Improving stability of emulsions

Question 1

How can you improve the stability of an emulsion?

Answer 1

1. Increasing viscosity of continuous phase or give it a yield stress (slower creaming, slower coalescence) –> Thickening agent
2. Increase repulsion between droplets (electrostatic repulsion [pH, salt], or steric repulsion [ adsorption of large emulsifiers on the interface or polymers as an interfacial layer]; slows aggregation, coalescence)
3. Formation of strong interfacial films (proteins; slows coalescence)
4. Smaller droplets (less creaming)
5. Reduce density difference between oil and water (less creaming). Increasing the density of oil or decreasing density of water phase.

Question 2

What is the effect of surfactant size in the emulsion stability?

Answer 2

Emulsion stability is a combination of:
1. Emulsion formation
• Low interfacial tension, easier to make smaller droplets.
• Fast diffusion to interfaces
2. Interfacial thickness needs to prevent coalescence.
**Diffusion: small proteins are fast (BETTER good emulsion formation), large proteins are slow(may prevent emulsion formation).
**Thickness: small protein (thin interface), large proteins (less space between oil droplets, prevent coalesce)
BALANCE!!!

Question 3

Effect of repulsion between droplets:

Answer 3

1. pH: globular protein in the interface. Effect on the charge of the proteins.
   * Low charge: no repulsion between proteins, closer packing at interface. Lot of protein necessary to cover the interfacial area. No repulsion between the oil droplets, approach each other, flocculation or aggregation or coalescence.
   * High charge: positive charge at low pH, more repulsion between proteins. Less protein coverage. Electrostatic repulsion between the oil droplets. This leads more to stability. ELECTROSTATIC STABILIZATION.

Question 4

Steric stabilization is obtained by increasing interfacial thickness, this will lead to two changes that will keep the droplets from approaching each other:

Answer 4

1. Increase repulsion between droplets (steric repulsion)
2. Stronger interfacial film.
   To change interfacial thickness, proteins can be use as an emulsifier. It can make a protein film or a protein aggregates. Use a combination of protein/polysaccharides(larger), thicker interface. This combination can be added :* layer by layer (added separately) * performed protein/polysaccharides mixtures (added simultaneously–>complexes or coacervates, too large to diffuse to interface)