Whats the difference between a suspension and an emulsion?
Without any mixing, most oils will float on the surface of water because they are less dense than water. If oil is thoroughly mixed with water, you have a suspension. However, within a short period of time the suspended oil droplets aggregate and the oil separates from the water by floating back to the surface. If the mixture contains an emulsifying agent you have an emulsion instead of a suspension. The suspension becomes an emulsion when the oil particles are small enough (colloidal size) and stabilized so they do not immediately aggregate. A true emulsion is a uniform suspension that remains stable indefinitely unless acted upon by some outside agency or force. Milk is an emulsion of butter fat suspended in water. Emulsions and even temporary uniform suspensions of oil or solids with water are generally white in appearance. If water gets in the oil of your automobile, the mixture on your dipstick will have a milky appearance. This is bad news to a mechanic. Insoluble solids can also be uniformly suspended in water for special applications when the solid has an emulsifying component in its molecule. Such solids are commonly referred to as “wettable powders”. Many agricultural pesticide chemicals are applied in water as wettable powders.
A typical emulsion is a mixture of a polar and a non-polar fluid in which the smaller particles are coated with a molecule which has both polar and non-polar ends (like a detergent or soap). This "emulsifying" agent forms a thin layer around the smaller particle and keeps them suspended in the larger volume. The smaller component can be a powdered solid and not a liquid. The greater volume can be either polar with the non-polar suspended within or the reverse (like detergents in motor oil).
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