An emulsion is a dispersed system containing two immiscible liquid, one of which is dispersed as small droplets in the order as the dispersion medium. An aqueous medium such as water is usually one of the liquids and the other is an organic compound [oil], which is insoluble in the aqueous phase.
There are two types of emulsion, namely
[i] Oil-in-water and
[ii] Water-in-oil
This categorization depends on which is more in abundance. These two are often designated, simply by o/w and w/o emulsions respectively. In all cases, a third component, often known as the emulsifying agent is essentially for stability.
The familiar example include: milk, cream, butter, margarine, salad cream, cosmetic creams, etc. Similarly, bituminous emulsion used for road resurfacing and a variety of agricultural sprays are typical emulsions. Also, emulsions are used widely in pharmacy.
The familiar example include: milk, cream, butter, margarine, salad cream, cosmetic creams, etc. Similarly, bituminous emulsion used for road resurfacing and a variety of agricultural sprays are typical emulsions. Also, emulsions are used widely in pharmacy.
Emulsion droplets have diameters in the range 1-50 microfarad and are found to be larger than those found in colloidal solutions. These are often visible in microscope. In most common emulsion, the concentration of disperse phase is greater than that of sols, example, and cream contains about 20% of fat droplets dispersed in an aqueous medium.
Assuming spherical droplets of equal size, a simple geometrical calculations show that the maximum volume of one liquid which can be dispersed in another is 74% of the total available volume and is independent of droplets size. If this concentration is exceeded one might expect inversion to occur, the dispersed phase becomes the dispersion medium, e.g.,
change from o/w to w/o type emulsion. But, emulsions of both types of much lighter concentration are known and this is mainly due to the fact that the emulsifying agent allows the droplets to become distorted from their spherical shape without coalescing.
Assuming spherical droplets of equal size, a simple geometrical calculations show that the maximum volume of one liquid which can be dispersed in another is 74% of the total available volume and is independent of droplets size. If this concentration is exceeded one might expect inversion to occur, the dispersed phase becomes the dispersion medium, e.g.,
change from o/w to w/o type emulsion. But, emulsions of both types of much lighter concentration are known and this is mainly due to the fact that the emulsifying agent allows the droplets to become distorted from their spherical shape without coalescing.
It is relatively easy to determine whether a given emulsion is of the o/w or w/o type. Addition of water to the former results in rapid dilution of the emulsion but, would form another layer in the w/o cases. Also, the conductivity of an o/w emulsion should be high, and
of w/o type low. Another method is to add to the emulsion a dye will readily colour a w/o emulsion and conversely the o/w type is coloured by water soluble dyes
of w/o type low. Another method is to add to the emulsion a dye will readily colour a w/o emulsion and conversely the o/w type is coloured by water soluble dyes
Preparation of emulsion
The preparation of emulsion can be achieved by simply shaking up two immiscible liquids together, however, unless an emulsifying agent is present such an emulsion is unstable and liquids will separate into two layers. Emulsifying agent are normally substances that are
strongly adsorbed at the oil water interface thereby lower the interfacial tension since in the formation of an emulsion a very large surface area is achieved between the two liquids, a reduction in the interfacial tension facilitate the formation of droplets and also reduces their tendency to coalesce.
strongly adsorbed at the oil water interface thereby lower the interfacial tension since in the formation of an emulsion a very large surface area is achieved between the two liquids, a reduction in the interfacial tension facilitate the formation of droplets and also reduces their tendency to coalesce.
It is important to note that:
- The substances which lower the interfacial tension markedly do not necessarily give rise to a stable emulsion.
- The concentration of an emulsifying agent is normally small with value range of about 1-5% of the other materials
There are many types of emulsifying agents, namely (a) o/w emulsions are promoted by many hydrophilic colloids, such as proteins, gums, most ionic soaps and detergents (b) w/o emulsions are made from long chains alcohols and esters and the oleates and stearates of alluminium, calcium and magnesium nd (c)some finely divided solid which are preferentially wetted by one of the liquid re also capable of acting s emulsifying agents e.g various carbons blacks promotes w/o emulsions and clays give the o/w type emulsions.
Again experiment has shown that the stability and particle size of an emulsion depends on the mode of preparation as follows;
- The preparation that involves high speed mechanical stirring or other agitation usually produces emulsions containing large droplets with a variety of range of
particle size. - A coarse emulsion subjected to homogenization results in the production of a smaller and more uniform particle size.
- The fat droplets in milk can be reduced from about 10 -0.5µ by homogenization and the resultant emulsion is stable and shows little tendency for the cream to separate.
- Indeed, the stability of an emulsion is determined essentially by the nature of the
interfacial film. We also realize that water soluble proteins are very effective emulsifying agents ow type emulsion. - Some stabilities of emulsion are enhanced by [1] the oil droplet in an ow emulsion is stabilized by the mechanical protection provided by the protein casein.
Electrical effects are important in the stabilization of both ow and w/o type’s emulsions when ionic soaps and detergent are used as emulsifying agents.
Generally, it is of interest to recognize that a reasonable stable emulsion can only be prepared if a third component, which is an emulsifying agent (or emulsifier) is present.
The materials which are most effective as emulsifying and foaming agents are classified
as
as
1. Surface active materials
2. Naturally occurring materials
3. Finely divided solids
Therefore, the functions of the emulsifying agents are the to facilitate emulsification and subsequently promote emulsion stability. The emulsifying agents form an adsorbed film around the dispersed droplets which helps to proportionally prevent flocculation and coalescence.
Breaking of emulsion
After much consideration, the majority of oil is lighter than water, the oil droplets in an emulsion, if larger than the particle size of about, 1µ in radius, rise to the surface under the
influence of gravity. This phenomenon is known as creaming and can be reduced by the addition of glycerin, gums or glycetin as emulsifiers. Examples are the creaming, breaking
and inversion of milk to obtain butters and the breaking of w/o oil-field emulsions.
influence of gravity. This phenomenon is known as creaming and can be reduced by the addition of glycerin, gums or glycetin as emulsifiers. Examples are the creaming, breaking
and inversion of milk to obtain butters and the breaking of w/o oil-field emulsions.
Indeed subsequently a number of techniques are applied commercially and industrially to enhanced emulsion breakdown. The mechanical methods include centrifuge, which is based on the principle of separation distillation and filtration. Another method is based on the
addition of o/w promoting emulsifier which tends to break w/o emulsions and vice versa.
addition of o/w promoting emulsifier which tends to break w/o emulsions and vice versa.
Emulsions can also be broken down by the application of intense electrical fields; this involves being electrophoresis in the case of o/w emulsions and droplet deformation in the case of w/o emulsion.
Read Also: The significance and Breaking of Foams
