Preparation and Breaking Of Emulsion

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  Preparation and Breaking Of Emulsion
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.
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.
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
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. 
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
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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
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.
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. 
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.

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