Colloids 7 W4

Question 1

What is an emulsion

Answer 1

mixture of two immiscible liquids (liquids that do not naturally mix, like oil and water) where one liquid is dispersed in the other in the form of tiny droplets. Emulsions are stabilized by an emulsifying agent, which prevents the droplets from coalescing (merging back together).

Highly thermodynamically unstable

Question 2

2 types of emulsion

Answer 2

• oil in water (o/w) and
• water in oil (w/o)

Question 3

What is a cream

Answer 3

is a semisolid emulsion typically used for cosmetic, pharmaceutical, or therapeutic purposes. It is a mixture of two immiscible phases, usually oil and water and stabilized by an emulsifying agent.

Question 4

Why use complex, thermodynamically unstable formulations?

Answer 4

thermodynamically unstable formulations, such as emulsions, suspensions, or foams, are commonly used in various industries

Certain drugs have poor solubility in water but formulations like oil in water emulsions improve delivery of poorly water soluble drugs

They can be designed to release active ingredients over time reducing dosing frequency

They have a smooth and pleasant feel on the skin

Question 5

There are different routes to breakdown of the dispersion to a two-phase ‘split’ or ‘cracked’ emulsion: creaming

Answer 5

Creaming is sedimentation where the dispersed phase is less dense than the continuous phase, so the ‘sedimenting’ droplets rise rather than fall.

Question 6

There are different routes to breakdown of the dispersion to a two-phase ‘split’ or ‘cracked’ emulsion: flocculation

Answer 6

Flocculation is the same process as in suspensions but now leads to coalescence and cracking – why?
Now, when droplets are in secondary minimum, they can bridge and merge due to the mobile interface between the droplets.

Question 7

Stabilising emulsions means

Answer 7

stabilising the interface

Question 8

Suspension vs emulsion : suspension

Answer 8

Solid particles ~ 0.1 – 10 μm diameter: Particles generally retain their size (although recall Ostwald Ripening).

Thermodynamically unstable: Stability managed by control of particle motion and interactions.

Particles move by Diffusion and Sedimentation: Viscosity modifiers used to control particle motion.

Particle interactions determine flocculation state: Flocculation is generally a quasi-stable state for suspensions

Question 9

Suspension vs emulsion : emulsion

Answer 9

Liquid droplets ~ 1 – 100 μm diameter:
Size distribution changes can occur rapidly as droplets coalesce.

(Even More) Thermodynamically unstable: Liquid:liquid interfaces very easily merge when droplets meet – more difficult to control.

Droplets move by Diffusion and Sedimentation: Viscosity modifiers used to control particle motion. ‘Sedimenting’ droplets may rise (creaming) rather than fall, depending on their densities.

Particle interactions determine flocculation state: Flocculation quickly leads to an unstable state for emulsions.

Question 10

What is dispersed phase and what is continuous phase?

Answer 10

Dispersed phase: The liquid that is broken into tiny droplets
Continuous phase: The liquid in which the dispersed phase is distributed