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A colloidal solution is a mixture of a dispersed phase into a continuous phase, which can be solid, liquid or gaseous. Colloidal particles range in size from 1-1,000 nanometers and vary in shape. Stabilization is called peptization, while destabilization is called flocculation. The categorization of colloidal solutions depends on the form of dispersed and continuous phases. Brownian motion is the most noteworthy mechanical force stabilizing colloidal fluids. Electrical forces peptize colloidal particles, which can be observed by bringing a colloidal solution under the influence of an electric field. Flocculation can be achieved by using different additives. Instruments such as the zeta meter, nephelometer, and turbidimeter are used to study colloidal solutions.
Also called colloidal suspension, a colloidal solution is the result of uniform mixing of one phase, the “dispersed phase”, into another, the “continuous phase”. The continuous phase can be solid, liquid or gaseous. A colloidal solution is not a true solution, as colloidal particles are usually visible under a microscope, typically ranging in size from 1-1,000 nanometers. These particles vary considerably in shape, from plates to rods to spheres. The stabilization of a colloid is called peptization, while the destabilization is called flocculation.
The broad categorization of a colloidal solution can be narrowed down to the form of dispersed phase and continuous phase. Liquid dispersed in a gas is called an aerosol, whether it be a mist or mist, while a gas dispersed in a liquid is referred to as a foam, exemplified by shaving cream or whipped cream. If the liquid is dispersed in a solid it is a ‘gel’, but the solid dispersed in a liquid is a ‘sol’ – an example of the former is jelly desserts, while varnish is a sol. Milk is an emulsion, a liquid-liquid colloid called a hydrocolloid.
Brownian motion is the most noteworthy mechanical force stabilizing colloidal fluids. The continuous phase, sometimes called the “solvent” phase, agitates the particles of the colloidal solution by means of single molecules bombarding the colloidal particles. This Brownian mechanical force is successfully stabilized, simply because the downward gravitational force of the small colloidal particles is not great enough to overwhelm them. A further factor, the repelling electric forces, shows a short-range stabilizing behavior towards a colloidal solution. There are other forces, attractions, which seem to modify the nature of the colloids, producing voids; these are under investigation.
Evidence that the action of electrical forces peptizes colloidal particles can be observed by bringing a colloidal solution under the influence of an electric field. The particles migrate in response. Peptization can be increased by the addition of an appropriate surfactant or substance that provides ions that attach to the colloidal particles. Conversely, flocculation can be achieved by using different additives which remove the electrostatic charge and which can also add volume. Flocculation is especially important for the removal of solids in wastewater treatment plants.
An instrument used to study a colloidal solution, a zeta meter, measures the potential difference between the dispersed layer of colloidal particles and the surrounding continuous phase. The smaller the potential difference, the greater the probability that the particles will flocculate; the higher it is, the more stable the colloid. Another important tool is the nephelometer. It is often used to detect particles suspended in a liquid or gaseous colloid. Closely related to this is the turbidimeter, used to detect cloudiness in water samples such as that taken from lakes and streams.
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