ABSTRACT

There are many substances consisting of particles that are substantially larger than atoms and ordinary molecules, but still much too small, to be visible to the unaided eye or under an optical microscope. These are referred to as colloidal systems or simply as colloids. A simple colloidal solution or a sol system is generally dened as a system of such small particles of a solid dispersed in a liquid phase. More generally, a colloidal system may exist as dispersions of a substance in one phase (called the dispersed phase, which can be a solid, liquid, or a gas) into a different phase, called the dispersion phase. As an example, mist consists of tiny liquid water droplets dispersed in air (gas phase), whereas smoke is a colloid system in which solid particles (carbon, soot) are dispersed in air. Dispersions of plant gums and rubber latex are colloid systems having molecules of a plant polysaccharide or a polymeric rubber hydrocarbon, both of which are solids, dispersed in a liquid water phase. All these are biphasic systems, where the dispersed particles are much smaller in size than the coarse particles. The dispersed particles are either polymeric macromolecules, or larger aggregates of smaller atoms or molecules, which are not visible to the naked eye or even with the help of an optical microscope.1