As we’ve outlined in recent blogs, homogenization is a process utilized for particle size reduction and works by employing mechanical force to break down particles or droplets in a liquid into smaller and more uniform sizes. The result of homogenization is a dispersion, wherein fine particles of one substance are scattered throughout another substance. Furthermore, dispersions are able to be classified by the sizes of these scattered particles: solutions, suspensions and colloids. In this blog, we’re focusing on the difference between suspension and colloids.
Simply defined as a heterogeneous mixture of two substances in which one is dispersed into the other, suspensions involve particles larger than those found in solutions, typically over 1,000 nm. The bigger particles of a suspension usually settle or separate out of a mixture upon standing or are able to be filtered out, although not through filter paper. Gravity is able to pull the visible particles in a suspension down if undisturbed, and they will stay that way unless being actively mixed. Examples of suspensions include oil and water, dust or soot in air, sand and water and muddy water.
Although a heterogeneous mixture of two substances like suspensions, colloids involve particles from 1-1,000 nm that do not separate upon standing and cannot be separated by filtration. The particles in a colloid land in size between those in a solution and a suspension and may be solid, liquid or gas. The two parts in every colloid mixture are its particles and the dispersing medium, and the particles are spread evenly in in the medium, which can also be solid, liquid or gas. Examples of colloids are foams (shaving cream, Styrofoam), gels (gelatin, jelly), emulsions (mayonnaise, lotion), aerosols (fog, insecticide spray, smoke) and sols (shampoo, gemstones).
Even though the particles in a colloid are very small in size, they can be seen through a process called the Tyndall Effect, the effect of light scattering in colloidal dispersion while showing no light in a true solution. This effect is used to determine whether a mixture is a true solution or a colloid.
Colloid mills, like homogenizers, are able to process particle reduction formulations, although each is preferential for certain applications. They are best used for samples comprised of solids immersed in a liquid suspension or a liquid suspended in another liquid because they can enhance the stability and/or reduce the size of suspended particles.
In summary, following are some of the main differences between a suspension and colloid:
- Particles in a suspension are usually more than 1,000 nm, while those in a colloid range from 1-1,000 nm.
- Unlike those in a suspension, particles in a colloid do not separate when sitting still.
- The particles in a suspension may be separated by filtration unlike those in a colloid.
- Colloids are able to scatter light, but suspensions cannot transmit light.
- Particles in a suspension can be seen by the naked eye, but those in a colloid must be viewed using a light microscope.
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