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MPharm 2 - PH2107 > PH2107 - Emulsions 2 > Flashcards

PH2107 - Emulsions 2 Flashcards

1
Q

What are the four types of instability that can occur with emulsions?

A

Flocculated
Creamed
Phase inverted
Cracked

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2
Q

What is a flocculated emulsion?

A

Globules associate

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3
Q

What is a creamed emulsion?

A

Flocced globules rise to the surface

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4
Q

What is a cracked emulsion?

A

Flocced globules completely separate and merge to form an oil layer

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5
Q

What is an inverted emulsion?

A

Emulsion flips from o/w to w/o, or from w/o to o/w

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6
Q

what are some different methods for emulsifying

A

High shear stirring
(heat/melting required if viscous)

High pressure homogenization
force the premix through a narrow orifice or valve at high
pressures (typically 10–100 MPa). Forcing the emulsion
through a valve at high pressure creates turbulence and
very high shear forces, thus reducing droplet size.

Microfluidics/ultrasonication

The resulting emulsion is temporary,
without an emulsifier

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7
Q

What is the difference between creaming in w/o emulsion compared to o/w emulsion?

A

It is upside down

  • in o/w emulsion creaming occurs on top
  • in w/o emulsion creaming occurs on the bottom
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8
Q

What is the difference between cracking in w/o emulsion compared to o/w emulsion?

A

It is upside down

  • in o/w emulsion cracking occurs on top
  • in w/o emulsion cracking occurs on bottom
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9
Q

Why is creaming and cracking inverted depending on the structure of the emulsion?

A

Density - oil floats on water

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10
Q

What causes flocculation in emulsions?

A

Due to interaction of VA and VR

  • can be primary minimum or secondary minimum phenomenon
  • if primary minimum, it is extremely difficult to break up floccs
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11
Q

Why is flocculation in emulsions a reversible state?

A

Globules remain separate

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12
Q

What causes cracking in emulsions?

A

Closeness of flocculated globules any weakness in the interfacial film may result in irreversible coalescence (cracking)

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13
Q

What causes emulsion creaming?

A

Globule flocculation

  • dispersed phase rises to the top (o/w)
  • settles to the bottom (w/o) of the emulsion
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14
Q

Why can creaming in emulsions be redispersed?

A

Each globule is still surrounded by its protective emulsifier

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15
Q

Why is creaming likely to progress to cracking?

A

Globules in cream layer are close to each other and may overcome repulsion

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16
Q

What is emulsion cracking?

A

Complete and irreversible separation of the emulsion into its two constituent oil and water phases

17
Q

Why can’t a cracked emulsion be re-dispersed?

A

The emulsified layer surrounding the globules has been destroyed

18
Q

What causes an emulsion to crack?

A
  • pH change
  • improper storage
  • chemical incompatibility (bad formulation)
19
Q

What causes phase inversion of emulsions?

A
  • heat
  • chemical instability
  • phase volume ratio (PVR) > 60-70% dispersed phase
20
Q

Why is phase inversion of emulsions sometimes useful?

A

Sometimes induced in manufacturing as a means of obtaining a finer product

21
Q

What requirements are needed for emulsion stability?

A
  • globules to retain their original character
  • size
  • polydispersity index
  • globules must remain uniformly distributed throughout continuous phase over shelf life
  • no settling
  • no agglomeration
22
Q

What are the problems with phase separation (cracking) in parenteral emulsions?

A
  • modulated rate of drug release

- dosage irregularity (potentially fatal)

23
Q

What is emulsification?

A

The process of dispersing one liquid (often containing the bioactive compounds, drug) in a second immiscible liquid as small globules

24
Q

What are the possible methods of emulsification?

A
  • high shear stirring
  • high pressure homogenisation
  • microfluidics/ultrasonication
25
Q

How does high pressure homogenisation work?

A

Force the premix through a narrow orifice or valve at high pressures (typically 10 - 100 MPa)
- forcing the emulsion through a valve at high pressure creates turbulence and very high shear forces, thus reducing droplet size

26
Q

What is needed to create a permanent emulsion following emulsification?

A

An emulsifier

27
Q

What is mayonnaise made from?

A
  • oil and water
28
Q

What is added to oil and water in mayonnaise as an emulsifier?

A

Egg yolk (lecithin)

29
Q

What are lecithins?

A

Phosphatidyl cholines

Ionic emulsifiers
- also used to form micelles and liposomes

30
Q

What are the advantages of using lecithins compared with synthetic alternatives?

A

Totally biodegradable and metabolised

- integral part of biological membranes making it virtually non-toxic

31
Q

What is the structure of lecithins?

A

Same zwitterion headgroup but vary with alkyl chain esterifying groups

MPharm 2 - PH2107 (26 decks)

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