Emulsifiers

Question 1

Why are emulsifiers/emulsifying agents added to emulsions?

Answer 1

Emulsions are unstable, therefore emulsifiers are added to keep the oil dispersed in water or the water dispersed in oil.

Question 2

Describe how an emulsifier would associate with different phases of the emulsion?

Answer 2

Polar groups of the emulsifier will associate with the water molecules, while the non-polar groups of the emulsifier will associate with the oil phase.

Question 3

What must happen for an emulsifier to stay at the interface?

Answer 3

Emulsifier must concnetrate at the interphase which is where the water and oil meet, and for this to happen, there must be a balance between its hydrophilic and lipophilic characteristics.

Question 4

What would happen if the emulsifier for an o/w emulsion was too hydrophilic?

Answer 4

All the emulsifier would stay in the continuous pahse and would’t be concnetrated at the interface.

Question 5

What are the 5 ways emulsifiers work? from best to worst:

Answer 5

1. Form an interfacial film - a physical barrier
2. REduce interfactial tension
3. Electrostatic repulsion
4. Steric Hindrance
5. Increasing continuous phase viscocity.

Question 6

How do emulsifiers form an interfacial film?

Answer 6

This is the strongest emulsifier activity:
A physical barrier to help prevent coalescence when globules meet. The interfactial film must be flexible to avoid cracking of the film when globules bump into each other. THe emulsifier has a good balance between hydrophilic and hydrophobic characteristics, and arranges itself around the globule.

Question 7

How do emulsifiers reduce interfacial tension?

Answer 7

This decreases the energy in the system by decreasing the adhesive and cohesive forces meaning that the system is less likely to break down.
The emulsifier lowers the interfacial tension between the hydrophilic part of the molecule and the water, and the interfacial tneison between the lipophilic part and the lipid. There are 2 small interfacial tensions instead of 1 big tnesion.

Question 8

How do emulsifiers work by electrostatic repulsion? What is the issue with this?

Answer 8

The emulsifier will give a surface charge to the globules, causing repulsion thereofre decreasing coalesence.
The issue is that the system is greatly affected by electrolytes therefore anything added e.g. flavouring will interfere with the charge film, cauisng coalesence.

Question 9

How do emulsifiers worc by steric hindrance?

Answer 9

Introduce an emulsifier that will attach to the surface of globules, with side chains that will act as a sort of barrier, preventing the globules from coming too close together. The side chains become hydrated and creates a bulk of steric hindrance. WOuld only use this as an addition to another method as on its own, would not have a long shelf life.

Question 10

What is the last resort mode of action of an emulsifier and how does it work?

Answer 10

This is Increase the continuous phase viscosity, therefore slowing down the globule movement and decreasing the chance of coalesence. Last resort because viscosity changes easily with changes in temperature thereofre any change in storage conditions will change how viscous the emulsion is.

Question 11

What are the possible mode of actions of emulsifiers in an o/w emulsion?

Answer 11

Barrier can be elecrical/polar or non-polar. So can be Interfacial film, or electrostatic repulsion (electrostatic/polar)
or steric hindrance (non-polar)

Question 12

WHat are the possible mode of actions of emulsifiers in an w/o emulsion?

Answer 12

Non-polar barrier only - steric hindrance

Question 13

What type of emulsion is the easiest to stabilise and why?

Answer 13

o/w becasue there are 3 possible mode of actions that an emulsifier would work, and also, being able to form a polar barrier is the best because polar groups are far better barriers.

Question 14

Choosing an emulsifier: what must be considered?

Answer 14

1. the type of emulsion o/w or w/o
2. route of administration, potential toxicity, and irritancy
3. emulsifier mechanism of action
4. Compatibility with other exipients e.g. flavouring

Question 15

What is the order from least toxic to non-toxic of emulsifiers?

Answer 15

non ionic emulsifier < anionic emulsifier < cationic emulsifer.
Although non-ionic are the least toxic, a charge is favoured.

Question 16

What phase usually becomes the continuous phase in terms of emulsifier?

Answer 16

The phase that the emulsifier is more soluble in becomes the continuous phase. This is the BANCROFT rule.
The other rules are the Phase Volume Ratio (PVR) or Hydrophile-Lipophile Balance (HLB)

Question 17

What is the Phase Volume Ratio?

Answer 17

PVR rule is that the phase present in the greater amount usually becomes the Continuous phase. If the PVR is 1:1, then the biggest volume will become the Continuous phase

Question 18

What is the Hydrophile-Lipophile Balance?

Answer 18

HLB is the balance between hydrophilic and lipophilic, therefore determining the type of emulsifier that should be used. 
Low HLB (3-6) would be used as a w/o emulsifier.
Higher HLB (8-16) would be used as an o/w emulsifier.
The higher the HLB, the more polar (hydrophilic) the emulsifier.

Question 19

WHat would happen if the emulsifier had a HLB of 0?

Answer 19

It would be completely non-polar thereofre wouldn’t concentrate at the interface, just dissolve in the oil - useless.

Question 20

What is RHLB?

Answer 20

This is the REQUIRED Hydrophile-lipophile Balance of OILS for a given emulsifier.

Question 21

What can we calculate exactly concerning the amount of emulsifier required?

Answer 21

We can calculate exactly the minimum amount of emulsifier required, but can only experimentally find out the actual amount required.

Question 22

If the RHLB for mineral oil is 10 (o/w) and for Lanolin 12 (o/w), and you had an emulsion of 50ml mineral oil, 150ml lanolin ad 300 ml water, answer the following questions:

1) What an emulsifier, what type of emulsion would this be?
2) What would the RHLB for this mixture be?

Answer 22

1) o/w because more water (Phase Volume Ratio)
2) 50/200 x 10 = 2.5
150/200 x 12 = 9
9 + 2.5 = 11.5 RHLB total

Question 23

What is a ‘Mixtures of Emulsifiers’:

Answer 23

This is a combination of emulsifiers that is often used to construct a strong complex film at the interface. The mixture normally has emulsifiers of different hydrophilicities to produce a closely packed and complex film.

Question 24

Chemical structure of the emulsifier will effect the film produced. Emulsifiers with long hydrocarbon chains will form a film that is:

Answer 24

A closely packed film with maximum cohesion between adjacent molecules

Question 25

The most stable emulsios are formed when both emulsifiers are:

Answer 25

of similar chain length e.g. Span and Tween.

Question 26

What is the equation for the proportation of mixed emulsifiers?

Answer 26

proportion of x (most hydrophilic emulsifier) = (RHLB - HLBy) / (HLBx - HLBy)
Proportion of y = 1 - x

Question 27

What is teh equation for The total amount of emulsifier x or y?

Answer 27

Must know the proportion and the The total amount of emulsifier
Emulsifier x = (proporion of x) x (total emulsifier)