Preparation of emulsions

Question 1

Why are emulsions meta-stable? Gibbs energy

Answer 1

To create surface between oil and water therefore cost energy, Gibbs free energy. Gamma= surface tension (N/m), delta A= change of surface area (m^2).

• Creating interface: delta A will be positive–> delta G positive. As the G is positive, indicates that the process is nos spontaneous and not preferred.
• Reducing interface: delta A negative–> delta G negative. As the G energy is negative, process may occur spontaneously.

Question 2

What is surface tension ? And what happen when is low ?

Answer 2

The surface tension is low, the energy is low, and therefore it is easier to create an interface. Easier to create emulsion droplets or air bubbles.
-Surface tension: the change of energy resulting from a change in surface area.
The interfacial and surface tension can be reduced by adsorbing different types of molecules or particles at the interface. Creating more surface area.

Question 3

Explain what is surfactant?

Answer 3

Molecules that can be absorbed in the oil-water , have hydrophilic (head) and hydrophobic groups (tail).
In water: tails inside, micelles.
In emulsions with surfactants: hydrophobic into the oil, favorable mixing of hydrophobic tails with hydrophobic oil.

Question 4

Emulsion with and without surfactants, differences ?

Answer 4

1. No surfactant: only energy cost for creating unfavorable contact between hydrophobic oil and hydrophilic water. G>0, not stable.
2. Surfactant: energy cost for creating unfavorable contact between hydrophobic oil and hydrophilic water. G>0, however we also have a slight energy gain by avoiding contact between the tails of the surfactant and water. G<0, more favorable. Lower interfacial tension. Less energy is needed to create the same interfacial area.

Question 5

Surface active materials reduce the energy input for the emulsification process–> the lower the surface tension, the easier is to make small droplets. TRUE OR FALSE?

Answer 5

TRUE

Question 6

The process of increasing emulsion droplets size is referred to ………..

Answer 6

Coarsening, this leads to the increase of the droplets size, since the oil is lighter than oil, it will also move upwards, leading to a phase separation.