PHA 327 - Exam 2 - Emulsions 5

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  1. What type of emulsions are Hydrophilic colloids usually used for?
  2. Are hydrophilic colloids usually used with other emulsifying agents?
    Yes, though they can be used alone, they are usually used with other or thickening agents
  3. When applied to water what happens to hydrophilic colloids?
    They swell or dissolve in water
  4. What does a particulate film produced by finely divided solids prevent in an emulsion?
    Coalescence of particles
  5. What subgroups are included in Finely Divided Solids?
    • Non-swellable clays
    • Polar and non-polar inorganic solids
  6. Non-swellable clays and polar and non-polar inorganic solids are in what group of Emulsifiers?
    Finely divided solids
  7. Polar solids make better emulsifiers for what type of emulsion?
  8. Why do polar solids make better emulsifiers for O/W emulsions?
    They are wetted better by water
  9. Non-polar solids make better emulsifiers for what type of emulsion?
    W/O (in the absence of wetting agents)
  10. What are the three problems commonly encountered with emulsions?
    • Creaming or sedimentation
    • Phase inversion
    • Aggregation and Coalescence
  11. What is creaming of an emulsion?
    The upward movement of dispersed particles in an emulsion
  12. What is sedimentation?
    The downward movement of dispersed particles
  13. Do creaming and sedimentation represent the breakdown of the emulsion?
    No, they maintain their individual particles and only need mild agitation to re-disperse
  14. How do you fix an emulsion that has creamed?
    Mild agitation
  15. How can you determine the rate that creaming or sedimentation will occur in an emulsion?
    Using Stoke’s equation
  16. What is phase inversion?
    • When an O/W emulsion becomes a W/O emulsion
    • OR
    • Vice versa
  17. What is the term for the situation where an O/W emulsion becomes a W/O emulsion or vice versa?
    Phase inversion
  18. What is stok’s equation?
    V = d2(ps-po)g/18n
  19. V = velocity of sedimentation(cm/sec)
    • D= diameter of particles
    • ps =density of dispersed phase(g/cm3)
    • po= density of dispersion medium (g/cm3)
    • g = acceleration due to gravity (981 cm/sec2)
    • n = viscosity of dispersion medium (poise)
  20. Why does creaming and sedimentation occur?
    • Due to density differences between the internal and the external phase
    • Internal phase is less dense =creaming
    • Internal phase is more dense =sedimentation
  21. Why is creaming undesirable?
    • Increases the chance of coalescence
    • Is inelegant
    • May lead to variable dosing due to lack of uniformity
  22. How can you decrease the chance of creaming?
    • Reduce particle size
    • Increase the viscosity of the dispersion medium
    • Adjust the density differences between the two phases
  23. How can you increase the viscosity of the dispersion phase to prevent creaming?
    Add thickening agents
  24. What is aggregation of an emulsion?
    Dispersed droplets come together but do not fuse
  25. What is it called when dispersed droplets come together but do not fuse?
  26. What is Coalescence?
    The complete fusion of dispersion droplets and the separation into two immiscible liquids
  27. What is the term for the complete fusion of dispersion droplets?
  28. Coalescence is preceded by what?
  29. Aggregation can lead to what?
  30. Is aggregation reversible?
    To some extent, yes
  31. Is Coalescence reversible?
  32. What is Coalescence dependent on?
    • The structural properties of the interfacial film
    • Temperature
  33. Coalescence and aggregation can occur when what things happen?
    • Addition of emulsifier incompatible substances
    • Bacterial contamination
    • Too high internal phase volume
    • Freezing of aqueous phase
    • High temperatures
  34. What emulsion issue is dependent on the structural components of the interfacial film?
  35. Aggregation is dependent on what property?
    • The electrical potential of the dispersion droplets
    • Temperature
    • Additional of emulsifier incompatible substances
  36. What emulsion issue is dependent on the electrical charge of the dispersion droplets?
  37. Why do aggregation and coalescence increase with increasing temperature?
    • Increase the number of collisions
    • May coagulate the emulsifier
  38. What can increase the number of collisions in an emulsion; coagulate the emulsifier and increase aggregation and coalescence?
    Increased temperature
  39. How does freezing of an aqueous phase effect an emulsion?
    • Ice causes pressure on oil droplets
    • Salts may precipitate and affect the electrical barrier
  40. What can cause unusual pressures on the oil droplets in an emulsion and cause concentration of salts, disrupting the electrical barrier?
    Freezing of the aqueous phase
  41. What three things can cause inversion of an emulsion?
    • Addition of an electrolyte
    • Change in phase volumes
    • Cooling of an emulsion that was prepared by heating and mixing
  42. Addition of an electrolyte, changes in phase volumes and cooling of an emulsion that was created by heating and mixing are all causes of what emulsion issue?
    Phase inversion
  43. What is flocculation?
    Aggregation of dispersion droplets
  44. What is breaking of an emulsion?
    Complete phase separation
  45. Name the four mechanical emulsifiers used in large scale industrial emulsification:
    • Colloid mills
    • Ultrasonifiers
    • Mechanical stirrers
    • Homogenizers
  46. Colloid mills, Ultrasonifiers, Homogenizers and Mechanical stirrers are all used for what?
    Industrial large scale emulsification
  47. For extemporaneous compounding of emulsions what tool would you use?
    • Mortar and pestle with a rough inner surface
    • Hand homogenizers
    • Electric mixers
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PHA 327 - Exam 2 - Emulsions 5
2013-04-22 01:37:47
PHA 327 Exam Emulsions

PHA 327 - Exam 2 - Emulsions 5
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