Emulsions: Principles and preparation - Physical characteristics of emulsions - Droplet size, droplet size distribution

6 important questions on Emulsions: Principles and preparation - Physical characteristics of emulsions - Droplet size, droplet size distribution

Which properties of an emulsion are quite dependent on size?

  • Larger droplets cream/sediment easier due to gravity
  • The appearance of a product
    • Small droplets (<50 nm) --> almost transparent
    • Larger droplets (50 nm - 10 um) --> scatter light (milky white)
    • Even larger --> scatter light much less (yellowish)
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What are 2 different ways of counting particles to obtain the distribution curve?

  1. Count the number of particles smaller than a size --> particles that are much larger also count for 1
  2. Total interfacial area present on the particles --> smaller droplets count less than larger droplets --> more realistic
  3. Volume of the particles smaller than the specific size --> total amount of oil present in small, medium or larger droplets
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Which 4 ways can be used to determine the average droplet size?

  • By looking at the frequency distribution and taking the size at which the distribution is maximal --> modal size
  • Summing up the size of all particles and dividing by number of particles --> number average diameter (d10)
  • Sum up the volumes of all particles and divide this by the total number of particles --> volume average diameter (d30)
  • Summing up the volume of the particles and dividing it by the surface are of the particles --> Sauter diameter (d32)
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Which 3 things about droplets can be measured?

  • Droplet size distribution
  • Average droplet size
  • Width/span of the distribution
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What is the difference in stability of droplets with a different distribution width?

Monodisperse (same sized droplets) --> more stable
Polydisperse (smaller and larger) --> less stable, larger droplets can initiate creaming
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What are 4 different methods to measure the droplet size distribution?

  1. Microscopy
    1. Droplets larger than 1 um --> optical microscopy
    2. Droplets smaller than 1 um --> electron microscopy
  2. Light scattering
  3. Following the dynamics of the droplets (dynamic light scattering) --> Doppler shift, larger droplets slower Brownian motion
  4. Count droplets individually --> Coulter counter method
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