Physical aspects - Preparation of emulsions

7 important questions on Physical aspects - Preparation of emulsions

Why are emulsions meta-stable?

Oil and water have no affinity for each other. Contact is not a favourable situation. The creation of interface in a system costs energy.

What is the Gibbs free energy when creating an interface or reducing an interface?

Creating --> G is positive, process will not occur spontaneously
Reducing --> G is negative, process will occur spontaneously

What is the surface tension?

The change of free energy resulting from a change in surface area.
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What happens when you decrease the surface tension?

You get a decrease in energy and this makes it easier to create a surface.

How can the interfacial/surface tension be reduced and what does it result in?

By adsorbing different types of molecules or particles at the interface the surface tension can be reduced. For the same energy input, more surface area can be created as the surface tension is lower.

What happens when a surfactant is added to water? And in oil?

Water --> The hydrophobic tails are clustered on the inside, the hydrophilic heads are on the outside. A micelle is spontaneously formed. 

Oil --> hydrophobic tails are present in the oil.

What changes in the Gibbs free energy when surfactants are added?

It still costs energy to create the contact, G is positive. However, there is also an energy gain by avoiding contact of hydrophobic tails and water, so that gives G is negative.

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