Properties of Colloids: Electrical, Optical, Kinetic, and Physical Properties

Properties of Colloids that are phase-separated mixtures vary due to their microscopically small particle size. In colloids, one substance is suspended into another substance. A diameter of around 1 to 1000 nanometres exists between the dispersed-phase particles. In a colloidal solution, the particles are uniformly distributed and do not settle down during the process. In this article, we will explore the various properties of colloids like physical, electrical, and kinetic properties.

Keyterms: Colloid, Colloidal Solution, Physical Properties, Electrical Properties, Optical Properties, Tyndall Effect, Electro-Osmosis, Electrical Double-Layer Theory, Electrophoresis, Electrokinetic Potential, Collision Theory of Chemical Reactions

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What is a Colloidal Solution?

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Colloidal solutions are heterogeneous mixtures that have particles of one substance dispersed in another. The particles in this type of solution don’t settle down and are distributed evenly. However, these staggering particles are so minute that they are not visible to the human eye. The color of the colloidal solution is dependent on the particle size of the solution and the wavelength of the absorbent light. 

The substance that get distributed is called the dispersed phase and the substance in which it is suspended is called dispersion medium. Colloidal solutions are part and parcel of all our lives. We see them in the food we eat like cakes, bread, ice-cream butter etc. The following tables summarises the common examples of colloidal soultions with respect to the dispersed phase and dispersion medium. 

Examples of Colloidal Solutions

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Physical Properties of Colloids

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• Colloidal solutions are heterogeneous (unlike) in nature. These solutions dwell with two phases i.e., dispersed phase and dispersed medium.
• Despite the unlike nature of colloids, the dispersed fragments are not visible to the human eye due to their microscopic size.
• Due to their small size, the colloidal particles can be passed through a traditional filter paper easily.
• They can also be filtered with the help of membranes like ultrafilters and cellophane.
• The colloids have a big enough size to scatter the light that passes through their solution.
• The wavelength of the light absorbed by the particles depends upon their size. Larger the particle size longer will be the wavelength of light absorbed.
• The color of the colloidal solution is based upon the size of its particles.

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Electrical Properties of Colloids

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The electrical properties of colloidal solutions can be classified as:

• Electrical Double-Layer Theory
• Electrophoresis
• Electro-Osmosis

Let us look into the electrical properties in detail below.

Electrical Double-Layer Theory 

In the electrical double layer theory, the particles are charged by placing ions at immovable points in the first layer. Diffused mobile ions are placed in the second layer. On both these layers, the charge present is equal. This two-layer arrangement leads to the development of a potential known as the electrokinetic potential. Due to the development of the potential around these particles, they show movement under the influence of the electric fields.

Electrical Double Layer

Electrophoresis

In electrophoresis, an electric field is applied to a colloidal solution which enables the movement of colloidal particles. Based upon the accumulation near the electrodes, the charge of the particles is predicted. The charge of the particles is negative if the particles get collected near a positive electrode and vice versa.

Electrophoresis Schematic

Electro-Osmosis 

Electro-osmosis is a process wherein the colloidal solution's dispersing medium is brought under the influence of an electrical field and the particles are arrested.

Electro-Osmosis Schematic 

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Optical Properties of Colloids

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Tyndall Effect: When a beam of light is passed through a colloidal solution that is kept in dark, the path of the beam gets illuminated. This effect is known as the Tyndall effect and the path that is formed is referred to as the Tyndall cone. The Tyndall effect is due to the scattering of light by particles present in a colloidal solution. A true solution does not exhibit the Tyndall effect. This is due to the fact that particles in the true solution are too small to be able to scatter light.

Tyndall Effect Illustration

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Kinetic Properties of Colloids

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Brownian Movement: The continuous zigzag movement of particles in the dispersion medium of a colloidal solution is called Brownian movement. The Brownian movement takes place due to the unequal bombardment of moving molecules of dispersion medium on colloidal particles. This movement decreases as the size of the colloidal particles increases.

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Uses of Colloids

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• Manufacturing: Colloids are used for making lotions, toothpaste, lubricants, coatings, etc. 
• Processing: useful in inks and paints processing industry. 
• Fluid Replacement: Crystalloids and Colloids are used in the field of medicine.
• Pharmaceutical: Colloidal gold can be used in medicine for carrying antibiotics and drugs.
• Dispersion: Colloidal particles enable the dispersion of insoluble materials like metallic gold and fats. They can be used and absorbed more easily. 
• Nutrient Absorption: The colloidal suspension of fats in milk prevents it from being thick and allows easy absorption of nutrients. 
• Roadways: Asphalt emulsified in water is used in preparing the roads.

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Things to Remember

• A colloid is a mixture in which particles of one substance are suspended in another substance.
• The particle size of the dispersed phase particles ranges from 1-1000 nanometres.
• The colloids are microscopic particles but they are big enough to scatter light.
• The electrical properties are classified as: double-layer theory, electrophoresis and electro-osmosis.
• The illumination of a beam of light that is passed through a colloidal solution kept in dark is known as the Tyndall effect.
• The zig-zag movement of particles in the dispersion medium of the colloidal solution is known as the Brownian movement.
• Colloids are used for purposes like manufacturing paints, lotions, preparation of roads, dispersion of insoluble materials, and fluid replacement.

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