1. Emulsion technology
SCS Summer school July 13, 2013
Steve Boothroyd 1

2. Thinking about how you would develop any sort of product what are the key things you should consider during development?

3. My thoughts in no particular order of importance Does your Consumer love it? Does it meet the Claims you want to make for it? Is it safe? Is it stable? Can you make it on a larger scale consistently? Can you afford it?

4. Does you consumer love it?
Why would you choose to use an emulsion instead of another technology?
Take a few minutes in your tables to come up with 5 possible answers

5. Does you consumer love it?
Possible answers…
They feel good!
You can pack different actives in different phases
You have the option to change lots of things
They can take a range of formats
They are cost effective

6. What is an emulsion?
A dispersion of one or more immiscible liquid phases in another, the distribution being in the form of tiny droplets.

7. What is an emulsion?
A dispersion of one or more immiscible liquid phases in another, the distribution being in the form of tiny droplets.

8. Simple emulsion types Oil-in-water Water-in-oil Water
Oil droplet
(dispersed phase)
Water
(continuous phase)
Water-in-oil
Water droplet
(dispersed phase)
Oil
(continuous phase)

9. Emulsion orientation
The phase that is added tends to become the internal phase
The predominant solubility of the emulsifier tends to determine the external phase (Bancroft’s rule)
Generally, the phase of the greatest volume tends to become the external phase
The phase in which the stirrer is placed tends to become the external phase

10. Droplet size measurement
Laser method
Laser Particle Analyser
Audio method
Use of sound waves (Malvern)
Optical
method

11. Microscopy Uses Droplet size and size distribution
Quality of manufacturing process e.g. undispersed thickener
Detecting unwanted crystallisation
Early indications of instability e.g. flocculation, coalescence, synerisis
Comparison of different emulsions
Liquid crystals

12. What does an emulsion look like?

13. What does an emulsion look like?

14. What does an emulsion look like?

15. What don’t you want to see?

16. Is it Stable? What are the stability risks associated with emulsions?
Take a few minutes in your tables to come up with some possible answers

17. Is it Stable? What are the stability risks associated with emulsions?
Creaming
Sedimentation
Flocculation
Coalescence
Phase Inversion
Ostwald Ripening

18. Is it Stable? Why is that? Emulsions are thermodynamically unstable
Their natural tendency is to revert to a state of least energy i.e. separated into two layers
The process of emulsification is to produce droplets but also to maintain them in this state over a reasonable shelf life

19. Creaming / Sedimentation
No change in droplet size
Reversible
Driven by density difference
Usually results from gravitational forces
Creaming
Sedimentation

20. 20

21. Coalescence Not reversible
May lead from flocculation, creaming / sedimentation or Brownian motion
Involves 2 drops coming together
May lead to complete separation 21

22. Stokes’ Law Defined as:-
Velocity of droplet (v) = (2a2 g (ρ1 – ρ2)) / 9η
Where
a = Radius of dispersed phase droplet
ρ1= Density of continuous (external) phase
ρ2 = Density of continuous (internal) phase
g = Acceleration due to gravity
η = viscosity of the continuous (external) phase 22

23. Van der Waals forces 12H Defined as F = - Aa Where
F = Van der Waals forces of attractions
A = Hamaker constant
a = Radius of dispersed phase droplets
H = Distance between two adjacent dispersed phase droplets 23

24. Is it Stable?
What can these two equations tell us that will help us make formulating decisions to improve stability?
Take a few minutes in your tables to come up with some possible answers

25. Thicken the continuous phase. This increase η and reduces the velocity
From Stokes’ Law
Thicken the continuous phase. This increase η and reduces the velocity
Reduce the particle size by greater or more effective mixing.This has a major effect as a is squared
Reduce the difference in specific gravity between the phases
Additionally from Van der Waal
Increase the distance between droplets either through thickening the water phase to reduce mobility, reducing particle size, or introducing materials that avoid droplets getting too close e.g. polymers 25 25

26. Improving emulsion stability
Charge stabilisation
Interfacial film strengthening
with powders
with polymers
With non-ionic emulsifiers
Steric stabilisation
Continuous phase viscosity
Droplet size
Co-emulsifiers / polar waxes
Liquid crystals 26

27. Improving emulsion stability
Charge stabilisation - +
Negatively charged
oil droplets repel
each other
Stability affected by
quantity of electrolyte
and whether M+ or M++

28. Improving emulsion stability
Interfacial film strengthening
Reduces the probability of coalescence when droplets collide 28

29. Improving emulsion stability
Interfacial film strengthening with powders
Powder particle size must be
very small
Powder must have an affinity
for both the oil and water
phase 29

30. Improving emulsion stability
Interfacial film strengthening with polymers
Polymer sits at emulsion interface
Polar groups orient into the water phase
e.g. Cetyl PEG/PPG-10/1 Dimethicone
Acrylates/vinyl isodecanoate
crosspolymer 30

31. Improving emulsion stability
Interfacial film strengthening with non-ionic emulsifiers
Oil
Tighter packing
at interface
Interface strengthening is dependent
on the number of molecules that
are packed into the interface

32. Improving emulsion stability
Steric stabilisation
Polymer molecules adsorb on the surface of oil droplets, leaving tails and loops extending into the water phase
Polymer molecules must be strongly adsorbed at interface
There must be high coverage of droplet surface with polymer
The 'tails and loops' must be soluble in the water phase
e.g. Cetyl PEG/PPG-10/1 Dimethicone 32

33. Improving emulsion stability
Continuous phase viscosity
Thickening the water phase restricts movement of oil droplets
Thickeners with yield points are most effective
Droplet size
Increasing stability

34. Improving emulsion stability
Co-emulsifiers / polar waxes
e.g. Cetyl alcohol
Co-emulsifiers have weaker surface activity than primary emulsifiers
Adds body and helps prevent coalescence 34

35. Is it Safe?
What are the key components of an emulsion that contribute to safety risk?

36. Is it Safe?
What are the key components of an emulsion that contribute to safety risk? Here are some possibilities
Preservatives
Fragrance
Actives
Emulsifiers

37. What is an emulsifier? Water loving head Oil loving tail 'Hydrophilic'
'Lipophobic'
'Lipophilic'
'Hydrophobic'

38. Potential irritation therefore
Emulsifiers, since they are surface active, may be a factor in increasing the risk of irritation
therefore
Excessive levels of emulsifier should be avoided
The most appropriate type of emulsfier should be chosen

39. Types of emulsifiers - Anionics
The emulsifier carries a negative charge e.g. Sodium Stearate soap
C H COO Na 35 17 - +

40. Types of emulsifiers Pros and Cons Were very common Old fashioned
Not as versatile
Cheap
Limitations for actives due to high pH
Give negative charge to the oil droplet

41. Types of emulsifiers Cationic
The emulsifier carries a positive charge e.g. Palmitamidopropyl Trimonium Chloride _ Cl
CH3(CH2)14C
NH(CH2)3 O
CH3 N +

42. Types of emulsifiers Pros and Cons Usage is not high in Skincare
Good barrier
Excellent silky skin feel
Give positive charge to oil droplet
Can be used at lower pH

43. Types of emulsifiers Non-ionic
Emulsifier carries no overall charge and can be made to form both Water-in-oil or Oil-in-water emulsifiers e.g. Steareth-2
CH3 (CH2 )16 CH2 (OCH2 CH2)2 OH

44. Types of emulsifiers Most common Wide range Versatile
Strengthen the emulsion interface
HLB system to predict choice

45. HLB system 10 20 Hydrophilic Lipophilic Water loving Oil loving Polar10 20
Lipophilic
Oil loving
Non polar
Oil soluble
Hydrophilic
Water loving
Polar
Water soluble

46. HLB system Water Emulsifier HLB 5 Emulsifier HLB 10 Oil
phase
Water

47. Determining HLB values
Source: Croda ( Taken from Croda’s time saving guide to emulsifier selection” - training course available from Croda PLC)

48. How can you tell the difference?
Measure conductivity – conductivity is higher with an O/W emulsion than a W/O emulsion
Dye uptake - a water soluble dye will be taken up by an O/W emulsion
Dispersion – an O/W emulsion will easily disperse in water

49. HLB system Required HLB for oil-in-water emulsion
Benzophenone-3
Mineral oil
Caprylic/Capric triglyceride
Cetyl alcohol
Vitamin E 7 6
Required HLB for water-in-oil emulsion
Mineral oil 4

50. Emulsifier selection using HLB
Oil phase components can be given required HLB values
Required HLB and emulsifier HLB are matched up
Each oil will have 2 required HLB’s, one for oil-in-water emulsions, the other for water-in-oil emulsions
The required HLB is published for some oils

51. HLB Summary Pros Cons Not good for anionics and cationics
Empirical system giving starting position
Can be assessed practically
Cons
Not good for anionics and cationics
Need to know HLB of oil which can vary
Can be time consuming working out or measuring
Does not determine the amount of emulsifier needed

52. Emulsifier blends
In the HLB system the HLB of the emulsifier blend is additive for example if an oil system had a required HLB of 10 you could use either
Emulsifier
HLB 10
HLB 5
HLB 15 or

53. Emulsifier blends
For a given blend of non-ionic emulsifiers, where Emulsifier A is more lipophilic than Emulsifier B
Emulsifier A
Emulsifier B
Oil
Oil
Tighter packing
at interface

54. Considerations when choosing an emulsifier
Type of emulsion
Oils to be emulsified
Processing - hot or cold
Effect on skin
Properties of the emulsion
Cost
Level of electrolyte

55. Can you make it on a larger scale consistently?
What are the differences that would impact on the manufacture of an emulsion between lab and factory?
Take a few minutes in your tables to come up with some possible answers

56. Can you make it on a larger scale consistently?
What are the differences that would impact on the manufacture of an emulsion between lab and factory?
Heating/ Cooling rates
Stirring/ Shear rates

57. Chemical energy + Mechanical energy
How are emulsions formed?
In order to overcome the barrier between the oil and water we need to add energy
This is derived from two sources:-
For long term stability both forms are needed
Chemical energy Mechanical energy
(emulsifier) (homogeniser)

58. Two key requirements for creating a stable emulsion
Apply enough energy to the two phases to create a dispersion
Stabilise the created dispersion
Maintain a small droplet size
Increase the external phase viscosity to reduce movement
Reduce phase density difference

59. Two stages of creating an emulsion
Stage 1 – apply energy to the two phases to create a dispersion
Generally heat to °C
Stage 2 – stabilise the created dispersion
Maintain the small droplet size
Increase the external phase viscosity
Reduce phase density difference 59

60. Emulsion manufacture
Heating to this temperature can change the level of the oil phase e.g. Cyclomethicone
If you need to add sensitive ingredients hot e.g. sunscreens, then do it just prior to emulsification
Avoid post emulsification addition of preservatives etc that partition between oil and water 60

61. Emulsion manufacture
After cooling the remaining ingredients are added e.g. heat sensitive preservatives, perfumes.
For W/O emulsions if you have to add preservatives these MUST be added prior to emulsification
Only Oil-in-water emulsions can be made to weight easily
BUT you must start thinking about scale up from the first formulation attempt 61

62. Emulsion manufacture Laboratory Oil phase added with Silverson mixing
Beaker placed in bowl of cold water and stir cooled
Takes approx 30 min
Factory
Oil phase added with gate stirring followed by homogeniser mixing Size and distance
Cold water passed through water jacket with gate stirring
Can take hours! 62

63. Emulsion manufacture

64. Phase Inversion Temperature (PIT)
Occurs in some non-ionic emulsifier systems
Linked to solubility of emulsifier in the respective phases
At different temperatures
In the presence of electrolyte
Mostly used to transition water in oil to oil in water at a given temperature to produce desired small particle size

65. Phase Inversion Temperature
(PIT)
Unique for any given emulsifier or blend of emulsifiers
Useful for explaining behaviour of emulsion systems
Helps to understand formation of differing types of emulsion observed for a given blend of emulsifiers

66. Phase Inversion Temperature
Within the marked band a complex three phase mixture is found
Above TU a W/O emulsion exists, below TL O/W
This temperature and band will be different for different systems 0o
75o 20
% emulsifier blend
Temperature oC TU T TL
2 phase
1 phase
3 phase
Source: Kahlweit M: Microemulsions, Science 29 April 1998, p

67. Phase Inversion Temperature
Why might this be the case?
Solubility of ethoxylated emulsifiers increases with increasing ethoxylation
Solubility 8 20
Number of ethoxylate groups

68. Phase Inversion Temperature
Bancroft’s rule suggests that the emulsion formed will depend on where the emulsifier is most soluble
Oil in water where most water soluble (hydrophilic)
Water in Oil where most lipid soluble (lipophilic)
Consequently changes the effective HLB observed
By correct choice of emulsifier conversion from a W/O to an O/W is possible