes like cellophane, capillary endothelium, and collodion.

In some cases, the particles that make up the dispersed phase are proteins. When they are in the aqueous phase, the proteins fold, leaving the hydrophilic part towards the outside for a greater interaction with water, through ion-dipolo forces or with the formation of hydrogen bonds.

Proteins form a reticular system inside cells, being able to sequester part of the dispersant. In addition, the surface of the proteins serves to bind small molecules that give it a superficial electrical charge, which limits the interaction between the protein molecules, preventing them from forming clots that cause their sedimentation.

Stability

Colloids are classified according to the attraction between the dispersed phase and the dispersant phase. If the dispersing phase is liquid, colloidal systems are classified as sols. These are subdivided into lyophilic and lyophobic.

Lyophilic colloids can form true solutions and are thermodynamically stable. On the other hand, lyophobic colloids can form two phases, since they are unstable; but stable from the kinetic point of view. This allows them to stay in a dispersed state for a long time.

Examples

Both the dispersing phase and the dispersed phase can occur in the three physical states of matter, that is: solid, liquid or gas.

Normally the continuous or dispersing phase is in the liquid state, but colloids can be found whose components are in other states of aggregation of matter.

The possibilities of combining the dispersant phase and the dispersed phase in these physical states are nine.

Each one will be explained with some respective examples.

Solid solutions

When the dispersing phase is solid it can combine with a dispersed phase in solid state, forming so-called solid solutions.

Examples of these interactions are: many alloys of steel with other metals, some colored gems, reinforced rubber, porcelain, and pigmented plastics.

Solid emulsions

The solid state dispersant phase can combine with a liquid dispersed phase, forming so-called solid emulsions. Examples of these interactions are: cheese, butter, and jelly.

Solid foams

The dispersing phase as a solid can be combined with a dispersed phase in the gaseous state, constituting the so-called solid foams. Examples of these interactions are: sponge, rubber, pumice stone, and foam rubber.

Suns and gels

The dispersing phase in liquid state combines with the dispersed phase in solid state, forming the sols and gels. Examples of these interactions are: milk of magnesia, paints, mud, and pudding.

Emulsions

The dispersing phase in liquid state combines with the dispersed phase also in liquid state, producing so-called emulsions. Examples of these interactions are: milk, face cream, salad dressings, and mayonnaise.

Foams

The dispersing phase in the liquid state combines with the dispersed phase in the gaseous state, forming the foams. Examples of these interactions are: shaving cream, whipped cream, and beer foam.

Solid aerosols

The dispersant phase in the gaseous state combines with the dispersed phase in the solid state, giving rise to the so-called solid aerosols. Examples of these interactions are: smoke, viruses, corpuscular materials in the air, materials emitted by automobile exhaust pipes.

Liquid aerosols

The dispersing phase in the gaseous state can be combined with the dispersed phase in the liquid state, constituting the so-called liquid aerosols. Examples of these interactions are: fog, mist, and dew.

True solutions

The dispersing phase in the gaseous state can combine with the gaseous phase in the gaseous state, forming the gaseous mixtures that are true solutions and not colloidal systems. Examples of these interactions are: air and gas from lighting.

References

1. Whitten, Davis, Peck & Stanley. Chemistry. (8th ed.). CENGAGE Learning.
2. Toppr. (sf). Classification of Colloids. Recovered from: toppr.com
3. Jiménez Vargas, J and Macarulla. JM (1984). Physiological Physicochemistry, Sixth Edition. Editorial Interamericana.
4. Merriam-Webster. (2018). Medical Definition of dispersed phase. Recovered from: merriam-webster.com
5. Madhusha. (November 15, 2017). Difference Between Dispersed Phase and Dispersion Medium. Recovered from: pediaa.com