Emulsion technology

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

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

9. 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 Emulsion orientation

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

11. 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 Microscopy

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

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

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

23. Van der Waals forces Defined as F = - Aa 12H 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

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. 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

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

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

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

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

31. Oil Tighter packing at interface Improving emulsion stability Interfacial film strengthening with non-ionic emulsifiers 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

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

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

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

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

40. 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 Types of emulsifiers

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

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. CH3 (CH2 )16 CH2 (OCH2 CH2)2 OH 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

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

45. 0 10 20 HLB system Hydrophilic Water loving Polar Water soluble Lipophilic Oil loving Non polar Oil soluble

46. Water phase Emulsifier HLB 5 Emulsifier HLB 10 Oil phase Emulsifier HLB 15 HLB system

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 10 - 11 515 - 16 6 Required HLB for water-in-oil emulsion 4 Mineral oil

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