MDM: emulsions Flashcards
What is an emulsion?
composed of 2 phases consisting of fine droplets of oil or water dispersed in water or oil
What emulsion types is there?
- Oil in water O/W: oil is the disperse phase and water the continous phase
- Water in oil (W/O): Water is the disperse phase and oil is the continuous phase
- Multiple emulsions (O/W/O or W/O/W): Oil droplets enclosing a water dropelt suspended in water or a water droplet enclosing an oil droplet suspended in oil
What is a microemulsion?
- when the dispersed droplets are 1nm - 1um in size
- They are thermodynamically stable, homogenous and transparent
What ways can be used to determie if it is a W/O emulsion or O/W emulsion?
- Hydrophillic/ Hydrophobic dyes: If the emulsion is O/W then a hydrophillic dye will quickly and uniformly colour the bulk of the emulsion bar the oil droplets. If it is a W/O emulsion it will quickly colour the water droplets. VIce Versa for hydrophobic dye
- Conductivity tests: oil is an insulator so will not conduct electricity well whereas water will coduct a lot better
- Miscibilty in water: W/O more miscible with oil where as O/W more miscibile with water
- What is an interface?
- What can be said about the forces in and between the 2 liquids?
- The boundary between 2 phases
- THe cohesive forces in each liquid is greater than the adhesive forces between the 2 liquids
Describe how an emulsion is formed and how ir seperates
- Water and oil droplets are mixed together and both phases form droplets
- As the surface area of the droplets are high the droplets coalsece/ join to reduce durface free energy and interfacial tension.
- the phase which stays in droplet form the longest is called the disperse ohase and the other the disperse medium
- Complete phase seperation occurs
Why would an O/W emulsion be used for oral use?
- fats/oil medication generally more plesant to take as O/W emulsion
- Can add water soluble flavouring (sugar) to mask tastes
- fine emulsification may enhance the absorption of lipid-soluble compounds
- synthetic non ionic surfactants, hydrocolloidss and gelatine are commonly used as an emulsifying agent
Why would an O/W emulsion be used for IV?
- Used for patients who are unable to feed orally. Total parental nutrition.
- The disperse phase (oil) will solubillise many lipophillic vitamins and proteins
- emulsifiers for TPN are limited due to toxicity concerns. Lecithin is commonly used
What emulsion can be used for topical use?
O/W and W/O
W/O acts as barrier to aqueous solutions
What does HLB tell you?
The degree of hydrophyllicity and lipophobicity of an emulsifying agent.
The higher the HLB the more hydrophillic
Are sorbitan esters hydrophillic or lipophillic?
Are tweens hydrophillic or lipophillic?
- sorbitan - lipophillic
- tweens - hydrophillic
NON IONIC
How is the Required HLB calculated?
- Calculate over all RHLB of the emulsion based on the weight fraction of each oil component (i.e multiphy each RHLB by weight fraction and add)
- Choose 2 emulsifying agents with HLBs above and below required HLB
- % surfactant of high HLB required = RHLB - LHLB/ HHLB- LHLB
- Multiply value with amount of emulsifier. That gives amount of HHLB required and then take this value away from amount of emulsifier needed dor amount of LHLB
What are properties of an ideal emulsion?
- Globules remain evenly distributed - don’t coalesce and don’t sediment
- globules retain their intial character - same shape and size
- emulsions don’t support microbila growth - polymers and non ionic surfacants are food for bacteria
What are the properties of an ideal emulsifying agent?
- Produced stable emulsion at low temperatures - no floc/de floc, no phase inversion, no cracking
- Tastless
- Colourless
- odourless
- non-toxic
- non-irritant
COT
what is the equation for degree of creaming?
degree of creaming = (volume of cream/ sediment)/ total volume
