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Colloids are referred as particles with dimensions ranging from micro-meters to nano-meters. The rampant use of colloids in our everyday life has led to develop better and precise colloidal materials. This has helped in developing better daily use personal care products and industrial materials which requires extensive usage of these particles. Colloidal science is basically the science of heterogeneous system and depends mainly upon particle size, their shapes and specific surface properties. 

Apart from these the particle to solvent interactions and optical properties of particle solvent system are also taken into account to understand these colloidal system and work on to develop better and precise products. The advent of nanotechnology is just another of such usage.

Colloid Definition

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Colloids are considered as dispersions of small particles ranging from 1 nano meter to 10 micro meter and may either could be dissolved macro molecules or their structures which are created from tiny structural units and they might constitute a separate phase like in aerosol. The size of the colloid particles relative to larger particles differentiate by some specific set of properties.
  1. Mobility due to thermal kinetic energy
  2. Inertial effect absence
  3. Adhesion or inter system molecular interactions
  4. Thermodynamic properties and the effect of size
  5. Particle behaviour with electromagnetic radiation
These are also referred as mixtures where one material is dispersed into another with the dispersed material or also known as dispersoid sub divided into independent units. The term colloid doesn’t take into account doesn’t take into account dispersions or normal sized molecules and macroscopic phase materials. Very often the emulsions and suspensions might also act like colloids but with several times bigger in size. 


The dispersion medium or the continuous phase of the system is composed of small to moderate sized molecules. Hence, we might also take these as dispersions of distinguishable particles within a size range of 1 nm to 10 μm.

Colloidal Particles

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Colloid particles are with us for many centuries but from the scientific and technological ideas started cropping up only in recent times. The interest level on these study matter has led to enhanced understanding principal factors which helped in understanding the stabilising and interaction of such colloidal system.

Colloidal particles are very important as far as their characteristics are concerned and moreover, these size of particles decide the manner in which they will interact. The interactions lead to development of building blocks. These are mainly utilised in pharmacy, paint industries diagnostic units and as various catalysts in chemical reactions.

Types of Colloids

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The main category of colloids are either based on whether or not they are water loving or water hating. Whenever we consider the dispersion medium, it is either liquid or is liquid. In case it is liquid we take into account of whether it is lyophobic (water hating) in nature or lyophilic (water loving) in characteristics. 

In case of lyophilic or water loving there is no interface between the participating particles and medium. The lyophobic colloids are further classified based on their patterns of phases. 

Dispersed phase  Dispersion medium  Type of colloids 
Solid Solid Micro or nano composites
Liquid  Solid Solid emulsion
Gas Solid Solid (micro / nano) foam
Liquid  Gas Aerosol
Solid Gas Aerosol

Examples of Colloids

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There are plenty of examples but the most common examples that we come across but fail to identify are as follows:
  • Fog, fine sprays and smoke belong to aerosol category.
  • Shaving cream belongs to micro foam category.
  • Milk and mayonnaise belong to emulsion category.
  • Paint and ink belong to sol category.
  • Foam plastics belong to solid foam while opal and pearl belong to solid emulsion. 

Purest Colloids

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The purest form of colloids are basically the ones where the particles size are made specific to cater to specialised service departments. In medical fraternity the dialysis plays a big role for kidney patients. In dialysis the particle size is very important and it helps in exchanging the exact size of particles across the membrane. The exchange of particles across the membrane helps in retaining the right amount of vital salt within and also helps in excreting the toxic part. 

Apart from medical emergency, the purest form of colloids are found in all kinds of plasma materials necessary for producing the perfect display boards. 

Colloid Fluids

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Colloids fluids are crystalloid electrolyte solution with macro molecules within which helps in binding water by sheer osmotic pressure. Colloid fluids refer to sterile water solution added with macro molecules which pass through the capillary wall with difficulty. The osmotic strengths of macro molecules is not very good and hence a colloid fluid is necessary to have electrolytes in order to make it hemolytic.

As long the macro molecules are within the capillary walls the overall contributions to overall osmolality is good enough to maintain large proportion of infused fluid inside blood stream. Colloid fluids are also used as plasma volume expanders.