Question

Coalescence of dispersed globules and separation of dispersed phase as a separate layer of emulsion is known as

Answer 1

Is the coalescence of dispersed globules (internal phase) and separation of the disperse phase as a separate layer. (It is irreversible process and re-dispersion cannot be achieved by shaking). Emulsion can be stabilized by electrostatic repulsion between the droplets, by increasing their zeta potential

Answer 2

Answer:

Coalescence of dispersed globules and separation of dispersed phase as a separate layer of emulsion is known as Cracking

Explanation:

• Coalescence  is the process where the dispersed droplets re-unite due to the high surface energy of the dispersed phase, which may lead to the cracking of the emulsion. A cracked emulsion cannot be re-dispersed permanently by shaking. Coalescence is reduced by the addition of an emulsifying agent, which decreases the surface tension at the oil-water interface
• Emulgent usually consist of larger molecules with a lipophilic and a hydrophilic part; one part of the molecule tends to associate with the oily phase and the other one with the aqueous phase, thus being able to form an interfacial film at the oil-water border. For example, with an oil-in-water emulsion the emulgent molecules will form a film around the oil globules with the lipophilic end of the molecule directed towards the oil drops and the hydrophilic end towards the aqueous phase. Which type of emulsion is formed, o/w or w/o, is determined mainly by the solubility of the emulgent; the phase in which the emulgent is more soluble will form the continuous phase.

Creaming

• Creaming occurs when globules aggregates and concentrates in one specific part of the emulsion. The aggregated globules can move upward through the continuous phase and form a layer of concentrated globules at the surface of an emulsion. e.g. when fresh milk stands for some time a layer of cream appears at its surface. A creamed emulsion can be redisposed by shaking or stirring.  The rate of creaming depends on the factors indicated in Stoke’s law and can be reduced by decreasing the globule size and by increasing the viscosity of the preparation.

Phase inversion

• Under certain conditions an o/w emulsion can be turn into (‘invert’ to) a w/o emulsion or vice versa, which means the continuous phase of the original emulsion becomes the dispersed phase and the dispersed phase becomes the continuous phase.
• Phase inversion may be caused by changing the solubility of the emulgent e.g. addition of calcium ions to an o/w emulsion, which is stabilized by a sodium soap, results in the formation of w/o emulsion, which is stabilized by the formed calcium soap. Phase inversion may also occur when the volume of dispersed phase becomes very large.

Cracking

• This involves coalescence of the dispersed globules and separation of the disperse phase as a separate layer (cracking), and re-dispersion cannot be achieved by shaking. Cracking can be caused by
• Additional of an emulsifying agent of opposite type
• Decomposition or precipitation of emulsifying agent
• Microbial action on the emulsifying agent
• Addition of a common solvent
• Incorporation of excess disperse phase