Emulsions Flashcards
What passes make up an emulsion?
Two phases consisting of droplets of oil in water, or droplets of water in oil.
Most common oral emulsions are oil in water.
What is an emulsion?
Emulsions are a mixture of oil and water, which is normally forced to coexist by use of an emulsifying agent.
This normally is in reference to an emulsion for internal application, as external emulsions are normally known as lotions etc.
What is a microemulsion?
This is when the dispersed phase droplets are very small, less than 1um. Sometimes termed colloidal emulsions.
They ar often transparent
What is a crude emulsion?
This is emulsions where the particulars are larger. Most emulsions we will make in the lab are crude emulsions.
How can we test to find out if a emulsion is o/w or w/o?
By use of dyes.
If we used a hydrophilic dye, then the part of the emulsion that is water will be coloured.
If we use a hydrophobic dye, then the part of the emulsion that is oil will be dyed.
What is interfacial tension?
The boundary between two phases is the interface, and interfacial tension causes both faces to remain separate.
The total energy is dependant on the surface area in contact with the other phase.
This means that droplets will quickly join together to form larger globules as this lowers the tension.
What factors are important when choosing an emulsion for oral use?
Mostly o/w as large quantities of oil are unpleasant to drink.
Oil is often good for dispersing medicine in
Water soluble flavourings can be used to make taste more pleasant
Fine emulsions can enhance absorption of lipid soluble compounds.
Synthetic non ionic surfactants, hydrocolloids( acacia, tragacanth) and gelatine are commonly used as an emulsifying agents in oral preparations.
Nontoxic .
What factors are important when choosing an emulsion for IV use?
Mostly o/w.
Formulated for total parental nutrition for patients who cannot eat, as the oil has high calorific value.
Disperse phase should solubilise lipophilic vitamins and protein.
Limited as to which types of oil are liscenced for this use IE olive.
Emulsifying agents are v limited due to toxicity, lecithin can be used.
What kind of topical emulsions are there?
Creams and lotions are normally oil in water
Ointments and greasy preparation are water on oil, and often act as barriers to aqueous solutions.
The most commonly use ointment bases are soft, hard or liquid paraffins.
Mostly use to treat skin conditions.
What is the hydrophilic/Lipophilic balance? HLB
The HLB number is assigned to an emulsifying agent to denote how hydrophilic/lipophilic it is.
The higher the number, the more hydrophilic it is, the lower the number, the more lipophilic it is.
What is the required HLB?
In an emulsion, each part requires a specific HLB. We can calculate the overall required HLB of the emulsion based of the weight fraction of each oil componant, and the required HLB of that part.
For this we choose two emulsifying agents which HLBs above and below the RHLB of the emulsion.
Example of how to calculate the RHLB a of an emulsion on Equasions sheet.
Remember to only do this for the oil components. Take the amount/total quantity of oil components and times by RHLB.
Example of how to work out how much of each emulsifying agent on Equasions sheet
Remember RHLB - HLB low
———————-
HLB high - HLB low
This is the proportion that the emulsifier that is high will be.
What are the characteristic of an ideal emulsion?
Globules of disperse phase should retain their initial character, ie size and shape
The globules should remain evenly distributed - not sediment or cream, or form larger lumps
They should not support bacterial growth - proteins in emulsions are idea food source
What are the characteristics of an ideal emulsifying agent?
Produces stable emulsions at low temperatures with no creaming,cracking,flocculation,deloculation or phase inversion
Should be not toxic and non irritant
Tasteless
Odourless
Colourless
